LOW-GRADE METAMORPHISM [N THE MEGUMA GROUP, SOUTHERN NOVA SCOTIA

by Roberta Jean Hicks

Submitted in partial fulfilment of the requirements for the degree of Master of Science

Dalhousie University Halifax, Nova Scotia December, 1996

O Copyright by Roberta Jean Hicks, 1996 UIDIIOUI ue nauonaie du Cana7 a Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. nie Wellington mwa ON K1A ON4 Ottawa ON K1A ON4 ~a~da canada

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The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fiom it Ni la thèse ni des extraits substantiels may be printed or othexwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation. Table of Contents Page Table of Contents ...... iv List of Figures...... vii List of Tables ...... si Abstract...... sii ... Acknowled~ements...... Xlll Chapter I Introduction...... i 1.1 Introduction ...... 1 1.2 Previous Work ...... 5 . . 1.3 Objectives and Approach ...... 1 1 Chapter 2 Regional Geology, Lithologies, Structure and Gold Mineralization ...... 15 7.1 Regional Geoloby ...... 15 7.1 Lithologies of the Meguma Group...... 20 1.2.1 New Harbour Member ...... 22 2-22 Risser's Beach Member...... 23 3.2.3 West Dublin Member...... 24 1.1.4 Tancook Member...... 34 2.2.5 Moshefs Island Member...... 16 2.2.6 Cunard Mcmber ...... 30 2.2.7 Feltzen Member...... 32 2.3 Structural GeoIosy ...... 33 3.3.1 Defornation History ...... 34 . . 3.4 GoId Mineralrzation ...... 41 Chapter 3 Petrography and NIineral Chemistry...... 44 3. ! Introduction ...... 44 3.2 Mineral Assemblages ...... 45 3.2. I General Petrogaphy ...... 45 3.2.2 New Harbour Member...... 56 3.2.3 Risser's Beach Mem ber ...... 57 3.2.4 West Dublin Member...... 58 3.2.54 Tancook Member ...... 3.2.6 Mosher's Island Member...... 3.2.7 Cunard Member...... 3.2.8 Feltzen Member ......

q-7 . 2.2 Mineral Chemistry...... 3 GeneraI Mineral Chemistry ......

2.2.2.-7 -7 Muscovite Chemistry...... 2.2.2-7 -7 -7 Chlorite Cheinistry...... Chapter 4 Diagenesis, Metamorphism, and Cleavage Formation...... 4.1 Introduction ...... 4.2 Definitions...... 4.2.1 Diagenesis......

4-22 Anchizone and Epizone Metamorphism ...... 4.3 XRD Illite-Muscovite Cwstallinity Studies ...... 4.3. 1 Background Information ...... 4.3.2 Sample Selection...... 4.3.3 XRD Illite-Muscovite Crystallinity Results...... 4.4 Diagenesis and Metamorphism in the Meguma Group, Mahone Bay ...... 4.4.1 Chlorite Porphyroblasts and Chlorite-Mica Stacks...... 4.5 Cleavage Development and Volume Loss ...... 4.5.1 General Pnncipies ...... 4.5.2 Clcavagc in Mcguma Group Rocks ...... 4.5.3 Volume Loss in Slaty Cleavase...... 4.5.4 Measuring Volume Loss in Meguma Group Rocks ...... 4.6 Summary ...... Chapter 5 411 ~r/"~rDating ...... - ...... 5.1 Introduction ...... 5.2 JI1 ~ri"')~rSysternatics ...... 5.3 Previous Work ...... 5.4 Sample Selection...... 5.5 Sample Separation ...... 5.6 Sample Analysis ...... 5.7 JO ~r/""ArDating Rcsults...... 5.7.1 introduction to Interpretation of Argon Age Spectra...... 5.7.2 Detrital Muscovite Results...... 5-73 Metamorphic Muscovite Results...... 5.8 Discussion of -10 Ar/-19 Ar Ages ...... Chapter 6 Discussion and Conclusions ...... 6.1 Introduction ...... 6.2 Low-Grade Metamorphism and Fabric Developrnent...... 6.7 Age of Metamorphism in the Megurna Terrane ...... 6.4 Late-Stage (Pre-Granite) Regionai Metarnorphic Tectono-Thermal Evolution of the Meguma Group...... 6.4.1 Gold in Low-Grade Meguma Group Rocks...... 6.5 tnhomogeneous Deformation and Metamorphism of the Megurna Terrane...... 6.6 Recommendations for Future Studies...... 6.7 Conclusions...... Appendix A Electron Microprobe Analytical Methods...... Appendix B Electron Microprobe Analyses ...... Appendix C Structural Formulae...... ,...... Appendix D XRD Sample Preparation and Labratory Methods...... Appendix E XRD Illite-Muscovite Crystallinity (KI) Results and Minerai Analyses...... Appendix F Range of XRD Crystallinity Values (KI) Used to Plot Crystallinity Ranges by Stratigraphie Depth...... Appendix G StepHeating Schedule for '%r13'Ar Dating...... Appendix H Critical Value Method for Defining an "~r/~"~rPlateau...... References Cited...... List of Figures

Chapter I Page Fig. 1.1 Geological map of southern Nova Scotia showing metamorphic zones. -.. . - ...... -...... -...... - ...... -...... -...... Fig. 1.7 Geological map of the Meguma Group in the thesis area ...... Chapter 2 Fig. 2.1 Map of the tectono-stratigaphic terranes of the Appalachian Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... Orogn...... - -. . . -. .. -...... - -..- -.. -. .-...... -...... Fig. 2.2 Geological map of the Meguma Group in the thesis area...... Fig 2.23 Diagram showing the lithostratigraphy of the Meguma Group in

the thesis area ...... ,..-,...... -...... -...... -...-• -- --. Photograph of dewatering structures ( loadi ng), Mosher's Island

Mern ber.. -...... -, ...... -. . - -.. - - -.. . . . - -... - - - - Fig. 2.5 Photograph of worm burrorvs, Mosher's Island Member ...... Fig. 7.6 Photograph of cone-in-cone structure, Mos her's Island Mern ber. .. Fis. 1.7 Photograph of layer of manganese nodules, Mosher's lsiand Mern ber...... -...... -...... Fig. 3.8 Photogaph of large carbonate concretions at Gaff Point, Cunard

Member...... -...... --...... , ...... -. .. . - -.. -...... Fig. 2.9 Photograph of paired worm burrows at Blue Rocks, Feltzen

Mern ber...... , ...... , ...... -. . ------.- ...... , . Fig. 2.1 0 Photograph of deformation at Feltz South, Feltzen Member...... Fig. 2.1 1 Photograph of breccia zones at Broad Cove, New Harbour

Mem ber.. ., ...... Photograph of cleavage arrayed in a convergent pattern around fold hinçes ...... Fig. 3.13 Photograph of a thmst developed in folded rocks west of The Ovens, Cunard Member...... -...... Chapter 3 Fig. 3.1 Microphotograph of chlorite-mica stacks in a fine-gained matrix...... -. .. . .-. .+...... Fig. 3.2 Microphotograph of biotite mirnetically overgowing a fractured chlorite porphyroblast...... Fig. 3.3 Microphotograph of biotite nucleating on matrix chlorite...... Fiç. 3.4 Microphotograph of sheared, poikiliiic biolile in breccia zone al

Broad Cove...... , ...... - - - .- - . -... . -. . . . . Fig. 3.5 Electron microprobe back-scatter image of opaque grain with coextsttnç7. ilmenite and rutile .. Fig. 3.6 Microphotograph of cone-in-cone carbonate structure...... Fig. 3.7 Electron microprobe back-scatter image of cross-hatch matris Fabric ...... -...... -...... -.---.. .-...... -. Fig. 3.8 Microphotograph of bimodal spessartine garnet, Mosher's Island Member ...... -...... --...... -...... -...--. Fig. 3.9 Electron microprobe back-scatter image of spessartine garnet with saphite alonç rnidline and interfacial boundaries...... Fig. 3.10 Microphotograph of concentnc layering in manganese nodule, Mosher's Island Member...... -...... --...... -... Fig. 3.1 1 Feldspar compositional diagram ...... -...... -. . - Fig. 3.12 Gamet compositional diagram ...... -...... -..-...... Fig. 3.13 Biotite composi tional diagram ...... Fig. 3.1 Ja Muscovite classit'ication diagram showing phengite trends ...... Fig. 3.1 Jb Muscovite classification diagram showing phengite trend ...... Fig. 3-15 Muscovite compositions piotted as Al - K - Na weight 90 osides.. Fig. 3.16a Muscovite compositions plotted as total weight 96 oxides vs. Na/(Na+K) for Halifas Formation sample analyses ......

Fiç. 3.16b Muscovite compositions plotted as total weight Oh oxides vs. Na/(Na+K) for Goldenville Formation sample analyses...... Fig. 3.17 Muscovite compositions plotted as total weight ?h oxides vs. Na/lNa+K) for different muscovite morpholog analyses...... Fig. 3.18 Muscovite compositions plotted as total weight 96 oxides vs. Ti for different muscovite morphologies...... Fig. 3.19 Muscovite compositions plotted as total weisht 96 oxides vs. Ti for analyses from detrital muscovite and muscovites [rom the Halifax and Goldenville Formations ...... Fig. 3.20a Chlorite classification diagram showing al1 analyses and analyses from the New 1-Iarbour, Risser's Beach and West Dublin

Members...... -. - - -- -.. . . . -. -...... -...... -. . . - - -.. . . , , , . - -.. . . , Fig. 3.20b Chlorite classitication diagram showing analyses from the Tancook, Mosher's Island, Cunard and Feltzen Members...... Chapter 4 Fiç. 4.1 Diagram of mineral changes associated with increasing depth of burial and metamorphism...... Fig. 42 Diagram of estimates of the limits of clay mineralogy in ternis of tirne and temperature...... Fig. 4.3 Diagram illustrating the structure of clay minerals...... Fig. 4.4 Diagram showing methods of defining illite crystallinity indices.. Fig. 4.5 Map of the thesis area displayinç XRD illite-muscovite . . crystallinity results ...... Fig. 4.6 Diagram of XRD illite-muscovite crystallinity results plotted against stratigraphie depth ...... Fig. 4.7 XRD illite-muscovite data plotted along a Iine perpendicular to .... the biotite-in isograd ...... Fig. 4.8 Dia~gamof chlorite compositions plotted as total weight % oxides vs. Fe/(Fe2+Mg)...... Fig. 4.9a Diaj~amof chlorite compositions plotted for Tschermak substitution - Hali fa. Formation analyses...... Fig. 4.9b Diagam of chlorite compositions plotted for Tschermak substitution - Goldenville Formation analyses...... Fig. 4.9~ Diagram of chlorite compositions plotted for Tschermak substitution - sandy and slaty lithologies...... Fig. 4.1 O Diagram of muscovite compositions plotted as ~g,+~e'vs. AI"+ Al "'...... Fig. 4.1 1 Cartoon diagram of chlorite-mica stack devehpment...... Fig. 4.17 Electron microprobe back-scatter image ofa pristine chlorite porphyroblast...... Fig. 4.13 Electron microprobe back-scatter image of pristine chlorite porphyroblasts with muscovite grotÿth on long edges...... Fig. 4.14 Electron microprobe back-scatter image of chlorite-mica stacks with some muscovite growth in fractures...... Fig. 4.15 Electron microprobe back-scatter image of chlorite-mica stacks with increasing muscovite growth in fractures...... Fig. 4.16 Electron microprobe back-scatter image of chforite-mica stacks showing truncation of stacks by cleavage lameIlae...... Fig. 4.17 Electron microprobe back-scatter image of chlorite-mica stack showing kinking and extensive replacement by muscovite...... Fig. 4.18 Electron microprobe back-scatter imase of fractured chlorite porphyroblast ...... Fig. 4.19 Contour maps showing Sioz,AI,O,, K,O, Fe,O, and TiO, distribution around macroscopic inner and outer fold arcs...... Chapter 5 Fig. 5.1 Map of thesis area showing location of samples previousiy dated. Fig. 5.2 Map of thesis area showhg location of samples dated by JO ~r/'"~rdating methods for this thesis ...... ---- Fig. 5.3 Microphotograph of detrital muscovite, ~ample93-RH 13Ob ...... Fig. 5.4 Microphotograph of detrital muscovite, sample 93-RHI07b...... Fig. 5.5 Microphotograph of'detri'tal muscovite, sample 93-RH42b...... Fig. 5.6 Microphotograph of rnetamorphic muscovite, sample 93-RH7O ... Fig. 5.7 Microphotograph of metamorphic muscovite, sample 93-RH26c. Fig. 5.8 Microphotograph of metamorphic muscovite, sample 93-RH62c. Fiç. 5.9 Microphotograph of metamorphic muscovite, sample 93-RH 1 13b...... -...... Fis. 5.10 Microphotograph of fabric-parallel muscovite, sample 93-RH59a Fig. 5.1 1 -111 Ar/-'"~rspectra for detrital muscovite analyses...... Fig. 5.12 JI1Ar/.")Ar spectra for metamorphic muscovite and whole-rock analyses...... -. .. - - -...... - .. .-.-. .---- Fig. 5.13 4)~r!"'~r spectra for metamorphic muscovite and whole-rock analyses...... List of Tables

Chapter 4 Page Tables 4. la & List of common clay minerals and micas and their 4. l b chemical and structural characteristics...... 96 Chapter 5 Table 5.1 Compilation of ages from the Meguma Terrane in southem Nova Scotia...... 162 Table 5.2 Summrq of '%r,@'~raçes from this thesis...... 190 Chapter 6 Table 6.1 S ummary of "'~r/~"Arages from this thesis...... 20 1 Abstract

Cambrian-Ordovician metasediments of the Meguma Group, Nova Scotia, fom the lowest esposed rocks of the most outboard of the terranes accreted to the northern Appalachian Orogen. The turbiditic sandstones and slates of the Goldenville Formation and overlying Halifax Formation escaped al1 but the last tectonic phase, the Early to Late Devonian Acadian Orogeny. Clues to the early geologic history of the Meguma Group remain in southern Nova Scotia, in Mahone Bay and the Tancook and LaHave Islands. Metamorphic grade is greenschist (locally sub-greenschist) facies, and rocks retain original sedimentary structures. A lack of higher-grade metamorphic overprinting makes the area an excellent laboratory for studying early stages of the Acadian Orogeny. Field studies, wïth petrographic, electron rnicroprobe, back-scatter electron image, XRD composition, XRD illite-muscovite crystallinity, and ""~r/"'~rtechniques provide new data that reveal details of the early history. This history can be described in three phases. Diagenesis and very-low-grade metamorphism caused reactions that produced a restricted mineralog of quartz, chlorite, muscovite, albite, graphite and accessory phases. Reactions were mainly controlled by the lithochernistry of the sediments, temperature as a function of depth, and restricted fluid flow. XRD illite-muscovite crystallinity data show that local areas retain diagenetic-iower anchizone characteristics. Detrital muscovite gives an age of 597 Ma: diagenesis is tentatively dated at 484 Ma. Regional metamorphism affected the Meguma Group between 395-388 Ma, causinç buckling of competent layers, cleavage, and tight folds ranging from the centimetre to the kilometre scale. The timing of metamorphism, based on "'Ar/''Ar ages from muscovite separates and whole rock samples subjected to rigorous step-heating schedules? is younger than earlier estimates. Combined with recent adjustments to the EarIy Proterozoic time scale, the new dates reported here resolve the oiitstanding problem of metamorphism in 4 17400 Ma rocks of the Torbrook Formation. Late-stage deformation, locally illustrated by reactivated folding and hydrothermal alteration, is dated at 376 Ma, and has afiècted XRD illite-muscovite crystallinity signatures in areas of the study. si i Sincere thanks go to Dr. Becky Jarnieson for her supervision of this thesis and for giving her val uable time, expertise and friendship. thank ail the members of rny supervisory cornmittee, Dr. Jarnieson, Dr. Nick Culshaw and Milton Graves for their continuing support, help and patience, especially afier 1 moved "across the pond". Dr. John Waldron at St. Mary's University also generously helped with field work and advice. A lot of people at Dalhousie University deserve thanks for providing help and advice: Gordon Brown for help with thin sections, Bob MacKay far micro probe assistance, Sandy Grist for teaching me the tricks of muscovite separation, Dr. Peter Reynolds and Keith Taylor for guiding me through the intncacies of argon dating, Charlie Walls for computer expertise, and Noma Keeping and Darlene Van De Rijt for keeping me and the whole department on track. Mike Collins is thanked for his hours of measuring and sampling in the field, as is Emily Gesner for her careful help with XRD sarnple preparation. Terry Hanson generously vol unteered her time to help col lect samples for XRD anaiysis. Sincere thanks to Steve Hirons at the XRD Lab at Birkbeck College in London, U.K. for al1 his help with the illite-muscovite crystallinity portion of the thesis. Fruitfd discussions with Rick Horne and his generous help with field photos is very much appreciated To fellow students at Dalhousie, thanks for the fun and fiiendships and I hope we keep meeting through the closely connected world of geology. New fnends at Mernonal University provided much appreciated help. To Pablo Valverde go muchas gracias for his excellent eye for taking microphotographs, and I thank Lindsay Hal I for computer help. Dr. Greg Dunning was generous with both time for working on the thesis during the final days, and with the use of his cotnputer equipment. Thanks go to Martha and David Farrar at The Cove Bed and Breakfast on Tancook Island for making us part of their family whiIe doing field work there: i value their continuing friendship. i especially thank my parents for their constant and Ioving encouragement. To John Ketchum, for practical heip with cornputer stuff, for a thousand other things connected ro this thesis, and for everything else, deepest thanks. This study was supported by an NSERC pst-graduate fellowship and a Geologicai Society of Arnerica research gant.

... Xlll Chapter 1 Introduction

1.1 Introduction

The Meguma Terrane of southem Nova Scotia, the most outboard of the accreted terranes of the northern Appalachian Orogen (Williams and Hatcher, 19831, records the

Palaeozoic and Mesozoic history of the orogen. The oldest rocks in the Meguma Terrane are Cambrian-Ordovician metasedimentary turbiditic sandstones and dates of the

Meguma Group (Schenk, 197 1 ) (Fig. 1.1 ). These were intnrded by (mainly) Devonian peraluminous granitoid plutons (Clarke and Halliday, 1980).

Meguma Group rocks escaped the early tectonic phases of the Appalachian

Orogeny but were strongiy affected by Early to Late Devonian (Acadian) delormation and related regional low-pressure metamorphism and granitic rnagrnatism. Metamorphic grade ranges fiom low greenschist facies (in some areas sub-greenschist facies) in the east-central portion of the Meguma Terrane, to upper amphibolite facies in the northeast and southwcst (Racside ct al, 1988). Tectonic pressures in the Mcgurna Group nowhcre exceed about 400 MPa (Raeside and Jarnieson, 1992). The dominant structures in the

Meguma Terrane are upright open to isoclinal folds with wavelengths of OSto 6 kilometres (O'Brien, 1988).

Previous metamorphic and structural studies provide information on the higher grade areas of the Megurna Group. Structural and geochernical work has been done in local areas within the lowest grade rocks (WiIliams and Hatcher, 1983; Henderson et al., Ill 1986; Graves, 1988; Graves and Zentilli, 1988) but the slates in particular lack petrologic

investigation with modem techniques

The south-central Meguma Group (Fig. 1.2) is known to be of lower greenschist

metarnorphic grade, but the degree to which these rocks have progressed beyond

diagenesis is unclear. Previous studies from the eastern Meguma Group noted signs of a

pre-cleavage fabric suggestive of an earlier metamorphic event (O'Brien, 1983% 1983b,

l983c, I985a, 1988). Although most such evidence was found within areas of higher

grade metamorphism and more complex deformation histories, the question persists to

what extent Meguma Group experienced an early deformation largely obscured by later events. The early history of the Megurna Group in general is poorly understood and ment data are lacking. Our present interpretation dates back to the work of Faribault in the early 1 900's (e.g. Faribault, 1899, 1908, 19 13, 1924, 1W9a, 1939b).

The regionally rnetamorphosed slates have been dated at 405-390 Ma, but an apparent inconsistency exists between these discordant m~r/3y~rwhole rock ages and regional deformation that affected rocks as young as -385 Ma (Reynolds et al., 1987;

Muecke et al., 1988; Schenk, 199 1 ; Raeside and Jarnieson, 1992; Keppie and Dallrneyer,

1994).

Controversy currently exists concerning relationships between metamorphism, deformation, granite intrusion, quartz veining, and gold mineralization. In particular, a definitive mode1 of gold rnineralization and a source for the gold rernain elusive, despite over a century of investigation (Faribault, 1888, 1899; Rickard, 19 12; Graves and

Zentilli, 1982; Henderson et al., 1986; 199 1; 1992; Zentilli et al., 1986; Mawer, 1986, .+- -. 3 Windsor Group (Carboniferous) South Mountain Batholith Megurna Group: Halifa~Formation: - Feltzen Mernber + Cunard Member IlIl Moshefs Island Member Goldenville Formation: = Tancook Member \ West Dublin Member G Rissets Beach Member "\ New Harbour Member

Figure 1.2 Map of the thesis area showing the members ofthe Meguma Group, the South Mountain Batholith, and the overlying Carboniferous Windsor Group. See Figure 2.3 for stratigraphie relationships. After Waldron ( l987), O'Brien ( 19881, this study. 1987; Kontak et al., 1990a, 1990b7 1996; Sangster, 1990; Williams and Hy, 1990; Wright

and Henderson, 1992, Kontak and Smith, 1993% 1993b).

This thesis examines the early history of metamorphism and deformation within the area of lowest metarnorphic grade in the Meguma Group and applies new data to the above problerns. The study area provides a window through which to view remnant evidence of events that was eclipsed elsewhere by a higher degree of deformation and metamorphisrn, contributing to a better understanding OF the early tectonic history of the

Meguma Terrane.

1.2 Previous Work:

The present level of understanding of the Meguma Group is based on geologic studies that began in the early 1800's. Jackson and Alger ( 1838- 1829) described the geofogyof the south Coast of Nova Scotia, and in 1855 Dawson recognised Meguma

Group rocks as a mappable unit distinct From Silurian and Devonian rocks. In 1898

Bailey systematically mapped the area and separated the sedimentary rocks into a quartzite division, a banded argillite division, and a black date division (Wentzell, 1985).

E.R. Faribault mapped the area for the Geological Survey of Canada from 1899 to 1929

(see references) and described three units, the oldest of which he called the 'gold-bearing series', tentatively dating it as Precambrian or Cambrian in age. He subdivided this series into two sedimentary formations and demonstrated the structural style of the region based on the distribution of these Formations. Faribault also recognised two main phases of

Devonian plutonism which he called biotite granite and muscovite granite, and the limestone and gypsum of the Lower Carboniferous Windsor series (O'Brien, 1988). Ami

(1900) flrst named the sedimentary units the Guysborough Formation and the overlying

Haiifau Formation. Woodman (I904a, 1904b) renamed the Guysborough Formation the

Goldenville Formation and called both the Meguma series, fiom the root of the native

word for the Mi'krnaq tndian people (Schenk, 1995). This term was changed later to the

Meguma Group by Stevenson ( 1959). Malcolm ( 1929), summarising the work of

Faribault, pubIished details of the sedimentology and gold occurrences of Nova Scotia.

Schiller and Taylor ( 1965) described spessartite-quartz rocks (coticules) from

what is now known as the Mosher's Island Mernber of the Meguma Group and produced

the first metarnorphic study of the Mcgurna Group (Taylor and SchiIler, 1966),

describing regional deformation and rnetamorphism, succeeded by contact

metamorphism. They also found local evidence of metasomatism and retrograde

metamorphism. In the sarne year Fyson (1966) studied the structures present in these

rocks, and in 1967 and 1969 Taylor produced a detailed compilation map of a large

portion of southwestern Nova Scotia. Other projects concentrated on specific rock units

such as the Goldenville Formation (e.g. Hams, 197 1, 1975).

The sedimentology of the Meguma Group has been extensively studied by P.E.

Schenk and his students, beginning in 1970, and continuing to the present (eg Schenk,

1970, 197 1. 1973, 1983, 199 1, 1992; Schenk and Lane, 1982). Much of his efforts were and are directed at testing his hypothesis, originally published in 1970, that the Megurna

Group sediments derived from the North African craton. Most of the more recent studies in the Meguma Group dealt with gold (and to a

lesser extent tin and zinc-lead) mineralization in the Meguma Terrane (e.g Graves, 1976;

Graves and Zentilli, 1982; Clifford et al., 1983; Crocket et al., 1983; Smith, 1984; Binney

et al., 1986; Crocket et al., 1986% 1986b; Farquhar and Haynes, 1986; Haynes, 1986;

Henderson and Henderson, 1986; Mawer, 1986, 1987, 1989; Richardson et al., 1988;

Henderson et al., 1989). Lithochemical characterisation of the Meguma Group resulted

fiom this interest in the mineralization of the sediments (Liew, 1979; Zentilli et al., 1986;

Sangster, 1987; Graves and Zentilli, 1988; Graves et al, l988), and supplied evidence for

the source rock type (Graves, 1988). Recent publications demonstrate the ongoing

interest in the mode of gold emplacement in Meguma Group rocks (Kontak et al., 1990;

Sangster, 1990; Williams and Hy, 1990; Henderson et al., 199 1 ; Kontak et al., 199 1 ;

Chattejee et al., 1993; King and Home, 1993; Kontak and Smith, 1993a, 19936;

O'ReiIIy, 1993; Smith et al., 1994).

Researchers also pursued topics in sedimentology (Harris, 1975; Stow et al.,

1984; Waldron and Jensen, 1984, 1985; Schenk, 1986; Waldron, 1987; Waldron and

Graves, 1987) and palaeontology (Cumrning, 1985; Pratt and Waldron, 199 1 ; Boucot,

1993). Some of these studies exarnined the sedimentary record for evidence of sea-level

changes (Schenk, 199 1 ; Waldron, 1992). Other investigations focused on structural

features as a means of identifying the deformational history of the Meguma Group

(O'Brien, 1983% 1983b, 1983c), and on cleavage and folding associated with main and

volume loss (Fueten et al., 1986; Henderson et al., 1986; Waldron, 1988; Henderson et ai., 1992; Wright and Henderson, 1992; Erslev and Ward, 1994). O'Brien's mapping in Lunenburg County ( 1988) resulted in the first new stratigraphie divisions of the Meguma

Group since the turn of the century.

There is a significant volume of work on the plutonic bodies hosted by Meguma

Group sediments, in particular the South Mountain Batholith (e.g. de Albuquerque, 1977;

Rogers and White, 1984; Smith, 1985; Clarke and Muecke, 1985; Rogers and Barr, 1988;

MacDonald et al., 1987; MacDonald et al., 1992; Tate and Clarke, 1993). The

relationship between the plutonic bodies and their host rocks has also been investigated

(e-g. Currie, 1975; Mahoney, 1996). Xenoliths encased in Upper Devonian larnprophyre dikes were analysed for dues to the composition of the lower cmst undemeath the

Meçuma lithotectonic zone (Owen et al., 1988; Ru ffman and Greenough, 1 990; Eberz et al., 1991). Their combined data suggest a heteroegeous basernent (Owen et al., 1988) that may be the Avalon Terrane (Eberz et al., 199 1 ). Xenolith protol iths may be rnetasedirnents similar in composition to the Meguma Group, and volcanic arc igneous rnaterial derived from a somewhat depleted mantle source (Rufian and Greenough,

1990; Eberz et al., 199 1). Chattejee and Giles ( 1988) described a three-stage P-T evolution for the xenoliths beginning with peak metamorphic conditions of 1030-1 166°C and 14.2-1 4.8 kb, followed by rapid decornpression and heating as xenoliths were incorporated into ascending host dykes, and a later low-P-T hydration event that affected both xenoliths and dykes.

Metamorphic studies in the Meguma Group have focused on areas where the degree of rnetamorphism is high enough to produce interesting metamorphic mineral assemblages. Megacrysts of staurolite, cordierite and andalusite were documented as early as the tum of the century (Bailey, 1898). Taylor and Schiller ( 1966) published details of the distribution of specific metamorphic facies and the metamorphic history of the Meguma Group, based on their mapping of two thirds of the area underlain by

Meguma Group rocks. Studies by Raeside et al., (1988) and Raeside (1993) concentrated on aspects of the metamorphism seen in the southwest and northeast of the Meguma

Terrane where metamorphic grade is the highest. Several theses at the honours, MSc. and Ph.D. levels also addressed specific problems in the higher-grade area of the

Meguma Group (e-g. Pumes, 1974; Chu, 1978; Cullen, 1983; Ross, 1985; Wentzell,

1985).

Several of these authors and others have proposed tectonic models for southern

Nova Scotia (Poole, 1967; Dewey, 1969; Rogers, 1970; Schenk, 1971 ; McKerrow and

Ziegler, 1972; Keppie, 1977).More recently, workers applied palaeogeographic and geochronologic data to interpreting the tectonic evolution of the Meguma Terrane (e.g.

Reynolds et al., 1973, 198 1 ; Dallmeyer and Keppie, 1987; Bouyx et al., t 993; Keppie and Dallmeyer, 1994).

More detailed investigation within this study area focused primarily on producing geological and geophysical maps (e. g. Hall, 1 98 1 ; Rowley, 1 985; Geological Sumey of

Canada Aeromagnetic 125,000 and 150,000 scale maps, 1984). The most recent detailed mapping was done by Waldron (Waldron and Jensen, 1985; Waldron, 1987,

1992; Waldron and Graves, 1987) and O'Brien (O'Brien 1985b, L985c, 1986, 1987,

1988). This thesis is based on field relations established by these recent studies. Previous geochronological studies of the region are particularly significant for

this thesis, and considerable work was done within the thesis area itself Several authors

dated the slates, sandstones and granites to constrain the age of the sediments (Keppie et

a[., 1985; Krogh and Keppie, 1990), the age of deposition, compaction, and diagenesis

(Wanless et al., 1971; Lambert et al., 1984), the age of metamorphism (Reynolds et al.,

1973; Reynolds and Muecke, 1978; Dallmeyer and Keppie, 1987; Keppie and Dallmeyer,

I994), the timing of emplacement of the various plutons in southem Nova Scotia

(Reynolds et al., 198 1; Clarke and Halliday, 1985; Dallmeyer and Keppie, 1987), and the

timing of mineralization (Zentilli and Reynolds, 1985). The timing of the accretion of the

Meguma Terrane to the rest of the Appalachian Orogen (Keppie and Dallmeyer, 1987;

Muecke et al, 1988) has been investigated, and a combination of J0~r/3"~rand fission

track dating was applied to these rocks in order to reveal their thermal history and the

timing of significant events (Elias, 1986; Ravenhurst, 1987; Reynolds et al, 1987).

Despite the extensive work done in the Meguma Terrane in the past, the lack of

interest in the low-grade rocks has left a gap in our knowledge of the early metamorphic and structural history of the terrane. One of the main reasons this area has been relatively

neglected is that the metamorphic geology was not considered an important control on

gold or tin mineralization. Some of the data presented here may have some bearing on

theories regarding gold mineralization in the Meguma Group.

Optical study of such fine-grained rocks poses a challenge, and it is difficult to characterise them in terms of metamorphic grade because the constituent phases are

present over a wide range of metamorphic conditions. Recent techniques and instrumentation provide ways to examine such fine-grained material and reveal evidence of past geofogic events and processes. This early history is important for understanding the earIy accretionary history of the Meguma Temne and the nature of regional metamorphism and deformation.

1.3 Obiectives and Amroach:

The field area encornpasses that portion of the Meguma Group which has retained evidence of the earliest metamorphic and structural history. These are the low-grade rocks of the Meguma Group that outcrop around Mahone Bay and to the southwest past the LaHave Islands (Fig. 1.2).

For the most part the rocks are fine-grained sandstones and slates that preserve primary sedimentary features and have homogeneous mineral assemblages comprising c hlorite, muscovite, quartz, Feldspar, and accessory phases.

Coastai exposure in the area is excellent, and road access throughout the region is fair to good with numerous roadcuts and lakes that expose inland outcrops. Several rivers crosscut regional folds and also provide access to inland rocks. Some of the islands are accessible by road and feny: others can be reached by boat with minimum difficulty.

Detailed field work was designed to discover any evidence of early (pre-cleavage) strain fabrics such as structural breaks or layer-parallel high-strain shear zones. Over 300 oriented samples from every unit and rock type provided material for a sizeable database of petrologic and compositional information. Frorn these, specific samples were chosen for -'OA~/~~A~dating and another sample set furnished matenal for an X-ray diffraction

(XRD)illite-muscovite crystallinity study.

Optical examination of the majority of the samples disclosed microtextural details, and microprobe work on 86 polished sections supplied cornpositional data.

Back-scatter electron (BSE) microprobe images revealed details previously shrouded by the fine-grained nature of the slates. This technique proved useful in searching for evidence of an early schistosity, predating both the formation of gamet and ilmenite porphyroblasts and a sIaty cleavage. The rocks of the Goldenville-Halifax transition zone

(GHT) are of particular value here because of the unusual rnineralogy of one of the units.

Elsewhere in Nova Scotia the GHT zone is only a metre or two wide, but in the field area the zone increases up to two kilometres in thickness and individual members and uni& can be distinguished (O'Brien, 1985b, 1985c, 1986, 1988). The Mosher's Island Mernber, the basal unit of the Halifax Formation, is a slate-dominated, calcareous, manganiferous argiIIite. This member has a high carbon and manganese content and contains early spessartine gamet, ilmenite, and quartz porphyroblasts as well as gamet-quartz coticules.

The stability field of gamet is influenced significantly by even small concentrations of manganese (Symmes and Ferry, 1992), in this case producing gamet porphyroblasts in low-grade rocks. The early porphyroblast phases were examined for evidence oFany pre-regional metamorphic fabrics and textures preserved as inclusion trails (e.g. Vernon

1978).

XRD crystallinity studies performed on the white mica phases aided in understanding the low-grade metamorphism of the area. While it is usually not feasible to map conventional isograds in very low-grade pelites (sub-greenschist to lower

greenschist facies), XRD illite-muscovite crystallinity studies can reveal variations in

grade. The work of several authors (e.g. Memman and Roberts, 1985; Frey, 1987; Awan

and Woodcock, 199 1; Kisch, 199 2) indicates that the degree of white mica crystallinity is

correlated with pst-depositional diagenesis and metamorphism. The ct-ystallinity index

of white mica increases with temperature and deformation because it is influenced by

such factors as lithology, stratigraphic age, thickness of stratigraphic overburden,

geothermal gradient, and strain (Awan and Woodcock, 199 1; Kisch, 199 1a, 199 1b). The

crystallinity of illite increases as it recrystallizes, coarsens, and becomes white mica,

producing sharper peaks on the difiaction trace with increasing grade (Yardley, 1989).

XRD values can be equated with metarnorphic processes ranging fiom diagenesis

through anchimetamorphism to lower greenschist grade metamorphism.

Sixty samples collected from throughout the thesis area were analysed by XRD

techniques for mineralogical and crystallinity data. Results revealed more precise details

about the degree of diagenesis and metarnorphism experienced by the rocks, and

delimited areas where "'~r/~"~rdata suggest a more recent event has locally overprinted the muscovites.

Petrological examination showed the presence of more than one generation of

white mica. Multiple generations of white mica may complicate the intcrpretation of

'OAd3'Ar data. Previous dates from the Meguma Group were based on whoIe rock analyses and produced many disturbed spectra (Muecke et al., 1988). In this study seven samples of detrital and metamorphic muscovite grains were separated and analysed by ''OA$~A~ dating, together with two whole rock sarnpies. The results helped improve estimates of the timing of regional metamorphism (Chapter 5).

With the exception of the XRD illite-muscovite crystallinity studies, full access to al1 the necessary equipment and support facilities is available within the Earth Sciences

Department of Dalhousie University. Birkbeck College of the University of London in the United Kingdom has good facilities for XRD il lite-muscovite crystallinity studies and their operating procedures satisQ international standards and recommendations.

The results contribute to an integrated metamorphic and structural history for the low-grade area of the Meguma Terrane. They provide data useful to workers concerned with Meguma Group and Appalachian Orogen studies. Chapter 2 Regional Geology, Lithologies, Structure and Cold Mineralization

2.1 ReAonal Geology

The Meguma Terrane encompasses al1 of southern Nova Scotia fiorn the

Cobequid-Chedabucto Fault Zone to the Atlantic Ocean (Fig. 2.1 ). Although the on-land

area is relatively small, it is the largest of the Appalachian Terranes with an area of about

200,000 km' (Schenk, 1995). Geophysical research suggests it underlies a large part of the continental shelf, southward beneath the Scotian Shelf and possibly as fâr as the tail of the Grand Banks (Haworth et al., 1988; Pe-Piper and Loncarevic, 1989). Offshore to the east, the Meguma-Avalon Zone boundary is thought to extend along the Collecter

Magnetic Anomaly (Williams and Haworth, 1984; Shih et al., 1993). Westward, the

Meguma-Avalon boundary lies in the Bay of Fundy, coincident with the Mesozoic Fundy

Graben (Schenk, 1995) and with the Nauset magnetic anomaly (Keen et al., L 99 1 ), although further to the southwest this anomaly may not follow the Meguma-Avalon boundary (le0 et al., 1993).

The oIdest exposed rocks are the Meguma Group, a thick package of metamorphosed Cambrian-Ordovician turbiditic sandstones and shales (Figs. 2.2,2.3).

These are overlain by a thinner sequence comprising slates, quartzites and rnetavolcanic rocks of the White Rock, Kentville, New Canaan and Torbrook Formations, latest

Ordovician or Silurian to Early Devonian in age (Schenk, 1970; Schenk and Lane, 1982;

Schenk, 199 1). Possible correlatives of the Meguma Terrane exist in northwest Africa

(Schenk, 1992). 15 Figure 2.1 The tectono-stratigraphie terranes of the Appalachian Orogen. The Meguma Terrane is delimited by the Cobequid-Chedabucto fault zone (CCFZ), the Nauset anomaly (NA) and the East Coast magnetic anomaly (ECMA). The continuation of the Nauset anornaty to the north into the Bay of Fundy (broken line) is uncertain. NF, Norumbega Fault; FF. Fredericton Fault; TH, Turtle Head Fault; GM, Grand Manan Island; NMB, North Mountain Basalt; SMB, South Mountain Batholith. Seismic lines as per Keen et al. ( 1991 ). After Williams ( 1979), Hutchinson et al. ( l988), Keen et al. ( 199 1 ). Figure 2.2 Map of the thesis area showing the members of the Meguma Group, the South Mountain Batholith, and the overly ing Carboni ferous Windsor Group. See Figure 2.3 for stratigraphic relationships. After Waldron ( 1987), O'Brien ( 1988), this study. Repeat of Figure 1.2. Fel tzen Member Units of Tancook Mernber exposed on Tancook Islands and Aspotosan Halifax Cunard Peninsula Formation Member -- =T4= Upper Slaty Unit Mosher's Island Mem ber - - T3 [Ipper Sandy Unit West Dublin Tancook Member Member Goldenvil le -T2- Lower Slaty Unit Formation Risser's Beach Mernber -1-1= Lower Sandy Unit New Harbour Member

Figure 2.3 Lithosratigraphy of the Meguma Group as exposed in the study area (after Waldron, 1987). The Meguma Group and the overlying formations are variably metarnorphosed

from lower greenschist hcies (lmally sub-greenschist) to upper amphibolite facies. The

lowest metamorphic grade is found in the east-central part of the terrane with

metarnorphic grade increasing away from this region to the east-northeast and to the

southwest (Fig. 1.1 ). A more detailed discussion of the metarnorphism is in Chapter 4.

These Lower Palaeozoic rocks are folded into large-scale upright fol& with

wavelengths of 0.5 to 6 kilornetres, with an associated penetrative axial-planar cleavage.

Fold axes trend northeast-southwest, generally parallel to the Atlantic Coast, but trend

more southward to the southwest of Shelburne. Metamorphism and deformation are attributed to the EarIy to Late Devonian Acadian Orogeny (Raeside and Jamieson, 1992).

All these sequences are intmded by Devonian peralurninous granitoid plutons (Clarke and Halliday, 1980) that are exposed over more than 7300 square kilometres (Figs. 2.3,

2.3) (MacDonald et al., 1992).

Metasedimentary, minor metavolcanic and granitic rocks are al1 unconfonnabIy overlain by little-deformed Lower Carboniferous clastic sedimentary rocks of the Horton

Group, and clastic, evaporitic and carbonate rocks of the Windsor Group. The remaining overlying rocks are feldspathic sandstones of the Scotch Village Formation, and

Triassic-Jurassic rocks including sandstones and shales of the Annapolis Formation, the

North Mountain Basalt, and sandstones and limestones of the Scots Bay Formation (Bell,

1960; Crosby, 1962). Cretaceous sands and clays survive in certain river valleys (Stea et ai., 1996). The study area contains rocks of the Megurna Group, the South Mountain

Batholith and small, isolated remnants of the Windsor Group. Of these, the Meguma

Group rocks are of interest for this study as they record the early history of the Meguma

Terrane. The following sections describe these lithologies in more detail.

2.2 Litholorries of the Meguma gr ou^

The Meguma Group is composed of two main formations, the lower Goldenville

Formation and the conformably overlying Halifax Formation. The Goldenville Formation has a calculated minimum thickness of seven kilometres (O'Brien, 1988). This is an approximation since the base of the Goldenville Formation is nowhere exposed and the contact with the Halifax Formation is obscure in many areas, The Goldenville Formation typically consists of fine-grained sandstones, often in thick uniform packages separated by thin layers of grey to green siltstone and slate (Schenk, 199 1).

The Halifax Formation varies from an estimated two to seven kilometres thick, the thickest areas being in the southeast (O'Brien, 1988). It is composed of thinly laminated black, pyritiferous date with interbedded siltstone and argillite (Taylor, 1967,

1969; Schenk, 1970; Waldron, 1992).

The sedimentary rocks are interpreted as deposits of high-density turbidity currents that flowed in major submarine-fan channels, likely derived from the mouth of a major river system that drained a large area of Gondwanaland (Schenk, 1970; Stow et al.,

1984; Waldron and Jensen, 1985; Waldron, 1993; Schenk, 1992). Sediment type varies hom sands to mu&, and the presence of units rich in organic material or manganese is attributed to sea-level fluctuations in the source area (Schenk, 199 1; Waldron, 1992).

Schenk proposed the West Afncan Craton as a source for Meguma sediments

(e.g. Schenk, 1992). Detritus from the craton, generated by Late Proterozoic glaciation and tectonism, collected in what is now Mali and discharged intermittently on to the

North Gondwana rnargin.

The alternating nature of the upward transition from the Goldenville sandstones to the Halifax dates creates dificulties in defining the contact between the two. tn areas where the Meguma Group is thin and individual members cannot be distinguished, and where outcrop is poor, the contact is obscure. Where the Meguma Group is thicker, the contact between the hohas been placed where the ratio of sandy to slaty layers is 1 :1

(Waldron, 1987).

Within the study area, however, contacts are clear, and the Meguma Group can be further subdivided into distinct lithostratigraphic units. O'Brien ( 1 %Sb, 1995~2,1986,

1988) mapped these units thoroughly and proposed a three-way division of the Meguma

Group into the Goldenville Formation, the Halifax Formation, and an intermediate transition unit, the Green Bay Formation. O'Brien included the New Harbour Member in the Goldenville Formation, and the Risser's Beach, West Dublin, Tancook and Mosher's

Island Members in the Green Bay Formation. The Cunard and Feltzen Members cornprised the Halifax Formation. Waldron and Graves (1987) subsequently proposed reverting to the older two-fold division of the Meguma Group while retaining the individual units mapped by O'Brien. Waldron (1 987, 1992) placed the lower four members - the New Harbour, Risser's Beach, West Dublin and Tancook Members - in the

Goldenville Formation, and placed the boundary of the Halifax Formation at the base of

the Mosher's Island Member. This arrangement, which is used here, has the advantage of

placing the boundary between the Goldenville and Halit-kx Formations at the base of the distinctive Mosher's Island Mernber. Figure 2.2 shows the distribution of these units in the thesis area and Figure 7.3 depicts the lithostratigraphy of the Meguma Group.

The following member descriptions are based on fieldwork conducted for this thesis, using the maps of O' Bnen (1988) as guides to distibution of members and outcrop locations. In the Tancook Islands, Waldron's (1987, 1992) map is also used. In the very rare case where O'Brien's and Waldron's maps differ, as in the placement of a boundary between members, O'Brien's mapping appears to agree best with observed field relations. The following descriptions are augmented where appropriate with information and interpretations from other workers in the area. Fieldwork concentrated on looking for evidence of early strain fabrics and on sample collection, and observations were intended to corroborate, not duplicate, existing mapping.

22.1 New Harbour Member

The New Harbour Member is dominantly grey- to buff-coloured, massive sandstone layers, in places two to three metres thick, with local thinner green slate layers.

The sandstone packages are t'ne- to very fine-grained and featureless except in the top 20 cm, where fine laminations and cross-laminations are visible. The green slate layers show laminar bedding. Other prirnary sedimentary structures include varyng styles of worm burrows, channel fills, slumping, loading, and other escape structures. Cleavage is visible only in the few slate layers.

Brown-weathering carbonate concretions are present in some layers, ofien as a series of ovoid pods measunng up to 50 cm along the longest axis. At Long Point, in the southwest of the study are% these pods measure 30 by 10 cm and are typically deeply pitted where carbonate has ieached out.

The Rissefs Beach and West Dublin Members succeed the New Harbour Member in the southwest of the thesis area, fiom the LaHave Islands to Broad Cove.

2.2.2 Rissefs Beach Member

Buff to green sandstones, 5 to 20 cm thick, are interbedded with green siltstone layers ranging fiom 1 to 15 cm thick. Some sandy layers are massive and lack distinguishing features. resembling those of the underlying New Harbour Mernber. others exhibit laminations and cross-bedding. Starved ripple beds give a "pinch-and-swell" effect to some layers. Worm burrows are cornrnon locally and soft-sediment deformation

(small-scale slumping, loading, sand volcanoes) exists throughout. Siltstone layers contain ilmenite porphyroblasts, and pyrite cubes appear in some sandy layers, becoming more abundant near the top of the member.

Sandy layers in the Risser's Beach Member also contain carbonate concretions, both as pods and as brown weathered tayers. Cross-bedding is sometimes visible in the concretions. Cleavage ranges fiom non-existent in massive sandy layers, to slight in cross-bedded layers, to strong in siltstone layers. The contact between the Risser's Beach Member and the underlying New Harbour

Member is sharp and confonnable, in contrast to the gradational contact between the

Risser's Beach Member and the overlying West DubIin Member.

3.2.3 West Dublin Member

The West Dublin Member is composed of buff-coloured sandstone altemating with grey-green finer-grained sandstone and green siltstone. The sandstone layers are massive, laminated, or cross-bedded and dominate the other types of layers by a ratio of

2: 1. They can be up to 50 cm thick while the finer-grained Iayers never exceed 20 cm and have Iaminar bedding.

The types of soft sediment deformation seen in the lower members and the cobble- and boulder-size ovoid carbonate concretions are also present in this unit. A few of the massive sandstone layers contain carbonate lenses that are partly leached out.

Ilrnenite porphyroblasts are visible and pyrite is locally abundant in sandy layers.

Cleavage is weak in massive sandstone layers and bemr developed in layers with visible bedding features containing a higher proportion of phyllosilicates.

2.2.4 Tancook Member

The Tancook Member is in sharp confomable contact with the New Harbour

Member in the Tancook Islands and the Blandford Peninsula. Stratigraphically, i t correlates with the Risser's Beach and West Dublin Mernbers, and may represent a lateral facies change fiom the southwest to the northeast. The nature of the contact between the West Dublin Member and the Tancook Member is not known, but rnay be gradational, or sharp across a syn-sedimentary fault (O'Brien, 1988).

Figure 2.3 shows the stratigraphic relationship between these members. In the

Tancook Islands, where the Tancook succession is thickest, Waldron (1987) subdivided the rnernber into four informal subdivisions, described below.

iT; Loww SanJv Unit

Buff-green sandy layers up to 75 cm thick, with laminar bedding and cross-bedding, alternate with date layers ranging from 1 '/t - 2 cm to 12 cm thick.

Bioturbation, loading, slumping and dewatering structures are al1 preserved. There are visible ilmenite porphyroblasts and some of the sandy layers contain carbonate concretions.

1;- Lower Shaly iJnif

Green slate layers with a relatively high sand content altemate with dark, laminated slates. The few sandy Iayers present are up to 50 cm thick and are featureless or have laminar bedding or cross-bedding. They also contain faint evidence of bioturbation and burrows on the tops of the layers. Loading and slumping are present as wef l as rut-weathered carbonate concretions. The dark slates show strong cleavage and have large (up to 6 cm) pyrite cubes, comrnonly arranged in layers.

7: 7: @per Sundy Ihir

Packages of massive or faintly cross-bedded grey-green sandstones measure up to

50 cm, loçafly up to 1 m thick, and alternate with 10 to 20 cm thick green shaly layers.

Shale layers are less abundant than sandstone layers although the ratio of the two is 1: 1 in places. Sedimentary structures include wonn burrows, flute and 1oad casts and ripup

clasts. Carbonate concretions in sandy layers form both smaI1 ovoids ( 1-1 !h cm) and thin

layers. Cleavage is strong in shale layers but does not penetrate the sand layers. A

fossiliferous bed containing trilobite fragments is present in this unit (Waldron and

Graves, 1987; Pratt and Waldron, 199 1).

T, [fpperShy Unif

Light to medium grey-green slates with a high proportion of silt are finely laminated to featureless and show some rust staining in layers containing pyrite cubes.

Sand layers range from 3 to 20 cm thick (locally 50 cm thick) and are massive or cross-bedded. They also have carbonate concretions and worm burrows in the top portions of the layers. The ratio of date to sandstone is 4:1 and clcavage is pronounced in slaty Iayers.

Contacts between the units are transitional although they can bt fairly abrupt. In the past, the top of the Tancook Member was placed above the top of T,, the upper sandy unit, placing T,, the upper slaty unit, within the Mosher's Island Member (Waldron and

Graves, 1987). O'Brien (1986) placed the base of the Mosher's [sland Member at the last thickly bedded sandstone layer measuring behveen 30 and 100 cm thick Waldron ( 1987) has since adopted this boundary and it is used in this thesis.

2.2.5 Mosher's Island Member

This distinctive member of the Meguma Group is used as a marker horizon delimiting the Goldenville-Halifax Transition (GHF) zone. It overlies the West Dublin Member and the Tancook Member with a gradational contact in both cases, and is present throughout the thesis area.

Pale to medium grey-green or blue-grey shales and dark slates dominate sandy layen by a ratio of 9: 1. The thick massive sandy layers seen in the Goldenville Formation are absent and most sandy layers are 10 to 15 cm thick with a rare example of 30 cm thickness. Laminar beds and cross-beds are millimetres to centimetre thick and some sandstone layen are weathered brown. Shales and slates are between 15 and 40 cm thick and some dark slates appear rich in organic matter. Sedimentary features include scouring, loading (Fig. 2.4), dewatering structures and starved ripples, as well as small

(0.5 cm diameter) worm burrows and rare, large ( 1.5 cm diameter x 20 cm length) wom burrows ( Fig. 7.5). Locally, outcrops are stained mst coloured.

Carbonate concretions are smaller than in underlying rnembers and there are thin brown weathered carbonate lenses. One outcrop on Tancook Island has weli developed cone-in-cone structures not seen elsewhere in the field area (Fig. 2.6). They are thought to result fiom the growth of individual fibrous calcite crystals in partialiy lithified shales, where individual crystals displace the sediment and produce a cone-like interference pattern with other crystals (Franks, 1969; Pettijohn, 1975). Pynte cubes Vary fiom 1 mm to 3 cm and are most abundant in sandy layers. Ilmenite porphyroblasts and arsenopyrite are also present. Cleavage is moderate to strong.

Two features in the Mosher's Island Member are distinctive. One is a layer of small (up to 3 cm diameter), sphencal nodules in organic-rich layers near the top of the Figure 2.4 Dewatering structure (loading) in Mosher's Island Member, Bush Island. Dime for scale.

Figure 2.5 Large worm burrows on bedding surface, Mosher's Island Mernber, Bush Island. Dirne for scale. Figure 2.6 Cone-in-cone structure in layer of Mosher's Island Member, Tancook Island. Dime for scale.

Figure 2.7 Bedding layer of manganese carbonate nodules, Mosher's Island Member, Bell's Cove. Lens cap for scale. member (Fig. 2.7). These, along with tiny, arnber gamets that are locally large enough to

be visible and impart a granular texture to weathered rock surfaces, are diagnostic.

2.2.6 Cunard Member

The Cunard Member is in sharp, conformable contact with the Mosher's Island

Member and is easily identified by the conspicuous grey to dark grey, pyritiferous (up to

50% locally), suIfide stained slates. Bedding is finely laminated but irregular in places.

Very dark layers exhibit a high organic content that may contribute to the strong fissility of the member (Waldron, 1987). Most sandy layers are grey, lens-shaped, or 1-1 -5 cm thick layers with laminated bedding, but some are up to 50 cm thick and have graphitic layers at their bases. Intermediate sandy layers (8-10 cm thick) range from featureless to cross-bedded, and comrnoniy host carbonate concretions and their leached, pitted equivalents. At Gaff Point near Kingsburg, ovoid carbonate concretions up to I m long lie in a thick sandy Iayer (Fig. 2.8). Primary structures such as starved ripples, loading, escape structures, tipup clasts and slumps exist although iron sulfide weatherinç obscures them in many places.

Cleavage is very strong in slaty Iayers, less so in sandier layers and refracts across contacts between slate and sandstone layers. Py-rite is concentrated in sandstone layers and both pre-dates and overgrows cleavage. Folding is more intense in date layers. Total thickness of the Cunard Member is highly variable, much more so than in other members in the Meguma Group. O'Brien ( 1988) suggested that upward block-faulting during deposition of the Cunard Mernber was responsible for abrupt local thinning of the Figure 2.8 Layer of Iarge carbonate concretions (dark layer to the lefl of Mike Cunard Mem ber, Gaff Point, Kingsburg.

Figure 2.9 Paired worm burrows (small white ovals) on bedding surface and oblique to bedding surface. Feltzen Member, Blue Rocks. Dime for scale. thickest rnember in the group. The lack of bioturbation or worm burrows together with the high pyrite and graphite content suggest deposition under anoxic or near-anoxic conditions. Sulphur isotope work by MacInnis ( 1986) and Sangster ( 1987, 1990) provides good evidence for restricted circulation, resulting in two anoxic intervals at the base and top of the Mosher's Island Member. Waldron (1 987) suggested a period of basin-wide stagnation as the cause of anoxic conditions at the base of the Cunard Member.

32.7 Feltzen Member

This member has a higher silt component than the underlying Cunard Member and is medium to dark grey, in places blue-grey. Slate layers are the darkest and are either homogeneous or have fine, laminar bedding. Rhythmically interbedded siltstone layers range in thickness from less than I cm to 20 cm and can fom as much as 20% of the outcrop. Features such as cross-bedding, starved ripples, and sofi sediment deformation (slumping, loading, and escape structures) are most evident in siltstone layers. Pynte with associated rust weathering and small carbonate concretions are most abundant in these layers. Weathered patches, larger than the small carbonate concretions, indicate where concretions may have been. The Feltzen Mernber contains abundant worm burrows, with spectacular examples of paired burrows exposed at Blue Rocks, near

Lunenburg (Fig. 2.9). The contact with the underlying Cunard Member is gradational and its upper boundary is not exposed in the study area.

The Meguma Group was intruded by granodiorites and quartz monzonites of the

South Mountain Batholith at 370 Ma (MacDonald et al., 1992), and in the study area, al1 except the Risser's Beach and Feltzen Members are in contact with the SMB. Rocks within the contact aureole are spotted homfels with porphyroblasts of cordierite and andalusite (var. chiastolite). Primary sedimentary structures are commonly visible.

Limestone and associated rocks of the Lower Carbonikrous Windsor Group unconformably overlie Meguma Group rocks and intnisives around northem Mahone

Bay. In the LaHave Islands, the Triassic-Jurassic diabase Shelburne Dyke intrudes the

Risser's Beach, West Dublin and Mosher's Island Members.

2.3 Stmctural Geolom

The dominant regional structures are broad, upright folds that trend north-northeast, and plunge gently to the northeast and southwest forming culminations at Ca. 10 km. intervals (O'Brien, 1988). These F, folds, show as antiches in figure 2.2, can extend for 50 km or more and have wavelengths varying fiom 0.5 to 6 km and relatively constant amplitudes of 0.5 to 1.5 km (O'Brien, 1988). [n the study area, folds range from the kilometre scale of the major anticlines to centimetre and half-metre to metre scale folds. Measured axial traces Vary in orientation fiom 030" to 070" and 197" to 243" with a maximum plunge of 38". [n general, the thick, sand-dominated lithologies have open folds with rounded to chevron profiles whiie those in thinner date layers are tight and have chevron profiles, although exceptions to these foId stytes were observed in both rock types.

Beds are oriented right way up everywhere in the region with the exception of outcrop at Feltz South where Feltzen Member sediments exhibit folding and shearing unique in the study area (Fig. 2.10). Overîumed beds also appear in Feltzen Member

rocks at Sunnybrook, confined to one part of the outcrop. Axial planar, sub-vertical to

vertical cleavage is visible in ail siltstone and slate layers, less evident or absent in

sandstone layers. In the hinges of major anticlines on Tancook Island and, in particular,

on The Ovens peninsula, more intense deformation is visible as brecciated zones,

abundant quartz veins, thrusts, duplex structures and flexural slip in folds. in the

southwest of the thesis area, at Broad Cove, distinct breccia zones have a very narrow

range of orientation, striking between 705 and 21 5" (Fig. 2.1 1). Numerous faults and kink

folds displace cleavage throughout the thesis area, usually in a sinistral fashion.

3.3.1 Deformation History

In the thesis area deformation can be separated into stages, beginning with

syn-sedimentary and diagenetic processes that produced features such as dewatering structures, slumps, bioturbation, carbonate concretions and compaction. These sedimentary structures are visible throughout most of the study area, despite subsequent deformation.

The main stage of deformation in the Meguma Group produced cleavage and folding, attributed to the effects of the Acadian Orogeny. Bedding-parallel veins result

€rom compaction and hydraulic fracturing. in the thesis area, cleavage displays convergence and divergence as it passes fiom sandy to slaty beds in buckled layers.

Cleavage measurements taken at several locations in the hinges and on the limbs of fol& commonly have the same strike and dip although examples exist where cleavage is Figure 2.10 Highly defonned Feltzen Member rocks at Feltz South. Bedding is essentially horizontal, shallowly dipping and folded. Sheanng has transposed beds (visibIe as pale vertical layers) into vertical layers orihoçonal to original beds.

Figure 2.1 1 Breccia zone in Risser's Beach Member, Broad Cove. Zone is visible as weathered trenches under and lefi of hammer. arrayed in a convergent pattern around fold hinges (Fig. 3.12). This latter pattern is seen

Iucally on Tancook Island near the crest of the Indian Path Anticline and immediately

West of The Ovens in the crest of the Ovens Anticline. Bedding-parallel quartz veins are buckled, locally very tightly, by layer-parallel shortening and cleavage.

These features suggest that in the study area the main deformation involved layer-parallel shortening, with concomitant cleavage developed normal to bedding planes and buckling of eariy bedding-parallel veins and more competent carbonate-rich layers.

Progressive layer-paralle1 shortening produced folding on scales ranging from centimetres to kilometres, and cleavage. In local areas, such as on Tancook Island and west of The Ovens, in the crests of anticlines, folding continued afier cleavage formation ceased, expressed as the tightening of existing folds. Just west of The Ovens, a fold in the hinge of the anticline has tightened to the extent that a thwt has developed (Fig. 2.13). A study by Henderson et al- ( 1986) in the Goldenville Formation described the same progression of fold and cleavage development. Recent work by Home and Culshaw

( 1994) and Home et al. ( 1994) suggests that folding accompanied by flexural slip continued from the early deformation stages to as late as during contact metamorphism associated with the 370 Ma emplacement of the South Mountain Batholith.

The late stage of Folding may be synchronous with the defonnation demonstrated by the overturned beds and shear zones at Feltz South. Vertical sheanng (striking

050+90°), indicative of ductile deformation, is axial planar to folding and in regularly-spaced zones is intense enough to obliterate al1 sedimentary features and main-stage folding. These rocks lie in the syncline between the Ovens Anticline and the Figure 2.12 Cleavage arrayed in a convergent pattern around folded layers, Cunard Member, Bel 1's Cove.

Indian Path AnticIine (Fig. 2.2) and deformation has been interpreted as vertical shear zones developed in foId cusps to accommodate anomalous amounts of shortening

(O'Brien, 1988). This rnay be the same deforrnation seen in the crests of the anticlines, such as at nearby Ovens Anticline where abundant quartz veins, produced during late-stage folding (Home and Culshaw, 1994), suggest that fluids may have facilitated some of the deformation at the crest of the fold. At Feltz South quartz veins are absent and a more ductile and intense deformation may have accomrnodated the folding in the trough of the anticline. The crests of anticlines also contain breccia zones, and numerous faults with slickensides in va~ngorientations. These effects may al1 be features of late-stage folding when previously developed folds tightened (O'Brien, 1988, Home and

Culshaw, 1994). The observed late-stage deformation may also have implications for anornatous ''~r/~'Arages and XRD crystallinity data f?om this region, discussed in later chapters.

The most recent deformation seen in the thesis area is ductile to brittle in character, At Broad Cove, in the southwest, distinct breccia zones have a very narrow range of orientation, usuaily striking between 205 and 21 5". There are numerous faults and kink folds that displace cleavage, usually in a sinistral fashion. Most measured sinistral kink fold and fault orientations are oriented northwest, while less numerous dextral features have a northeast orientation. These exist everywhere, most commonly in the southwest of the study area, and cross-cut sedimentary and deformation fabrics, pst-dating the but k of the regional deformation. They have been interpreted as a conjugate set resulting from horizontal east-west compression (Fyson, 1966; Graves,

1976; O'Brien, 1988; Henderson et al., 1992).

There is evidence fiom elsewhere in the Meguma Group for some regional-scale fold growth as late as during or afier pluton emplacement (e-g. Home and Culshaw,

1994; Culshaw and Liesa, in prep). A thirty kilometre wide band of pst-main stage

Acadian deformation between Meteghan and Yarmouth, along the southwest shore of the

Bay of Fundy, has structures that mirror those on the Cobequid-Chedabucto Fault zone and may also demonstrate deformation that post-dates the initial docking of the Megurna

Terrane.

The stmctural features described above indicate a relatively simple strain history for this part of the Meguma Group. Burial and compaction preceded regional deformation. During the main deformation phase, layer-parallel shortening was accompanied by cleavage formation, buckling and folding. A third stage of tectonic deformation characterised by intense deformation in the crests and troughs of some of the large anticlines resulted fiom late-stage tightening of the existing folds. None of the tectonic effects were strong enough to obscure the earliest features except in the rare example at Feltz South.

More recent events include the intrusion of the South Mountain Batholith, ductile-brittle faulting and jointing, and later still, emplacement of the early Mesozoic

Shelburne dyke (Wanless et al., 1968; Papezik and Barr, 198 1 ). The extent and pattern of the outcrop seen today are the result of these events, uplifi and erosion, and final sculpting by glaciation. 2.4 Gold Mineralization

Metals such as W, Cu, Zn, Mn, Total C, Pb, Ba, Mo, Au, As and Ag are found in

Megurna Group sediments and granite intrusions in varying concentrations (Sangster,

1990). Within the study area, manganese (in coticules) is present in the Moshets Island

Member. Gold occurrences are recorded in several locations such as The Ovens,

Blockhouse, Gold River and Tancook Island, although none are now mined.

The genesis of Meguma gold deposits is of ongoing interest and speculation.

Faribault ( 1888) thought the gold was emplaced by granite-derived, ascending hydrothermal fluids which leached quartz, gold and other metals from the host metasedimentary rocks and deposited them in saddle veins on anticline crests. He later refuted his own model, observing that grmitic dykes and veins cross-cut auriferous quartz veins so that there could be no genetic association between the granites and gold deposition (Faribault, 1899).

More recently, Graves and Zentilli (1982) described a process of early vein emplacement, at the onset of horizontal compression, by hydraulic fracturing. Folding and axial-plane slaty deavage development followed. Mawer ( 1986) suggested that the gold-bearing, bedding-concordant veins formed late in the folding regime. Henderson et al. (1990) suggested vein formation by hydraulic extension-fracturing (water silIs) in a tectonic regime where there was no shearing along bedding planes. Thus veins couId have formed by dewatering during compaction and lithification of sediments.

The granite-gold hypothesis was revisited by Kontak et al. (1990a, 1990b), who dated micas and amphiboles fiom veins in gold districts and obtained 'OAd3'~r ages of 380-362 Ma. They conciuded that gold-bearing veins were emplaced after regional metamorphism, likely during granite emplacement. The debate over timing and mode of gold-bearïng vein deposition continued with fiesh vigour as a result of these observations. Reynolds and Muecke ( 1978) dated the metamorphic event at 400-415 Ma, but also found that some slates produced argon ages of 370 Ma, probably because of resetting by heat fiorn the emplacement of the SMB. Kontak et al. (19906) rejected the suggestion that the argon ages of the veins they dated may have been similarly reset

(iienderson et al., 1992). The model proposed by Kontak et al. was also criticised by

Henderson et al. ( 199 1) who cited field evidence of the geometry and deformation of the veins as evidence for a metamorphic origin for gold emplacement; their arguments were in tum disputed by Kontak et al. (199 1).

Kontak and others (Kontak et al., 1990; Kontak and Smith, 1993% 1993b;

Kontak, 1996) compiled evidence fiom 'OA~/~"A~dating, fluid inclusion, mineral chemistry, C, S, O, D, Pb and Sr isotopic, and REE studies, al1 frorn rocks from the central Meguma Terrane (Liscomb area). The combined results were applied to a model whereby fluids that formed Meguma gold deposits were generated deep in the cmt and deposited as veins in brittle-ductile shear zones. During passage through the cmst the fluids inherited a variety of geochemical signatures by interaction with wall rocks, O and

D isotopes suggested a metarnorphic origin with a small magmatic component: C and S isotopes pointed to the host Meguma metasedimentary rocks; Sr and Pb isotope data indicated the Liscomb Gneisses as the only exposed reservoir, and REE data suggested a variety of sources. The Liscomb Gneisses and mafic dykes host xenoliths that are interpreted as

fragments of Megurna Group basement rock (Owen et al., 1988; Eberz et al., 199 1). It is

not known if rocks equivalent to the gneisses or xenoliths underlie the south-central

Meguma Group and so their involvement in gold mineralization in the thesis area is

speculative.

Horne ( 1993) and Home and Culshaw (1994) studied flexural slip as it is demonstrated in the large regional folds of the Meguma Group. In places, such as within the hinge of the Ovens Anticline, they interpreted localisation of gold-bearing veins to be related to flexural slip during the late stages of folding. XRD illite-muscovite crystallinity and ''A~I~~A~data from this thesis also have a bearing on late-stage regional deformation in this part of the Meguma; they may have significance for the timing of gold mineralization in Meguma Group veins as well. Chapter 3 Petrography and Mineral Chemistry

3.1 Introduction

The basic mineralogy of the Iowest-grade part of the Meguma Group is relatively simple and well known (O'Brien, 1986, 1988; Schenk, 1991; Waldron, 1987, 1992).

Detailed examination is aided by the use of the backscatter electron (BSE) image analysis function of the electron microprobe. Textural distinctions, such as different generations of phylIosilicates, muscovite grains defining a cleavage fabric, or muscovite growth within fractures in chlorite-mica stacks can be imaged and compositionally analysed. In this study, optical petrography, electron microprobe chemical analyses, backscatter electron imagery, and X-Ray Diffraction (XRD)analyses produced data needed to understand the metarnorphic and deformational history of the area.

The lithology and thus bulk composition of the rocks exert the strongest control on mineral chemistry (Guidotti, 1984; Weaver, 1984, 1989; Lopez Munguira et al. 199 1 ).

It is therefore uscful to describe the rnicroscopic characteristics of the minera1 assemblages in the same way as the macroscopic features, by lithological unit, beginning with the lowest member of the Goldenville Formation and progressing upward through the stratigraphic sequence. A description of the general minera1 assemblage of the

Meguma Group is followed by characteristics of each member and details of microtextural features. Thereafier the chapter focuses on the phyllosilicates and their textural and compositional characteristics. 3.2 Mineral Assemblages

The petrology of the low grade area of the Meguma Group is quite uniform.

Although quartz-rich rocks predominate in the Goldenville Formation and the Halifax

Formation contains a higher proportion of pelitic units, bot, formations contain the same essential rninerals and differ mainly in their relative proportion and the intensity of cleavage. The Mosher's Island Member at the base of the Halifax Formation and the overlying Cunard Member are the most distinctive units.

3.2.1 General Petromaphv

Quartz grains of varying sizes, some detrital, many recrystallized to some degree with subgrain development, sutured grain boundaries and triple junctions, are surrounded by a matrix of very fine grained sericite, muscovite and chlorite. Detrital quartz is in the form of sand-size, single, embayed grains and, more commonly, grain aggregates. Some grains have chlorite and opaque minerals associated with them or are mantled by chlorite and muscovite. The aggregates may be rernnants of lithic tragrnents or the product of recrystallization of large single quartz grains (Taylor, 1967). If porous, lithic fragments can serve as nucleation sites for other phases. Aggregates in these rocks commonly have chlorite growing on them.

Feldspar grains accompanying quartz are predominantly albitic and are diagenetic or metamorphic in origin (Cullen, 1983). Large, oflen bent, detrital muscovite grains persist in the sandier members. Sandstone packages are more resistant to cleavage development and so permit some of these grains to survive. [n addition to sericite and 46 detrital muscovite, muscovite exists as randornly oriented matrix laths and metarnorphic laths oriented parallel and sub-parallel to cleavage. The latter are rnost common in the sand- and shale-rich layers of the Goldenville Formation and in the slaty Halifax

Formation. The Halifax Formation also contains rninor Na/K mica. None of the muscovite microprobe analyses showed NalK mica, but XRD analyses clearly demonstrate its presence, suggesting that it resides in the finest-grained fraction. Some sarnples from the West Dublin Member of the Goldenville Formation and samples fiorn al1 overlying mernbers contain mixed-layer venniculite-mica and mixed-layer smectite-mica.

Metamorphic chlorite porphyroblasts are ubiquitous although in a few areas they are only slightly larger than the fine-grained surrounding rnatrix. They are commonly oval, as large as 0.5 mm, with the long axes of the grains parallel to their cleavage planes.

Some appear pristine while others show considerable deformation and muscovite growth in fractures in cleavage planes. They are usually oriented with long axes paral lel to the bedding plane (Fig. 3.1). These features and the processes forrning them are described in

Section 4.4.1. The presence of detrital chlorite has been documented by other workers

(e.g. Cullen, 1983) but is not obvious in these rocks. Much of the matrix is composed of fine-grained chlorite that has grown by rneans of diagenetic and low-grade metamorphic reactions. The protolith of these grains may be detrital chlorite but the latter is not distinct from other matrix chlorite in the thesis area.

Biotite is found in rocks within the regional biotite zone in the southwest of the thesis area, and within the contact aureole of the South Mountain Batholith. Most biotite Figure 3.1 Microphotograph of metamorphic chlorite porphyroblasts oriented with basal cleavages parallel to bedding. Cleavage visibly wraps amund porphyroblasts. Sample 93-RH142b, Cunard Member, Aspotoçan Peninsula. Scale bar is 0.5 mm. PPL.

Figure 3.2 Biotite mimetically overgrowing fractured chlorite porphyroblast, with same bedding-parallel basal cleavages as original chlorite. Sarnple 93-RE -138. Risser's Beach Member, Broad Cove. Scale bar is 0.5 mm. PPL. 48 fiom samples within the regional biotite zone has either a rounded, irregular, poikilitic morphology, mimetically overgrows fractured chlorite purphyroblasts (Fig. 3.2) ,or nucleates on matrix chlorite (Fig. 3.3). Sorne grains are lath-shaped, Iocally parallel to cleavage. There is no evidence of biotite being replaced by any other phase. A sample from a late brittle deformation zone at Broad Cove, within the biotite metamorphic zone, contains sheared, poikilitic biotite (Fig. 3.4). Sarnples fiom within the biotite zone also contain chloritoid locally. Biotites From samples within the contact aureole of the South

Mountain Batholith differ in appearance in that they are more comrnonly lath-shaped and have fewer inclusions.

Carbon in the fom of microscopic graphitic layers is present throughout but exists primarily in the pelitic layers of the Halifax Formation, particularly the Cunard and

Feltzen Members. The abundance of carbon contributes to the extreme fissility of these members (Waldron, 1992). In the Mosher's Island Member graphite is a common constituent of inclusions in gamet porphyroblasts.

Opaque minerais, comprising ilmenite and TiO, grains, are everywhere as both irregular, ovoid, poikilitic grains, and as laths that can be poikilitic or inclusion-free. It is dificult to distinguish between rutile and anatase optically. Cullen (1983) tentativeiy prefemd rutile over anatase in his investigation of greenschist facies Meguma Group rocks in the Yarmouth region. He based his choice on an observed higher degree of anisotropy in the grains. Samples from this study have many opaque grains with patchy areas of coexising ilmenite and rutile (Fig. 3.5). Compositions reflect this as varying proportions of MnO, TiO, and FeO. Titanite usually occurs as single grains and locally Figure 3.3 Microphotograph of biotite overgrowing matrix chlorite. Sampl 93-RH42c, New Harbour Member; Long Point. Scale bar is 0.05 mm. PPL.

Figure 3.4 Microphotograph of sheared poikilitic biotite from sample with late, brittle deformation. Sample 93-RH37, Risser's Beach Member; Broad Cove. Scale bar is 0.5 mm. PPL. Figure 3.5 Back-scatter e[ectron image of ilmenite and rutile coexisting in the same grain. Bright patches are ilmenite, darker patches are rutile. Sample 93-RH-29d, Mosher's Island Member, Bell's Cove. Image is 0.14 mm across. 5 1

as patches on rutile. Tourmaline is the most common accessory mineral, but epidote,

apatite (as apatite and hydroxyapatite in the Mosher's Island Member and perhaps elsewhere) and rare monazite are present. Pynte exists in the upper units of the Tancook

Mernber and becomes more abundant higher in the stratigraphie succession. Sulphur

isotope studies (Sangster, 1987; 1990) suggest that sulphides in the Goldenville-Halifax

Transition (GHT) zone formed by biogenic reduction, primanly in open marine conditions. The exception is at the top of the Mosher's Island Member, where higher SM values indicate biogenic fractionation within a closed system basin. In the study area, sulphides are weathered out locally and in places replaced by silicates. Arsenopyrite is also present, mainly in the Cunard Member, although in lesser amounts than the pyrite.

Carbonate is a diagenetic cernent mineral in a11 members and ranges fkom small, patchy grains at the micro-scale, to concretions larger than 30 cm dong their long axes and layers up to 10 cm thick. Carbonate preferentially grows in sandier layers, retaining inclusions of the host rock within grains that range in shape from anhedral to rectanylar with long edçes parallel to bedding. In one location on Tancook Island in the Mosher's

Island Member, well developed cone-in-cone structures are present. Here, carbonate grows in the fan-shape pattern typical of these structures (Franks, 1 969) (Fig. 3.6).

Pnmary sedimentary structures are visible in thin section. Bedding appears as layers of quartz-rich and phyllosilicate-rich material. Other features include loading of more comptent sandy layers into sofier mud layers, escape smictures, bioturbation, and soft sediment defonnation features such as small scale slumping and disturbance of semi-consolidated material. Chlorite porphyroblasts and chlorite-mica stacks are usually Figure 3.6 Microphotograph of concin-cone carbonate growth. SampIe 93-RHIOSa, Mosher's Island Member, Tancook Island. ScaIe bar is 0.75 mm. PPL. oriented parallel to the bedding plane but they are randomly oriented in thin sections

exhibiting soft sediment deforrnation. Long, detrital muscovite grains are sirnilarly

oriented with the long axis parallel to bedding, but are often bent and kinked, perhaps

due to compaction forces warping them around quartz grains. Primary bedding structures

are also preserved in carbonate concretions and the concretions themselves formed

during diagenesis or in the very early stages of regional metarnorphism (O'Brien, 1988).

Chiorite-mica stacks are preserved in some concretions, suggesting early stack

developrnent andlor protracted carbonate cementation, likely both.

Chlorite (diagenetic and non-porphyroblast metamorphic), opaques, carbonate,

sulphides and, locally, tourmaline, al1 preferentially grew in sandy layers and lenses and

on quartz aggregates. Clearly the porosity of sandier areas helped mobilise the necessary

elements. Sandy layers also controlled the quantity of muscovite present within

chiotite-mica stacks. While these stacks may be more abundant in shaiy layers and more

subject to deforrnation in these layers because of cleavage formation, the amount of

muscovite found within fiactured chlorite porphyroblasts increases in sandy layers. This

suggests that these sediments retained some pemeabiliw through diagenesis and into

low-grade metamorphism.

In thin section, progressing stratigraphically higher from sandstone-dominated members to slate-dominated members, phyllosilicates show less bedding-parallel orientation and considerable to extensive cleavage-parallel orientation. Some thin sections exhibit a cross-hatched matrix texture in the finer-grained layers (Fig. 3.7). This may be a deformation effect resulting from compression applied parallel or sub-parallel Figure 3.7 Back-scatter electron image of cross-hatch matrix fabric (faintly visible). Brightest grains are opaques, darkest are quartz and feldspar. Bulk of matrix is chlorite and muscovite. Sarnple 93-RH 10 1, Mosher's Island Member, Tancook Island, [mage is 0.5 mm across. 55

to the bedding plane (Weaver, 1984). Weaver noted that where detrital or diagenetic

muscovite grains are oriented with long axes parallel to bedding, compression ben& and

kinks the grains. The bent areas suffer the most strain and become the loci for

recrystallization, resulting in grains oriented roughly 90" fiom each other. Altematively,

the pattern rnay simply result from a combination of bedding-parallel diagenetic grains

aligned by compaction, together with some cleavage-parallel metamorphic muscovite

growth.

Chlotite-mica stacks and detrital quartz grains and aggregates were defonned during cleavage formation. The quartz grains and aggregates are usually oval in shape with the long axis of the oval parallel to cleavage. Opaque laths locally exhibit sorne degree of c leavage-parallel orientation but often grow randomly. Tourmaline is randomly oriented in al1 samples, indicating pst-tectonic crystallization.

Features that formed early in the history of the rock, such as the diagenetic carbonate concretions and layers, and early quartz veins, were composed of more competent material than the surrounding layers during layer-parallel shortening and cleavage formation. As a result they buckled and folded. Very thin carbonate layers, visible in thin section, are sirnilarly buckled and deflect cleavage.

Individual members of the Megwna Group exhibit al1 of the above features but also have particular characteristics. These are described below beginning with the lowest member stratigraphically, the New Harbour Mernber. 3-32New Harbour Member

Quartz is the main constituent although there are minor pelitic layers that define

primary layering. Cleavage is minimal, visible only in the pelitic areas as a crenulation

cleavage or spaced cleavage. Recrystallization of quartz grains is rnoderate and more

detrïtal muscovite (up to 1 mm in length) is preserved here than in any of the overlying

units. Feldspars are most abundant in this member of the Meguma Group. Schenk and

Lane ( 1982) reported that IocalIy up to 30% of grains are feldspar but none of the

samples fiom this thesis showed such high concentrations. As in the rest of the Meguma

Group, albite is by far the most abundant feldspar but microprobe analyses of randorn

gains proved that minor K-feldspar exists in the New Harbour Member. K-feldspar is

likeiy detrital (Cullen, 1983). Chlorite porphyroblasts are usually small and pristine

without fractures, but in some sandy layers they have muscovite growing on grain edges

and, rarely, in fractures in the grains. Microscopic diagenetic carbonate patches exist as very poikilitic grains but a thin section cut through the core of a concretion showed no

carbonate present, only embayed quartz and the usual matrix phases. In outcrop sorne of

these concretions are very pitted, suggesting that carbonate leached out of the rock.

Opaque grains and rare sulphides randomly overgrow the cleavage.

The New Harbour Member outcrops in the southwest of the thesis area where the

metamorphic grade increases from chlorite to biotite zone. Samples from Long Point

(due east of the LaHave Islands) contain biotite, locally growing parallel to the cleavage but usually overgrowing the fabric. A grain fiom a sheared zone at Long Point shows that

the brittle deformation happened afier biotite growth (Fig. 3.4). Biotite is also present where this member lies within the contact aureole of the South Mountain Batholith, at

Aspotogan Peninsul a.

3.2.3 Risser's Beach Member

This member is also predominantly quartz-rich but phyllosilicate layers are more abundant, ofien in sharp contact with quartz-rich layers. Original layers are thus more visible and locally exhibit graded bedding. There are micro-structures interpreted as bioturbation effects, and sofi sediment deformation such as micro-scale slumps and breccias. Cleavage is visible in thin section only in the phyllosilicate-rich layers.

Metamorphic chlorite porphyroblasts, mainly present in the pelitic layers, are more abundant than in the New Harbour Member. Their orientation ranges Ekom predominantly bedding-parallel to IocaIly orthogonal to cleavage with a concomitant increase in fracturing and chlorite-mica stack formation. Rare stacks have cleavage strain shadows of quartz and chlorite. There are also longer chlorite laths with muscovite growing on the long edges; these are concentrated in bedding-parallel layers, oriented parallel to bedding.

Opaque grains Vary fiom round, heavily embayed, poikilitic grains to ovals and laths with inclusions. [Imenite and rutile are present, commonly in the same grain. Laths are usuaIIy randomly oriented although some thin sections have areas where Iaths are preferentially oriented parallel to cleavage. Strain shadows of quartz and chlorite are present locally. Carbonate grains are large and poikilitic with host rock phases as inclusions. At Broad Cove, in the far south-west of the study are* the Risser's Beach

Member lies within the biotite metamorphic zone. Py-rite and biotite are present in these samples and the pyrite has pressure shadows of quartz and fresh, bright green chlorite.

Chlorite-mica stacks here are almost 100% muscovite (see Section 4.4.1 ). None of the samples from this area shows evidence of chlorite replacing biotite although chlorite sometimes grows in poorly developed pressure shadows next to biotite grains. Biotite replaces chlorite in some porphyroblasts in the fonn of stacked aggregates of lath-like biotite that mimics the fiactured chlonte porphyroblasts (Fig. 3.2). Biotite grains that nucleate elsewhere are irregular, roughly round and poikilitic. Cleavage-parallel biotite laths are visible in one sample.

3.2.4 West Dublin Member

The West Dublin Member is finer-grained than the underlying members, with relatively less quartz and feldspar and more phytlosilicates. Primary sedimentary structures such as quartz-rich and phyllosilicate-rich bedding layers and load structures are present and detrital muscovite is still visible. In sandier Iayers opaques are round, abundant, and disseminated throughout while in shalier Iayers they are larger, Iess common and often form poikilitic laths.

3.2.5 Tancook Member

The Tancook Member was divided into four units by Waldron (1 987, 19921, based on stratigraphie considerations. PetrographicalIy, the units are similar to underlying 59

mernbers except that grain size is smaller (silt-size) and there is a higher proportion of

shale occumng in much thicker layers (see Chapter 2, Section 2-2-41. Primary layering is

evident with local disturbance attributed to bioturbation, and cleavage is more visible because of the increase in fine-grained material. Detrital muscovite is still present in quartz-rich layers. Opaque grains are preferentially concentrated in quartz-rich layers and detrita1 quartz aggregates, as are carbonate patches and layers. Carbonate layen are parallet to bedding, rnost commonly in the top unit T, (upper slaty unit), and are buckled by cleavage. Unit T, also has pyrite, and on the Aspotogan Peninsula, within the South

Mountain Batholith contact aureole, it contains gamet. Graphite is visible in the slaty units, particularly the upper slaty unit, T,.

The abundance and fonn of chlorite-mica stacks varies from unit to unit. At the bottom of the Tancook Member, in the T, (lower sandy) unit, stacks are few in number and are relatively unfkactured with little or no muscovite. In unit T, (lower slaty) there are also few stacks but most have sorne component of muscovite, usually on the long edges of grains. An interesting contrast is a sarnple fiom the east shore of Little Tancook

Island where muscovite laths have chlorite growing on edges and in grain cleavage fractures. In the upper sandy unit, T,, there are both ptistine chloite porphyroblasts and chlorite-mica stacks, the latter with varying quantities of muscovite. In some cases muscovite is abundant and stacks have been rotated orthogonal to cleavage. Unit T,, the upper slaty unit, has the same variety of rnetamorphic chlonte porphyroblasts as unit T, but they are more abundant. A single K-feldspar analysis comes fiom unit T,. 3-2.6 Mosher's Island Member

The Mosher's Island Member is the lowest of the true slate members although it

contains a considerable proportion of siIt. Quartz is still the main constituent but the

amount of sericite, muscovite, carbon and chlorite is higher. Chlorite porphyroblasts and

chlorite-mica stacks Vary from pristine to very deformed with abundant muscovite.

Chlorite porphyroblasts and stacks tend to concentrate in specific prirnary layers.

Spessartine gamet (30-36 wt. % oxide MnO) is present in two forms (Fig. 3.8).

Tiny (

the rock. Larger grains and aggregate grains (- 1 mm) have inclusions and are

concentrated in lines or layers one or hvo gains thick corresponding to bedding-parallel

layers. In places these large gamets grew on carbonate layers and around detrital quartz

aggregates. The large grains and composite grains have incIuded carbon or graphite that

has been incorporated into the porphyroblasts along interfacial boundaries during growth

(Fig. 3.9). Graphite is usualIy concentrated dong a midline through the garnet grain or aggregate, parallel to the bedding pIane. Almandine garnet is present in one sample fiom the South Mountain Batholith contact aureole north of Chester. Although these grains are iron-rich they still have contain 13-15.5 wt. % oxide MnO.

In the upper layers of the Mosher's Island Member, srnaIl(- 4 cm diameter) carbonate-gamet nodutes provide a distinctive marker horizon. Viewed microscopically, these nodules are ovoid concentric layers of coarse-grained cazbonate and garnet with minor quartz, phyllosilicates and opaque phases (Fig. 3.10). Figure 3.8 Microphotograph of spessartine gamet growing as both small, disseminated grains, and large gamet clusters, nucleating on bedding-parallel carbonate layers. Dark material in cores of gamet clusters is graphite. Sample 93-RH29b, Mosher's Island Mernber; Bell's Cove. Scale Bar is 0.75 mm. PPL. Figure 3.9 Back-scatter electron image of gamet cluster with graphitic material concentrated along a bedding-parallel midline and radiatinç outward along interfacial boundaries. Sample 93-RH29b, Mosher's Island Member, Bell's Cove. [mage is 1 mm across. Figure 3.10 Microphotograph oFpart of a manganese nodule, sh iowing concentric layered effect of carbonate and spessartine gamet gr01 wth ove matrix material. Gamets are most visible just above the mid-line of the photograph. Nodule sample, Mosher's Island Member; Tancook 1iland. Scaie bar is 0.75 mm. PPL. Primary layering is defined by chlorite-rich layers and by dark lamellae of graphitic matter. Cleavage is most visible in the slaty layers and is more pronounced in this member than in any of the underlying members. Cleavage is deflected around the large garnet porphyroblasts and composite grains and pressure shadows are present locally. This texture may be due to gamet growth pre- or early syn-cleavage, or may be due to the large gamets nucleating on carbonate layers that were more resistant and had previously deflected the cleavage. The individual gains forming the composite gamets and layers of garnet are equant and unembayed, indicating nucleation on existing buckled carbonate nodules and layers. Hingston ( 1985) suggested that spessartine in coticules in the Mostier's Island Member grew at the expense of manganese carbonate. Elsewhere in these samples carbonate layers are buckled and fiactured by cleavage, and fractures are filled with quartz or muscovite. Smaller, equant, disseminated gamets both deflect and overgrow the cleavage.

Ilmenite overgrows al1 phases, including gamet, and varies in orientation fiom random to strongly cleavage-parallel. Pyrite is common near the contact with the overlying sulphide-rich Cunard Member. It preferentially nucleates on quartz-rich layers and aggregates. Rare bomite is in one of the samples.

3.2.7 Cunard Member

Cunard Member samples are slaty and graphitic, with some layers containing more than 50% sulphides. Chlorite-mica stacks are variably deformed depending on the degree of cleavage; al1 have moderate to abundant muscovite incorporated in the stacks. Some chlorite porphyroblasts have graphite within the fraçtures along the basal cleavages. Bedding-parallel detntal muscovite grains are rare in these highly cleaved rocks, but metamorphic muscovite laths nucleated on chlorite in random orientation.

Carbonate grew on quartz aggregates and in carbonate-quartz-pyrite veins.

Microprobe analyses confirm the presence of afbite but XRD analyses show no albite in any of the 29 samples, except for one where albite is suspected. Albite may exist only in the basal layers near the Mosher's Island-Cunard Member boundary where the th~esamples known to contain albite originated, or may not have been included in the (2pm grain-size fraction analysed by the XRD method. XRD analyses also reveal the presence of minor paragonite which does not appear in any of the microprobe analyses. Paragonite typically exists in the finest grained fraction (Guidotti,

1984), and these gains may not be amenable to accurate microprobe analysis.

Cleavage varies from crenulated to a strong slaty cteavage and deflects around detrital quartz aggregates and ilmenite grains. Two sulphide phases locally nucleated on quartz layers and aggregates. Large, poikilitic, irregular to subequant pyrite overgrew the cleavage fabric. Large, equant cubes of pyrite and arsenopyrite have few inclusions and either overgrew the fabric, or deflected it, producing strain shadows of quartz and chlorite. Pyrite observed in fold lirnbs commonly has pressure shadows. XRD analyses fiom the Cunard Member show rare jarosite, lepidocrocite and hematite, each in one sarnple only. These minerals can occur in sediments as aIteration or weathering products, or may indicate hydrothemal activity (Nesse, 1986). One sample from the Mosher's

Island Member has ankerite which is also present in hydrothemal mineral deposits 66

(Nesse, 1 986). Sarnples containing these minerals are from outcrops in the hinge zones of

the major anticlines.

3.2.8 Feltzen Member

The Feltzen Member is less graphitic and poorer in sulphides than the underlying

Cunard Member, and the predominance of muscovite over chlorite gives the rocks a grey colour. Pristine chlorite porphyroblasts and chlorite-mica stacks appear in the siaty layers

but in the siltstone layers the stacks have more muscovite within them. Most porphyroblasts and stacks are bedding-parallel but some that rotated perpendicular to the cleavage have more muscovite than the bedding-paral lel variety. Some pristine, elongate ovals of chlorite grew parallel to cleavage. Samples fiom Blue Rocks, near Lunenburg, contain porphyroblasts varying fiom pristine grains to stacks with almost total replacement of c hlorite by muscovite.

Microscopie primary structures include layering, cross-bedding and load structures. [n places cleavage is crenulated; elsewhere there is a strong slaty cleavage that deflects across slaty/siIty layer boundaries. Cleavage wraps around chlorite-mica stacks and detntal quartz aggregates. In one sample local chlorite-mica stacks have pressure shadows of quartz and minor chlorite. Both srnall, irregdar, disseminated opaques, and large, subhedral to cubic sulphides overgrow the cleavage. 3.3 Mineral cher ni^

3.3.1 General Mineral Chemistw

Microprobe analytical methods are outlined in Appendix A and full microprobe analyses are presented in Appendix B. Appendix C contains structural tomulae fiom representative phases in al1 rock types of each member. Analyses show that chemical compositions of phases within memben are homogeneous. In contrast, compositions Vary from member to member. The Mosher's Island Member is particularly distinctive because it is rich in manganese and this is reflected in several phases where the Mn0 content is relatively high. Gamet, nomally not found in such low-grade rocks, is stable here because of the Mn0 content (Symmes and Ferry, 1992). Carbonate analyses are of typical calcite in other members but in the Mosher's Island Member up to 48% weight Mn0 is present in kutnohorite. The phyllosilicates also show relatively high Mn0 levels in

Mosher's Island samples.

This section of the thesis presents basic details of feldspar, gamet and biotite compositions. The minera1 chemistry of chlorite and muscovite is described in more detail since their chemical characteristics have a direct bearing on the techniques used in this thesis to reveal the metamorphic history of this area. AH plots shown are generated by Minpet for Windows, version 2.0 (8Richard, 1994), based on microprobe analyses.

Microprobe analyses report al1 Fe as FeO; Minpet recalculates Fe0 and uses Fe2' to plot diagrams.

Figure 3.1 1 illustrates that most of feldspar is albite or another plagioclase feldspar. Ab content ranges Frorn 63.5% to 100%, and 34 out of 39 (87%) analyses have 4 Felizen Member + Cunard Member Mosher's tsland Member V Tancook Member X West Dublin Mernber Risser's Beach Member A New Harbour Mernber

Figure 3.11 Feldspar compositions ploned as orthoclase (KAISi308), albite (NaAISi308) and anorthite (CaA12Si208) end rnembers. Ca- and K-rich grains are From sandy layers and units in the Goldenville Formation and are probably demtal. n = 44. 69 an Ab content of 90% or more. Sarnples 93-M42b (New Harbour Member), 93-RH107b

(upper slaty unit, Tancook Member) and 93-RH 189 (New Harbour Mernber) contain both albite and K-feldspar with Or content of between 95.4% and 98.5%. The samples containing K-feldspar are unremarkable except that they are from sandy layers with a relatively high proportion of quartz and feldspar. Two sarnples from the Cunard Member contain feldspar with a component of K. Sample 93-RH100b (K$k5.57 wt. % oxide) is also fiom a relatively sandy layer while sample 93-RH142b (&O=3.68 wt. % oxide) is

From a contact metamotphosecl slate.

Four samples have plagioclase containing some Ca. AH are from layers with a relatively high proportion of quartz and feldspar. One sampie is from a brecciated zone in the Rissets Beach Member at Broad Cove (93-RH37). Another is fiom a massive sandy layer of the New Harbour Member at Bayswater on the Aspotogan Peninsula

(93-RH189). The remaining two are from the Mosher's Island Member (93-RH 109d and

93-RH146b). The feldspars containing K and Ca could be detrital grains that survived within quartz-rich layers in much the same way that detrital muscovite survived in sandier layers. Original sediments may have contained a higher proportion of

Ca-plagioclase that was subsequently consumed by diagenetic reactions producing albite and releasing Ca for cementation or concretion formation. K-feldspars may have been similarily sacrificed to fonn smectite and iIlite (see Section 4.2.1).

Figure 3.12 shows that nearly ail gamet is spessartine, with the exception of contact metamorphic gamets frorn sample 93-RH151. These are almandine but with a significant spessartine content of between 30 and 36 weight % oxide. Those samples with Spess

AI1 sarnples except RH1 1 2b. RH151. RH154, RH170 and RH178. VVVVvV\IVV Alm And

Spess Spess

Samples RH1 12b. RH1 54. RH1 70 and RH1 75. 1 /""VVVV"""\ Alm PYr Alm G ross

Figure 3.1 2 Gamet compositions plotted as spessartine, almandine, andradite, pyrope and grossular end-rnernbers to show full compositionaI range. Al1 analyses are from the Mosher's Island Member. 71

a significant pyrope or grossular component are plotted separately to better display their

compositions. Both gamet morphologies, the large or composite grains, and the small

disseminated grains show normal growth zoning with higher MnO, Ti0 and AI,O, and

lower SiO2,FeO, Mg0 and Ca0 in cores of grains compared to rim compositions (e-g.

Tracy, 1982). The srnall, disseminated grains exhibit less compositional variation from

core to rim.

Biotite is present in very few samples; only those at the south-west limit of

the field area within the biotite metamorphic zone and near the contact with the South

Mountain Batholith have experienced temperatures high enough for biotite growth.

Figure 3.13 illustrates the way composition varies by member. Two analyses fiom the

New Harbour Member are fiom contact metamorphic biotite. They plot within the small field occupied by the other analyses tiom that member, not with other contact metamorphic grains. The diagram represents a measure of the pressure-controlled

Tschermak exchange, (Mg,~e")+ Si" u AI" + ~l~,and the biotites fiom members in the Goldenville Formation show a higher degree of Tschermak substitution compared to biotites from the Mosher's Island Mernber. This suggests increasing metamorphism with depth. The Rissets Beach Member, which is slightly higher stratigraphically than the

New Harbour Member, plots with corresponding less Tschermak exchange, as would be expected if the degree of metamorphism is depth-controlled (Guidotti, 1984). Schenk and

Lane ( 1982) report abundant detrital biotite locally but none appears in thin sections fiom the thesis area and there is no evidence of biotite replacement by other phases. Other Mosher's Island Member Risser's Beach Mernber New Harbour Member Contact metamorphosed samples

Figure 3.13 Biotite analyses plotted as the principal biotite end-mem bers. Uns haded area represents the field of most natural biotitçs. Diagam rcprcscnts a mcasure of Tschcrrnak cxchangc with GoldenviIle Formation biotites showing a higher degree of exchange compared to Mosher's Island Member biotites. Note that metamorphic grains plot with other grains in members, not together. n = 15. (after Guidotti, 1984; Dcer ct al. 1992). 73

analysed phases include apatite, carbonate, epidote, ilmenite and rutile, pyrite and titanite

(Appendices B and C).

3.3.2 Muscovite Chemistry

Muscovite compositions from microprobe analyses on samples from throughout

the thesis area are shown in Figures 3.14 to 3.19. Figure 3.14% a muscovite classification

diagram afier Guidotti (1984) plotting ~g+~e~vs AI" vs AIV', shows that al1 muscovites

plot within a small field. Although al1 analysed grains classifi as muscovite, some are

phengitic. Higher phengite content is related to a pressure-dependent increase in

rnetarnorphic grade, and its presence is sometirnes attributed to high pressure/low

temperature metarnorphic conditions, although it exists in rocks representing a range of

pressures and temperatures (Frey et al. 1983) (see Chapter 4). Those analyses with the highest phengite content are from detrital grains and sarnples From the Tancook and

Risser's Beach Mernbers. Figure 3.14a also shows the same data plotted on two separate diaçrams with the data divided into analyses from the Goldenville and Halifax

Formations. Although there is a large overlap of the two populations, the Goldenville

Formation population shows a slightly higher phengite component. This probably reflects the presence of detrital grains with their remnant memory of a pre-Meguma geologic history, and a higher degree of metamorphism associated with the stratigraphicalIy iower formation.

Figure 3.14b displays the same data separated into sandy and pelitic samples fiom the Halifax and Goldenville Formations. Differences in lithological composition can Cd = celadonite Mg+Fel FMu = femmuscovite *FPh = ferrimuscovite of Kanehira and Banno, 1960 FPh = femphengite Lc = leucophyllite Mu = muscovite a Ph = phengite l

1 I

'\ 18 I I Feltzen Member I Cunard Member FMu 1 , Moshefs Island Mernber \ Tancook Member , West Dublin Member ', * ' Rissefs Beach Member *FMU New Harbour Mernber vvvvvv Matris grains A L" In chlorite-muscovite stacks Cleavage-paral le1 grains b Detrital grains Halifax Formation \ n = 158 \ \

Goldenville Formation n= 107

Figure 3.14a Muscovite classification of al1 muscovite analyses (top). Lower diagrams are plots of Goidenville Formation and Halifax Formation sample analyses. Despite tight clustering of points, there is a slight trend toward higher phengite content in Goldenville Formation analyses (classification after Guidotti, 1984). Halifax Formation, Halifax Formation, SIaty Layers. n = 104 Sandy Layers. n = 40

Goldenville Formation, Goldenville Formation, Slaty Layers. n = 45 Sandy Layers. n = 70

\ \

Figure 3.14b Muscovite classification of muscovite analyses as in tlgure 3.14a. Examination of analyses from sandy and slaty layers in the Halifax and Goidenville Formations reveals that Goldenville Formation muscovites show a slightly higher phengite content, regardless of lithology type. See text for further discussion. 76 produce apparent contrasts in phengite content, but these plots show that stratigraphie position, not lithology, played the dominant role in determining phengite content in these rocks.

XRD analyses conducted for the illite-muscovite crystallinity portion of this study reveal the presence of paragonite in sarnples frorn the Cunard Member. Paragonite typically exists in the finest grained Fraction (Guidotti, 1984), as sericite, where Ca and

Na comrnonly replace K (Deer et al. 1992). The smallest grains (< 2 pm)are not suitable for microprobe analyses but are employed in XRD illite-muscovite crystallinity studies.

XRD analyses also show that the top of the Mosher's Island Member and the overlying

Cunard and Feltzen Members contain minor Na/K mica. This white mica rnust also be present in the finest grained fraction.

The AI-K-Na diagram in Figure 3.15 shows the similarity within the sample set.

Both plots contain al1 acceptable muscovite analyses, regardless of minera1 morphology, host member or lithology. Figures 3.16 and 3.17, plotting total weight % oxides vs

Na/(Na+K), are more revealing. In Figures 3.16a and b the influence of the bulk rock composition of each member is evident. As in Figure 3.14b, sandy and pelitic samples are distinguished by different symbols to reveal trends attributable to sample lithology. In these plots analyses From both sandy and slaty layers have similar distributions. The exception is the Cunard Member where muscovite fiom slaty Iayers plot over a wider range. This may result hom a relative lack of sandy layers in the Cunard Member or reflect a true compositional range for these muscovites, not unlikely considering the Feltzen Member Cunard Member Mosher's Island Member Tancoo k Mem ber West Dublin Member Risser's Beach Mernber New Harbour Member Matrix grains In chlorite-muscovite stacks Cleavage-parallel grains Detrital grains

Figure 3.15 Muscovite compositions plotted as weight % AI - K - Na. Note tight clustering of analyses. n = 275. 100 ...... 99 Feltzen Member n = 73 98 i 9 7 f i 96 a %% #* 95 . ***a -i a 94 I

9 1 90 0.0 O. 1 0.2 0.3

Figure 3.16a Muscovite analyses from the Halifax Formation plotted as total weig ht % oxides vs. Na/(Na+K). Squares are sandy layers; circles are slaty layers. Total weight % is used in these diagrams because it best shows trends in these rocks. "'""",~"'~'~~','~"~"" Risser's Beach Mernber n=JO i

100 ...,.....,...... l.,...... 99 1 West Dublin Meniber r oa New Harbour Mernber

91 90 0.0 O. 1 03 0.3

Figure 3.l6b Muscovite analyses from the Goldenville Formation plotted as total weiçht 96 oxides vs. Na/(Na+K). Squares are sandy layers; circles are slaty layers. Total weight % is used in these diagrams because it best shows trends in these rocks. 100 ,.rl~~~~~r~~~Is~m~~-~~~ 99 In Chlorite-Muscovite Stacks 4 9s n=32 97 96 9, Ai 8. i 94 '.&c 93 92 i i 91 ; i

90F'" """" "' ' '' ' '' 0.0 0.1 0.2 0.3 0.0 0.1 0.2 0.3

Grains

$961 + S2 yS* 59s +*u + 94 .*, .* 3= 1 + = 93 92 1 1 91 1 90 .' . ".'""" " "'

Figure 3.17 Muscovite analyses plotted as total weight % osides vs. Na/(Na+-K) for different muscovite morphologies. See test for discussion. cornpositional variability of this mernber. Figure 3.17 shows the compositional characteristics of random matrix grains, muscovite within chlorite-mica stacks, cleavage-parallel grains, and detrital grains, respectiveIy. Matrix grains plot within the full range of al1 analyses and show the same distribution by member. Cleavage parallel laths show a similar arrangement. There may be minor mixing of cleavage grains in the general matrix group.

Analyses of muscovite within chlorite-mica stacks plot within a smaller field because chlorite porphyroblasts in the Cunard and Feltzen Members contain little or no muscovite. The sole outlier on the plot is from the Feltzen Member. Detital muscovite analyses also occupy a smaller area but this probably reflects the Iack of this morphology in the Cunard and Fehzen Members.

Although matrix, detrita1 and cleavage-paralle1 grains al1 fall within the same compositional range, a close inspection of the diagram for muscovite within chlorite-mica stacks shows tighter clustering. This may be because, again, there are few analyses fiom the Cunard and Feltzen Members. Although c hlorite porphyroblasts are numerous in these members, they are neither as hctured nor contain as much muscovite in the fractures as porphyroblasts in the underlying sandier members.

Plotting specific elements against total weight % oxides in these diagrams, while essentially showing the amount of OH and other light elements rneasured during analysis, has also proved to be one of the best way of demonstrating compositional differences in these rocks. Atternpts with other types of plots showed such tight clustering that trends were difficult to see. 82

Muscovite compositions can be plotted in several ways to show trends in Fe" Mn,

Mg, Fe2+~g,etc ..., but in al1 such plots for these samples the only variation seen is behveen mernbers. Figure 3.18 showing weight % TiO, versus total weight % oxides, demonstrates that al1 morphologies show the same distibution. The exception is the graph for detrital grains where the main cluster of points is to the right of the rest of the data. This is partly due to the lack of analyses with very little or no Ti content since there are no detrital grains in the Cunard and Feltzen Members, members with muscovite gains that habitually have very little or no Ti. Figure 3.19 shows the main reason for the distribution of detrital grains. Most detriîal muscovite is preserved in the sandier layers of the Goldenville Formation, particularly the Tancook Member. There is a slight trend for muscovite in the Goldenville Formation to be higher in Ti than muscovites in the overlying Halifax Formation. Higher Ti concentrations are an indication of higher metamorphic grade (Guidotti, 1984), and the trend expressed by these analyses suggests that units lower in the succession experienced slightly higher-grade metamorphic conditions. Altematively, the slight shift to the right by detrital grains may reflect an inherited higher Ti concentration. If so, detital grains may be a source of Ti for later growth of Ti-bearing phases. Examination of plots for sandy and slaîy layers in each formation shows that analyses are generally rnost similar within each formation, regardless of rock type. Some Iithological influence can be scen in the plot of sandy layer analyses fiom the Halifax Formation, where analyses plot slightly to the right compared to slaty layer analyses. 100 IO0 : 99 1 In Chlorite-iMuscovite Stacks - 98n=32 - 97 : - a

I - 93 93 I 92 91 - ...... ' ---." .-.. . -..-". .... ' ...... " 0.11 0. 1 0.2 0.0 a. I 0.2

100 in0 : . Cieavage-Parallel Grains 99 Detritai Grains - 9s: n= 19 - 97 = -

Figure 3.1 8 Muscovite compositions plotted as total weight '-/O osides vs. TiO. for different muscovite morphologies. AH morphologies show similar distributions. Details of each plot are discussed in the text. Sandy Layers. n = 49 Slaty Layers. n = 95 98 98 97 9 7

'O0 ' Goldenville ~ormatlon.' ' Sandy Layers. n = 70 Slaty Layers. n = 45 98 9 7 '1 9 7

Figure 3.19 Muscovite compositions plotted as total weight % oxides vs. TiO,. Goldenville Formation analyses show slightly higher Ti concentrations, indicative of a higher degree of metamorphism in these samples. Details of each plot are discussed in the text. A close look at individual analyses of larger muscovite grains reveals no consistent pattern of core to rim growth, except, to some extent, within rnember or occasionally within thin section. The sarne is true with core-rim-tip compositions of the longest (usually detrital) grains. This suggests that grains are beginning to equilibrate with the bulk rock chemistry. The availability of particular elements will always depend on reactions between phases, fluids and environmental conditions present at any particular time. At such low temperatures, element diffusion rates are slower than in higher-grade rocks, although this effect rnay be mitigated by small grain size and high fluid content.

3.3.3 Chlorite Chemistrv

As Figures 3.30a and b show, ail 342 chlorite analyses are very similar, with almost al1 grains plotting in the ripidolite field of Foster ( 1962). This is a common chlorite type; according to Foster, 25.8% of al! chlorites fall into this category.

Chlorites, like muscovites, Vary in their compositions by rnember more than by any other factor. Within each mern ber most analyses are quite tightly clustered.

The exceptions are analyses fiom the Cunard Member which are more scattered and include analyses with the least amount of Fe. This rnember shows greater cornpositional variability in other aspects as discussed in Chapter 4, Section 4.4. The Cunard Member is exceptional as the rnost variable in estimated thickness of al1 the members, ranging from

500 to 5000 metres thick (O'Brien, 1988). Other workers have noted cornpositional variability within the Cunard Mernber, attributing it to anoxic conditions prevalent at the Figure 3.20a Chlorite compositions plotted by Foster ( 1962) classification scheme (Minpet 2.0 for Windows). See text for discussion. Figure 3.20b Chlorite compositions plotted by Foster ( 1967) classification scheme (Minpet 2.0 for Windows). See text for discussion. 8 8 very base of the member and an oxic environment above the basal 50 metres (Maclnnis,

1986; Sangster, 1987, 1990; Graves, pers. comm.).

Matrix, porphyroblasr, and cleavage-parallel chlorites show no distinct compositional trends when plotted separately. Detrital chlorite is reported by O'Brien

( l988), and Waldron ( 1987) described large sand-sized chlorite grains and aggregates believed to be detrital fragments. Analyses of such grains for this study reveal no composi tional di fferences, and the chlorite associated with quartz aggregates is Ii kely not detrital but a diagenetic or low-grade metamorphic phase nucleating on detrital quartz grains or aggregates.

The homogeneous nature of phyllosilicate compositions within each rnember, regardless of morphoIogy, has implications for the diagenetic and metamorphic features of these rocks, discussed in the following chapter. Chapter 4 Diagenesis, Metamorphism, and Cleavage Formation

4.1 Introduction

Within the study area, the Meguma Group has been described as greenschist facies and locally sub-greenschist facies metamorphic grade (e-g. Keppie and Muecke,

1979; Raeside and Jamieson 1992). However, beyond mapping the biotite-in isograd,

Little else has been done to characterise these rocks. Cullen (1983), in his MSc. thesis on the metamorphic petrology of the Goldenville Formation in the Yarmouth area, described rocks straddling the biotite-in isograd, mid- to upper greenschist facies Iithologies.

The use of mineral facies to delimit metarnorphic zones is effective for volcanic rocks because they contain such minerals as prehnite, pumpellyite, and the zeolite group.

Unfortunately, low-grade chlorite-muscovite-quartz-graphite slates do not lend themselves to precise metamorphic definition; there are no usefui phase diagrams for this assemblage because it covers too wide a field (Frey, 1987; Lopez Munguira et al., 199 1 ).

XRD illite-muscovite crystallinity indices affird the best way to describe an area of this low metamorphic grade. Results from the XRD illite-muscovite crystal linity study portion of this thesis address the question of a possible metamorphic event predating the main phase of regional metamorphism, and their distribution pattern has implications for interpreting Jo~r/3y~rmetamorphic ages obtained for this thesis (Chapter 5).

Present metamorphic mineralogy and fabrics partly obscure the original character of these sediments but evidence reinains to suggest the progression of reactions and mineral growth. To begin, an oveMew of processes of diagenesis through to early

metarnorphism is given for rocks of this type. The diagenetic and metamorphic

environment of the study area is described in conjunction with the MU) illite-muscovite

crystallinity data and minerat compositional trends related to degree and history of

metarnorphism are shown.

4.2 Definitions

Much discussion centres around the precise definition of diagenesis and very

low-grade metarnorphism, whether or not a distinction should be made behveen the two,

and the problem of where to place boundanes behveen these processes and those of

sedimentation and burial (e-g.Turner, 1958, 1968, 198 1; Pettijohn, 1975; Turner and

Verhoogen, 1960; Coombs, 196 1 ; Miyashiro, 1973, Winkler 1979; Weaver, 1989). The

Glossary of Geology (Gary et al., 1972) describes diagenesis as all changes, chemicaI,

physical and bioIogicaI, occumng in sediments afier deposition and before and during

lithification, exclusive of weathering and metamorphism. The changes may be due to

bacterial action, to digestive processes of organisms, to solution and redeposition by

permeating water, or to chernical replacement. Certain pre-diagenetic changes such as

the decomposition of phytoplanktonic matter may even occur during sedimentation

(Bames et al., 1990). Some authors disclaim diagenesis and describe al1 changes resulting

fiom the burial of rocks to depths and conditions differing from those under which they originated (exclusive of weathering and cementation) as rnetamorphic (Tumer, 1968,

198 1; Pettijohn, 1 975; Coombs, 196 1 ). Others (e.g. Packham and Crook, 1960) 9 1

recognise diagenesis and further subdivide this category based on stages in the evolution

of hydrocarbon source rocks. Miyashiro (1973) suggested that any changes occumng at

the temperature of original deposition are diagenetic while changes involving an increase

in temperature are metarnorphic. Von Engelhardt (1967) indicated that diagenesis should

include reactions associated with fluid flow. When fluid flow stops because

interconnected pore spaces close by physical or chernical means, metamorphism begins.

Some sedimentologists and clay petrologists consider processes operating up to the appearance of slaty cleavage as diagenetic (Frey, 1987). Coombs ( 1954) arbitrarily assigned a boundary between diagenesis and metamorphism where plagioclase is extensively albitized and laumonite is the principal zeolite. Velde (1992) marked the boundary between diagenesis and metamorphism at the point where kaolinite disappears, at a maximum temperature, experimentally established, of 77O0C.

The nomenclature and boundaries used Vary by the type of specialist (e-g. sedimentoloçist, coal or metamorphic petrologist) and the type of matenal under investigation (Kisch, 1983). The fact that temperatures and pressures at which changes set in depend strongly on rock type further obscures the issue. Significant transformations of organic matter, evaporites, or vitreous material begin at markedly lower temperatures than those required for alteration of most silicate rocks (Frey, 1987). Some of the confusion is here avoided by the use of XRD il1ite-muscovite crystallinity data. Since lawsonite, prehnite, purnpellyite and zeolite minerals are absent in these rocks and coal rank cannot be measured, XRD illite-muscovite crystallinity indices are the best rnethod 92

of defining the changes wrought in this area. The techniques employed in establishing

XRD illite-muscovite crystaltinity indices are described in Section 4.3.1.

Kübler ( L967) suggested dividing low-grade metamorphism into zones of

diagenesis, anchizone (very low-grade metamorphism), and epizone (low-grade

metarnorphism - greenschist facies). By convention, described later in this chapter,

boundaries between diagenetic, anchizone and epizone realms are cleady assigned according to XRD illite-muscovite crystallinity measurements, and so this thesis uses these divisions, The following sections describe the characteristics of these zones as they develop in fine-grained clastic sediments.

4.2.1 Diagenesis

As sediments are buried, the nurnber of phases present diminishes due to early loss of unstable minerals. A normal clay assemblage in pelitic clastic sediments may contain sepiolite, palygorskite, illite-smectite, illite, glauconite and nontronite, berthiérine, kaotinite, quartz, and commonly vermiculitic soi1 clay minerals (Velde,

1992). Some of these can exist only near the surface. In early b~rialstages the assemblage is reduced to il1 ite-smectite mixed-layer minerals, chlorites, mixed-layer chlorite-smectite, glauconite and kaolinite. Non-clay minerals like quartz and analcite are also present. With further burial illite-smectite and illite persist together with chlorite, and perhaps corrensite and kaolinite, while other phases disappear. Analcite is replaced by albite. Figure 4.1 shows the mineral changes associated with increasing depth of burial and diagenesis and metamorphism. -

shallow burial illite srnectil kaolinite diagenesis

1 1 lickite diagenesis i ind ,' temps 100°C lacrite,' increasing mixl / :rystallinit)i 1 1 clay I I / ilite ,'ilMe

incipient i nd f r and metamorphism :hlorite chlorite (anchizone)

greenschist metamorphisrn (epizone) sericite and chlorite

Figure 4.1 Diagram showing the changes of clay minerals with increasing depth of burial and into metamorphism (Tucker, 198 1 ). Like organic maturation. the paramount factors in these transformations are

temperature and time (Fig 4.2). The degree to which clay assemblages change into the

restncted rnineralogy present in low-grade Megurna Group sediments depends on a combination of both, although temperature effects dominate.

The diagenetic zone is primarily characterised by the transition of muds to micas by converting smectite to illite (Weaver, 1989). Tables 4. la and b list the common clay minerals and micas involved in these transformations together with their characteristics.

Figure 4.3 illustrates the structures of clay minerals. Mite is a clay-size (+m ) phylIosilicate present in argillaceous sediments (Grim et al., 1937). Initially a regular mixed-layer illite-smectite (US)phase develops, composed of equal proportions of illite and smectite. With increasing depth and temperature the proportion of illite to smectite rises. When there is about 85% illite the mixed-layer I/S forms the [SI1 ordered structure

(one Iayer of smectite to three layers of illite), and finally discrete 1Md illite develops.

With increasing temperature the 2M1 polytype forms. The 2M, polytype refers to both illites and muscovites and the greater the degree of metamorphism, the greater the muscovite-illite ratio. These phases are not mutually exclusive and the prescnce and proportion of any of these varies (cg. Lynch and Reynolds, 1984; Srodon and Eberl,

1984; Pollastro, 1985).

These transformations are essentially dehydration processes. Burst ( 1969) suggested a one-step water loss rnodel, while Perry and Hower (1972) proposed water loss frrst when the smectite layers collapse, and a later stage related to a change in interlayering style fiorn random to ordered. Smectite dehydrates with increasing iliite + chlorite metamorphism

dioctahedral smectite/illite (diagenesis) 50 200 millions of years

Figure 1.2 Estimation of the limits of clay mineraloby in terms of time and temperature. For short heating periods clays can be found up to 200°C. This thermal limit is decreased as the heating period is prolonged. Illite- chlorite signais the end of clay facies (Velde, 1992). l'able 4.1 n Summsry of îht Principal Characteristics

w - Shictiire type: (ratio 1:I 2: 1 tetrahedral and octahedral coiiiuoneiits) Octahedral coinponent Di-octahedral. hiostly di-octahedrril, - Di- or tri-octdiedral. Mostlv trioctrahedral Principal interlayer Nil K cation lnterlayer water Only in halloysite (one Sonie iii Iiydroiiiuscovite. Ca, two layers; Na, one Two layers. layer water iiiols). - liiyer water mols. Basal spacing 7.1 A (1 Oa iii Iialloysite). 10A Variable. iiiost - 15A for Ca Variable; 14.4A when fully hydrated. Glycol Taken iip by Iialloysite No effect. Takes two layers glycol, Takes one layer glycol, oiilv. 17A, i4A. ~1'' ,( p.,p')h(~i,~l)8 D2,,(OH),81-40 Holloysitc collapses to 1 NO inorked cliaiige. Exfoliation; shiiiikage approx. 7.4A; others of layer spacing. i~nclian~ed, 1 Heating 650°C Kaolinite+iiietakaolinite I OA (7A) Dickite+ iiietadickik stroiig ( I J A). Paragenesis Alteration of acid rocks, Alteration of micas, Alteration of basic rocks, Alteration of biotite feldspars, etc. Acidic feldspars, etc. Alkaline volcanic tnaterial. flakes or of volcanic conditions. conditions. High Al aiid Y Alkaline conditions. inaterial, chlorites, concentrations. Availability of Mg & Ca; hornblende,etc. deficiency of K. Table 4la (cont.) Summary of the Principal Characteristics of the Clay Mineral Croups Polytypes* n/a I Md = low In origin, iiiixcd 1 M or iiiost often I Md if idn witti iiiinor siilectite iriterlayered witti iiiica coinpoileni; 2M = high T" layers. origiii. Rare 3T fonn, higli P-low T origin siiggested, other theories debated. - - * 3 polytypes found in clay iiiicas, al1 based on a iiioiioclinic cell. ( 1 ) 2-layered polytype - 2h4 1; (2) regular 1-layer polytype = IM; (3) disordered, 1-layer polytype = I Md. 3T structure is ri tliree-layer trigoiid striictiire. F

Table 4.lb Approximate Chcmical Formulae of Common Micas Di-octatiedrnl Is l v lz I Miiscovite K, Al, Si,A12 Polytype: 1b1 or 2Ml Paragonite Na2 Al, Si,AI, Polytype: 2Ml

Glauconite WW12.21, ( Fe,Mg,AI), Si7.7 ,AI, ,MI 4 Polytype: 1 M when of pure mica composition

I Phlogopite KI (h4g,Fe2'), Si,A12 Polytypes: l h4 inost coiniiioii, I Md, 2M anc Biotite K, (Mg, Fe, A1 ),, Sif,.5A12.3 3T iiiay occur.

Chlorite (~~,F~",F~~',M~,AI),~[(s~,AI),o~~~](oH),, 12: I + I Structure f fier Frey et al, 1983; Drer cl al. 1992; Velde, 1997. temperature and burial depth, and can release interlayer 40 to pore spaces (Ransom and

Helgeson, 1995). Compositionally, smectites are quite heterogeneous, compared to illites which increase in compositionat homogeneity with increasing buriaf ( Weaver, 1 989).

Reactions can begin at temperatures as low as <50°C (Weaver et al., 1984). The boundary between diagenesis and metamorphism is commonly placed at -200°C but mixed-layer US can persist up to a temperature oF35O0C. Weaver et al. (1984) suggested further subdivision of the diagenetic zone into early, middle, and late diagenesis. A discussion of these stages is unnecessary here since diagenetic rocks in the thesis area are few and are on the boundary between diagenetic and low-anchizone.

Most authors agree that the reaction which produces illite fiom smectite ofien begins with montrnorillonite as a precursor. During the conversion, Al and K content increase while Fe and Mg content rnay decrease (Weaver, 1989). The precise mechanism of conversion is held to be either primarily solid-state (e.g. Bethke and Ahaner, 1986) or dissolution-precipitation (Boles and Franks, 1979; Jahren and Aagaard, 1992) although both mechanisms contribute something to any case studied. Ahn and Peacor ( 1986) suggest a process intermediate between the two, based on the findings of their TEM study. Hunziker et al. (1 986) described the progression of IMd illite to 2M, muscovite as involving a continuous lattice restructuring without recrystallization. Some proposed reactions follow. smectite (Fe3')+ K-Feldspar andior kaolinite + VSfChlorite (FeZ') + Si" Al fiom K-feldspar replaces Si; K cornes From K-feldspar and to a lesser extent fiom mica (Weaver and Beck, 1971 ). smectite + AI^' + K' = illite + Si'' Smectite also contributes some Mg and Fe to chlorite formation (Hower et al., 1976).

smectite + K*+ illite + chlorite + quartz + H' increase in Al occurs through dissolution of Si in the smectite layers (cornmonly called cannibalisation), not from an external source (Boles and Frank, 1979).

Ahn and Peacor ( 1986) believe most of the K derives From an extema1 source,

K-feldspar and/or mica, and substitutes for Na in the smectite pnor to conversion to illite.

The way in which expandable clays acquire K is as follows. As temperature increases, AL isomorphically substitutes for Si, thus upsetting the electro-neutrality of the crystals. To compensate for the increased negative charge, K is adsorbed on to the clay surface

(Foscolos, 1990). This causes first the release of Ca and adsorbed -0 followed by Mg and Fe, the latter two elements necessary for chlorite growth. Foscolos and Kodama

( 1974) suggested that the transition of smectite to illite is a two-step process with venniculite as the intermediate phase.

Srodon and Ebert (1984) believe K-feldspar is the reaction-limiting phase for smectite to illite reactions but other factors may exert an influence sinçe Mite production has been observed to continue well beyond the consumption of al1 K-feldspar (Weaver,

1984). Poltastro (1993, 1994) noted a vanety of influencing factors, with temperature and availability of potassium predominating.

Several authors have published data suggesting the presence of chlorite within the

VS Iayers and in illites (Raman and Jackson, 1966; Lee et al., 1984; 1985; Ahn and

Peacor, 1985; Velde, 1W2), and some believe some chlorite is a by-product of the 101 smectite + illite reaction (Weaver, 1989). Others (e-g. Füchtbauer, 1967; Dunoyer de

Segonzac, 1970; Weaver and Beck, 1971) note that chlorite is an alteration product of kaolinite. Kisch ( 1968) suggested that kaolinite goes to chlorite when Mg and Fe are present in phases such as siderite or ankerite. Schiffinan and Fridleifsson (199 t ) documented randomly interstratified chlorite and smectite at temperatures between 300" and 340°C in the Nesjavellir çeothermal field, Iceland. At temperatures between 245" and 26S°C, randomly and regularly interstratified chlorite-smectite exists. Discrete chlorite appears at 270°C and persists with randomly interstratified chlorite-smectite to higher temperatures.

As temperature rises, an increase in the quantity of chlorite occurs. Ahn and

Peacor (1985) found a preferential loss of Fe relative to loss of Mg during the conversion of smectite to illite. They correlated this with the high Fe/(Fe+Mg)values in diagenetic chlorites and concluded that the smectite4llite reaction provides the Fe and Mg for diagenetic chlorite growth. With advancing metamorphic grade and concomitant increasing equilibrium recrystallization, c hlorite compositions in di fferent samples become more homogenous (~rkai,1991). Chlorite crystallinity also improves with metamorphic grade and can be used in the same way illite-muscovite crystallinity indices are used.

Diagenetic albite can form fiom the alteration of analcite, or through consumption of Ca-plagioclase in reactions like: 2Si0, + Y'O + H' + Na' + CaAI2Si2O,(plagioclase) = NaAlSi,O, (albite) + %AI~S~,O~(OH),(kaolinite) + calt.

The Ca" may form cement or concretions (Boles, 1982).

4.22 Anchizone and Epizone Metamorphism

The anchizone constitutes very iow-grade metamorphism while the epizone

category is considered low-grade metamorphism (Winkler, 1979). Together they span the

temperature range of 1 50-200° to 350-400°C (Frey, 1987). These temperatures are

necessarily imprecise because, as mentioned before, the temperatures at which Iow-grade

metamorphic reactions occur Vary with rock type and composition. For example, the

lower limit of 150°C is the temperature of specific reactions involving zeolites and other

minerais that are not found in al1 rock types (Miyashiro, 1973).

The use of the terms anchizone and epizone is confined to rocks where the

illite-muscovite crystallinity index is known. The epizone is generally correlative with

the greenschist facies and the anchizone is a zone between diagenesis and the

epizonelgreenschist facies arbitrarily chosen on the basis of XRD illite-muscovite

crystallinity index values (Frey, 1987; Weaver, 1989)-Some authors use sub-categories

like burial metamorphism for rocks lacking foliation, and incipient regionai

metamorphism where cleavage exists (e.g. Coombs, 196 1 ). Others Iike Turner ( 198 1) do

not separate the two. In this study area cleavage is extensive and dependent on the proportion of phyllosilicates, not on the degree of diagenesis or low-grade metamorphism attained. Rocks at this grade of rnetarnorphism retain many sedirnentary structures and

characteristics. Phases present are a combination of detrital grains, partly to completely

transfomied detrital grains, and new minerais. The essential mineralogy, in this case

white micas, chlorite, quartz, and some feldspars, is the same, but the phylIosilicates in

particular comprise both detrital and metamorphic elernents. For this reason the reactions

in these rocks are subtle and mainly involve quartz recrystallization, improved

crystallinity of illite-muscovite and chlorite, the transition fiorn mica polytype 1 Md to

2M,,and the growth of white micas and chlorite laths and porphyroblasts. Muscovite

demonstrates increasing phengite content, symptomatic of a pressure-dependent increase

in metamorphic grade (Frey et al., 1983). Weaver et al., ( 1984) suggested that phengite

Forms fiom biotite and chlorite during late-stage diagenesis and throughout the

anchizone. Weaver ( 1989) found that as temperature increased during buriai

rnetarnorphism and smectites are transformed to illites, at the stage where no more smectite remains, the product is a true illite, or phengite.

Effects associated with cleavage developrnent include deformation of detrital phases, cleavage-paraIlel phyllosilicate growth, deformation of chlorite porphyroblasts and the evolution of chlorite-mica stacks. The ways these processes affect the argon systematics in muscovites are also significant for this study.

4.3 XRD [Ilite-Muscovite Crvstallinitv Studies

The term crystallinity usually refers to the amount of crystalline matter present in a substance. Its meaning here, as defined by Kübler (1967), is the degree ofordering in a 1 O4 crystal line lattice; it applies to several sheet silicates, but rnainly to i llite-muscovites and, less commonly, chlorites. Most researchers in this field use the tenn illite-crystailinity, but some authors prefer the more precise illite-muscovite crystallinity. Geologists at

Birkbeck College of the University of London, U.K, who performed the XRD crystallinity measurements for this thesis, prefer the latter term, so it is used in this thesis.

4.3.1 Background Information

In 1960 Weaver noted a relationship between the shape of the 10 A (illite) X-ray difiaction (XRD) peak and the degree of metamorphism ofshales (Frey, 1987). He defined a sharpness ratio based on the intensity of the peak at 10.0 A and 10.5 A. The value of this ratio increases as illite-muscovite crystallinity improves, and he assigned specific crystallinity values, known as Weaver indices, to the diagenetic zone, the anchizone, and the epizone. This technique works well for unrnetamorphosed sediments although there is increasing error in rocks of the anchizone and epizone (Frey, 1987).

The Kübler index (KI) is a measurement of the width of the first illite basal reflection on the XRD trace, taken at half the height of the peak. The numerical value, formerly given in millimetres, is now expressed in A028 and decreases as crystallinity improves. This technique is the most commonly used. In contrast to the Weaver index, error decreases with increased crystallinity (Frey, 1987), although Merriman et al., (1990) found a loss in sensitivity of the Kiibler index within the epizone. A variation of this method, the Weber index, relates the Kübler index to the same measurement on the quartz peak. It is used mainly by German authors and is not as widely used as the Kübler index. Two other methods not comrnonly used are the Flehmig index, based on an

expensive infrared technique, and the Weber-Dunoyer de Segonzac-Economou index,

Figure 4.4 illustrates three of the methods mentioned.

Temperature is the most significant physical determinant in the degree of

phyllosilicate crystallinity but other factors contribute sorne effect ( Frey, 1987; Jiang et

al., 1990; Awan and Woodcock, 199 1; Roberts et al., 199 1). Rock composition is

important, as demonstrated in studies of the Welsh Basin (Mackie, 1987; Pratt, 1990;

Awan and Woodcock, 199 1 ; Roberts et al., 1991). Some coarser grained rocks record

higher crystallinities either because of a greater proportion of detrital micas with

inherited crystallinities (Pratt, 1990), or because of higher permeability and the circulation of interstitial fluids and the building of layers on mica surfaces (Mackie,

1990). Altematively, rnudrocks adjacent to intrusive bodies rnay record lower crystallinities, probably because the contact metarnorphosed sediments resisted Later recrystallization and cleavage formation (Roberts and Merriman, 1985). Carbonate lithologies are deficient in K which influences the degree of crystallinity, and the same is true for organic-tich sedirnents. In the latter case, illite crystals are isolated from circulating solutions by the hydrophobic organic rnaterial and crystallinity is retarded

(Frey, 1987). Crystallinity may also be retarded by the presence of significant paragonite

(Dalla Torre et al., 1996). Lithological influences diminish with increasing metamorphism (Frey, 1987). The crystal chemistry of illite itself is important since a higher potassium content leads to irnproved crystallinity (Weaver and Beck, 1971;

Hunziker et al., 1986), as does a high percentage of 2M, mica polytype (Dalla Torre et Flehnig - index - €AI-O-S~/€OH

Figure 4.4 Definition of illite crystallinity indices. The Weaver index (a) and the Kübler indes (b) are deterrnined from the shape of the first illite basal reflection on X-ray diffractograms. The Flehmig index (c)is derived from the extinction ratio of two absorption bands on infrared spectra (from Frey, 1987). al., 1996). Aluminium content may also have an effect although this is controversial

(Esquevin, 1969; Hunziker et al. 1986; Frey, 1987). The amount of fluid pressure exerted

is generally thought to be of little significance, however, direct evidence for or against

this assumption is lacking (Frey, 1987). Although fluid pressure may be ineffectual for

illite-muscovite crystallinity, the presence and circulation of fluids is important.

Tirne is also important since increasing illite-muscovite crystallinity progresses

slowly at low temperatures. When dealing with a continuous succession in, for example,

a basin setting, the greater the stratigraphic age, the better the crystallinity. Difficulties

anse where the geologic history of an area is more cornplex, or where correlation

between two locales of different age and geologic setting is desired (Awan and

Woodcock, 199 1). Overburden thickness is a related problem since the greater the depth

of overburden, the higher the crystallinity. Variations in geothermal gradient may also

affect crystallinity (Awan and Woodcock, 199 1 ).

The question of whether or not strain influences crystallinity was debated for

some time. Initially, Kübler (1967) concluded that there is no perceptible efiect, although the same author and others noted increased crystallinity in shear zones (Kübler, 1967;

Frey et al 1973; Aldahan and Morad, 1986). Some later studies showed no sign of strain-enhanced crystallinity using the Kübler index, but use of the Flehmig index gave contradictory evidence (Frey, 1987). More recently, high crystallinity has been correlated with high strain (Teichmuller et al., 1979; Roberts and Merriman, 1985; Mackie, 1987;

Awan and Woodcock. 199 1 ). Roberts and Meniman ( 1985) suggest kinetic effects are the most important, with strain heating a subsidiary factor. The recrystallization activation temperature for white mica may be lowered by strain (Teichmuller et al.,

1979). Where cleavage is present, increasing strain may promote the removal of interlayer water fiom more permeable P dornains, thus increasing the supply of potassium ions and the degree of crystallinity (e.g. Roberts et al., 1989). Direct correlation has been found between improved illite-muscovite crystallinity and strain in tightly sheared anticlines and in intensely cleaved hinges of tight fol& (e-g. Flehmig and

Lançheinrich, 1974; Kalkreuth, 1976; Nyk, 1985; Roberts and Merriman, 1985).

[n addition to these natural factors are those inherent in XRD illite-muscovite crystallinity techniques. Most rocks analysed contain a variety of phyilosiiicates, and some of these have XRD basal reflections close to 10 A. The presence of phases like pyrop hy l lite, paragonite, mixed-layer paragonite/muscovîte. margarite and biotite can broaden the illite peak and distott the crystallinity measurement (Frey, 1 987). Sample preparation, X-ray diffraction equipment settings, and the lack of comparative analysis with accepted interlaboratory samples can al1 influence the results and make cornparisons between studies dificult and reduce their value (Kisch, 199 I b). These problems are largely avoided if researchers adhere to specific standards of operation. The workshop on illite crystallinity (IC) techniques held in Manchester in 1990 made recommendations to enable standardisation of techniques. Descriptions of these recommendations and the methods used in this study are in Appendix D. 4.3.2 Sam~leSelection

Sample choice is determined by some of the previously rnentioned factors.

Ideally, sarnples for a regional study should come fiom the same stratigraphic levei and from areas of little or no deformation. If enough samples are analysed, lines of equal crystallinity index values, called isocrysts, can be drawn (Roberts and Mem-man, 1985;

Roberts et al., 199 1; Merriman et al., 1992; Bevins et al., 1994). Memman et al. ( 1992) recommend a sample density of one mudrock per 1.5 km'. Sarnpling at that density is not practical in Nova Scotia where there is considerable glacial till cover. Therefore sampling density in the thesis area is irregular with the greatest density achieved along shorelines. Figure 4.5 shows the location of XRD illite-muscovite crystallinity samples.

Not al1 samples are from the same stratigraphic level, since the same unit does not outcrop over the entire field area. From northeast to southwest the members generally are from deeper in the succession. The Cunard Mernber occupies the greatest expanse in the thesis area so most (29 samples, 47.5%) of the sarnples are from the Cunard Member.

The rest of the samples come From members closest to the Cunard Member wherever possible. Eighteen samples (29.5%) are fiom the Mosher's Island Member which directly underlies the Cunard Member, and seven samples (1 1.5%) are from the Feltzen Member overlying the Cunard Member. The remaining seven samples are fiorn the Tancook

Island Member, the Risser's Beach Mernber and the West Dublin Member. Because overburden can affect the degree of crystallinity, no samples are from the lowest rnember, the New Harbour Member. Areas near the contact with the South Mountain

Batholith and approaching the biotite-in isograd were not sarnpled. Al1 samples are Frorn L. . ------L ------Figure 4.5 Map of field area with XRD illite-muscovite crystallinity resdts displayed as metapelitic grade (derrnethods of Kisch, 199 1 ). Samples are +- ' identified by number. - - - . ------. - - . y :,

A thtic

. , . . -, Ocean

Sample Locations White mica Metapelitic crystrilliniîy Grade index A02t3 > 0.42 + Diugcnctic 0.30-0.42 Low Anchkonc ' ;13-RII II~-RI120 - 0.25-0.30 High Anchiznnc ; 15 . @3-~ii63a ',aHai~ cn.3 Epkonc (und contact I , .: . . A Islands rnctamoryhirrn) . . 93-RiIf+) O Invalid Samplcs (sa tcxt) %-. 5 Km a - a' Plot Line for Figure 4.7 Ill

the most pelitic layers within members. Rocks containing carbonate were avoided but it

was impossible to exclude sarnples containing organic matter since it is a significant

constituent of the HaLifax Formation, especially the Cunard Member.

Obtaining sarnples fiom undeformed regions poses a problem in the Meguma

Group because tight to isoclinal folding and cleavage predominates throughout. Some of

the sarnples corne fiom intensely deformed rocks through efforts to achieve a semblance

of sample density. One of the objectives of the survey was to measure the crystallinity

index West of The Ovens where argon data (Chapter 5) suggest strong overprinting by

some mechanism or another, so sampling in this area was critical, despite obvious

deformation.

4.3.3 XRD Illite-Muscovite Crvstallinitv Results

The results of the survey include both qualitative mineral analyses with mineral phases listed in semi-quantitative order, and illite-muscovite crystallinity values for each sample. Full details of the results are in Appendix E. Most samples gave good results but in two cases the 10 A illite peak was too small (samples 93-RH03aand 93-RH04). In seven cases the presence of paragonite interfered with the illite peak and gave poor results. Mineral analyses revealed paragonite in another 16 samples but on these XRD traces the illite peaks were not obviously distorted. Kübler indices (KI) from these samples rnay be acceptable but analysis of the crystallinily pattern fiom the thesis area includes them with caution. Paragonite is confined to the Cunard Member but rnay be present in other samples in arnounts too small for XRD analyses to detect (Dalla Torre et 112 al., 1996). One sample (93-RH219) from the Cunard Mernber showed the presence of amphibole. Thin sections from the same outcrop do not contain hornblende so its presence in the XRD data is probletnatical. The sample cornes from the vicinity of the

Indian Path Anticline, and deformation, possibly with hydrothennal mineral growth, may have happened in small, very localised areas. Alternatively, contamination during crushing, sample misidentification at the laboratory in London, or an analytical error may account for this anomalous result. Two analyses from Mos her's Island Member samples were discarded- Sample 93-RH97 showed evidence of late stage retrogression and sample

93-RH 154 contains material indicative of possible cold reworking, faulting or hydrothermal activity.

Appendix F contains the KI results grouped by member, with the computed maximum, minimum and mean values for each member. Figure 4.5 shows the map distribution of Kiibler indices plotted as diagenetic, low and high anchizone, and epizondcontact metamorphisrn fields. Figure 4.6 shows the crystallinity results plotted against stratigraphie depth. Al1 samples from the Mosher's Island Member and below give Kt values of 0.25 A028 or less which places them in the low-grade metamorphism epizone. Of the 29 Cunard Member sarnples, slightly over half are from the low anchizone (six samples) and the high anchizone (eight samples). The range spanned by

Cunard Member samples extends from the boundary between the diagenetic zone and the anchizone, to just within the epizone. One Cunard Member sample gave a KI of 0.44

A020, within the diagenetic zone, but paragonite linterference predudes the use of this

114 analysis. Because of the great depth of the Cunard Member, relative to other members,

Cunard Member results are plotted at three stratigraphic levels so as to reveal depth-related trends. Al1 but two of the Cunard Member samples contain paragonite, but in many cases it does not appear to interfere with the Ki results.

Figure 4.6 shows a pattern of stratigraphic depth control. There is a steady decrease in KI values with stratigraphic depth up to the Mosher's Island Member. Above the Mosher's Island Member the trend changes. Cunard Member values, particularly in the top of the member, are the lowest of all, perhaps because the degree of crystallinity improvement was inhibited by the presence of organic matter or paragonite or poor porosity during maximum burial (Graves, 1996; pers. com.). Values tiom the lowest, middle and highest stratigraphic levels of the member al1 show a trend of improved crystallinity with stratigraphic depth.

Samples fiom the Feltzen Member show a greater degree of crystallinity improvement that those from the Cunard Member, but when they are compared with values from the Mosher's Island Member and below, they are not anomalously high.

However, when they are compared to the trend expressed by Cunard Member samples, they suggest crystallinity improvement by sorne means other than depth of overburden.

Figure 4.7 shows KI values fiom samples along a path parallel to line a - a' in

Figure 4.5. This line is orthogonal to the biotite-in isograd and the metamorphic trend in the Meguma Group The hend of KI values may in part reflect the metamorphic grade of the region, with highest values coming forrn samples in the lowest-grade metamorphic ana of the Meguma Group. However, there are samples with a high degree of crystallinity improvement fiom within this lowest-grade area, some of them in close proximity to anchizone sarnples. This also suggests local crystallinity improvement not attributable to the effects of regional metamorphkm or depth of overburden.

Al1 but one of the Feltzen Member XRD samples come from the same area, encompassing peninsulas on the north and south sides of Lunenburg Bay (Fig. 4.5). As discussed in Chapter 5, this area has also produced anornaIous ages indicative of thorough resetting of muscovite. Improved crystallinity could be related to early stages of emplacement of the South Mountain Batholith, if the batholith underlies the metasediments at a shallow depth in the area (see Chapter 5, Section 5.8). This does not explain the degree of crystallinity in the fifth Feltzen Member sample, 93-RH156a, which cornes fiom the Gold River area, due west of Chester. Here, the Ki is 0.25 A028, also within the epizone, like the other Feltzen Mernber analyses.

XRD illite-muscovite crystallinity data from the vicinity of The Ovens show three close samples with highly contrasting KI values. Sample 93-RH 176a from the Feltzen

Member has a Ki of 0.24 A020 and sample 93-RH52a from the Cunard Member has a KI of 0.42 A028. Sample 93-RH57 from the Cunard Member gives a KI of 0.24 A028. If the

SMB underlies this area at a depth shallow enough to affect the crystallinity of the white micas, al1 the above samples might be expected to produce similar KI values indicative of the epizone.

Sample 93-RH57 from the Cunard Member gives a Ki of 0.24 A020. This last sample comes fiom an area west of The Ovens where intense folding with flexural slip Ili also defoms the sedimentary rocks. Shearing, cataclastic zones, duplex structures and abundant related quartz veins exist at the tip of this peninsuia at The Ovens and just to the West of The Ovens (Horne and Culshaw, 1994; this study). Several recent publications deal with the influence of strain on ilIite-muscovite crystallinity values (e-g.

Roberts and Memman, 1985; Mackie, 1987; Roberts et al., 199 1 ;Awan and Woodcock,

199 1 ). These authors and others have noted a correlation between strain, expressed as cleavage and shear zones, and improved crystallinity values (Awan and Woodcock, 199 1;

Roberts et a[., 199 1). Some of the most intense deformation seen throughout the study area is in Feltz South, near sample location 93-RH 176a. Here repeated fol& are truncated by shear zones unique in the thesis area (see Chapter 2).The defornation at Feltz South may be related to that seen nearby on The Ovens peninsula, although Feltz South has a more ductile style of deformation and lacks the quartz veins characteristic of The Ovens peninsula. The im proved crystallinity could therefore be caused by deformation in the hinge of The Ovens Anticline. XRD data indicate the presence of various phases in several samples indicative of hydrothetmal activity, faulting or cold reworking.

When judging the value of XRD illite-muscovite crystallinity data, influencing factors mut be recognised. The intensity of cleavage present in al1 the stratigraphically higher rnernbers rnay have improved the crystallinity of samples from the Halifax

Formation, and the presence of organic matter and paragonite may have inhibited crystallinity improvement, particularly in the Cunard Member. The presence of detrita1 phases (Pratt, 1990) or higher penneability (Mackie, 1990) rnay have improved crystal linity in the lower rnembers. 4.4 Diagenesis and Metamoruhism in the Meruma Group. Mahone Bav

Petrography, backscatter image analyses, mineral chemistry and XRD illite-muscovite crystallinity anaiyses of phyllosilicates reveal details of the history of these phases in this region of the Meguma Group. These details in tun help constrain the early geologic history of the area

Although rnany primary sedimentary structures remain, the original mineralogical signature of the Meguma Group is gone. The source of the sediments is described as a continental margin, and Graves (1988), using bulk chemical composition data, suggested that the fine-grained matrix of the Goldenville Formation was derived from volcanic rock

Fragments of andesitic composition and mineralogy. There is a substantial quartz component and, increasingly in members higher in the succession, significant organic matter. Detrital muscovite persists, particularly in the sandier units, as do rock fragments that now appear as quartz or quartz aggregates with chlorite. However, the full, original, suite of phases has been transformed through diagenesis and low-grade metamorphism into the restricted mineralogy present today.

The abundance of muscovite testifies to the presence of potassium. If this potassium was derived fiom detrital K-feldspar, the K-feldspar has been consumed by reactions producing muscovite and albite. Minor K-feldspar remains in the New Harbour

Member. The plentiful chlorite may result from detrital chlorite, from the smectite to illite transformation, ft-om kaolinite, from detrita1 biotite, or fiom a combination of these sources. Detrital biotite is not a favoured source for chlorite in these rocks since hundreds of electron microprobe analyses of al1 matrix phases failed to produce one biotite Il9

analysis except fiom samples within the biotite-grade metamorphic area at the boundary

of the thesis area, or within the South Mountain Batholith contact aureole. XRD analyses did not show biotite in any of the samples. This contrasts with studies such as that by

Jiang and Peacor (1994) where evidence of detrital biotite persists in rocks ranging fiom the diagenetic zone to the epizone. Only one sample (93-RH 15) produced a peak suggestive of kaolinite but the metamorphic grade, epizone, is apparently too high for kaolinite, placing the identification of this phase in doubt. Six other samples contain mixed-layer vermiculite-mica andlor mixed-layer smectite-mica, but in al1 cases but one the grade is epizone and the presence of these phases may resuit from low temperature hydration, late-stage retrogression, or hydrothermal alteration (S. Hirons, 1995 pers. comm.).

Chemical analyses of muscovites and chlorites, encompassing detrital, bedding parallel, cleavage parallel, and srnall random matrix grains, as well as components of chlorite-mica stacks, al1 show a remarkable homogeneity and that most detectable compositional trends are between individual members. Figure 4.8 shows Fe2/(Fe2+~g) content of chlorites plotted against total weight % oxide composition and reveals the same variation by individual rnernber, a general trend of decreasing Fe2/(Fe2+Mg)with stratigraphic depth. This suggests increasing metamorphism with stratigraphic depth, not a surprising tendency. The exception to this pattern is the Cunard Member which has a wide scatter loosely defining two groups. The group with the greatest Fe2/(Fe2+Mg)is from samples at the top of the Cunard Member, at or near the contact with the Feltzen

Mem ber. 85 4 84 .; 83 1 " 2 ieltzen Member 81 n = 18 80-...... 1 ....1 ...... a.... .+.- *,..L ....4 n.0 0.1 0.2 0.3 u.4 n.s 0.6 0.7 n.8 0.9

n2 1 Cunard Member si n = 58 - ,j,,+'." ...... 1.. .'-...'....', ..: O.U 0.1 0.2 0-3 a4 n.s 0.6 n.7 n.n 0.9

- -

- 82 f Risser's Beach Mernber Harbour Member - 81- n=69 - - a...... 1 .-..1. ,....,...., . 0.0 0.1 0.2 0.3 0.4 us 0.6 0.7 n.8 0.9 Fe'/( Fel+Mg) Figure 4.8 Chlorite compositions plotted as total weight % oxides vs. F~'/(F~'+M~). Square: are sandy layers; circles are slaty layers. Plots generally shows decreasing Fek/(Fe-+Mg)with depth, suggesting increasing metamorphism with depth. Details of plots are discussed in the text. 12 1

Analyses were also plotted to show if the rock type of the samples was more of an influence on chlorite composition than the degree of metarnorphism associated with increasing stratigraphic depth. In the Cunard, West Dublin and New Harbour Members there are too few analyses from either sandy or pelitic layers to produce any definitive trends. In the Feltzen Member both lithologies plot in the same area, and the same is true of the Risser's Beach Member. In the latter case there is a cluster of data points to the left of the bulk of the analyses. These are fiom Broad Cove sarnples, within the biotite metamorphic zone, and from an area of greater deformation demonstrated by numerous breccia zones. The Mosher's Island Member shows that slaty layer samples indicate a higher degree of metamotphisrn that sandy layer samples, although there is considerable overlap. The opposite is hue of Tancook Member samples. The majority of Cunard

Member samples show the greatest degree of metamorphism of all, in contrast to the

XRD illite-muscovite crystallinity data. The unusual chemistry of the Cunard Mernber may have been an influencing factor. Figure 4.8 is piotted as total weight % oxide composition versus Fe2/(Fe2+Mg)because this plot best shows the variation, albeit slight, between members and morphologies.

Plotting the Tschennak substitution of Si + Mg e AI'^ + A!" (Figs. 4.9a, b and c) shows a similar trend. There are no discemible differences between individual morphologies of chlorite, but there is slight variation by member. There is a general trend of decreasing AI'~+AI~and increasing Mg+Si with increasing stratigraphic depth. In general, chlorites become richer in Mg with increasing metamorphic grade; this also [ Feltzen Member O i,n;.ls,,,,, , , , , , , , , ,,1 4 5 6 7

Figure 4.9a Tschermak substitution in chlorites from the Halifax Formation piotted as weight % oxides. Squares are sandy iayers; circles are slaty layers. Cornparison between members reveals increasing metarnorphisrn with depth. See text for discussion. 20 ..!...... -

1

10 - - I

Tancook Mernber : West Dublin Member n = 76 - n=5 O O ' "' 4 5 6 7 4 5 6 7

Risser's Beach Member t n =69

Figure 49b Tschermak substitution in chlorites from the Goldenville Formation plotted as weight % oxides. Squares are sandy layers; circles are slaty layers. Cornparison between members reveals increasing metamorphism with depth. See test for discussion. io ri fli .I 1 " E .- Halifax Formation, Halifax Formation, t Sandy Layers. n = 48 Slaty Layers. n = 109

Goldenviile Formation, Goldenville Formationf t Sandy Layers. n = 83 I Slaty Layers. n = 71

Figure 4.9~Tschermak substitution in chlorites plotted as weiçht % oxides. Both sandy and slaty layers in the Goldenville Formation show a slight increase in metamorphism over sandy and slaty layers of the Halifax Formation. See text for discussion. holds for diagenetic rocks (Weaver, 1984). The increasing Mg content with depth suggests increasing metamorphism with depth.

Figure 4.9~disptays the effect of lithology on these analyses. Both Goldenville

Formation sandy and pelitic layer samples plot in the same field, as do sandy and slaty samples from the Halifax Formation. The four data points that plot above the others in the Halifax Formation sandy layer diagram are al1 fiom Cunard Member samples.

Compositional trends in muscovites, displayed in Chapter 3, show the same lack of variation except by individual rnember. Figure 4.10, displaying pIots of Mg+FeCvs.

AI'"+AI~ vs. K, shows that while none of the analyses are of phengite semu srricto, a slight trend toward phengite substitution is visible in the higher ~e'+~gvaIues of some of the sarnples. The top two plots show analyses of Halifax Formation samples and the bottom plots show data fiom the Goldenville Formation. AIthough the differences are slight, analyses from sandy and slaty lithologies in the Halifax Formation plot higher on the diagram than analyses from both lithologies of the Goldenville Formation. This suggests a small increase in phengite substitution with stratigraphically deeper sampIes.

Solid solution between muscovite and phengite (one of the illite group of clay minerals) is most common in graphite-bearing rocks (Guidotti, 1984), and graphite is present in the shaliest lithologies, particularly the Cunard Member. Another study (Hunzi ker et al.,

1986) documents a decrease in chernical variation with increasing diagenesis- metamorphisrn. Despite this homogenization, detrital muscovite persisted to the anchizone-epizone boundary. Twenty-four Cunard Member samples also contained minor NaK mica, revealed by XRD analyses. These must be very fine-grained since Halifax Formation, Slaty Layers. n = 95

Goldenville Formation, Sandy Layers. n = 70

Nlg+Fe2 K

Figure 4.10 Muscovite compositions plotted by Al - Mg+~e'- K content. Note trend toward phengite substitution in Gofdenville Formation sarnples. Details of plots are discussed in the text. extensive microprobe work failed to reveal their presence. All six Feltzen Member

samples analysed showed the same duaIity in mica composition, and two Mosher's Island

samples contained NaK mica. The latter two samples come fiom the very top of the

Mosher's Island Member, next to the contact with the overlying Cunard Member. Again, the evidence from the Cunard Member suggests relatively greater compositional variability, and, compared to the rest of the succession, Cunard and Feltzen Members have the most distinct phyllosilicate composition.

The presence of 2M, K-mica throughout attests to a certain level of metamorphism. The transition fiom 1 M to 2M, polytype accompanies temperature increase as samples progress kom the diagenetic through the low-grade rnetamorphic realms. The conversion is cornmonly complete by the high anchizone metamorphic level

(e.g. Hunziker et al., 1986).

Details revealed through petrography and backscatter image analyses show a variability that contrasts with the relatively uniform compositions of the phases. As described earlier, detrital phases persist and quartz is variably recrystallized. Very fine-grained matrix phyl losilicates contrast with metamorphic phyllosilicate porphyroblasts and with cleavage-parallel phyllosilicats.

4.4.1 Chlorite Porphvroblasts and Chlorite-Mica Stacks

Intergrowths of mica and chlorite have been noted in rocks since Sorby ( 1853b) described them in 1853. Vanous researchers gave them different names in the past but recent authors prefer the term chlorite-mica stacks. The origin of chlorite-mica stacks has 128 been attributed to several processes. Beutner ( 1978) considered them primary, detrita1 grains, clastic in origin, either unrnodified or composed of muscovite altered to chlorite during weathering and transport. Others (Voll, 1960; van der Pluijm and

Kaars-Sijpesteijn, 1984) thought that detrital micas provided the nucleus for diagenetic or metamorphic growth of mimetic chlorite or chlorite and muscovite. Weber (198 1 ) suggested that the whole aggregate grows during metamorphism, a conclusion shared by

Craig et al. ( 1982) who refuted a detital origin on the basis of the fiagility of the grains.

They considered them unlikely to survive because of their lack of hydrodynamic equivalence with their clastic host grains. Craig et al. (1982) and Woodland (1982, 1985) believed that chlorite and illite replaced clay minerals (smectite) mirnetically during pre-tectonic diagenesis and low-grade metamorphism. A more recent study by

Milodowski and Zalasiewicz ( 199 1) exarnined arrested chlorite-mica stack development as preserved in diagenetic concretions. Relict textures indicative of pyroxenes, amphiboles and volcanic rock particles suggest that these detital grains were precursors to the stacks. TEM, SEM, and AEM techniques applied to chlorite-mica stacks (Li et al.,

1994) show that chlorite replaced volcanogenic biotite and other ferromagnesian minerals in slates fkom Central Wales. The transformation may have occurred via an intermediate expandable trioctahedral phyllosilicate phase. The mica portion of the stacks formed by replacement of chlorite and altered biotite along cleavage planes.

Most studies describe a high proportion of chlorite-mica stacks oriented parallel to bedding (e.g. Craig et al., 1982; van der Pluijm and Kaars-Sijpesteijn, 1984;

Mi lodowski and Zalasiewicz, 199 1; Li et al., 1994). Their growth is thus considered 179

pre-tectonic, with later deformation attributed to cleavage. Deformation, as revealed by

microscope and TEM studies (van der Pluijm and Kaars-Sijpesteijn, 1984; Bons, 1988)

accomplishes two things: mica porphyroblasts spIit along the 00 1 slip plane, creating

extensional sites where phylIosilicate growth occurs, and porphyroblasts rotate from the

bedding plane to an orientation perpendicular to cleavage. Bons (1988) noted that

chlorite deforrns plasticalIy at temperatures of 300 OCand less.

Mechanical rotation of the grains is one mechanism of adjusting the position of

stacks dunng cleavage development, but recrystallization, solution, and growth

contribute to both stack development and cleavage related orientation and modification

(van der Pluijm and Kaars-Sijpesteijn, 1984; Li et al., 1994).

Virtually every sample from this study contains chlorite-mica stacks, and the

volume of material provides abundant evidence of the mode of development of these

features in this part of the Meguma Group. Figure 4.1 1 illustrates the general progression of chlonte-mica stack formation in these samples.

Most important are the numerous samples with pnstine, oval-shaped chlorite porphyroblasts that appear to be precursors to the chlorite-mica stacks (Fig. 4.12). They have few or no fractures along their 00 1 planes and give no evidence that they grew on detntal mica grains, although many have thin laths of muscovite growing along one or both long edges of the porphyroblast (Fig. 4.13). In some thin sections al1 the porphyroblasts have the muscovite growing on the same side of the grain. These mica laths may be the nucleation site for some chlorite porphyroblasts but this must be a Iocal 1Cleavage ' Lamellae

Figure 4.11 The development of chlorite-mica stacks from chlorite porphyroblasts. 1, pristine chlorite porphyroblast; 2, fracturing dong basal cleavages and growth of muscovite in fractures; 3, extension of chlorite-mica stack and Mermuscovite growth in fractures; 4, truncation dong stack edges by cleavage lamellae - stack assumes a barre1 shape; 5, kinking and tiirther dissolution of chlorite-mica stack edges with strong cleavage development. Figure 4.12 Back-scatter eiectron image of pristine chlorite porphyroblast with minimal fracturing and muscovite growth along fracture. Larçer dark equant grains in finer grained matrix are quartz and albite. Bedding -paraIlel long axis of chlonte porphyroblast. Sample 93-RH93a,upper slaty unit, Tancook Member, Tancook Island. Image is 0.5 mm across. Figure 4.13 Back-scatter electron image of pnstine chlorite porphyroblasts with minimal fracturing and muscovite growth. Muscovite visible as darker materiai on long edges of porphyroblasts. Porphyroblasts are oriented with long axes parallel to bedding, as are many of the rnatrix grains. Sample 93-RH 130b, upper slaty unit, Tancook Member; Little Tancook Island. Image is 1 mm across. 133

effect since not al1 porphyroblasts have them. The abundant fine-grained chlorite in the

matrix may be the nucleus for chlorite porphyroblast growth since both types of chlorite

are compositionally similar. The chlorite ovals are often concentrated in bedding-paralle1

layers, usually with the greatest nurnber of them in layers rich in phyllosilicates, rather

than in sandier layers. They are commonly oriented with the 00 1 plane paraIIel to

bedding (Fig. 4.14), the exception being those in samples with evidence of bioturbation

or soft sediment deformation. They can be as fi ne-grained as the surrounding mahix, but

most are larger, ranging up to 0.5 mm.

Throughout most of the thesis area cleavage is at a high angle to bedding and is

evident in al1 but the sandiest layers. The effect of this deformation was first to split the

chlorite porphyroblasts along 00 1 fracture planes parallel to the long axis of the grains.

Muscovite grew in these extensional sites, creating chlorite-mica stacks (Fig. 4,15).

Milodowski and Zalasiewicz ( 199 1) noted at least two generations of mica fillings,

probably accompanied by secondary chlorite growth. This may be a common feature

since extension perpendicular to fracture planes in chlorite grains is probably a

progressive rnechanism, linked to cleavage developrnent. Further Fracturing and mica

growth in the fiactures is accompanied by rotation of stacks into a position perpendicular to cleavage. Rotation aligns the fractures perpendicular to cleavage which favours wider extension of the fractures and more mica growth. Further cleavage development causes pressure solution of the edges of the stacks that abut the cleavage larnellae. Chlorite-mica stacks becorne barrel-shaped, elongate parallel to cleavage, and the amount of muscovite growth in the fractures may be considerable (Fig. 4.16). Some grains show almost Figure 4.14 Back-scatter electron image of chlotite-mica stacks with basal cleavages oriented -paraIlel to bedding. Stacks exhibit some fracturing with muscovite growth in the fractures. Sarnple 93-RH 15, Risser's Beach Member, Risser's Beach. Image is I mm across. Figure 4.15 Back-scatter etectron image of typical chlotite porphyroblast with moderate fracturing and moderate muscovite growth within fractures. Chlorite- mica sîack mains original oval shape of chlorite porphyroblast. Cleavage is -perpendicular to basal cleavage of stack, visible as matrix grains wrapped around stack. Sample 93-RH24, Mosher's Island Member, Bush Island, LaHave Islands. Image is 0.33 mm across. Figure 4.16 Chlorite-mica stack development is well advanced with rotation of the stack perpendicular to cleavage and truncation of edges parallel to cleavage, resulting in 'barrel' shape. Cleavage is vertical in this back-scatter electron image, visible as matnx grains wrapping around truncated sides of stack. Sample 93-RH38, Risser's Beach Member, Broad Cove. Image is 0.4 mm across. 137

complete replacement by muscovite (Fig. 4.17). Where the angle between bedding (and

chlorite porphyroblast orientation) and cleavage is smaller, it is easier for the segments of

extended chlorite to slide past one another producing a stepped arrangement of the pieces

that is overall almost parallel to cleavage (Fig. 4.18).

The factors controlling the degree of muscovite growth within the stacks are

interesting. Muscovite growth seems to depend most on the degree of deformation

present demonstrated by cleavage intensity. This is shown by the higher proportion of

pristine porphyroblasts in the lowest sandiest members relative to the overlying, more

pelitic and intensely cleaved members. The amount of cleavage development and

muscovite present in the stacks gradually increases progressing up through the members.

While the degree of defonnation provided some control, in these samples the

composition of the host lithology exerted an influence too. Within individual samples

chlorite porphyroblast growth was more abundant in the most pelitic layers, but

muscovite growth along fracture planes in chlorite porphyroblasts developed best in the

sandier layers. Although relatively quartz-rich layers exhibit less cleavage, chlorite-mica

stacks in these layers have a higher proportion of muscovite along the fractures. The

higher porosity in these rnicroscopic layers and lenses mut have aided in mobilisation of

elements for progressive stack development.

In the most advanced stages of cleavage development, stacks with a higher

length-to-width aspect ratio perpendicular to cleavage became kinked and broken. The

progress of chlorite-mica stack growth and defonnation was synchronous with cleavage-paraltel matrix grain growth. Figure 4.17 Back-scatter eIectron image of chlorite-mica stack with almost total replacement of chlorite by muscovite. Brightest patches are chlorite. Black areas are voids where material has been plucked out. Stack shows severe fracturing and kinking due to advanced cleavage formation. Sample 93-RH70, Mosher's Isiand Member, Cape LaHave Island. Image is 0.33 mm across. Figure 4.18 Chlorite-mica stack in top centre of back-scatter electron image exhibits displacernent of fragments along fractures and rotation of fragments away from the bedding plane and into the cleavage plane. Bedding orientation is from top left of image to bottom centre, illustrated by orientation of basal cleavages in chlorite grain in top left of image. Cleavage is sub-horizontal. Large poikilitic grain in lower left is biotite; brightest laths are opaques. Sample 93-RH37, Rissets Beach Member, Broad Cove. image is 0.9 rnm across. 140

Some chlorite porphyroblasts are slightly zoned with higher Fe2 in the core and higher Mg at the rim, but there are too many exceptions to draw any definite conclusions.

The only other compositional trend is the previously mentioned homogeneity of chlorite and muscovite compositions within individual members, regardless of the morphology of the chlorite or muscovite grains. The only notable variation in composition is fiom member to member. This contrasts with studies such as that of Li et al. (1994), where the chemistry of chlorite and mica within the stacks differs fiom that of matnx grains. The chemical homogeneity noted here suggests very little outside influence on the chemistry of each member. Fluid flow was significant on a local scale, producing a higher proportion of muscovite within stacks in sandy layers, but movement of reacting elements may have been predominantly lateral within members. Upward fluid movement from member to rnember rnay have been restricted by the horizontal aIignment of platy minerais, particularly in the rnembers of the Halifax Formation. The other contibuting factor was the stratigraphie depth of each member. ChemicaI signatures indicate progressively higher levels of diagenesis-metamorphism with increasing depth.

Chlorite porphyroblast growth commenced early in the history of these rocks.

Many are preserved in carbonate concretions that formed before compaction was complete. These concretions also preserve chlorite-mica stacks, suggesting early growth of these features. Initial fracturing of porphyroblasts may have begun during the early stages of compression, before cleavage fully formed. Muscovite growth in the fractures and along the long edges of some chlorite potphyroblasts with long axes perpendicular to compression may represent one of the earliest responses to compression in these rocks. Progressive layer-parallel shortening caused more advanced cleavage development, further fracturing of chlorite-mica stacks, and increased muscovite growth in the fractures, particularly in the sandy layes. Cleavage is ofien warped around chlorite porphyroblasts and chlorite-mica stacks, suggesting that either these features were well formed early in the deformation history or that cleavage development was relatively long-lived. The later stages of cleavage development caused more deformation, such as tmncation of grains on edges parallei to cleavage, and growth on ends in the pressure shadows. Kinking and breaking of grains followed by replacement of chlorite by muscovite (Fig. 4-17) are aiso probably a product of the final stage of cleavage.

4.5 Cleavage Development and Volume Loss

4.5.1 General Princi~les

Cleavage has been studied since the earIy 1800's, beginning with the work of

Bakewell in 18 15. His descriptive terminology is in use today. "Slate divides into layers or plates... owing to the magnesian earth, or to the mica, which it contains. It is the result of crystallisation, or of the internai arrangement of the particles .... The division of the laminae of slate is fiequently in a different direction fiom that of the strata, a decisive proof that the slaty structure is not owing to stratification." (Bakewell, 18 1 5 in Siddans, 1972). Slate was recognised at that time as a metamorphic rock, intermediate between lithified clay-bearing sediment and schists and gneisses, and the control exerted by lithologic and tectonic factors likewise appreciated.

Subsequent work focused on detecting the mechanism(s) involved in producing slaty cleavage. The relative importance of pressure-solution-transfer, mechanical rotation induced by compression, and the growth of new phases in the plane of flattening, was debated well into the late 20th century (e.g. Sorby, 1879; Wood, 1974). The relationship between folding and cleavage development and their relative timing is another issue that remains contentious, the Meguma Group being no exception (e.g. Williams and Hy,

1990; Henderson et al., 1992).

Investigators recognised early on that both mechanical and chemical processes contribute to cteavage development but differed in their opinion as to which mechanisrn dominates (e-g. Sorby, 1 853a; Van Hise, 1 896). It is now generally acknowledged that although mechanical re-orientation is a factor, chemical processes, with few exceptions, are of far greater importance (Knipe and White 1977; McClay, 1977).

The general mechanism for solution-transfer, as outlined by Durney ( 1972), involves a stability anisotropy between faces of a single crystal when different faces are under different stresses, and between different crystals when there are differing rnean stresses. Crystal growth requires that x (mole fraction of solute in solution) > xq

(equilibriurn mole fraction of solute), and dissolution requires that x < xq. Diffusion transfers solute from regions of high x (0,faces; those under maximum principal compressive normal stress, and crystals under either high average mean stress [O, + o2+

O, / 31 or low fluid pressure), thus lowenng x and causing dissolution at that point. The solute migrates to areas of low x (O, faces and crystals under low average mean stress or high fluid pressure), thus raising x in that area and causing crystal growth. A continuing process of dissolution, migration and growth ensues, driven by and tending to remove heterogeneities andfor stress anisotropies. The region under high average mean stress suffers a volume reduction and becomes relativeLy eruiched in clays and micas while the solute migrates and crystallises elsewhere (Durney, 1972). Pressure solution of soluble minerals such as quartz, calcite and dolomite often occurs on discrete undulating surfaces. A dark insoluble residue of clay, micas, carbonaceous rnatter and heavy minerals gathers on this surface. These residual minerats assume a strong alignrnent or preferred orientation perpendicular to maximum compressive stress once the support of the dissolved phases is removed. The micas and clays can rotate into the cleavage within the cleavage lamellae (Williams, 1972; Knipe and White, 1977). The resulting platy mineral alignment produces slaty cleavage. Some workers have interpreted the lack OF bent micas at the border of cleavage laminae to indicate recrystallization of micas within the cleavage laminae by pressure solutioddiffision (White and Knipe, 1978; Wintsch,

1978; Woodland, 1982; Lee et al., 1986). Since diffusion generally is irreversible, the resulting heterogeneous strain or external shape change of crystals is permanent.

Fossils and ooliths in defomed rocks are often observed to have dissolved in the direction of compression and to have syntaxial overgrowths or pressure shadows in the direction of extension (Sorby, 1879; Ramsay, 1967). Shales experience relatively high rates of solution transfer because of finer grain size and shorter diffusion paths (Durney,

1972). At lower temperatures in particular, Iattice diffusivity and solid state grain boundary diffusivity are likely too slow to produce the strain observed in low-grade rnetamorphic rocks (McClay, 2 977). 144

Dissolved material typically crystallises in veins and pressure shadows. The direction of growth is usuatly parallel to the 0,(minimum principal compressive normal stress) axis or crystal face because it requires the least work against the extemal surroundings when expansion occurs in this direction. When the rate of pressure solution and crystal growth are not in equilibrium there is a net gain or loss of material.

4.52 Cleavage in Meguma Group Rocks

The degree of cleavage in this area of the Meguma Group is variable. Sandier layers and packages exhibit little cleavage, macroscopically or microscopically, and in the thick sandstone layers of the lowest member, the New Harbour Member, cleavage is vinually absent. Progressing upward through the succession, cleavage becomes increasingly evident as the proportion of pelitic material increases. There is a concomitant progression from spaced to slaty cleavage as the quantity of pelitic material increases. Some sampies do not show a strong cleavage in thin section but have a cross-hatch texture believed to be incipient or incornpletc cleavage. The mechanism thought responsible for this mattix fabric is descrîbed in Chapter 3. Briefly, where bedding-parallel phyllosilicates are oriented at a high angle to the cleavage plane, a common feature in low-grade metamorphic rocks, strain causes dissolution at points where grains kink. New minera1 growth commences at these points and grows parallel to cleavage, contrasting with relict bedding-parallel grains. Electron microscope backscatter 145

images of study samples showed no such kinking; if this process operated in these rocks,

it progressed past the kinking stage, leaving a pattern of new and old matrix grain growth.

Elsewhere in the slaty rocks, cleavage is well developed, ranging fiom a

crenulation cleavage to a penetrative sIaty cleavage. Early quartz and carbonate veins and

layers were more resistant than adjacent shalier layers and buckled in response to

layer-parallel shortening. Cleavage warped around these buckled and kinked layers.

Two groups studied cleavage formation in the Meguma Group. Henderson et al.

( 1986) conducted a study in the Goldenville Formation of northeast Nova Scotia and concluded that cleavage formation preceded folding. Their analyses of sîrain in the rocks suggested between 40 and 60% shortening, accomplished by significant volume loss in the rocks. In contrast, Williams and Hy ( 1990), working in the same part of Nova Scotia, concluded that although cleavage formation began prior to regional folding, it continued throughout the folding process.

Differing styles of cleavage/folding relationships were noted during the course of field work for this thesis. At the centimetre to decimetre scale, cleavage deflects as it passes from sandy to shaly layers. At outcrop scale cleavage commonly fans around antiforms in a convergent pattern. However, cleavage that rernains parallel and undisturbed as it crosses folds also exists, and indicates that at least locally cleavage may have been imposed during late, homogeneous strain. Workers have suggested a late-stage tightening of the large fold systems in the Meguma Group (Graves, 1976; O'Brien, 1988;

Home, 1993; Home and Culshaw, 1994). The effects of this later tightening of fold axes 146 may not have influenced a11 of the region uniformly, producing locally different styles of cleavage-folding relationships.

4.5.3 Volume Loss in Slatv Cleavage

As the role of pressure-solution transfer was recognised as a mechanism for movement of volumes of material, investigations into slaty cleavage development evolved into studies on volume loss in slaty cleavage.

In 1965 Plessman studied slates of the Rheinisches Schiefergebirge and concluded that the cleavage laminae were areas of pressure-solution residue, with grains and fossils in the microlithons tnincated against the cleavage along which pressure-solution had removed material. He showed that offsets of bedding along cleavage were the result of the amount of material removed, observations that were confirmed elsewhere by Williams ( 1973)- Groshong (1976, 1988) and Bell ( 1978).

Plessman calculated a shortening strain of up tu 50%, an arnount matched by authors such as Alvarez et al. (1 978) and Wright and Platt ( 1982). Beutner and Charles ( 1985) reported 59% shortening strain. ALI suggested that volume loss might account for much or al1 of the observed shortening (Groshong, 1988).

Volume loss is a significant factor when evaluating deformation. Generally, the use of natural strain indicators involves measuring the axes of the deformation ellipsoid of the indicator and comparing the measurements with those of some original parameter.

This assumes that either the intermediate axes of the ellipsoid has not changed (e-g. 147

Cloos, 1947) andfor that volume has remained constant (e-g. Wood, 1973), both of which assumptions may be invalid.

Evaluating the extent of volume change has proved dificult, provoking debate arnong many workers. Compounding the issue is the degree of lithification of the rocks prior to the initiation ofcleavage. Sedgwick (1835) was the first of several to suggest that cleavage development could commence during the final stages of alteration before comptete lithification (e.g. Cloos, 1947; Maxwell, 1963). Ramsay and Wood ( 1973) considered pre- and post-deformation densities and concluded that volume losses of 10 to

70% might be involved in the progression from lithified mudstone to slate. Structural and stratigraphie evidence suggeçts that most slates were wider high conf ninç pressure and overburdens of several thousand metres at the time of deformation. Since bulk densities of dates are - 10% greater than densities of shale protoliths, there is an apparent limit of about 10% on the amount of volume loss that could occur without rnatenal loss (Beutner and Charles, 1985).

Volume loss due to local (microscale) redistribution of material by permeating solutions or by pressure-solution transfer need not be reflected in a density change. The fundamental problem is whether or not dissolved rnaterial has been redeposited or has migrated out of the rock unit. In many cases, material dissolved fiom surfaces parallel to the cleavages is Iocally redeposited as veins, pressure shadows, or as crystallographically continuous overgrowths (e.g. Clifford et al., 1983; Clendenen et al., 1988; Waldron and

Sandiford, 1988; Cox and Ethendge, 1989; Bhagat and Marshak, 1990), resulting in no 148

volume loss. in other situations, no such redeposition occurs and workers have assumed

that volume loss resulted fiom the removal of material from the rock.

Estimates of the amount of volume loss in rocks varies considerably. Wood

(1974) suggested that pressure-solution transfer is Iikely to operate at the local scale only

and that total volume loss entailed in cleavage formation does not exceed 20%. Erslev

and Mann ( 1984) and Wintsch et al. ( 199 1) concluded, using a chemical mass balance approach, that little or no volume loss resulted From slaty cleavage formation in rocks similar to those where others had estimated a loss of as much as 50% (e-g. Wright and

Platt, 1982; Beutner and Charles, 1985).

4.5.4 Measuring Volume Loss in Meguma Grouv Rocks

Methods employed in measuring volume loss in rocks are either geometric or geochemical in approach. Specific case studies from the Meguma Group illustrate both procedures. Wright and Henderson ( 1992) coIlected data fiom the Ecum Secum area of eastern Nova Scotia (Goldenville Formation) and from Blue Rocks in this thesis area

(Feltzen Member, Halifax Formation). Data for the Fueten et al. ( 1986) study also corne from the Ecum Secum area, and the Erslev and Ward ( 1994) study used samples from various locations including the Moose River gold district in eastern Nova Scotia

(Goldenville Formation).

As an example of geometric measurement of volume loss, Wright and Henderson

(1992) conducted a study using sand volcanoes, dewatering pipes, and silt-filled worm burrows as originally circular markers on bedding surfaces to measure volume loss 1 49

geometrïcally. They estimated pre-cleavage (compaction) strain From early diagenetic

carbonate-cemented concretions afier establishing that cleavage fonned after

compaction. Buckled, early tectonic, bedding-parallel veins and carbonate laminae in

slate beds served for estimating layer-parallel shortening.

Wright and Henderson calculated that diagenesis accounted for 70% compaction

in muds and 15% in silts and sands. They estimated bedding-parallel, normal to S,

coaxial shortening at 60%, and saw no evidence, independent of that shown by strain

markers like worm burrows and sand volcanoes, for fold-hinge parallel extension. The

estimate of tectonic vertical extension in the cleavage plane was complicated by diagenetic compaction corrections to the primary main markers, but could not compensate for the estirnated 60% shortening. The estimated volume loss durïng cleavage formation was 40-60%. Since cleavage formed at least 50 My after deposition and at a depth of about 6 km, porosity was probably less than 15%. This study is interesting because it proposed that the cleavage formation and associated volume loss were on a large regional scale and at a stratigraphic thickness of several thousands of metres, suggesting a large volume of material was transported out of the system. The authors saw no sign of redeposited material. This raises the question of how far such volumes can migrate. In the Meguma Group numerous generations of quartz veins (e-g.

Mawer, 1987; WiIliams and Hy, 1990; Henderson et al., 1992; Home, 1993; Home and

Culshaw, 1994; this study) could be interpreted as evidence of redeposition. Other evidence seen in the thesis area includes strain shadows of quartz (locally overgrown by chlorite) adjacent to chlorite and pyrite porphyroblasts, and microscopic bedding-parallel quartz lenses overgrowing rnatrix matenal. The quartz lens overgrowths are here interpreted as incipient sites of quartz redeposition, possible precursors to bedding-parallel quartz veins.

Fueten et al. ( 1986) employed a geochemical approach to measure the amount of quartz lost frorn a cleaved suite of greywackes in the Meguma Group. They divided the samples into lithons and cleavage zones (areas where insoluble minerals were concentrated) and analysed the bulk chernistry of each. They assurned that the lithons are representative of the original, pre-deformation rock composition, that volume loss occurred along axes normal to cfeavage,and that volume loss is due solely to loss of quartz. Shortening was calculated to be 60-70% in cleavage zones. This amount of shortening would require ten percent of al1 quartz originally present to leave the system.

To do so would require volumes of water about an order of magnitude higher than the amount of connate water likely to be present. The authors proposed a dynamic transport system involving most of the rock volume.

Erslev and Ward ( 1994) conducted an analysis of non-volatile elernent and volume flux in slates. They were intrigued by geometric studies that found from 25 to

60% volume loss of non-volatile components during cleavage formation (Sorby, 1853a,

1853b; Wright and Platt, 1982; Bell. 1985; Beutner and Charles, 1985; Henderson et al.,

1986; Wright and Henderson, 1992). This contrasted with the findings of geochernical studies that showed compositional similarities between whole-rock analyses of slates and shales suggestive of very minor net flux of non-volatile elements during cleavage formation (Shaw, 1956; Wintsch et al., 199 1 ; Ague, 199 1 ). The authors noted that volume losses of 50% by quartz flux commonly reported would produce a rock

composed of approximately equaI weight % proportions of SiO, and AI,O,, which is not

a slate. Erslev and Ward (1994) used an XRF-macroprobe to rnap element distributions

across cleavage lithons of variably cleaved rocks The Meguma Group samples contained

bedding-parallel buckled veins. Axial planar cleavage did not cut the veins and was most

intense and heterogeneous in the inner arcs of the folded veins, becoming more

homogeneous with distance tiom the veins. The average compositions of both

heterogeneously and homogeneously cleaved beds in the same sample suggested that

most of the non-volatile element and volume flux in the slates happened on a hand

sample scale, with quartz depletion in cleavage zones balanced by a corresponding

enrichment in adjoining microlithons. This is supported by evidence of triangular-shaped

zones enriched in SiOzand Si02/A120,present immediately adjacent to the outer arcs of

hand-sample size folds in the Meguma Group analyses (Fig. 4.19).

A possible source of error (in the authors' opinion) is their choice of an

appropriate starting slate composition for comparison with compositions from

phyllosilicate-rich cleavage bands (P) and quartz-rich (Q) domains. Their work

nevertheless places previous estimates of volume loss in Meguma Group sediments in question.

This thesis makes no attempt to measure volume loss in slates in the Mahone Bay area, but certain findings may have a bearing on volume loss estimates fiorn other authors. The degree of shortening in Meguma Group rocks is estimated to be as much as

40-60% (Henderson et al., 1986) and certain field observations support this figure.

153

Bedding-parallel quartz veins and carbonate layers are ptygmatically folded and buckted.

How much of this shortening was accompanied by volume loss is unclear.

Some quartz veins formed early in the history of the area, prior to cleavage

formation and regional folding (Graves, 1976). Fluids released by compaction and by

diagenetic reactions like montmorillonite-illite or smectite-illite transformations rnay

have been resûicted in their rnovement directions. Settling habits of phyllosilicates in a

water medium cornbined with deposition of sediments in horizontal interbedded sands and pelites, al1 enhanced by later compression, forced platy grains into a parallel arrangement that retarded upward movement of fluid. Fluids were directed along bedding-pardlel pathways or in uni-directional flow from dewatering pelitic layers to sandy layers. Excess fluid pressure resulted in hydraulic fracturing and formation of early quartz veins and local carbonate veins oriented parallel to bedding (Graves, 1976). These were more competent than surrounding lithologies, and so buckled in response to compression. Pressure shadows on chlorite porphyroblasts, sulphides and some quartz aggregates were also sites of quartz deposition.

The individual chemical signatures of the Meguma Group rnernbers may be in part due to restncted fluid and element movernent. Changes in chemistry by means of element migration along chernical gradients between mernbers or units was hampered by restricted fluid migration and a Iack of strong compositional gradients between members.

New phase growth depended on a Iocally derived element supply that moved Iaterally but was largely deterred From migration upward. This ensured that ail phyllosilicates, be they detrital, diagenetic, metamorphic, matrix, porphyroblast, or chlorite-mica stack, acquired a similar chemistry within their respective members. If, as Erslev and Ward (1994) suggest, volume flux was mainly on a hand sample scale with local redeposition of SiO,, the arnount of fluids that migrated out of Meguma Group rocks may be less extensive than previously thought. A significant proportion of fiuids generated by compaction and diagenesis-rnetamorphism may rernain as various generations of quartz veins and in local sites of redeposition.

4.6 Summarv

The oldest features present in these rocks are sedimentary. These are detrital phases with their chernical inheritance from a pre-sedimentary provenance, and pnmary structures such as sedimentary layering, cross-beds, pre-lithification slumps and load structures, sand volcanoes and other fluid escape structures. Compaction bent large detrital phases such as muscovite around more comptent quartz grains. Diagenetic reactions began and chlorite porphyroblasts grew paralle1 to bedding and in places were tumbled along with other grains during sofi sediment deformation. Carbonate nodules, lenses and layers forrned as carbonate cernent and cone-in cone-structures grew. As compaction progressed it flattened carbonate concretions into "footballs", and fluids migrated along bedding-parailel layers to form quartz lenses and veins. With burial, compaction and lithification came diagenetic and very low-grade metamorphic reactions that reduced the number of phases present, transforming clay minerals into smectite, then illite and eventually muscovite. The proportion of chlorite increased, as both matrix chlorite and chlorite porphyroblasts, and albite became the dominant feldspar phase. Those units deeper in the succession experienced slightly higher degrees of metarnorphism.

The initiation of compression caused early cleavage development, possibly in the form of a cross-hatch matrix fabric, and then crenulation of S,. ChIorite porphyroblasts deformed, grew muscovite in thin layers along their long edges and within the fractures along the basal cleavages in the porphyroblasts. As spaced and slaty cleavage developed, and the orientation of the stress axis changed fiom S, = vertical (compaction) to S2. S, = horizontal (cleavage and folding), matrix phyllosilicates kinked and deformed, providing nucleation sites for cleavage-parallel phyllosilicate growth. Layer-parallel shortening further deformed chlorite-mica stacks, rotating them perpendicular to cleavage or sliding fractured pieces past one another and rotating the fragments into the cleavage. Large chlorite laths grew parallel to cleavage. Chlorite-mica stacks experienced dissolution on cleavage-parallel sides, and possible deposition on ends perpendicular to deavage, giving them a barre1 shape. Pressure shadows formed adjacent to some chlorite-mica stacks.

Comptent quartz veins and carbonate layers were severely buckled and deformed by layer-parallel shortening.

Sulphides, commonly nucleating on sandy patches and layers, grew throughout the period of cleavage development, both deflecting the cleavage and overgrowing it.

Where sulphides deflected cleavage, pressure shadows of chlorite and quartz grew.

Opaque phases are present as rounded, very embayed grains and as metarnorphic laths that grow both across the cleavage plane and in it. SeveraI of the latter also have pressure shadows of quartz and chlorite. At some point gamet grew both as small, largely 156

inclusion-fiee disseminated grains and as aggregates nucleating on previously deformed

carbonate layers. The smaller disseminated grains both deflect and overgrow the

cleavage fabric. Tourmaline overgrows cleavage.

Folding, initiated after layer-parallel shortening could no longer accommodate the

cornpress ive stresses, continued after cleavage format ion had ceased in most areas.

Locally, cleavage formation progressed until afier folding ended.

The above chronicle summarises the early history of most of the study area Later

events such as folding associated with late-stage regional metamorphism and possible

hydrothermal reworking, and fracturing with predominantly sinistral faulting are

recorded in these rocks but did not obscure the early progression of diagenesis and

metamorphism. In the regions at the boundanes of the thesis area, where metarnorphism

progressed into the biotite zone, chlorite-mica stacks are almost 100% muscovite and

pyrite has pressure shadows of quartz and bright green, very fiesh-looking chlorite. Here,

biotite randomly overgrows the cleavage fabric but is deformed by later brittle

de formation.

Metamorphic grade progressed to the epizone in rocks underlying the Cunard

Member and to the anchizont in the overiying rnembers. Later, brittle defomation and associated hydrothermal effects may have increased the metamorphic grade locally in the

uppemost Cunard and Feltzen Members.

These features are indicative of a single regional rnetamorphic event in this part of the Meguma Group. Porphyroblast phases such as gamet and ilmenite exhibit inclusion patterns that mimic bedding layen or their own growth patterns, not an early 157 fabric. The very-Iow-grade metamorphic euidence retained by these rocks also suggests that no subsequent metamorphic event affected this area of the Meguma Group. Chapter 5 "~r?%rDating

5.1 Introduction

The Megurna Terrane, as the last tectonic unit accreted to the North Amencan

Craton, records the final stages of the Appalachian Orogeny. The Meguma Terrane

docked with the North American Craton afier the Taconic Orogeny so its tectonic history

is relatively simple compared with older parts of the orogen, having been deformed

solely by the Devonian Acadian Orogeny and subsequent events. Since it is located too

far north in the Appalachian systern to have experienced significant post-Devonian deformation, it serves as a laboratory where Acadian deformation is isolated.

The history of the Meguma Terrane has complexities that become apparent when considering the terrane as a whole. In the thesis area, however, some of these complexities are absent, and this, combined with the Iow rnetamorphic grade of tne rocks and the small amount of magrnatic overprint, provides an area where early Acadian events may be dated more accurately. Previously, the very fine-grained nature OFthcse rocks discouraged dating mineral separates in most cases. Unfortunately, the results of whole-rock analyses are likely to be a combination of detrital ages and overprinting by subsequent metamorphic episodes. K-Ar dating of mineral separates may also be suspect since loss of radiogenic argon or excess argon cannot be detected (Hanes, 199 1 ). The objective of this part of the thesis was to isolate and date detrital and rnetamorphic muscovite by the J0~r/3"~rstepwise heating method and thus better constrain the timing of metamorphism in the area. --5.2 "OA~/~'A~ Systematics

The K-Ar dating method, as described by Merrihue and Turner (I966), is based

upon the radioactive decay of parent "OK to stable daughter isotopes "'Ca and "'Ar. The

decay path of interest, "'K to "'Ar, affects 11-3% of ""Katoms, with a decay constant of

4.962 x 10-'Oyr-[(Steiger and Jiiger, 1977). Since argon is an inert gas and not prone to

entrapment in minerals during their growth, the "OA~ present is a result of the decay of

40 K. This arçon is known as radiogenic argon, or "'AP.The age of the mineral is thus

proportional to the relative amounts of jOAr*and "'K.

In the case of the J0~r/3"~rdating variant, 'OK is measured by neutron activation

analysis (McDougall and Hamson, 1988; Hanes, 199 1 ). Samples are irradiated with fast

neutrons in a nuclear reactor, converting a small proportion of 39~atorns to ""r. Samples

are then fused, or heated, in an ultra high vacuum, and the gas produced is analysed and

measured by a mass spectrometer to obtain the "O~r*/~%rratio. The amount of 39~ris

proportional to the amount of 3'K in the sample, and since the ratio of 3YKto 'OK is fixed,

measuring the amount of 3"~rreveals the arnount of4*K in the sample. Thus, the ratio

"OAr*p"~ris proportional to the "'Ar*?K ratio and therefore the age of the sample. The age t comes frorn the equation

t = l/h ln [("'Ar*SY~r)(.O + Il, where

Â. is the decay constant and J is the measure of efficiency of conversion of "K to "~r../ is obtained by simultaneousIy irradiating a flux monitor or standard of known K-Ar age, heating it, and analysing the gas to obtain a J"Ar*/3S~rratio. J is calculated by the equation

J = (eXLm- 1)/(J0~r*?9~r)s ,where tm is the age of the standard and ""A~*/~~AI-,is the ratio measured for the standard saniple.

In JflAr/3"Ardating, gas is extracted in sequential temperature steps and measured for isotope ratios at each step. The apparent age of each step is plotted against the percentage of total 39~rreleased at each step, and the resulting graph is called an age spectnim. The amount of gas produced at each step determines the weight the corresponding apparent age cam-es in calculating the age of the sample (Hanes, 199 1 ).

The geological meaning of ages so derived depends on the temperature range over which a mineral goes fiom being completely open to argon acquisition or loss, to being completely closed to argon loss. This range is termed the closure, or blocking temperature, and for muscovite it is 350*50 OC(Jager, 1979). Closure temperatures are functions of such factors as diffusion parameters, cooling rates, effective radii of diffusion, and activation energy for diffusion. Orogenic and related processes determine cooling rates which in turn influence closure temperatures.

In low-grade metamorphic rocks white micas and related clay minerals can crystallise below their closure temperatures. Muscovite begins to retain argon at

150-200°C (e.g. Dewey and Pankhurst, 1970). When dated by the 'OArI3"Ar method, these rninerals produce growth ages instead of the cooling ages obtained from higher grade metamorphic rocks (Hanes, 199 1 ). If growth minerals can be identified as resulting fiom, for example, cleavage formation, and can be isolated From detrital grains of the same

phases, it is possible to closely date the metamorphic event that produced the cleavage

(Reuter and Dallmeyer, 1989; Hanes, 199 1).

5.3 Previous Work

Table 5.1 is a sumrnary of the geochronological data fiom southern Nova Scotia.

Figure 5.1 of the thesis area shows the locations of samples previously dated by other authors. Geochronology of Meguma Group metasediments began in 1960 when Fairbaim et al. dated cordierite-amphibolite facies biotite in the Goldenville Formation by the K-Ar method. Their data suggested a metamorphic age of 338 Ma. Lowdon et al. ( 1963) obtained a K-Ar date of 383 Ma for biotite in the same metamorphic zone, also in the

Goldenville Formation. Poole ( 1971, reported in Wanless et al., 197 1 ) dated detrital muscovite from the Goldenville Formation near Tangier by the K-Ar method and obtained ages of 476* 19 Ma (recalculated to 484 Ma., M. Graves, 1996, pers. comm. ) and 496*20 Ma, ages judged to be either detrital or diagenetic or a combination of both

(Wanless et al., 1971).

Reynolds et al. ( 1973) were the first to attempt to date Meguma Group slates when they applied K-Ar dating to whole-rock samples within this study area. Their data yieided a 403-332 Ma age range from which they suggested a minimum age of390 Ma for regional metarnorphism. Their dates frorn granite samples in the South Mountain

Batholith indicate cooling occurred ai about 367 Ma. Other dates fiom granites in the

South Mountain Batholith and elsewhere in the Meguma Terrane (Fairbaim, 1971; Table. . of Ter-

Unit Age Significance (as interpreted by Reference (Ma) authors)

South Mountain Batholith 180 Apatite fission track ages, final Reynolds et and Southem Satellite cooling below 100 OC. al. 1987 Plutons Southem Satellite Plutons 230-220 '"'~r/~"ArK-feldspar. MiId thermal Reynolds et pulse. al. 1987 Davis Lake Pluton and 295*5 '"~r/~''Armicas, greisenization Zentilli & Goldenville Formation zone associated with tin de posit. Reynolds, 1985 Goldenville Formation - 300 J"~r/3"~rwhole rock. Thermal Keppie and East Kemptville overprint. Dal Imeyer, 1994 Southwest South Mountain 320-300 '"Ar/"Ar muscovite concentrates. Keppie and BathoIith and Host Partial rejuvination. Dallmeyer, GoIdenville Formation 1994 Southem Satellite Plutons 320-300 K-Ar and/or "~r/~"~rbiotite and Reynolds et muscovite. Overprinting by major al. 198 1 transcurrent or transpressive reactivation of suture zones. Southern Satellite Plutons 320-300 '"~r/~"Arhomblende, micas, Reynolds et K-feldspar, later thermal event. al. 1987 Meguma Group - 320-300 J"~r/3"~rmicas, hornblende, Muecke et al. Southwestern Nova Scotia whole rock slatdsiltstone, major 1988 transcurrent or transpressive reactivation of suture zones. Goldenville Formation - 338 K-Ar biotite, cordierite- Fairbairn et NE of Chester, Mahone amphibolite facies zone, al. 1960 Bay metamorphic age. Southwest South Mountain 340 '"Ar/-"Ar muscovite concentrates. Keppie and Batholith, Undeformed 330-320 Thermal overprinting. Dallmeyer, Granite Dyke and Host 3 10-300 1 994 Goldenville Formation 280 Goldenville Formation - 340-350 Jn~r/3"Arwhole rock ages. Keppie and East Kemptville Dal Imeyer, 1994 Unit Age Signi ficance (as i nterpreted by Reference (Ma) authors)

Southwest Meguma Group 352-269 "~r/~~Arbiotite concentrate. Keppie and - Defonned Dyke Dal lmeyer, 1994 South Mountain Batholith 355 Rb-Sr biotite. Fairbairn et al. 1960 South Mountain Batholith, 366.7 K-Ar andfor 'O~r/j"~rbiotite and Reynolds et Northern Satellite Plutons muscovite. ai. 1981 South Mountain Batholith - 367 K-Ar biotite in granite. Reynolds et Aspotogan Peninsula al. 1973 Meguma Group - 368-360 '"A~/J"A~hornblende, biotite and Keppie and Southwest Nova Scotia muscovite. Cooling of most of Dallmeyer, Meguma Terrane through 300°C 1994 Minas Geofracture - 370-360 '"'~r/~"~rbiotite and muscovite, Keppie & Eastern Nova Scotia D, dextral shear zones. Dal Imeyer, 1987 South Mountain Batholith - 370 "~r/~'Arhornblende, micas, Re-ynolds et North of St. Margaret's Bay K-feldspar. Host rocks reset by al. 1987 and Mahine Bay intrusion. Meguma Group - Host to 375-3 15 "~r/"~rbiotite, muscovite, Dallmeyer & Southern Satellite Plutons homblende, M, response to Keppie, 1987 pluton emplacement. Eastern Meguma Plutons, 380-270 U-Pb (mineral unspecified) Keppie & Bamngton Passage Pluton Granitic and Minor Mafic Dal l meyer, and Shelburne Pluton Magnatism 1994 Goldenville Formation - 383 K-Ar biotite, cordierite- Lowdon et al. Mahone Bay amphibolite facies zone, 1963 metarnorphic age. Meguma Group - various 385-360 J0Ar/3"Armicas, hornblende, Muecke et al. locations in Southern Nova whole rock slate/siltstone, 1988 Scotia thermal overprinting due to intrusion. Barrington Passage Pluton 3 85 4"Ark39Arhomblende, micas, Reynolds et K-feldspar, oldest intrusive. al. 1987 Unit Ase Significance (as interpreted by Reference (Ma) authors)

Meguma Group - Tancook 390 K-Ar whole rock hornfels and Reynolds et Island date, minimum regional al. 1973 metamorphic age. Southem Satellite Plutons 395 Rb-Sr (mm.isochron). Fairbaim, 197 1 South Mountain Batholith 396 K-Ar muscovite (probably at least Lowdon et al. near Queensland IO Ma too high). 1963 Minas Geo fracture, outside 400-395 "'~r/"'>~rwhole rock date, Keppie & hiçh temperature pluton 390-385 phyllite. Diachronous formation Da1 l meyer, aureoles 380-375 of S, fabncs and concomitant 1987 low-grade rnetarnorphism. Meguma Group - 405-390 JO~dw~rmicas, hornblende, Muecke et al. Kingsburg Peninsula and whole rock slate/siltstone, 1988 Southwest Nova Scotia regional metamorphism. Meguma Group - 4 10-400 '''M3''~r biotite, muscovite, Dallmeyer & Southwestern Nova Scotia homblende, age of D,and M,. Keppie, 1987 Meguma Group - Mahone 11 5400 '''~r/~')~rwhole rock slates, Reynolds & Bay reçion reçional rnetarnorphism. Muecke, 1978 Goldenville Formation - 476~20K-Ar age, dett-ital muscovite. Poole, 1971 Phoenix Island, Eastern Shore Goldenville Formation - 496*70 K-Ar age, detrital muscovite. Poole, 1971 Taylor Head Peninsula, Eastern Shore Goldenville Formation - 600 U-Pb detrita1 zircon and titanite Krogh & Eastern Shore ages. Keppie, 1990 Meguma Group - near 1 173h95 SmNd mean crustal residence Clarke & Halifax, Tancook Island, time (separation from mantle). Halliday, Aspotopn Peninsula, 1985 Goldenville Formation - 3,000 U-Pb detrital zircon and titanite Krogh & Eastern Shore ages. Keppie, 1990 Goldenvil le Formation - 2,960 U-Pb detrital zircon and titanite Krogh & Eastern Shore ages. Keppie, 1990 . , Figure 5.1 Location and ages of samples previousiy I by *- . dated- other authors. ------* - -- - -. -- / .. <

Atlan tic Ocean

y-':..., 4.. 371 Ma. u K-Ar ages on whole rock 377 Maj -'l '-.?+ 393Ma slates and homfels. :- 392 Ma Reynolds et al. 1973 381 Ma JOAd39Ar ages on whole 4 rock samples. Muecke et al. t 988. Reynolds et al., 1981; Dallmeyer and Keppie, 1987; Reynolds et al., 1987; Muecke et al.,

1988) include 370 Ma for the South Mountain Batholith and ages of 385 Ma, 320-300

Ma, and 230-220 Ma for other plutons in southem Nova Scotia. Table 5.1 shows the dating techniques used to obtain these results.

Reynolds and Muecke (1978) applied the 'OA~/~~A~stepwise outgassing method to whole-rock samples in two regions of the Meguma Group, one of the areas being in this thesis locality. Their work suggested a minimum age of -4 15-400 Ma for a regional metamorphic event of the Acadian Orogeny in this region. Keppie et al. ( t 985) published UPb ages of 2685-1945 Ma and 602-580 Ma from detrita1 zircons, and a 580

Ma age for detritai titanite, all from the Goldenville Formation in eastern Nova Scotia

They also dated whole-rock slate/phyllite samples fiorn the same area and obtained

"~r/~"Arages ranging from 407 to 384 Ma, interpreted to be the times of developrnent of a penetrative cleavage and folding. Dallmeyer and Keppie ( 1987) dated biotite, homblende and muscovite separates fiom various plutons in southem Nova Scotia and their host rocks by "0~r/39~rmethods. They deduced that regional D, folding with greenschist to lower amphibolite facies (M, metamorphism) cleavage formation occurred at -4 10-400 Ma. Keppie and Dallmeyer (1 987) obtained whole-rock slatelphyllite

'OA~I~~A~plateau ages from the vicinity of the eastern end of the Cobequid-Chedabucto

FauIt System which they placed in groupings of 400-395 Ma, 390-385 Ma and 380-375

Ma. They interpreted these dates as corresponding to diachronous formation of S, fabncs and associated low-grade metamorphism. Muecke et al. (1988) conducted Ja~r/39~rstudies on samples fiom several

Meguma Group slate locations. They re-dated three whole-rock samples from previous work (Reynolds and Muecke, 1978) to improve resolution of the spectra and to calibrate directly against the international standard MMHb- 1, and they obtained new data fiom three whole-rock samples from the Kingsburg area of Mahone Bay. The cornbined data constrained regionai metamorphism in the Meguma terrane to the interval 405-390 Ma.

Dating by Krogh and Keppie ( 1990) involved U-Pb isotopic analyses of detrital zircon and titanite in Goldenville Formation rocks from the eastem Megurna Terrane.

Ages of 600 Ma, 2000 Ma and 2960 Ma corne fiorn samples progressively higher stratigraphicalIy. These data suggest that the youngest rocks in the source area were eroded and redeposited early in the deposition history of the Goldenville Formation, and that older source rocks were eroded and redeposited later, higher in the succession. The discordance patterns indicate that the 2960 Ma rocks were rnetamorphosed by the 2000

Ma event and that the 600 Ma event in tum left its signature on the 2960 and 2000 Ma rocks.

SmNd isotopic data from Meguma Group metasediments at Tancook Island, the

Aspotogan Peninsula and near Halifax provide a mean cnistal residence age of ï;,, =

1773195 Ma (Clarke and Halliday, 1985). This age could represent a true mean crustal residence age if the metasediments are clastics derived from a single crustal segment. It could also be a mixed age representing the weighted average of two or more sources with different cnistal residence ages. To the present, 'OA~/~'A~dating of mineral separates fiom the Meguma Group

involved late greisens in the East Kemptville area (Zentilli and Reynolds, l985), and

rocks within the contact aureoles of plutons in southern Nova Scotia (Dallmeyer and

Keppie, 1987). Keppie and Dallmeyer (1994) dated muscovite and biotite concentrates

frorn southem Nova Scotia and East Kemptville.

The fine grain size of slates and shales makes mineral separation a challenge. The

quality of the data obtained fiom whole-rock samples is sornewhat cornpromised by the

presence of different generations of muscovite as reflected in the disturbed spectra.

Previous "~r/~"Arstepwise analyses of muscovite employed relatively large heating steps

of 100°C in the case of Reynolds and Muecke (1978), and slightly more detailed analyses

in the Keppie and Dallmeyer (1987), Muecke et al. (1988) and Keppie and Dallmeyer

( 1994) studies.

In this study, petrographic analyses of numerous samples show that there are

apparent detrital, mctamorphic (ckavage-parallel) and post-cleavage muscovite grains in

Meguma Group sediments. A goal of this study was to isolate and date these separate

morphologies by means of more detailed stepwise heating schedules. The data obtained are usehl for discussing previous whole rock and muscovite separate data and for constraining the metamorphic history of the Meguma Terrane.

5.4 Sarn~leSelection

Ideally, "~r/~'Arstudies directed towards revealing the geologic history of an area should analyse a variety of phases with different closure temperatures in order to produce a geologically significant T-t path. Only muscovite is present in suficient

quantities to be useful here. Biotite, amphibole and pyroxene are absent and there is very

little feldspar or apatite. Figure 5.2 shows the locations of sarnples dated in this study.

Regional metamorphisrn in the Megurna Group metasedirnents is expressed as a

penetrative cleavage, particularly in the members of the Halifax Formation, and folds at

the centirnetre to kilornetre scale. No evidence of a pre-Acadian event was found in the

thesis area, and the XRD illite-muscovite crystallinity study indicates that the geologic

record here documents only very low-grade and low-grade metamorphism. Muscovite

grains alligned parallel to cleavage are believed to have grown within the cleavage fabnc

during the regional metamorphisrn.

Three morphologies of muscovite exist in the eight chosen samples. Long (up to

25 mm), randomly oriented, commonly bent, detrital grains (Figs. 5.3,5.4,5.5) are distinct f?om both fine-grained matrix muscovite or sericite and cleavage-paralle1 metamorphic muscovite. Detrital grains are preserved in the sandy units of the

Goldenville Formation where cleavage is weak. These samples (93-RH 130b, 93-RH 1O7b,

93-RH42b) contain mostly quartz with some albite, and show a distinct size contrast between the long detrital grains and the clay-sized interstitial fraction. Accordingly, separation and picking on the bais of size yielded a high proportion of the detntal fraction in these samples.

Samples with abundant fabric-paral le1 muscovite, and lacking a significant clay- sized fraction or any detrital grains, provided material for dating the age of metamorphism (Figs. 5.6,5.7,5.8,5.9). The process of sieving and hand-picking . . Figure 5.2 Location map for JOArl39Ar analyses and results~

Atlantic Ocean

\. . ., -. ORHS~A 376Ma(k.r) "Ar/n~rSnmple Ri26C1yJ'-. 6 Locations 391 (wcm) y: - 395(s,m)., " 7 s muscovite separate analysis 2 - iw whole rock analysis d detritaf age dg diagenetic age m metamorphic age r met (hydrothermal, deformation) age Figure 5.3 Microphotograph of long, clear detrital muscovite grains. Sample 93-RH1 30b, upper slaty unit, Tancook Mcmber, Little Tancook Island. Scale bar is 0.5 mm. PPL.

Figure 5.4 Microphotograph of long, clear denital muscovite grains. Sarnple 93-RH107b, upper slaty unit, Taifcook Member, Tancook Island. Scale bar is 0.5 mm. XN. Figure 5.5 Microphotograph of detrital muscovite grains. Sample 93-RH42b, New Harbour Mernber, Long Point. Scale Bar is 0.5 mm. XN.

Figure 5.6 Microphotograph of cleavage-parallel muscovite in siltstone layer. Sample 93-RH70,Mosher's Island Member, Cape LaHave Island. Scale bar is 0.5 mm. XN. Figure 5.7 Microphotograph of clear, metarnorphic, cleavage-parallel muscovite in graphitic date. Sarnple 93-RH76c, Cunard Member, Bell's Cove. Scale Bar is 0.5 mm. PPL.

Figure 5.8 Microphotograph of large, white, rnetarnorphic muscovite gowring parallel to a strong cleavage. Sarnple 93-RH62c, Mosher's Island Member, Mosher's Island. Scale bar is 0.5 mm. XN. Figure 5.9 Microphotograph of large, white muscovite laths randomly overgrowing cleavage. Sarnple 93-RH 1 17b, Moshets Island Member, Tancook Island. Scale bar is 0.5 mm. PPL.

Figure 5-10 Microphotograph of clear, fabric-parallcl muscovite. Matrix grain growth suggests a C-S fabric. Sample 93-RH59a, Cunard Member, West of The Ovens. Scale bar is 0.5 mm. PPL. effectively elirninated any clay-sized fraction present. The possibility that detrital cores

may be preserved within younger rnetamorphic muscovite rnust be considered when

interpreting results. Muscovite in samples 93-RH-62c (Fig. 5.8) and 93-RH-1 126 (Fig.

5.9) appear the youngest of the metamorphic grains dated, and in the case of sample

93-RH-1 12b, randomly oriented muscovite overgrowing a strong cleavage rnay constrain

the minimum açe limit of regional rnetamorphism in this area Sample 93-RH59a (Fig.

5.10) also has fabric-parallel muscovite growth originally attributed to cleavage

formation, and was analysed as a metamorphic sample.

The results of petrographic examination, microprobe analyses, and XRD

compositional data and XRD illite-muscovite crystallinity indices, alI described in

previous chapters, demonstrate that these ''OA~/~'A~ages are mica growth ages.

5.5 Sam~leSeDaration

All samples were cmshed in a rock crusher and a disc rnill, and, with one

exception, washed to remove the finest material, and air dried. Panning and sieving out

the less than 70 mesh (2 12 pm) fraction helped concentrate the desired muscovite grains.

In several cases the use of 97% TetraBromoEthane and sodium polytungstate, and

passing sarnples through a Frantz magnetic separator, preceded the hand picking stage. [n

sample 93-RH1 12b separation of individuai grains proved impossible so a whole-rock

sample was dated. In this case, both a sarnple with the clay-sized tiaction washed away, and a sample where al1 material was irradiated, were dated. Sample 93-RH26c, with abundant metamorphic muscovite, was submitted as both a whole-rock sample and a muscovite separate in order to compare the resulting spectra.

5.6 Samole Analvsis

The samples were individually wrapped in thin aluminium foi1 and stacked in an aluminium canister with between five and seven (depending on which of the three irradiation batches included the samples) interspersed flux monitors wrapped in the same fashion. The flux monitor used was the homblende standard MMHb-I which has an apparent K-Ar age of 520i3Ma (Samson and Alexander, 1987). Recently, Rex and Guise

( 1994) and others noted evidence of inhomogeneity of the h4MHb- I standard, mainly in resuIts fiom srnall aliquots of the sample (Ravenhurst, 1995, pers. comm.). Whether or not these are serious concerns remains to be seen and for the purpose of this study the standard is accepted as reliable. The J values obtained fiom analyses of standards were plotted with mors against their positions along the length of the canister. A straight line fitted to these points using the method of York ( 1969) provided sampIe ./ values.

The sarnples were irradiated with fast neutrons in position SC, typicaily for about

10 hours, in the nuclear reactor at McMaster University in Hamilton, Ontario. After a few weeks storage the samples were safe to handle and were analysed at Dalhousie University with a VG3600 mass spectrometer attached to an intemal double-vacuum tantalum resistance fumace. In each case, prior to loading a sample, the furnace was outgassed at temperatures of 1250-1300 OC until the rneasured Ar blank was sufficiently low. The stepwise heating procedure involved heating each sample for 20 minutes,

exposing the gas to a getter for IO minutes, and analysing the gas for 20 minutes. The

heating schedule consisted of heating at 50 OC intervals beginning at temperatures of 500

or 600 OC, and reducing the temperature intervals to 30 OC intervals beginning at 71 0 or

750 OC. At 1000 OC, heating intervals reverted to 50 "C and continued until al1 the gas had

evolved at about 1300 "C. The arnount of gas evolved at each step partly detennined the

temperature steps, causing slight variation in heating schedules among samples. Details of heating schedules and amounts of gas produced at each step are in Appendix G.

The mass spectrometer sequentially scanned for masses of each argon isotope.

Amplified signals €rom the mass spectrometer were digitized and calculated to produce ratios of 37~r/39Ar,36~r/3"~r and '0Ar/3"~r. Measured isotopic ratios may Vary over the course of 15 deterrninations lasting about 20 minutes. A linear extrapolation of ratios was made back to O time when gas was first admitted to the mass spectrometer.

Necessary corrections include a correction for interfering argon isotopes (IIC), particularly those resulting from irradiation of Ca, and the standard atmospheric correction calculated by measuring the amount of 3"Ar present and using this along with the present-day value OF the atmospheric 'O~r/~%rratio (295.5) to calculate the atmospheric ''Ar content. Errors are reported at the 20 level and include the uncertainty in J but do not incorporate uncertainty in the assumed age of the flux monitor- AI1 data for each sample were plotted as age spectra (apparent age in Ma vs. % 3%r released). An age plateau is defined when contiguous steps containing 50% or more of the total gas evolved are calculated to be the same within error by the critical value method (Fleck et

al., 1977) (Appendix H).

--5.7 J"Ar/EAr Datin~Results

5.7.1 Introduction to Interpretation of Argon Age S~ectra

Ideally, the diffusion of argon in a minera1 lattice follows the single site, volume

diffusion model of Turner (1968). Gas evolved from the sample at successiveIy higher

temperature steps cornes fiom sites progressively deeper in mineral grains. If samples

cool quickly through their closure temperature without subsequent thermal disturbance,

they should produce perfectly flat age spectra, or plateaux, representing the age of

cooling through the closure temperature or the time of crystal growth below the closure

temperature. Where samples are therrnally disturbed, they wilI exhibit an age gradient

indicative of partial argon loss. The original age as recorded by such spectra is reduced

by varying arnounts, depending on the degree of overprinting and argon loss. tri theory,

the corresponding K-Ar age of a sample with a disturbed spectrum will be the total ças

age and rnay not be geologically meaningful (Hanes, 199 1 ).

Experimentation has shown that real samples do not always adhere to this model,

likely because of violations of one or more assumptions of the model. In disturbed

spectra, the higher temperature steps often do record an original age (Berger and York,

198 1). Disturbed spectra can therefore give evidence of complex thermal histories and it

is not always necessary to produce flat plateaux in order to derive a geologically meaningful age. Some of the important considerations for spectrum interpretation follow. Impurities in the sample cm cause radiogenic argon release ftom alternate

sources of K. This is obviously a potential problem in whole-rock samples where more

than one phase likely contains K, but complicated age spectra also may result from single

phase separates that experience variable argon loss due to the presence of impurities,

exsolution lamellae or intergrowths within the mineral (Hanes, 199 1 ). Amphiboles and

pyroxenes, the latter rarely dated, are the phases most affected by this problem.

A second problem, and one that has significance for these samples, is that 3"~r,

produced by neutron activation of 39~,has enough energy to recoil by as much as 0.5 pm

(Turner and Cadogan, 1974). The effect of this is usually negligible in coarse-grained

material, but in very fine-grained mineral separates, recoil from near-surface sites can

result in loss of some '"~rduring irradiation or low-grade metamorphism, leading to

anomalously old ages. In fine-grained whoIe-rock samples with K-rich and K-poor

phases, such as samples from this study with abundant muscovite and chlorite, '"~rmay

recoil out of K-rich muscovite and into K-poor chlorite. The chlorite acts as a sink for

argon recoiling out of micas (Keppie and Dallmeyer, 1987; Reuter and Dallmeyer, 1989).

The effect of this phenomenon is noted in the results section (Section 5.7).

Another experimental artefact is sample breakdown during dry in vucuo heating.

As temperature increases, hydrous minerals become stnicturally unstable and gas is not evolved by simple volume diffusion (e-g. Hamson et al., 1985; Gaber et al., 1988).

Biotites and, to a lesser extent, amphiboles are the most sensitive to this effect. Since white mica can grow at low temperatures, more than one generation of white mica may CO-existin the same rock. A standard mineral separate may contain a mixture of two or more micas (e.g. detrital and metamorphic mica), and spectra fiom such samples rnay have a convex-upward shape due to the differing argon release characteristics of the individual types (Wiljbrans and McDougall, 1986).

Excess argon is 'OA~ not generated by in sifudecay of ''K. It can be incorporated into a mineral during crystallisation or at the time of some later themal/metamorphic event if there is localised argon overprcssure (e-g. zones of high fluid flow). If diffusion is too slow to expel this argon component before it is trapped in the minera!, the mineral will give erroneously high ages that cannot be corrected for by the normal atmosphenc argon correction (McDougall and Hamson, 1988). Biotite is the most susceptible of the minerals cornmonly dated, though others may exhibit the sarne effect. A characteristic signature of excess argon is a saddle-shaped spectrum.

The choice of muscovite for dating has, to a certain extent, avoided some of the above problems. Carefùl sample preparation ensured that mineral separates were as clean as possible. The potential for interference €rom other K-bearing phases is minimal since these sarnples do not contain any.

The whole-rock samples dated in this study exhibit recoil effects from the presence of fine-grained chlorite and this has been considered in interpreting the resulting ages. The problem of multiple generations of white mica was used to advantage here since the objective was to identi* and separate detrital and metamorphic muscovite.

Interpretation of the results incorporate this factor. X-ray diffkaction (XRD) analyses camed out as part of the illite-muscovite crystallinity study (Chapter 4) identified paragonite in some Cunard Member samples. Of the samples dated, two are fiom the

Cunard Member, one of which was dated by means of a muscovite separate sample, the other dated with both whole-rock and muscovite separate sarnples. Paragonite may have been present in the fine-grained portion of the whole-rock sample, so comparison with the muscovite separate from the same sample is useful.

5.7.2 Detntal Muscovite Results

Three samples from the Goldenvil te Formation provide data on detital muscovites. Cleavage is much Iess intense in the sandy members of the Goldenville

Formation and demtal phases thus are more likely to main evidence of their pre-rnetamorphic age than formations characterised by slaty cleavage. Sample 93-RH42b is fiom the New Harbour Member at Long Point and samples 93-RHI07b and

93-RH130b are from the upper slaty unit of the Tancook Member on Tancook Island and

Little Tancook Island respectively (Fig. 5.2). The samples contain long detrital muscovite grains and there is little evidence of recrystallization in other phases. In sample

93-RH130b (Fig. 5.3) most ofthe muscovite is bedding-parallei with minor amounts of random and cleavage-parallel muscovite. The spectrum (Fig. 5.1 la) is disturbed in a way spical of those where the phase dated has experienced thermal overpnnting to some degree (Hanes, 199 1). Apparent ages increase in a staircase-like manner fiom ca. 420 Ma until they peak at 597* 1.5 Ma over the final ca 20% of gas released. The similarity of this final age to the 600 Ma date obtained corn detital zircon and titanite fiom the

Goldenville Formation ( Krogh and Keppie, 1990) is noteworthy. Electron microprobe

analyses of some large (detrital?) grains show slight compositional variation from cores

to rims to tips. Some metamorphic grains may have persisted in the sample past the

picking stage. However, there is little visible metamorphic muscovite, probably not

enough to produce the apparent amount of resetting; resetting of outer rims rnay therefore

be the best explanation. in the case of sample 93-RH1 30b the detrital grains have been

partly reset by argon loss due to thermal disturbance associated with regional

rnetamorphism. The spectrum levels off somewhat at about 550 Ma (total gas),

suggestive of partial resetting of the detrital grains at that time.

Sample 93-RH107b (Fig. 5.4) also produced a disturbed spectrum (Fig. 5.1 1b),

similar to that of sample 93-RH1 30b, and for the same reasons. Again, the highest

recorded age (608k3.5 Ma) is close to the 600 Ma age of Krogh and Keppie ( 1990).

There is a level part of the spectrum giving an age of 567 Ma, which is similar to the 550

Ma inflection in the spectrum from sample 93-RH130b, and the 566 Ma age obtained

from a single zircon by Krogh and Keppie (1990).

Sample 93-RH42b (Fig. 5.9, although chosen as a detrital sample, contains

smaller muscovite grains compared to samples 93-RH l3Ob and 93-RH 1 O7b. The

spectnim (Fig. 5.1 1 c) shows in the early stages a more pronounced effect of thermal

overprinting. The oldest age recorded is 559*1.3 Ma which falls within the range of data

tiom detrital titanite and zircon produced by Krogh and Keppie (1990). An apparent

levelling of the spectnim at ca. 484 Ma could reflect the presence of a detritai component of this age, or record diagenesis in these rocks (see Section 5.8). This age is similar to K-Ar ages of 476119 and 496*20 Ma obtained from muscovites in quartzose greywackes

in the Goldenville Formation in eastem Nova Scotia (Wanless et al., 1971).

An interesting feature of Meguma Group muscovites is that although detrita1

muscovite differs so little cornpositionally fiom other muscovite morphologies (see

Chapter 3), it retains a distinct argon signature. Studies suggest that temperature controls

intra-crystaltine volume diffusion of argon. Fine grain size fractions will therefore be

more completely reset with respect to argon than coarser grains that have experienced the

same metamorphic conditions (Reuter and Dallmeyer, 1989). Detrital muscovites in

these rocks are distinctly larger than metamorphic muscovites. This may be why they

retain more of their original argon signature, probably in the cores of the grains, despite

experiencing the same temperature conditions as the metamorphic grains. This

temperature-controlled effect need not be tinked to a compositional change if there is no

compositional "gradient" to induce difkent compositions in newer pingowth-

5.7.3 Metamomhic Muscovite Results

The samples chosen for dating metamorphic muscovite al1 come from members

in the Halifax Formation where cleavage development is extensive. They are pelitic, and

with one exception have abundant muscovite growth within the cleavage fabric. The exception is sample 93-RH1 12b which has relativety young looking muscovite randornly

overgrowing a strong cleavage (Fig. 5.9). This is the sole sample of al1 those examined

petrographically containing muscovite that clearly pst-dates cleavage Formation. It therefore has potential to provide a minimum age of regional metamorphism in this area. The spectrum from sample 93-RH70 (Fig. 5.12a) has a convex-upward shape sometimes attnbuted to a mixture of muscovite phases (Wijbrans and McDougalI, 1986).

The most significant aspect is the level area of the spectmrn that gives an age of 395 Ma.

Although it is not a plateau, it demonstrates a strong overprinting effect that matches data from other samples. The oldest age on the spectmrn is 480I5.3 Ma which matches, within error, the age of the level area on the spectrum Ciom sarnple 93-RH42b (Fig.

5.1 lc). This sample contains both cleavage-parallel muscovite and muscovite that grows in the fractures along the basal cleavages of the chlorite porphyroblasts. The fractures in the porphyroblasts result fiom deformation accornpanying cleavage development.

Muscovite growth in these fractures produces chlorite-mica stacks described in Section

4.4.1. Compositionally, the two types of muscovite are virtually the same. Whether or not enough muscovite could be liberated fiom the chlorite porphyroblasts to cause the effect seen in the spectrum is questionable.

Samples 93-RH26c and 93-RH62c have spectra that give very similar ages. While muscovite in both samples is parallel to a very strong cleavage, in sample 93-RH62c the muscovite looks younger, as if newly overgrowing other phases while maintaining a cleavage parallel orientation (Fig. 5.8). Sample 93-RH26c, from the Cunard Member,

Bell's Cove, has muscovite that grows within a crenulation or early cleavage fabric (Fig.

5.7). This sarnple produced a disturbed spectnim that has a strong overpn'nting effect at

395 Ma (Fig. 5. t2b). A whole-rock sample fiom this rock was also analysed to compare spectra. The whole-rock spectrum (Fig. 5.12~)has a saddle, likely resulting fiom recoil in chlorite grains in the sample. The data fiorn this spectnun give a total gas age of 391 Ma APPARENT AGE (Ma) 2+

0000000gggL;hgg

APPARENT ACE (Ma) a

VI gggg,ggQ after removing the first three steps, but may be less meaningful than data fiom the

muscovite sample From the sarne rock. The muscovite spectrum has a stronger detrital

effect that rnay be due to enhancement of detrital grains through picking. In the

whole-rock sample this effect is swamped by very fine-grained new white mica. A

cornparison of the muscovite and whole-rock spectra from this sample shows how

analyses of separates can produce complementary results.

Sample 93-RH62c, fiom the Mosher's Island Member on Mosher's Island,

produced a good plateau with a total gas (al1 but 9%) age of 395 Ma (Fig. 5.12C), similar

to the 39 1 Ma age obtained €rom sample 93-RH26c. The relatively young age is

consistent with the appearance of the muscovite grains in this sample (Fig. 5.8).

It proved impossible to separate muscovite grains from sample

93-RH 1 12b fiom the Cunard Member on Tancook Island. The material dated constituted

two samples; one sample containing the clay-sized fraction (Fig. 5.13b) and the other

with the clay-sized fraction washed away (Fig. 5.13a). The two resuiting samples were

irradiated in different canisters at different times and dated several weeks apart. The

similarity of the spectra attests to a high degree of reproducibility in the 40Ar/3"~rdating

procedures used (Fig. 5.13~).Both spectra have slight peaks at the higher temperature end which are probably due to recoil resulting fiom the presence of chlorite in the samples. Average apparent ages over the major portion of the gas release (-95%) are 388

Ma in the untreated sample and 389 Ma in the washed sample (Figs. 5.13a and b). The muscovite in sample 93-RH1 12b looks young, like the grains in sample 93-RH62c, but in this case the muscovite randomly overgrows a strong cleavage (Fig. 5.9). Since this

sample was chosen as the one most likely to produce a minimum metamorphic age, the

resulting age (ca.388 Ma) is interpreted as a lower limit to the time of rnetamorphism in

this area.

Lastly, sarnple 93-RH59a produced surprising results. This sample was originally

selected as a metamorphic sample with muscovite growth assumed to be parallel to the

cleavage. It produced a good plateau with a total (al1 but 3%) gas age of 376 Ma (Fig.

5.13d), strongly suggesting significant resetting in this area just prior to the time of granite emplacement. A closer look at the mode of muscovite growth revealed a fabric

more like a C-S fabric (Fig. 5. IO), implying that the argon systernatics may have been

reset by a post-main-stage regional metamorphic deformation event. This sarnple comes

fiom The Ovens peninsula where late-stage folding, veining, tlexurai-slip and anomalous shear zones (Feltz South) are present (Horne, 1993; Horne and Culshaw, 1994; this study).

5.8 Discussion of *~r/~~rAg-

Table 5.2 summarises ages obtained fiom 'OA~/~"A~dating in this thesis. Samples

93-RHl3Ob and 93-RH107b give maximum ages of -600 Ma, in good agreement with

U/Pb zircon and titanite dates obtained elsewhere (Krogh and Keppie, 1990). The latter reflect apparent ages of source rocks of Meguma Group sediments. Middle Cambrian trilobite Fragments from Tancook Island, however, suggest a younger age of deposition for the top of the Goldenville Formation (Pratt and Waldron, 199 1). The oldest these Table 5.2 -QUD Thesis Sam~les

Age (Ma) Sample Type Signi ficance Sample

Muscovite 97% of total gis. Rcsct metamorphic agc. Whole-rock Clay-sized fraction present, metamorphic age. Whole-rock Clay-sixed fraction rernoved, metamorphic ase. Whole-rock Total gas age, 1st 3 steps rernoved . Muscovite 9 1 % of total gas, metamorphic age. Muscovite First gas (43%),metamorphic age. Muscovite Average age of ledarea, metarnorphic age. Muscovite Maximum age of spectrum, detrital, diagenetic age? Muscovite Average age of IeveI area, detrital, diagenetic, age? Muscovite Partty met detrital age. Muscovite Partly reset detrital age. Muscovite Partly reset detrital açe. Muscovite Detrital age. Muscovite Detri tat age. fragments could be is 536 Ma and their occurrence as a well sorted bioclastic layer

demonstrates that they did not form a living assemblage in this location.

The spectra fiom samples 93-RH130b and 93-RH107b also have slight inflections

at - 550 Ma and 567 Ma respectively, interpreted as partial resetting of detrital grains.

Samples 93-RH42b and 93-RH70 produced disturbed spectra with inflections at

484 Ma and 480*5.2 Ma respectively. It is difficult to judge the significance of these ages

since both are derived From disturbed spectra reset to varying degrees. Data from Poole

(1971) are the only dates known that match these in any way. He obtained K-Ar ages of

476I 19 (later recalculated to 484 Ma. M. Graves, 1996. pers. comm.) and 496*20 Ma

fiom Goldenville Formation detrital muscovites on the eastern shore of Nova Scotia. He suggested these ages may record the timing of 1) erosion, transportation, deposition and diagenesis of Goldenville Formation sediments, 2) diagenesis and alteration during compaction and lithification, 3) the first formation of a moderately well developed cleavage, or 4) an incomplete stage of overprinting during metarnorphism and deformation in the Devonian Acadian Orogeny. In the case of sample 93-RH42b, chosen as a detrital sample, the inflection may simply represent incomplete resetting of detrital grains to a greater degree than in the other two detrital grains. Hunziker et al. (1986) and

Reuter and Dallmeyer (1989) report that the transformation of illite fiom a I Md polytype to a 2M,polytype can also rejuvenate the argon system. Resetting of the argon system is not complete until al1 the detrital 1Md components are transformed, a process that is indirectly temperature dependent (e-g. Velde, 1965; Eslinger and Savin, 1973; Reuter and

Dallmeyer, 1989). No remnant grains of 1Md illite polytype were identified by XRD analyses in any of the sarnples but again, only the finest-grained fractions were analysed, and the specific sarnples under discussion here were not analysed.

The transformation From the [Md to the 2M, polytype is essentially a feature of diagenesis, so the suggestion by Wanless et al. ( 1971) that the 484-496 Ma ages (Poole,

1971) represent diagenetic ages rnay be valid. Graptolite fossils found in Halifax

Formation slates at Maitland Bridge, near Kejirnkujik National Park (Cumming, 1985), give a Tremadoc (-485 Ma) age. The similarity of their age to the age of the inflections in the spectra may also indicate that 484 Ma is a depositional-diagenetic age. However, if the infl ections resulted fiorn diagenetic effects, similar inflections might be anticipated for a11 the detrital samples. Spectra from detrital muscovite samples 93-RH 130b and

93-RH 10% (Figs. 5.1 I a and b) show no such features.

Samples 93-RH26c (Figs. 5.12b and c) and 93-RH70 (Fig. 5.1 la), metarnorphic muscovite samples, give similar maximum ages (with large errors) of 470 Ma and 480

Ma respectively. These ages may a!l reflect the presence of detrital cores within metamorphic muscovite, or remnants of diagenetic effects preserved in detntal cores.

Good metarnorphic ages from samples 93-RH26c, 93-RH62c, and 93-RH 1 1 Sb, and a corroborating date from sample 93-RH70 constrain the age of metarnorphisrn in this area, with respect to muscovite closure temperature, to between 395 and 388 Ma.

This is somewhat younger than ages of 400-4 1O Ma (Dallmeyer and Keppie, 1987) and

405-390 Ma (Muecke et al., 1988) published in earlier reports. Previously, most dating of

Meguma Group sediments has been on whole-rock samples which have cornponents of detrital and metamorphic signatures. Metamorphic ages so produced would be older than the metamorphic date produced fiom distinctly metamorphic muscovite separates. The

tighter heating schedule here employed in J0Ar/39Ardating also produced spectra capable of resolving other etements of the thermal history of the separates.

The younger metamorphic ages resulting fiorn this study also heip solve geologic

inconsistencies in the Meguma Terrane. Regional structures related to metarnorphism are present in rocks of the Torbrook Formation. Fossils in the Torbrook Formation suggest continuous sedimentation from Goldenville Formation deposition times to at least the

Middle Lower Devonian, perhaps until the Upper Lower Devonian (Reynolds et al.,

1973).

Recently, Bouyx et al. (1992) studied various benthic faunas fiom the Torbrook

Formation and confirmed the presence of Lochkovian, Pragîan and Lower Emsian faunas

(base of the Devonian to the base of the Middle Devonian).

These are the youngest sediments intruded by the South Mountain Batholith (370

Ma), Gedinian-Emsian in age, and since the top 30% of this formation is Iost to erosion, the upper layers may have been younger than Emsian (Elias, 1987). The

Gedinian-Ernsian was considered to span the range of 408-387 Ma. This suggests that regional metarnorphism began in the Meguma Terrane while upper parts of the Torbrook

Fonnation were still being deposited. The data From this study constrain metarnorphism to 395-388 Ma, at lest in the study area, which is lcss of an overlap with depositional ages for the Torbrook Formation. The geologic time scale has also recently been adjusted

(Tucker and McKerrow 1995). The Gedinian-Emsian is now considered to span 4 17 Ma to -400 Ma or slightly younger, and the base of the Ernsian is given as 400 Ma. Combining the new time span for the Gedinian-Emsian and new ages of rnetamorphism

from this study resolves the former problem of metamorphism in the Torbrook

Formation.

The youngest age, 376 Ma, cornes fiom a muscovite separate that produced a flat

plateau strongly suggestive of cornplete resetting by some later event. Why these rocks

should record this overprinting is unclear. Other ages similar to SMB ages corne from

nearby sample locations (Reynolds et al., 1973) and one suggestion, based on Bouguer anomaly data (Garland, 1964; O'Reilly, 1975), is that a large vertical cylinder of granite

intrudes to near-surface depths near the town of New Ross. Shallow granite sheets extending from this body to the northeast and southwest underlie the metasediments, one of them present between Sheiburne and Mahone Bay (Garland, t 964). The Williams and

Haworth (1984) Bouguer anomaly map shows no such anomaly in the study area although the Shih et al (1993) compilation gravity anomaly map does show an offshore anomaly in this area that may represent shallow granite emplacement here. This could account for resetting the argon clock of sample 93-RH59a, but XRD data discussed in

Chapter 4 indicate that the crystallinity value fluctuations rnay be too local to be explained by a large shallow igneous body underlying the metasediments in this area.

Alternatively, the resetting of argon in muscovites may be linked to deformation noted in the area of the anomalous ages. The intense shearing observed at Feltz South

(this study), and pronounced chevron folding with flexural-slip duplex structures and numerous auriferous quartz veins in the area of The Ovens and elsewhere in The Ovens peninsula (Home, 1993; Horne and Culshaw, 1994; this study), attest to considerable deformation in these areas. The fabric demonstrated by muscovite growth in this sample

(Fig. 5.10) is evocative of C-S fabrics produced in strained rocks. The relatively high concentration of quartz veins in the hinge zone of the Ovens Anticline indicates significant fluid involvement late in the structural history of the area The muscovite in the sarnple located just west of The Ovens, also within the anticline, rnay have been reset by the late-stage deformation that produced the fabric, perhaps together with hydrothermal activity associated with the deformation. Similar, previously obtained ages frorn the study area (Fig. 5.1, Table 5.1) rnay be a resuIt of this late-stage deformation.

A connection to the intrusion of the SMB cannot be ruled out, however.

Late-stage regional metamorphism and deformation may be related to hydrothermal fluids advancing through the cmst ahead of the intruding batholith, causing local overprinting of regionally metamorphosed sediments. Chapter 6 Discussion and Conclusions

6.1 Introduction

Geological investigations of a regionai nature increasingly use a combination of

tools to solve problems in understanding the geoIogic history of an area. Techniques not

previously applied to the low-grade rocks of the Meguma Group were used in this thesis

to reveal the early history of the Meguma Group, producing data relevant to some of the

outstanding questions concerning these rocks. This chapter reviews these issues and

discusses ways in which the data can help solve them or provide some insight.

6.2 Low-made Metamorphism and Fabric Developrnent

Studies conducted by others indicate that the low-grade rocks of the Meguma

Group first experîenced a history of syn-sedimentary slumping and bioturbation followed by compaction and the formation of features such as carbonate concretions. The evidence

for this part of the story is in the sçdirncntary structures visible in outcrop. Thc

main-phase regional metarnorphic history of layer-parallel shortening, cleavage development and folding is likewise quite well understood.

tn this study, petrographic, electron microprobe, and XRD illite-muscovite crystallinity studies produced new data on the composition of the phyllosilicate phases, and more precise details of the level of metamorphism attained by rocks in the Mahone

Bay area. Back-scatter image analyses applied to porphyroblast phases showed that they do not preserve evidence of an early, pre-regional metamorphism schistosity. The 197

evolution of chlorite-mica stack development in these rocks is here described for the first

time, and rnicroscopic carbonate and quartz lenses are identified as possible remnant

incipient bedding-parallel carbonate layers and early bedding-parallel quartz veins.

J0~r/3"~rdating of detrital, metamorphic and pst-metamorphic muscovite separates and

whole rock samples constrained the timing of events in the history of these rocks.

The sum of these investigations displays the progress of the sediments from deposition through to low-grade metamorphism with no evidence of having passed through an earlier metamorphic event. An age of 600 Ma from detrital muscovite separates provides an older limit to the timing of deposition of the sediments. Spectra

from detrital muscovites al1 show signs of resetting by later regional low-grade metarnorphism, but inflections in two spectra may indicate that diagenesis took place at around 484-480 Ma. Lesser inflections in three spectra at 567-550 Ma are too weak to be characterized as more than partial resetting by regional metarnorphism.

The composition of the phyllosilicate phases and XRD illite-muscovite crystallinity data demonstrate that in rnost of the succession the main controls on diagenesis- rnetamorphism in this area were the original lithochemical signature of the sedirnents and the depth to which the sediments were buried. Reactions illustrated by phengite and Tschermak substitution, and Ti concentrations, show that the stratigraphically deepest sedimentary rocks experienced the greatest degree of metamorphism. XRD illite-muscovite crystallinity (KI) values follow a trend of improvement with depth in al1 but the uppermost Cunard and Feltzen Members. The pattern of KI values may also reflect increasing arnounts of organic material and 198 decreasing grain size progressively higher in the Meguma Group. The presence of 2M, mica may have lowered Ki values; alternatively, crystaltinity improvement may have been retarded by the presence of paragonite and organic matter.

Although the XRD data indicate that diagenetic reactions progressed to the stage where al1 the white micas were transformed to the 2M, polymorph, KI values range from borderline diagenetic zone-anchizone to epizone/lower jyeenschist facies metamorphism.

The presence ofdiagenetic-anchizone grade rocks supports the conclusion that Megurna

Group rocks in this area did not experience a previous metamorphism.

Cleavage and folding associated with the main phase of regional metamorphism

(395-388 Ma) influenccd the entire succession, particularly the more pelitic units of the upper Goldenville Formation and the Hal ifm Formation. Opinions differ on the relative timing of cleavage and folding in these rocks. Henderson et al. (1 986) suggest that cleavage predated folding, while Williams and Hy (1990) believe cleavage began prior to folding but continued throughout the folding process, at least locally. Cleavage-folding relationships observed during field work for this study include an axial-planar cleavage fabric cutting across folds, and cleavage in a convergent fan around fold hinges. The first pattern supports the claim (Williams and Hy, 1990) that cleavage formation persisted ahfolding ceased in some areas of the Meguma Group, the second pattern may result fiom local late-stage folding.

Previous estimates of volume loss during cleavage development in the Meguma

Group are contradictory. Workers have proposed as much as 60-70% shortening due to cleavage formation (Fueten et al., 1986) and a concomitant volume loss of as much as 199

4040% (Wright and Henderson, 1992). Clifford et al. (1983) calculated a bulk loss of

33% quartz This represents a lot of SiO, to transport out of the rocks and would require significant amounts of fluid. Erslev and Ward (1994) concluded that the bulk rock composition of cleaved Megurna Group rocks is too close to the starting composition of an average shale for these rocks to have sustained extensive volume loss.

The hornogeneity of phyllosilicate composition within individual members, regardless of phase morphology, suggests both depth-controlled metamorphism and a lack of extensive fluid movement upward through the succession. Outcrop evidence of several generations of quartz veins, including nurnerous bedding-parallel veins, and microscopie evidence of small-scale redeposition of quartz (e.g. Erslev and Ward, 1994; this study) point to fluid movement channelled along bedding-parallel pathways, and local redeposition. If true, this would contribute to the slight individual chemical characteristics exhibited by each mernber of the Meguma Group. The rocks could have

Iost volatiles without significantly altering their chemical signatures, and although some volume of material was likely lost fiom the system, the high volumes proposed by earlier studies may be unrealistic.

6.3 Age of Metamomhism in the Meguma Terrane

Previous ages obtained from low-grade rocks of the Megurna Group were based on K-Ar and J0~r/39~ranalyses of whole rock samples using large heating steps. Whole rock analyses can give ages that are a mixture of detrital and metamorphic ages, and may be adversely infiuenced by the presence of other K-bearing phases. This study used mineral separates of specific muscovite morphologies and subjected them to a rigorous

"0Ar/39Arstepheating schedule, producing more accurate and informative data fiom the low-grade rocks of the thesis area.

Visible detntal muscovite grains, predominantly cleavage-parallel metamorphic muscovite, and metamorphic muscovite randomly overgrowing cleavage were separated where possible and produced the ages show in Table 6.1.

The oldest ages, 6O8*3 -5 Ma and 597* 1.5 Ma, are fiom muscovite separates picked as detrital grains, and are in agreement with U/Pb zircon and titanite ages fiom the

Megurna Group (Krogh and Keppie, 1990). They are interpreted as apparent ages of source rocks of Megurna Group sediments. Two younger ages fiom muscovite separates,

484 Ma and 480*5.2 Ma, are inflection points in disturbed spectra. Poole (reported in

Wanless et al., t 97 t ) obtained K-Ar ages of 4761 19 (recalculated as 484 Ma, M. Graves pers. comm.) and 496*20 Ma from Goldenville Formation detrital muscovites. They were thought to be either depositional-diagenetic ages, or due to the first stage of cleavage formation, or the result of partial metamorphic overprinting. The transformation of illite €rom a I Md polytype to a SM, polytype, a diagenetic process, can also rejuvenate the argon system (Hunziker et al., 1986; Reuter and Dallrneyer, 1989). The 484 Ma age therefore may be a diagenetic age for these rocks.

Metamorphic 'O~rl'kages range from 395 to 388 Ma. These dates are in reasonably good accordance with previously obtained rnetamorphic ages for the Meguma

Group, but the range is slightly narrower and younger than ages from other studies. An outstanding problem in the chronology of the Meguma Group is the apparent Bb!e 6.1 ?MPAr- APS frorn -ma gr ou^ T hesis Samples (Reproduced frorn Table 5.2)

Age (Ma) Sample Type Significance Sample

Muscovite 97% of total gas. Reset metamorphic age. Whole-rock Clay-sized Fraction present, metamorphic age. Whole-rock Clay-sixed fraction removed, metamorphic age. Whole-roc k Total gas age, 1st 3 steps removed . Muscovite 9 1% of total gas, metamorphic age. Muscovite First gas (43%),metamorphic age. Muscovite Average age of level area, metarnorphic age. Muscovite Maximum age of spectrumt detrital, diagenetic age? 484 Muscovite Average age of level are* detrital, diagenetic, age? -550 Muscovite Partly reset detrital age. 559* 1.3 Muscovite Partfy reset detrital age. 567 Muscovite Partly reset detrita1 age. 5971 1.5 Muscovite Detrital age. 608rt3.5 Muscovite Dctrital agc. inconsistency of a 405 Ma metamorphic fabric imposed on the 385 Ma rocks of the

Torbrook Formation (Reynolds et al,, 1987; Muecke et al., 1988; Schenk, 199 1; Raeside and Jarnieson, 1992). This problem is reduced considerably by the results of two recent studies. The first, by Bouyx et al. (1992), reported the presence of Lochkovian, Pragian and Lower Emsian faunas (base of the Devonian to the base of the Middle Devonian) in the Torbrook Formation. The recent work of Tucker and McKerrow ( 1995) has revised the geologic time scale for the Cambrian and Early Devonian. Using the new absolute ages, the time period covered by the faunas is fiom 4 17 Ma to -400 Ma or slightly younger (the base of the Emsian is given as 400 Ma).

Previous ages from the study area represent a mix of detrital and metamorphic ages, and thus may be older than the true metamorphic age of these rocks. The metamorphic age range of 395 to 388 Ma here reported does not overlap with the new the period assigned to the Torbrook Formation. The top of the formation is eroded so its youngest age is unknown, however it is also not known if the overprinting metamorphic fabric deformed uppermost layers of the formation. Although rnetamorphism must have begun to affect these rocks very soon afier deposition, the problem of the timing of these events is resolved.

The ''A~I~~AA~dating portion of this thesis also demonstrates the feasibility and desirability of conducting analyses on muscovite separates. Separating muscovite grains fiom fine-grained rocks can be tedious without justification for the work involved. [n the case of the Meguma Group, XRD analyses revealed the presence of K-feldspar in a few samples which could influence whole rock 'OM3%r ages. As demonstrated in samples 203 from this study, more than one generation of white mica can CO-existand produce convex-upward spectra because of the differing argon release patterns. By separating muscovite identified as detrital, cleavage-parallel, or randomly overgrowing cleavage, there is a greater chance that the resdting spectra will be more informative and accurate.

Even where muscovite spectra are disturbed, as in sorne of these samples, the shape of the spectra can indicate the timing of meaningfûl overprinting events. Employing a detailed step-heating schedule is also important in order to adequately display nuances in the spectra that can indicate significant overprinting events.

6.4 Late-Sta~e(Pre-Granite) Regional Metamomhic Tectono-Thermal Evolution of The Mepuma Group Data from field work, the XRD illite-muscovite crystallinity study and "OA~/~~AA~ dating conducted during this study illustrate a later stage of deformation in specific places ofthe thesis area. Field work disclosed the presence of anornalous, strong, outcrop-scale defortnation such as overtumed beds and vertical shear zones developed in fold cusps at Feltz South (Feltzen Member). At The Ovens and west of The Ovens

(Cunard Member) late-stage reactivation of folding is accompanied by flexural-slip, thnisting, and extensive quartz veining (Home, 1993; Home and Culshaw, 1994; this study). The deformation at Feltz South is in the syncline between the Indian Path and

Ovens Anticlines, and the deformation visible in The Ovens peninsula is in the crest of the Ovens Anticline.

XRD illite-muscovite crystallinity KI values show that the trend of increasing crystahity improvement with depth may not hold for the Cunard and Feltzen Members. 204

The Cunard Member samples show the least amount of crystallinity improvement but this may due to the inhibiting presence of anomalous arnounts of paragonite and organic matter present in this member. Ki values from the Cunard Member are variable, and values from the Feltzen Member may result frorn crystahity improvement by some process other than depth of overburden and regional low-grade metarnorphism. XRD data demonstrate the presence of several phases attributed to hydrotherma1 effects. They are in samples fiom outcrops in the hinge zones of the major anticlines.

A muscovite separate from The Ovens peninsula where flexural-slip folding and thrusting are seen, produced a flat 'OA~/~'A~plateau comprising 97% of total gas and an age of 376 Ma. In thin section the fabric of this sample appears more like a C-S fabnc than a cleavage fabric suggestive of total resetting of the argon in muscovite fiorn this sample by a later deformation event.

The age pre-dates the South Mountain Batholith (-370*2 Ma) and is similar to an apparent age of 374 Ma from a sample at the southeastern end of Heckman's Island, and an apparent age of 377 Ma fiom a sample near LaHave (Reynolds et al., 1973). Both are

K-Ar ages obtained from whole rock analyses korn samples located within nine kilornetres of the sarnple from this study. The LaHave sample is from the hinge of The

Ovens Anticline, and the Heckman's Island sample is from between the crest of The

Ovens Anticline and the trough of the syncline that displays the deformation seen at Feltz

South.

The Reynolds et al. ( 1973) results were attributed to partial resetting by an isolated shallow area of granite too small to have a noticeable effect on the gravity field. Garland ( 1964) ascribed the pattern of negative gravity anomalies in southem Nova

Scotia to a large vertical cylinder of granite positioned near the town of New Ross with

sheets of granite extending fiom the main cylindrical body to the northeast and

southwest. However, XRD illi te-muscovite crystallinity data from samples near the SMB

show that diagenetic and very-low-grade metamorphic crystallinity signatures did not

survive the proximal intrusion of a granitic body. In light of the highly variable XRD

crystallinity data in the area of The Ovens peninsula - KI values range fiom

diagenetic-low anchizone to epizone rather abruptly - a shallow granite body underiying the region may be less feasible than defomation as a cause for resetting argon in the muscovites from this region.

The deformation at The Ovens peninsula is attributed to late-stage folding accompanied by hydrothermal activity, flexural-slip and thmsting. Both cross-cutting veins and late bedding concordant Ciexural-slip veins indicate late emplacement

synchronous with flexurat-slip (Home and Culshaw, 1994). The late quartz veins may be the result of hydrothermal fluids moving through the hinge of the anticline. Deformation

in Feltz South is more ductile in nature and lacks the abundant quartz veining visible at

The Ovens. The two areas are geographically close and may represent different responses to the same defomation; one characteristic of the hinge of an anticline, the other in the trough of a syncline and lacking the abundant fluids that penetrated the anticline hinge.

The anomalous age from The Ovens peninsula could be the result of this deformation and hydrothermal activity. 6.4.1 Gold in Low-Grade Memima Group Rocks

The same age, 376 Ma, also may have implications for gold studies in this area of

the Meguma Terrane. The plateau suggests strong overprinting pior to the emplacement

of the South Mountain Batholith. The timing and method of gold deposition in Megurna

Group sediments are strongly debated issues. One theory holcis that the source of the Au

was the Meguma Group itself and the method of emplacement was related to the

greenschist-grade metamorphism that affected the auriferou rocks (Graves, 1976;

Zentilli and Graves, 1977; Graves and Zentilli, 1982). Another hypothesis is that the gold

deposits were related to the 370 Ma intrusion of the South Mountain Batholith. Veins

formed during periods of fluid overpressuring (hydrofiacturing)allied to thermal and

tectonic activity associated with the intrusion (Kontak et al., 1990; Kontak and Smith,

1993a, 1993b).

The most recent work by Kontak et al. ( 1990) and Kontak (1 996) used data from

a variety of studies and described Au-forming fluids passing upward through the crust

and acquiring a variety of chernical signatures in passing.

Home and Culshaw (1994) and Home et al. (1994) describe Iate

bedding-concordant veins associated with flexural-slip and related conjugate

bedding-discordant veins in The Ovens. Many of these veins contain gold. The authors

suggest that emplacement of these veins resulted fiorn the late-stage folding and associated hydrothennal activity, and that gold mineralization in this area was related in

some way to the formation of the veins. If the apparent age of 376 Ma in these rocks is 207 due to resetting of muscovites by deformation and hydrothermal activity, it may also be significant for the timing of gotd mineralization.

6.5 Inhomoeeneous Deformation and Metarnomhism of the Mewrna Terrane

The deformation history of this part of the Megurna Group is less cornplicated than in other regions and leads to the question of why the Meguma Group experienced suc h inhomogeneous deformation.

The Meguma Terrane was jwctaposed against an irregular Avalon Terrane boundary along the Cobequid-Chedabucto fault zone (CCFZ), and (prior to Fundy rifting) along the 'New Brunswick' part of the North Arnencan continent. Deformation along the

CCFZ was thought to be Alleghanian-Variscan (Carboniferous) in age (e.g. Mawer and

White, 1987; Nance, 1987; Waldron et al., 1989). New data from Gibbons et al. ( 1996) document early transpressional terrane docking along the CCFZ as early as 370-360 Ma.

A complementary belt of pst-Acadian deformation extends along the Bay of Fundy side of Nova Scotia from Meteghan to Yarmouth (Culshaw and Liesa, in prep.) Earliest

Fabrics from this belt were dated at 370 Ma ("~r/~"~ramphibole age, Dallmeyer and

Keppie, 1987). The Meguma Terrane rnay have docked with the Avalon Terrane at an oblique angle to the North American rnargin (Williams and Hatcher, 1983). Continued compression forced the eastern fl ank to alter its direction of rnovernent by transpression along the CCFZ. The part of terrane boundary now parallel to the Bay of Fundy may have experienced a similar alteration of its collisionai boundary direction, fonning a rnirror image of the CCFZ. The overprinting crenulation cleavage in the southemrnost part of 208 the terrane (eg Chu, i978; Cullen, 1983; White, 1984) and the deformation parallel to the Fundy shore rnay be evidence of this coeval and opposing sense of transpression

(Culshaw and Liesa, in prep.). The more cornplex histories of those portions of the

Meguma Terrane to the south and the east result fiom terrane boundary deformation that prevailed from the Devonian through the Carboniferous. The low-grade part of the

Meguma Group lies at the apex of the angle forrncd by the irregular boundary zone which rnay have protected most of it frorn Iater reactivation of the large-scale folds. The late-stage deformation noted in Feltz South and in The Ovens peninsula (The Ovens

Anticline) rnay be one location where this deformation is expressed in the low-grade rocks of the Meguma Group. The hinges of other anticlines also rnay contain evidence of late-stage folding.

6.6 Recomrnendations for Future Studies

Three projects are proposed for this area. The first is to obtain more 4oAr/3y~rages

€rom the Meguma Group by analysing muscovite separates. The results of this thesis demonstrate that informative data can be derived from separates of specific generations of muscovite, using a detailed stepwise heating schedule. It rnay be possible to determine if the intense deformation present in the outcrop at Feltz South is the same age as the deformation in The Ovens peninsula. Dating samples from the hinges of the major anticlines rnay reveal that the pre-granite tectono-thermal event is not confined to The

Ovens peninsula. A similar study on samples fiom some of the gold districts could show if the age of 376 Ma is indeed the age of gold mineralization in Meguma Group rocks. 209

An 'OAd3"~rdating study on muscovites and biotites from breccia zones at Broad Cove

might provide additional data on deformational events in southern Nova Scotia.

XRD illite-muscovite crystallinity analyses cm provide data cornplementary to

"~r/~'Arstudies. While it would be difficult to achieve a sample density necessary for

contourhg KI isocrysts, it would be helpful to fil1 in some of the remaining gaps and to

obtain more data tiom areas where there are high contrasts in KI values between adjacent

samples. Data from the source area for anornalous '"'~r/~~~rand XRD data could be

augmented and better chronicle and delimit the extent of the late-stage deformation in

these rocks. A study confined to samples from the same stratigraphie level, perhaps at

the top of the Mosher's Island Mernber, might provide more conclusive data with respect

to the trends noted in this thesis.

The third project is a geobarometry study using XRD techniques to measure the b,,

ceII parameter of illite/K-white micas. This is essentially a measure of the MgFe cation

substitution in the h,, direction of the unit cell, and gives an indication of the celadonite

content which is pressure dependent (Sassi and Scolari, 1974). The possibility of doing

such a study has been discussed (S. Hirons, pers. comm.) with the conclusion that 12 well chosen, cleaved samples would sufice to determine the pressure regirne in this part of

the Meguma Group.

6.7 Conclusions

The results of this thesis can be surnmarised as three phases of early Megurna

Terrane history: 210

1) The earliest history encompasses the diagenesis and low-grade metarnorphism of

Meguma Group sediments. The strongest controls on these reactions were the lithochernistry of the sediments and temperature as a function of stratigraphie depth.

XRD illi te-muscovite crystallinity data show that some members higher in the succession may preserve borderline diageneticnow-anchizone characteristics. Diagenesis to very-low-grade metamorphism is tentatively dated at 484 Ma.

2) Regional metamorphism affected the Meguma Group between 395-388 Ma, producing layer-parallel shortening, buckling of competent veins and layers in the sedirnents, especially the more pelitic units, and cleavage. Tight folds formed at scales ranging fiom centimetres to kilometres. The timing of metamorphism determined by this study, combined with recent adjustments to the Early Paleozoic time scale, resolves the problem of metamorphisrn in 41 7-400 Ma rocks of the Torbrook Formation.

3) Late-stage deformation, illustrated by reactivated folding and hydrothermal activity, reset argon systematics in muscovite to give an age of 376 Ma. The extent of this deformation in this part of the Meguma Group may be illustrated by XRD illite-muscovite crystallinity KI values. The defornation also may be linked to Devonian defonnation seen in the Cobequid-Chedabucto fault system and the Fundy deformation belt. Local mobilisation of Meguma gold may be associated with veins formed synchronous with the defonnation, a hypothesis that needs to be tested in the Meguma 21 1

gotd districts. A connection between late-stage regional deformation and earliest effects of intrusion of the South Mountain Batholith (370 Ma) rernains problematic. Ap~endixA Elecîron Micro~robeAnalvtical Methods

JEOL 733 Electron Microprobe: 15 KV excitation voltage 12 nanoamps current

LmEDS (Energy Dispersive Spectrometer) Remlution of detector = 13 1 ev (dectron volts on manganese).

Matrix correction program = LINK analytical ZAF program.

Spectra accumuiated for 60 seconds.

Standards: Geological standards for chlorite, biotite, feldspars, gamet, muscovite used as controIs. MnO, (manganese oxide) standard used for Mn.

: ci O i -~!.~~*G/*Zl.*~.~ e;, ZI k15. - E~E:=!SITIEas. al O m atl cu

fi-m. Appendir B .Microprobe --- - - Analyses,..- Weight .-, % Oxide - Albile-- (~ont.). I ! j -1 1

1 Anqlysis Si02 Ti02 . A1203, Fe0 Mn0 a Mg0.. Ca0 , Na20 1 K20 , Total !~otes 1 1 I < I 'Mosherf.~~~d~m;~ett& - l.q& ivith &nrreti&r 1 29e02-4 70 40 20.37 O 55 , l

' Cunnrrl Mett~ber- SI~J;.nPer ' I 26~02-6 ' 6982 O 14 19.85 O 15 ' 0.05 * 0.20 -- - .- , 26~03-7- -- 70. 17 ' 0.09 ' 0.13 , O 04 , 8.52 0.02 ' 98.34 i~atnx : IPS : 1- - - 100b01-7 1 62.33 25.79 0.29 001 031 0.88 5.G 95 i8 Matrix -A- . - . --, 1 -- 142bO2-1-- : 78.58 ; 0.15 ' 18.24 ' 0.73 0.08 O 05 O 74 3.68 101.97 'Mattix ~eitzenk,t,bcr--- -- . Silir, (7) 1.rtyer 1 - 174a01-~ ' 70.52 19.93 - 0 29 0.10 ' 0.03 j 9.85 ; 0.01 ' 100.58 i~atrix 42.63 :,.-. 100.67 '~atrix -- 6.24 95 57 42.20-- -- , 98.64 41.46 ' 99.56 '~mai+.- -- grain i" s&dy -a&a -- ~fi.;. 41.93 ; 100.34-. Matrix - 1 I i , . 4 1.37 , 98- 79 , Largematrix grain 1 - .-

I Tmcwk ISlnnrl Memher, Imver Snnr@ Unit (TI) Saarly Iqer ,

- ~ ...- -- . .- . - .. ... - - . . .. . -. 1 ... - 1 8 57.58 ', . . .. - . 1 0.10 1 0,02 0.1 0.27--.[:.-- . -- ...... ~ 0.1s 1 42.35.. ., 100.35-1~-, Trincwk Ishnd Member, I.nrver Snnrlv Unit (TI)- Slm l.a)wr; 1

- - .-. , - '~nnc&kislnnii ~ettrher,~mer &dit Unit i~31- Santlv Lniler I 102.99 !Grain next to muscovite 7 - -.

1 1 1 , 78aOl-8 *- 2.30- 0 06- O 76 0.80 . O 1 1 40.92 . O 15 O If 29 75 ' 75.21 Irrepular matrix --- I . - 134b01-2- 0k 1 53.89 O 28 39.82 93.81 IA~coi= oflon8, large chlorip ' Tnncrmk i.slttnrl ~enrher,Üpper Skib, Unir (TV) - SWI& 1.uycr' l 107b01-4 0 31 . 0.07 1 0.06 , 56.38 O 13 ' 0.04 ' 41 53 98.17 i~a~rix -a- -- : : 107bO2-3 ' 0 10 O 07 O 03 ' 0.05 56 33 O 04 I 42 24 !, 100.39 ~atrix ------. I Appendix B- Microprobe-. Analyses,. Wright. % Onide - Apatite (cont.) ' I - . -. t l I I l 1 I -- - - f 1 , -- ~nalpi" -si02 Ti02 A1203 Fe0 Mn0 ' Mg0 ' Ca0 Na20 : K20 , PZ% Total 'Notes ; : : . - : ,- 7 1 -- : I ; Tancuuk lsli~nilMeniber, Upper- SIt~îyUnir (T4) - .%nt@ Lajw (conr.) ,- - 130b02-4-. -- i 0.30 1 10.16 033 a - 0.12 57.35 : 0 14 I1 100...... 22 Matrix --- . I~&c&k, -- Islrtnil ~enlber,~~~ci* - Slt~tyUni? (T4) - Slnf~f ~ujler 93cûi-7 , 0.21 0.07 0.07 O50 O 05 58.03 0.05 ,------. - Musher 's lslrrntl nfetrrbcr .Tand'y l.&cr *1 -- - 96a01-7 0.08 0.02 0i7 - 0.47 * 0.12 ' 5600 ' 0.05

I

40.75 : 99.56 '~atrix, --

42.75 ,' 101.53- - ,Matrix. -. - .. 42.46 1 101.39 Matrix

...... 99.1 1 ,..IMatrix ... 96.51-. Matrix ...

99.75- ...... -,Matrix

95.72- ,'Matrix. - -- - 98.55 Larke Grain .- . - - - -

98.42.. - ,: La~e. - ...... Grain 97.28...... Apatite - ... is the... matrix-.... 96.47 Apatite is the.. matrix- . 100.55 ah& Appendix B Microprobe Analyses, Weight % Oxide Biotite I . + ------.- - . -9 4

Analysis- -- + Si02 i Ti02 A1203 , Fe0 1 Mn0 Mg0 , Ca0-. Na20 , K20- . Total Nota - .t t-- -

0.28 9.21 , 95.13 lrregular grain

. - . ------.- O. 13 9.48 + 94.50- .lrregular - - -. - grain. .

- O 17 8.58 93.70 grain with albite, white mica : t ------. - - - O 21 . 8 86 94.60 iTinyg-in, - .-- with albite, white.. - mica- I

-

8.91 93.07 ;Mid-sizegrain . - - 8 68 1 93 45- i~orphyroblast.. . - . - 1 3701-2 34.41 i 1.59 18.35 20.48 ! 0.32 8.88 ....?. .*. .... i - ~~- - ...... ' , .... ,. 0.33.... 1, 6.38 90.74 ~oikiliticpo~hy!oblast. -- ...... - 3704-1 35.26 1.79 18.81 : 203 i 0.26 8.53 0.03 j 0.29 j 8.02 93.47 l~oikilitic~or~h~roblasf ..- .- - .- - , . 1 .... , . . , . . - ...... , ..... - .. 3704-2 35.11 1 1.96 18.64 20.01 1 0.24 8.55 0.05 0.03 , 7.81 92.33 l~oikilitieporphyroblast A...... - . 1 . , .-..... I -, t.. . .- .. 1 Mosher's IsInnd ~ctttber- .Sunrb Lnjer I 1 .. +- ...--...... ,.... , . ..., . , ...... 146b02-1 i 33.14 1 2.43 18 97 21.57 j 0.59 8.39 -.- -- -- . . 0.18- 8 33 93.59 Large porphyroblast- - 146b02-3- - - - .-. - , 3383-. : 239 : 1954 : 2185 0.57 9.06 009 0.19 : 773 195.16 . .- . - 146b03-4 1 34.55 1 2.20 19 58 19.42 0.51 8.06 0.04 0.41 9.20 03.93 Blocky porphyroblast Analyses,. , ...- ...... % Oxide Microprobe.. Weiglit- - Carbonate 1' - - .-.-- -. ~.

...... - . .- ,~ ...a...... -. - - . , , -- Risserfs Bewh Metriber - &nt& Lr~cr ...... -- ...... * -- ... 1703-1...... _.0.23 ; 0.03 -...... 0.06 I 1.18 i 1.12 ' 0.32 55.88 0.04 .' 5-- 8.72 / ~qi-.grain . - -.. - .... ,Ri.sser's . .,.. Hench -.Men~her - SrrnrlJ(. .- Lnjlcr ... ictillr Contrerions 32a02-7 : 0.14 , 58.03 -- -. , a .. + .- - , ..... 1 32a02-8- - A 0.20 I! I ...... A.... I T~nconkMettther, -- - - ...... -...... , ~ 83r03-1 ! 11.49... , O.!.:.. 15 l 6.75 1.75 1.58- 0.57 48.57 ...... ---8

i Tnnccwk Mentber, II,oiverSnnt& Unit (Tl) - Slnt~Lnycr .- ...... - ..

, ...... -......

...... ~nncookMemher, ..... Upper - . .~la~~~- ~nit(~dj Sint& j.nj& -. -- : - -

107b01-I- 0.10. -. 0.01 0.01 10.26 2.08 ' 29.58 ' O.?\ .,. i 15.34 ...... , - -y ...... : ...57.82 / Poikilitic porphyroblast lO7bO4-1- ...... -- ... 0.07 0.05 0.09 10.78 1.14 18.66 . 30.40 , 0.10 0.03 60.98 Poikilitieporpl~ymblssi ., - ; ~, ...... - ...... - .. . . 107b07-4.... 1 0.32 i 0.98- 0.21 7.61 2.31... 16.48 30.40 0.01 7 ,- . .-. , ~. 58.30 ,...Inclusion ...... in rutile 107b07-5...... - i 0.18 ' 2.78 0.02 6.21 , 2.1 1 ' 15.91 28.71 ' 0.05 ' 0.02 ' 55.90 Inclusion in rutile '1 --.~,. . ' ... . - -. ..I...... - ,I 0.09... I1 ...... 0.05 0.04 8.84 2.27 .' 16.66. 29.84 0.05 0.04 , 57.61 107b07-8 1 :Poikilitic porphyroblaa...... Tunrnok Mettther, Uppcr .~lu0~Ünir (TJ) - Slury 1.u~~ I - 7 , . 107e01-l 0y14 7 . 003 5.09 i 5.45 ' 17.23 30.83 : O.14 ' 0.08 1 58.95 ivery large prisndlathgrain Lppendix. - - .- B - -Microprobe- Analyses,--. LA Weight- % OxideY - Carbonate (cont.) , - * -- .- - , 1 1 i 1 l I l , - ' A&&& - Si02 ' Ti02-, ] A1203 : Mg0 : Ca0 1: Na20 K~O Total- - 1~oies 7 ---1 l

58.1 1 1 Vcy large Iath-shape patch

60.52 'Matri;I--- - 57.15 , Poikilitic gain --- 56.46 i Small arain - rhodochrosite?

108~01-4 1 0.13 0.06 .-. 1 ' A------, ------. 2.83 1 8 59 15.63 30.32 1-0.08 - ,1 Mosherls .- -- -- Islrind - - Menrber -;~&'y Iqer ~vithConcretions

10102-3-- ---' 0.17- - .1 0.40 0.03 'Ji- 11.53 . 11.78 . 4.84- . 26 73 ; 0.02 55.44 Fe-Mn carbonate (rest is Co2) 1 1

~-- CO~) , 55.85- .iIF~-~n carbonate.-- (rest is . -

55 90 _ ,I Inclusion? ------(or - patch?) - @ongamet 55.4 l inclusi~ifl Barn!! 56.63 l inclusion in gamet 57.35 ! lnclusionjn f --

58.62- - !Inclusion---y- in- prnet-- - 57.54 . Inclusion in pmet 60.I 7 kciU&! in grnet

- 1 - 97065 5.07 0.07 14.77 7.84 113.90: 8.22 - -- : 1 21.40' 0.17 : : 61.38 'Math 12801-1 ; 0.16 27.01 21.35 5.86 1.45 55.93 ' Appendix- - B Microprobe- - - - Analyses,-_- Weight- % Oxide - Cnrbonale (cont.) 1- - _. _ - . . . , -7 -

#r(cent., 1 i 12.76 4.77 26.11 54.41 ' Irreaular areas

64.36 /Patchy area . - 1-- - - 56.26 1 Mn-siderite or Fe-rhodochrosite. ---

56.08- --Mn-siderite - - - -- or- Fe-rhodochrosite- . 55.47 Small patch . - I. - . - - - - 0.26 I 0.1 1 23.17 . -, - I 0.18 0.04 0.03 1006 .- : - 1 0.17 't' 0.06 1 0.02 1.50 0.01 1 . 60.45.. .. 1' Irre.h wlar ._.. . grain ...... 1 l

/Inclusion in gamet ., 64l0 -. -- - --.- - .- - ...... - . . . 0.09. . ,' 0.02-- i 55.79. , -1-.'Matrix . .. -- . . . . . -.- ...... -.

O. 13 . . , 56.0- -- -1 - 1-, Br@ equas grain.: i~eplgedge - .~ 0.05 55.23 ,.-Bnglit- equant--- grain in niatrix- .. -. . . - 0.06 . . 0.13-. ' 0.28. .- .

0.04 0.14 . 56.66- . .----1 Dark- - patch--.- on-~ garnet -

60a03-7~ 1 0.16 , 0.13 , 22.52 ! 26.93 . 5.23 1.57 0.21 , , ...... 56.62 ,1 ~ong lath (not on iin~e) . - t ... 60a05-1 1 0.01 0.02 8.16 19.43 ' 2.68 . 24.99 0.12 . ------, - . , . ~ 55.26 ILawm!ch~are!. 60a05-3 i 0.45 0.06 12.47 36.33 I,9O ' 5.65 . .. --- .-. , .-, : 1 0.11 ',-, 0.02 ' 56.86 j~!obi~~t&.dri.~fa @met.. - 60.07-5 1 0.19 0.01 0.09 . 1,30 1.83 3.93 44.57 0.08 ' 0.03 1 52.48 A . j il"dusion ingamet - .. - -- - . : -, :. .. . ,... ------.. . .. 1 60a07-8 1 0.22 0.10 3.09 I 48.55 0.45 2.84 0.08 0.04 55.16 :~ri~htgrain in n~atrix

Aqpendix---- B Microprobe*. - - -. Analyses,- .. - Wei@ % Oxide - Chlorite (cont.) 1 i . ------Analysir ' Si02 ' Ti02 1 A1203 1 Fe0 ' Mn0 My0 Ca0 Na20 K20 , Total Noie! ------7 -- : -, f-- 1 --

Matrix... ..-...... !i cleavage Matrix

~ik~iticporph~robl~-- -

Poikilitic.. -- porphyroblast------In ilmenite- pressure--- shadow - .. 6tured-- -- porphyroblaçt-- Poikilitic-- - --Mairix Piokilitic-- - ... --...... _ .... I ... 1 Risser's Hench Menrher - Srrnrb Luyer idh Coricrctions -... -...... - .- ...... -...... - Porphyroblast -- - . . * -- - .... -- -Porphyroblast .- - - -

Mairix- -lath - - Small lath

: Risser 's Hench M

0.29 ' 0.08 87.77-i~rnall,- - - matrix - . - -lath - 0.28 1, 83.18-- ,Blocky - -- matrix- pin- 0.i~. 85.92- . .Fractured- - -- - porphyroblast O 25 1 85 60 Matrix t -- O. 19 0.03 , 85 69-- .'~hdl -- [email protected] O 16 1 13 88 55 1-Small - lath-. O. 10 86.5 1 . Porphyroblast-. - - core 0.30 0 01 86.41 :~i~h~roblas~rini : : .--- - -

0.2 1 0.05 89.02 !Inclusion--- in ilmenite ...... -, , ...... - . . -. 1502-1 4 23.93 23.30 28.87 ' 0.45 11.17 0.15 i ' 88.10 ,Chlorite'siack' w/ white mica ... ., .... : i ...... - 1502-2 ; 23.55 : 23.23; 28.32: 0.38 ' 11.12 0.10 : 0.33 : I 87.03 Irregular niatrix grain wendix B --Microprobe - , Analyses,---- Weight. %--- Oxide - Chlorite. . . (cont.)- .- - - ,

- -- -- l . - -. Analysis------Si02- .' Ti02.- ' A1203 1 Fe0 ' Mn0 Mg0 Ca0 ' Na20 K20 ' Total to oies : , - :

- -- , - W. : 0 35 3.02 ', 94.06 'ln- fradure- - in mica- lath--- 1 .O0 87.59 ,In nitileltitanite 1 -- --- O 17 0.22 . 88-- 03 ]ln nitileltitanite 1- -- - 0.13 88.06 :,-- Porphy - roblast- ' 0.27 87.99 *IMatrix - - - - - .- 0.14 0.02 87.18 1 Porohyroblasc - core . -- - ,------rim 0.49 1 .dl 89.39 / -~orphyroblast ------. - - 1 , 0.13 86.41 On edle of white mica lath 1 - -- ,------O 14 0.02 , 86-- 99 .Matrk -- 0.24 . . -87.52 --- -~orphyroblast------nni-- - - (repeat - - -. of 200 1-2)- 0.20 : 87 75 ~Polphyroblast- core 1 -- t- -- O. 16 0.09 1 86 79 I - ,- , -- _ _,Porphyroblast- _ - _ __ - rini- - - 0.32 0.08 1 86.87 ,SrnaIl matrix lath 1 -- O 37 ' O 01 1 87.44- -- '~o'p~r%Ïast>ire 1-- O. 14 , 86.53 ~Porphyroblast------rim 0.29- - ' 0.04 :, 88--- 45 clu us ion in ilmenite- 0.24 0.01 , 87.23 IPorphyoblastnath 1-t --- - O. 19 O 04 87 94 : , - -*---In ilmenitepressure------shadow? -

O O1 85.93 ,Pyrite - - - Pressure -- -- - Shadow.- - 86.09 Adjacent Pressure Shadow 1 ------0.0 1 ', 86.33- :~ath - Il Cleava~e

' O Il 008 85.60 'ln chlorite/miiscovite------stack- - - ' - 0.23 86.3 1 ;in- - chloritelmiiscovite------stack. 1 . 63a03-5 18 22 57 29 20 0.50 10 87 O 06 O 38 0.01 86 70 In chlorite/miiscovite siack 23 ' - -- g03-6 ' 23 25 ' O 05 ' 22.20 ' 29 22 ' O SI ' 10 38 ' O 02 ' O 25 ' 0.02 ' 85.80 'ln chlorite/miiscovite stack ------1 63.03-7 23.32 ' O 07 ' 22.20 ' 28.99 ' 0.50 ' IO 71 O 05 ' 0.34 O 06 86.07 - -. ' : ; '~atrix.Il slsck orientalion 63a03-8 [ 23.48 ' 0 02 ' 22.09 ; 28.98 ' 0.57 ' 10 33 ' 0 07 ' 0 21 0 03 ' 85.66 '~atrix.not // stackorientation - -mwvv, v>-r~lm m 00 - ",a N O '! O O P!! O d O NO- 00- ~~,~~~~ 820.0 0 0 000 COU

0 cl- s8 mm" ""0 8,s8 O e! !q 888. ooo ~li--mmin~moo Qo\~ivinmo~~o ci' 3/ci 4 ci ci ci - ci CI PI 5 cl ci ci ci cimru ci CI -.*---. *-.*.L * ----.-..*- 9 L *- m~~v~~mvam~~mclm,~r-~~~ear~avrnvi~goclci

ml- +!NI-+ CV 8 N % F 2 2 0 i.= OL _o! al -Ea. I 1 -- a =, -1- . "2 > .E 8 .- Zi z,,,21 .E1 CI~.E g sis st= x E.~I-;-2C rlç9 .- -" ET EL:+^,^ Zf alaiZ-Z13iZ'EO O I . - . - -- .-

m'9.m-t O -r r-a m mi-.- y:? r!:-!qC! o'.&:o'0~o~o:o;O O ......

mlm:a:oo +;& +;*mi- N,CI CI:W MIN

z,m O *: r! im m mmm lm' &;9'rnlm: g, - - 'CI. 2:' ":- Pi,&: N; - ci ci ci' - N ; :si 1m1CUim. PJ4CI Cl Cl CJ CZJ ,h qp:~n~m.y-q~Z-~o'-lCl~H~Ir,Cl -*m m~~c~---ciciciru'eiNci ciici ~I~CiiHiNCI CI Cl PI CU CU Ct

p~-4 - - *- * . *.- y..:-- mlci mlm r~ -r v, Q- m m - r -00.0. O 0.0~0~0,0~0~c 0000 O ooooooc -, , .v~\o;o:\oimo-:in,-!Nl\oIe, vi mtfi~m.orlolmlmIg!~~ml~;e~~-ivlmi-~e~:~ ' ' cym'm -.-.fi,ci - ~mi*o~m!o,~lc~.v~c~!\oq;.-:a:--r o-iq : Co' .\~~&IW~WI~'~\~;~~~~'I~~~&I~IP:~~~CII~~~I~I&~~CICII~~~&~~~~~\O~~~oc.m!mlm:m~~mmoo~coj~l~~~i~~~~~m~~~m~rn~~~ao~m~rn~m~m~m,oo~m -,fi

-. --.------.--. - - * * .------.-- L _--+ L . *- -* . . -- -, --, ------. . -..-

01 b,b,*:\~~mi- 9 m . .0;mim,m-N)CI \O,- \0:\o,n,o O-I0)q 00.0. - O:C!io!q miq 0.-'o. 9.9,- 2 ~omo:o.o, 8 !~:o'o,~~o,=!O' O O O 0,o O , . , . , . -. .- -. ~ *-- *~ -* & -..-..-. - . - . - - -..,. ------.- . -. - - - . -. - -. O ' CI. ~!&~!~,~i%%~!% ,001q&r?i;ri: iiq,3 ;,y. ~I~.~'OC,O 0~01o10~0~0~010~a'8~, ~ooo~o~o:o!o~o~o~oio o'o.oO O 2' , , , . . . ..*. . .* . . . . . - - b..*. -* --.--- --* - --.. ------_--- -. . * . L. ._ . - ..- ... - . - .- iri \Ob d m- -1~11.mir m.m W. v yi (2 q. q 1. 9: 3.9 2 z,o:o.ao:'olo'e! O O C, O, !O O. .O 0.0 0',~:ei0~:~:o~I~ 0.60

- - e: . . -I . : . - .L + . -.:--. * . . -.. , .- , O . ------. . . - . 2; -r.m N -,,.., -.** -IOI.~:mW.Vi - - 0 a c-1 9 fi -., a ,, , "?:-,T q:~C; ~lo!;~~q~l;ylr!!q~ql~~~q;-.D9 -,C!? - q q .-, n, C,.,,,.m -:c 00 00 &:O =0\.01.OIiOi OI,o:or.Ci'm.m'~~~0 0, oc,,, .-.-, . . . i. . ** ..--- .-.-. . . . < . P ,~o;q:m:-~ao~pL~m~-mvm~~min~~fiw~-~~o~m\oo-\o-ammfioYqImT-, u, , -'m'a, 9;. rwm..? q r! 0.'- ~'0: urzù -1'- 4.m' - -,- - - -.Cl,Ct,Cl,Cy';- - - - - CI CI N m0,0- 0.- .- , . : - - - *b ' - . - ..- . ------~-.- - - - -. - . ------.--- *. -. O :Q;m'ain:m,fifilm mi- (z rn,vii-!P m1mlr- -10CI:Q m N v, vi:gm fi op, .&; , a4d;\oOiF;O,q~oOi~iy,-.q:m,O:~!-ifl:~~~~~,C!1y~~:\q.O:~~:~1:~'m~m.~:~.m:6'~01mlm!mmm~fi CI ci ei m - -,Y,-!-.- O y,.0.0

2; ~~C~~N/N~~~C~~N~N~N~~~~~~~~~NIC~~~~~~~N'N~CICI~CJ~~U'~~INCc 8 m m~m,mci oa - .- . ------4---~------i-*---- +------A----- .- I - , ;,~o.cuI~:o-~oIHI~~o~~-.~m1-1~+ -v:- in IO,^ aFl-lvo v , g: ~,oo:*;!~~,t--;";q!~ g;-oq,a_qw qqlm?y l;wq,a'q m n m g:a: '7.$;Z~~Z!G;Z~!Z/%IZ 2.2 ~~~~~l~i~~~:%~~,m,m~e~,m:~lc~ mm mi- ~I~C~,N,CIm'w

-- -6-- - * + I -+-At * - -t ------A... -. - ,Zr - ----. -- . --. . , ------, . :CI! ' fi:m ~ciin:m~n~oa~v~oc~oo:o'cicl~~ - CI .vi

. 8 ppendix--. - . B- -Microprobe - - Analyses,-- Weight % Oxide Chlorile... (cont.) - Y ---1 ---- .- - -

*. Na20 K20 : Total :~otei

0.37.. - . . : .--:87 .....36 I-.&L-I.-T-Y---!!?'BU ered O h robl ......

,1 9--... 1.60 1 Cleavage--....-.-..-...... -...... /l matrix lath

: 86.99-...... 1~leav~e-- fl matrix lath -......

, 92.15 ..... 1,--- Cleavage II metrix lath ......

' ...86.98 I~orphyroblast- .....-...... - core 0.28 - ...... ' 86.94 -- -~oyp!!?!?!as' ...... 0.35 0.04 1 86.66... Matrix ...... - , I, ...... -.. 0.28- - ...... : 87.22-...... Cleavage --. - ... If -. lath ...... 0.29 0.06- 81.4' / ~or~h~roblast- core, II cleavage 1 ,------. - - 'Por@yoblast - rim, // cleaval;e .ka ...... -- -. 1 1 ...... Small matn~- .- - -...... lath . ,/Pophyroblast- - .. -- - ...... -.-...... - core, not 11 cleava&- - ... - i Porphyroblast...... - rim, no1 ....// cleavap... ., ...... - --. -. - -. - ! Matrix lath, not... //...... cleavage .-...... - ; In oval concentrated chlorite 'patch' . *--. .. - ...... >'In oval concentrated chlorite.- 'patch' . Porphyroblast ...-...... - . * 86.94 .-Porphyroblast ...

O~F~Oela-m- olq q-1-Y, Z ai rc atm oo~ooio\~m maOiA00- in--~omO\~wmor-mv>ci OC'ml.'moq r:o.qq.~y~qloqo.O\--m -00000 O-OOOOOOOOOOOO O 2OI Cri

2 m Ae~ndix-.- - B- - -Microprobe - - Analyses,- - Weight % Oxide - Epidote. - I I 1 - - ,

RecalFeO

0.05 0.06 ' 95 72 :~rnallmstrix pin . - 0 - - - Recal Fe0 1 1 1.56 - ps --. l 3706-3 ' 37.43 0.63 25.66 9.55 0.17 0.07 22.86 ' --A _ - -1 : ] 1 :

2004-2 38.41 0.37 24.78 1 10.35 0.28 0.05 24.36 [ 0.03 l 98 55 i~arkerarea on ilmenite- -- . - - ..j . 1 Recal Fe0 , 11.50 I : 9910 1 -- - ovin-n-oo 0. O - o. - o. 0000000

.A.---* r-2-0 O - - ooo 8400 -,---.. mmrtv-03-0 r-clr-mbQ"m ri rt CI ci PI m CI N .--.-.-. aoClmOaC\CQ L-I y r4 c! m C! CI m 00000000

v 4 oood-cl- d-d-omd--a0 b - -ns999g2 m.q-09.m.q~ a 5 hwmamaoaa-m obor-w.a~w m r CI~,CICI N:(U~CI CI'CI~WCI - m cr ct ci CI N CI ci - - ..O O 1%L O,'u n . . B qpendin-. B Microprabe, - .Analyses,- - - - Wcight,- % Oxide - Carnet (cont.) , I ,-. 1

- - + .- .. j 4 1 4 - , -- --, ^*sir . Si02 :. Ti02 .' A1203 Fe0 : Mn0 : Mg0 1 Ca0 : Na20 ,' K20- , Total Noles

I

100.74. .\Patchy - .- -. . grain .- - - core.L 99.57 1 Patchy gain - Rm 98.70 1 ~atchy&;Tn - core .. - -. - - 99.88..... ; patchy,-. - ....gain -...... rim ......

100.78- 1, ~~uant. . ...-----.---....---..with inclusions...... - core

..- , .. -- .- . - 101 .O2 , -Equant, with...... inclusions --.-.. - rim 100.79 i Porphyroblast...... core...... 101.60.. ~~or~h~roblaçt,- ...... mid- . . .

I ...--...100.8 -.I1 ...... Porphyroblast rim

100.58 / Porphyoblast core...... - .. - ... ,.... - - - -

0.04..... , 100.35...... i Pomroblast------...... rim 101.32 l~mallerpain - .. - ... 1 -. -- - - 1 99.76 ]PO --hmblast core .....-. 1.. . T.Y - .

101 74 1-Close -- to core- 101.77 Close to rim t -- - -- 101-50 1~ore(not on image) 1-- -- - 102.27 IRim (not on image) t------;- - 0.02 , 100.91-. 1--- Sniall grain 0.03 100.65 1 Close to core O 05 ' 100 74 j~im

t 100.27 1 Porphyroblast..... near core 29b01-2.---- 1 36.26 O 23 20.28 1 12 68 26 35 O 34 4.17 ' O 02 1 100.30 ~~or~hyroblastrim 1 29b01-4 132.01 8 010 1806 l II01 2794 O09 377 O07 , ' 92 79 i Missed the spot

m'n'n-oeo-m'00~-~~ W. -.3e'~!l"Fm 0. cl op: \O a cq i~im-1- O m w m vi qlru m PI -

606inOOI 0, m*'? r"P!1- E O O O orno . - il. . -- - -- ~ppndix-. B Microprobe Analyses, Wcight % Oxide - Carnet (cont.) l I 1 , -- 7- - ! - 1 -- f I

...... - . - - - .. - 96.71 Within gamet la@r in Mn nodules ..... -.----.---A-.--- ..

97.35-- .. Within gamet ....layer in Mn.. nodules . 97.70...... Porphyroblast - ..... -- - ... rim

96.32.... Porphyroblast-- .. - .- .-. . - core.- .. - ... 101.10 Euhedral, sn~all,no hiusions . -~ .-.. -. . 100.70 I Poikiliticlpatchy gain .. - . . - -- --. ------. ....

...... 99.7 1 IEuhedral--. . (almost)g.n--- - .... -.

99.53...... i~ewinclusions - core ...... 100.87..... l~ewinclusions riin .-...... -.....-....- - -

...... 100.35 lsmall subhedrakrain...... - core

101.. 33 1 small subhedral. pin -. - rini .... 99.34 I~uhedral,- -- -. - few- - - -inclusions -- - - - core- 1 100.65...... I~uhedral,- few inclusions...... - rim 1 99.45 1 Euhedral.-. --- @w - inclusions - cor! 101 .27 1 ~uhedral.few inclusion; - rim 00 V1 miO r-lml\D -1mtt- 2. 2; -:O 01- \O , m t- d+o tri -tri O CICI CIO- '30\QI'3mCI ...... --*.

CI 9lm%-PI' -Ir%- 9,9'0.'9o. =.,? - 5 ccccc ,S- C: =:

vib v- S 2 o. o. O u-! U 00 00 - - CI- O.0 lppendix B Micyobe Anaipis! Weighl% %ide - Ilmenite and- - Rutile (cont.) 1 I I I 1 - - 1 - ---- I I - I 1 Andpis 1 si02 j Ti02 ' Ai203 Fe0 Mn0 Mg0 , Ca0 -20 j K20 Total ]Notes - -- -- , - ' - ' t - : 1 . 1 .. .b ...... --..-l : .- --- l Tnncook Member, Upper Slnty,- .. unIf- ,- (T4) - - Sr;nr@- L~IJ& ; ..... ~--...... - -- ... 0.06 1 96.46... .-.-Irrgular - poikilitic-~ ..... rutile ......

1 . ., ......

0.10 \ 96.14. Rutile . .- - ...... 0.07 95.74 Poikiliiic ,1 ' ...... , .-* 0.01 1 95.73 ~Poikiliticrutile . , .--... , - A - . - . - .-- ...... -. - O. 1 O ;-i ....94 : 95. - ,..IPoikilitic .... mile ! ...... - .... - -.. Tnncook Memher, Upper Slaîy Unit (T4)- .Vhnl' Lqyer (cont.) ' I ---.1 .- - - _ . -

10401-1 2.28 86.49 1.91 ' 2.40 0.10 0.74 - / i - - , --- -.--- -- . - 1 Tancouk------.-Metnher,- Upper Slniy Unir (T4)- Sin@ Layer , - - - - .- * ------. 93a02-8 1 0.26 4980 I 0.07 1 31.64 1347 1 002 95.16 ,/ -Poikilitic - -- ilmenite------1 - .. I -

93101-6 4.62 I 49.30 + 0.24 i 2890 ' 12 20 ' O 10 ' 96.25- ,llmenite - . - - - -lath-- . ---+ t- - 93~01-9--- j 0.42 1 51.07 A 0.12 i 30 03 ; 12 92 0.08 ' 0.08 95.89 Ilmenite - irreguJar grain -97.84 'Smal~ilmenite~Gn- - - 97.14... ,/~lmenite . inside -. 'donut' ring.

-A - 94.75 i~mallilmenite grain 1------96.47- .Ilmenite - - - - iath- - -

96.17- * -Poikilitic .. - -.-- rutile . -.

.-.-I.-.,.. .- ' i 96.06 llmenite lath t -. f .. l ,------96a02-1 1 0.12 52.60 98% Poikiliticilmmite- - .- .- - .. .-...... -- , , I -- .-., : 77.77 : 1B.jl 96a03-2- i 0.49 1 50.53 0.10 26.23 18.89 j 1.36 j 0.22 0.03 1 98,66 l Ilmenite within carbonate ...... t . , . ,- - - . - - . .- . - .

94.04-i 0.24 52.37 0.05 , 27,33 18.84 ' 0.05 ? i 0.29 i ~ - j . -. .,.. . -~ -. - .- -- ...... 1 . ,--. ., , .... 99.81 !Poikilitic ilmenite 96~01-51 0.18 : 50.58 ! : 25.95 19.85 0.01 l 0.06 ! 97.63 :lImenite -t -s 3 ; E!al E'01 O' !dmiLYwu. .-8, 8 g!.- SI I .-CI *-, Ei .ai,-z s .si-$ g:-zj-z; . -,E! , : --, 4 9: ;$' ;=:= 8:E .41= i xi.flol'tl U'm ,, ,, ,O,-=.- -=, .-I kI,-i.Ss c .E! E!~~~!SIS.1, 8 k, 3, ! mi-- u./.-l w. w '.Q>! a1 WI 01Q>: Q> 01.2j2; .-..c.l.-,.-I.=I- - -'.=i.=' " Ei z!", Cl =, C *=%=,-e; ; +riGlZi& a UI 01w w! 0: O c~~~E~~~~~~~~I~~E~~~~;,E~~E!-,1'-13:- - -. ..+.- -.. - .- .--*-.- C-- * - -- . Microprobe Analyses, Weight % Oxide - llmenite and Rutile (~ont.) I l --- .. 7 - -- . . , - -- , . .. - - . t , -

l .. ...

99.14-- j~ame,- - .. lath-. - as.. above-- - -

97.66 I~ath. . -. 98.46 ]same latli as above .- - .- ,- - -.. .- --. . . - - - . - - -

.98.55 . .~ ILath .- perp.-.. - -. -to - .lath-- . -.above . - - . 95.66-. -4I~oikilitic- lath . . .- - 97.52 ipoikilitic lath ~~ ~ ~ ......

96.20 Poikilitic porphyoblast ~

---96.17 -- -,--T.-l~oikilitic ;-ilmenite lath 95.87 IPoikilitic ilmenite lath

95.88- - -- IPristine- - -- -ilmenite - - - lath- 95.54 .---l~utile lath .

.97.37 - - - 'Rutile,------lath- - . -95.62 -- Rutile lath 94.93 , Small irregular nit ile 1--:- - - 96 61 - - .lRutile- - - - - 94.77 llmenite lath .. - . . - ,i - -. - -. .- .. - . 95.70. . jllnienite... .- - - lath.. . . i 96.62- . ,lllnemite- .- .- -. . - . . 0.18 j 97.45 :Rutile

1 '' -. ~ -- 7 99 4.43 O 04 0.19 O 03 90.06 1-.limenite 015 , 1 0.09 96.43 ,Rutile I t I I 14 71 0.03 , O. 14 , 0.05 ' 93.58 lllmenite, - - - - -.. - 146b01-l- 0.19- - 49.08 36 03 9.42 , : 0.03 1 0.17 , 0.02 95.68 1 llmeni!e 15901-1 -1 0.62 : 94 20 1 0.21 ' 0.52 : 0.09 0.02 / 0.15 , 0 07 1 96 95 [Rutile - poikilitic 1783-- -. - - 0.16 : 49 08 ! O 04 24 IP . 21 16 0 01 ! 0.21 0.1 1 j 96 30 !llmenite - yoikilitic t : : m'a in a:ro 2 0 0- o. 0- 'X '0.~0-0 O O

- - I a~@t'~ O.. 0. @! 218 5 ='O 8 o oo* O oloO O

0 mlett$ Q a ? ?,qe.q- cg o.- r! CI'" r- s o ir, 9 Cs Cr G'lm g 0 a.0 00

1 Microprobe Analyses, Weight Oh Oxide - Muscovite (cont.) l -- 7 - r -- - . - - t

Na20 : K20 ; Total- - .'~otes --

0.54 ' 7.30 1 94.37 '~atrix O 52 ' 8.29 95.20 'ln chlorite porphyroblasr 1 -- ' , -- -- - 0.62-. 7.67 ; 93.91 .. Matrix-- - 0 51 I 8 83 i 93.49 With chlorite . --a - . . -- - - - 0.53 7.50 j 93 48 Matrix - 0.55 ;. 8.54- . .i 94.60 a----'Matrix 0.23 91.96 ...... 0.40 ; -- ..... ;ln-. chlorite -- ... - porphyroblast...... 0.24.-. 1 8.72 ' 89.99- - -.i~atrix- - .. - - 0.24 ' 8:98 1 94.68 ,--AMatrix 1 --4 -- 0.39 8.86 94.59 Matrix v -- - -.- -- - - 93.54 'steek' OIS i 837 - . ln------withchl&te-. - - - - 93.72 IMatrix .. - - - . -- . - 94.89.- IMatrix-- -.

--94.3 -- 1 I~r&roblart------core 93 65 1 Porpliyroblast - rim 93.95-- bat& - 94.45 I Within Chlorite l ------15 Within Chlorite k .------9476 Within Chio-e 93.7 1 '~atii--. 93.85 'In cracks in chlorite- --- 93.39 'MaG, // clea-ge 93 32 '~atrix, -

95.646'~oned . -. grain - cor! 95.62 ,Zoned arain - rim l -A B Microprobe. Analyses,- Weight % Oxide - Muscovite (cont.) . . ------r 7 - -1 - - -1 ,- - l 1 t i si02-, ' Ti02 A1203 Fe0 : Mn0 : MG : Ca0 1 Na20 ' K20 1 Total 1~oier : 1 - 1 1 - -. . 8 65 i 93.92 / Wiih- -- chlorite-- - - - darker area chlorite-- ..1...... ! 8.15 1 9359 Iwith . - @uer .... _ . . . 0 .- . ares li.sser!v Beach Aferrrher - Slrrt~I.nyer I -..----.y..- ~ ...... 46.93 0.39 30.76 2.96 0.03 193 ' 1 0.31 , 10.51 93.78 1 of.... 8.rain - -!ightkr 1 : ~~ ...... - ore -. - ...... : I -~ ...... ; 0.02 ! 0.44 I 9.72 93 85 IRim of grain - darker . * -~ ...... I....'.- :-- ...... ~.

-

- ~ - . .- .- ,L. - ..... 94.96.... ;klatrix.... - .. . . . 95.05-- .. ! Matrix ......

~ 96:16 1~@cxlo@e po~phymblast~ . ~ - 96.55.. -- ,Lath ......

-.....94.15 Matrix...... - .. 96.34 chlorite porph~roblast - ---- ,---11" ;-...... -- ...... -....96.14 Matrix ...... - .- .. .- 98.36 ,/In chlorite po~hrolast ...... --...... 95.1 1 I ln chlorite porphyroblast -.-. - - - ,-- -.. ., . -..... - -..... - ...... -...... - . - -...... 95.80 {Lathwith chlorite- growing- on -edxe - ..

... 93.43 IMatrix ...... ~. 93.77. . ;Along...... chlorite porphyroblasi...... ~~

94.19.... l~airix 1 - 95.95.. ln chlorite...... porphyroblast - .... 95.08 ;Matrix 1------95.88 1 in ilmenite nressure shidow? i ...... - . . - .... - . +---;-. -- .- , ,. --- 1 ..94.99 [Pyrite Pressure-..-..-... Shadow ... 3.71 . 1.38 , 0.36 6.90 1 92.72 ,/Adjacent - Pressure Shadow- ...... I West Dublin- Meniber - S(:ndy Lnyer -.. 1 i 46.44 ' O 23 I 35 67 1 1.28 O 08 0.64 . 0 5 1 O. 1 1 , 93.87 I ln chlorite/niuscovite- stack 1 46.55 0.29 35 17 , 1.53 O 06 0.86 ; 0.34 : X 2 1 l 92.95 11n chloritdrnuscovite stack, repeat O\ CI - w~r~riylm m 9.'- m4r-8mr- 2 2 vr r- ri 5 * ci. - - - ci. 0. \4 0. m. m. 0. . - O O 8~688'8000~00000868 8008 CI 00 mlv'cii- ml-,micifm oo in8cft\O'r.OIi vr cl O -lm aria 2 O, q -.qq - y y Tl? qm p q -* q ? T q:? ici a 6 21 Y bCbbCCbbbbuCQOtb00CCu?00 fioOb>rnbOO 9- V ri -10 2 Y'"?"-. Y IzCl\îr..

-1-im1m~Niv mie -lin 2'0O O a d ci m O O NtC!'?'dd - C!'ci!Y:- VSIY - CI N P1 oio 016 0 0 O 8'08(8 0'0 8 .O 2 R 8 O 8 -8 o

~I-y+yY -fNlN m'm 010'0!010(01 LD! a 0 0 o\!mimmlm10/010 4rlul

------I Appendix B Microprobe- Analyses,-- - . Wehht O/o Oxide - Muscovite- (cont.) : - 1- 3 - 1 1 l 1 1 I I --si02 Ti02 1 A1203 1 Fe0 ' Mn0 ' MsO Ca0 1 Na20 ' K20 Total i~otes - . --1 . - , I -

l?&her';------Island. ~e

- --- 95.7 1 I ln chlorite porPhyroblast y------96.52. 'Matrix 94.90 l~atrix -- - - .-- 93.90 With chlorite- .lath - -

96.64- - ,-Matrix ------94.20 i Broken porphyroblast with chlorite

I -~94.46 --Broken porphyroblast-- -.with - chlorite-- -- . .

95.19. -- ,'~ar~er, -- -- fractured.. lath, // -bedding - -- 93.62 ,-Lar~er, - - -ftactured - -- - - .-lath,- - II bedding- 94.53 'Marix lath, // cleavage 1 , ..-- . -- 0.63. .' 0.07. , . 0.27- . 6.58. .- . 1 93.72- .-. i~roken-- ~orphyoblast- - .- - - -- with- - chlorite- - . - 0.33 ; 5.97 ~ 9 1.49 '~atrix .. ., .. . - . . ' 0.46 , 7.59 i 93 00 'Matri; . * -1-

0.38 , 6.61 , 93.19 jMairix laih, -11 elëavatie ~-

* 0.34 , 6.99 ; 96.66.. 1[Matrixlath a- ...... ! l/cleavage- -~ - . . - .~- -

' 0.33. ', 6.34 .: .93.64 Broken ~~chl-mure ~ stack. // bedding

. , 6.30.- -. , 91.60 IBroken chl-musc stack, // bedding 0.33 . , --. " '. ' ~ 0.42 , 6.96 i 94.3 1 1Matrix. irreplar shape -3 -- , . . .. . - . .. - .- . - - .. -. - . ~~ 48.41 : 0.17 i 36.06 i 1.84 O. 15 0.76 . 0.06 0.32 7.16 ' 94.84 iMatrix, rectanaulat lath, -11 cleavage

I Appendix- B Microprobe Analyses, Weight O/a Oxide - Muscovite (cont.) - r - -- - 3- I t 1 - --. ------*...... [...... -1 l - Analysis...... Si02 - .. ;. -Ti02 ~~. AI203 Fe0 Mn0 ' Mg0 Ca0 Na20 K20 Tyal j~otes : I ., ; ; 1 ..-..-. , .... ---- ...... a. .. I 1 i Mnskcr's Islrinrl Mcrriher -'S'il@ I.nJ;cr {cmr.) l - - - - .. , ..- ...... 'I 62~10-1 : 50.16 ' 0.35 37.94 1 1.67 0.04 0.50 [ 0.27 ' 6.63 ] 97.53 !centreof lath . -- - -. - 8 ...... - .. - - , -- - , ..- . , - 62~10-2. - - - .... 4K79 . 0.33 ' 36.57 1.10 0.89 0.29- 7.46-- 96.95 ...~.~-;Tip oflatli i .i .~ ,- - ...... 62cll-1...... -...... i 51.16 , 0.16 i 38.30 i 1.84 1 0.04 . 0.65 . 0.02 1 0.23 5.72 / 98.42 ilath-cire -- . ' . - ...... - ...... , . . , ) , 6M1-2 \49,M>. 0.14 36.46 a 2.26 : 0.04 . 0.85 ' \ 0.29. 7.60..... i 97.08 :Lath rim 1. - .. ji.ii ; . -. -. , - .....

l. .. - -1 . I , ~ ~~~ ' 62~11-3- 4905 0.26 2.36 O. 17 0.86 : 0.32 7.57 97.32. -. - . .l .. -- . . 1 . --. 1 !Cith - fip. ...

...--.- 62cll-4 --!.48 50 i 0 11 ! 37.16... , 1.88 0.05 , 0.70.. , .. ..: .... - ...... I ~~ ; 0.48 1 7:57 1 96 88 1 lat------th -cor! , . 62~11-s- .- - i 46.46 : 0.10 j 35.01 ; 2.57 0.09 0.91 , 0.43 8.28 : 94.22 ;Lath - rim - 7 - .- .- . - - - 62c11-6 48.28 : 0.?8 36.26 1.92 i 0~13 . 0.66 . : - - - . 1, O... 7.86 i 96.20.. .- ,;Lath .. - . -- im(anothei-. . - . .- - spa) ..... -. 62~12-1--- -. . - 1 49.14 , O.26 T 37,74 : 1.51- - ,; 0.04 0.56 ; 0.38 .- -- -- .. . . - 7 - . - , 6.68 1 96.73 .Lath - CO-

t ~ ' ...... 62~12-2? 48179! 0.14 36.:- 56 1.98.-~ ] 0.02 0.81 ,; 0.34-.- - .' 6.87 t, 95.96 ,.---/Lath -& 1. i ; ...... 62~12-6i 49.02 ; 0.16 37.12 1.60 0.19 ' 0.73 ' ~ ~- ... - -- ~. - . : ~~

-.. -- ..- , .;. - - .*. , ,--.. T1 0.32- 7.58 / 97.30 ILath - core ~- . . . 62~12-7 48.71...... 0.23 36.70 2.08 0:18 . 0.74 + 0.03 0.39 ' 7.76 97.20 lat th - rim ...... 1 . - - ,- , . . -~.. !Mosher'.vbland Mewber - ,$ln@ Lnyr I 1 , ... -- -..... , ...... , . . . .- y-- - . 2401-4 1 47.31 1 36.06 1.80 0.65. . ' .. -. ; 0.39 8.45 94.67. - Matrix.~.- . . --- -1- I -. , 1~. i . -- 1 . , - ' -~ !' , i ; 2401-6 1 47 ...56 36.74 2.13 0.68 ,! ....0.44 ...... 8.83 1 96.38 1111 chloriteporpliyroblast . ~. . 6od01-5 1 47.40 0.22 ~36.801 0.72 0.02 0.57 0.26 , 8.32 94 86 I~atrix .- . '- ...... ! i - -- -. - .,.. ,. t - : i .:.-- .:-- ...... 6Od02-2; 48.11 i 0.32 ; 33.6i 3.42 0.lÏ , 1.28 , 0.3 1 , 8.05 1 95.51 -,..In chlorite porphyrobl~ . ,.. -, ~. : . ... .-...... 60602-3 -1 ...... 48.96 0.26 33.14 2.38 0.1 I . 1.34 ' 0.05 0.25 8.02 94.83 iMatrix / 1 . - 1 -- . 6OdO3-SI 50.95 I 0.40 32.82 , 2.42 0.12 . 1,02 ' 7 0.25- -- , 7.61~. .- 1 96.18 IMatrix - -- - - .- . ,. .. : 1.. --- t- 1- 60dO6-3! 48.54; 0.21 34.77' 2.65 . 0.07 1.08 ' 0.27 , 7.96 k.05 Matrix . ...* ...-. i : ... / ...... 60d06-4 47.54, 0.30 ' 34.22' 2.90 0.04 ' 1.19 ' , -- , .. : 0.25 , 8.05 1 95.22...... lin chlorite porphyoblast ...... 6901-6- ..... : 47.67 1 0.22 ' 37.40 1.16 0.11 . O52 ' ' 0.44 , 7.94 96.14 1.'~atrix .-, ......

' l ...... 6901-7- . 43.84 0.34 31.03 ' 4.23 0.43 238 0.10 ' 0.50 : 6.05 1 88.79 lnehloritefra$~re ~ : 1 t .- - i- - -- . .- 6902-5 47.40; 0.40 35.15: 1.70 , 0.16 a 1.09 0.12 0.41 , 6.94 93.69 Matrix . .-- .- . . . j , .- . . . . 6903-6 4734 14 ' 36.Si 1.74 , ...-. - -. .. 1 : o. . . 0.78 . f.0.41 1 8.19 1 96.37 ,.\Matrix ...... 6903-7 47.17 1 0.20 36.00 1.58 O. IO 0.64 1 ,.-. -~ ...... 0.34 7.17 ! 93.40 Sliphtly 'gpngy' grai" tao loy

6904-5...... 47.93 0.38 35.90 ' 231 0.03 0.90 ' 0.04 0.36 ' 8.12 / 95.91 :Ï" chlorite pprphyroblari- i .. . . , - . . t3 6904-6 48.11 i 0.21 35.26 1.83 ' 0.08 ' 0.99 ' 0.03 i 0.37 I 8.26 1 95.52 i~atrix rn14

"i!?!~ OjOlO--Cl Z!21 2 m U C .- O E i 'Cnls,-=< x!.xj5 2 -0, Ur: mlç' -----C'Z;Ei3: --

-- -- Microprobe- .. - - - Analyses, Weight % Oride Muscovite.-A-. (cont.) -.- - , I Appndix B -- - T 1 -

t ------* - Anaipis si02 Ti02 A1203 Fe0 ' Mn0 My0 ' Ca0 Na20 K2O ' Total '~otes - - - . ,. -. t - : : : , - : . - : I -- . ------. ~unnrd ~ember :,--.%t~ &i&?r, - (con{) 17102-5 47.i2 - 009 37.67 0.52 0.50 0.02 1.00 7.50 ' 94.40 '~atrix - -. - - . . - : : : ,- - - .-. - 17102-7 . 45.92- - 0.60 35.02 2.33 , 0.68 0.03 , 0.60 , 7.14 9233 lnc~oriteporphyroblast T -- : : : 173d02-1 48.09--- - 0.21 ' 36.64 0.99 . - ,- - 0.66 ' 0.04 0.22 7.22 94.03 '~arp-- - porphyroblast, --- forrnerly --chlorite? - - - - - ' ' ' ' ' ' 173dO2-2 j- 47.61 ; - 0.28-- 35.15 2.26 1.35 0.02 0.50 . 7.24 94.68 Math -. - 1 -- 173dO3-L y --4981 - O. 15 . 38.33 0.50 ' * 0.55 0.04 ' 0.12 5.63 94.8 1 '~liorite-> muscovite, darkerband - : : . - . - - - - - _ - - - _ - _ _ _ _ - - i - -'.. - - ' ' 173d03-2 48.85-- 0.07 37.23 0.86 ' 0.17 0.90 0.02 0.35 7.91 , 96.i~Chorite -> muscovite.-- - liyhter band 1 - -. ------

- - - -,Ctlnnrd-- Member---- .. -, ~meref~nury- - . --.~&er .- within Slnty L&wr--- -. 0501-3 1 46.56 O. 17 , 37.35 0.51 ' 0.37 , 0.02 1.04 7.78 , 93.60. ,------. -- : : '~atrix 0502-4 ; -48.17 O. 19 37.21 0.92 ' 0.99 7.75 95.87 Fabric // ------1 -- : 0.65 ------. t -- T - - 0502-5 46.97 o. li 37.72 0.45 ' 0.02 ' 0.42 ------. ------, : . 0.96- 7.33-. 93.84 - ,;Nat ---- fabric Il - -- , Feltzen Mentber - Sun@ I'pr - ---A -*- -r------A -- - - - 50a01-2 46.96 , , -- - -, - - , - . - , ------1 - 35.96 2.11 O. 12 0.42 [ 0.66 8.01 : 94.58 y---'~atrix - - - 50a02-4 47.08' 0.07 37.44 0.90 0.04 0.34 0.05 0.99 7.27 94.02

--- -. - , 0.01 .O2 . 7.71 ' 96.23 i~extto bl&ky chlorite

t * . : 174a01-4 48.26 0.03 38.32 0.56 0.07 0.32 + , -- .- - - -- . -- ' 0.73 6.96 ' 95.14 ,--Matrix -

174a02-5'+_ 47.21____ _ 0.13 ', 38.03-- -, ' 0.48 ' 0.12 0.32 ' 0.07 ' 0.92 8.55 95.51 Matri: . ' .-- . . -- 174bOl-Si- 47.74 0.80 35.08 1.53 0.07 1.16 0.28 a 8.- - 96.21 '~o&fabric//-~g~- -- -- 174bOl-6 47.96 0.74 35.76 1.42

------. - - - : : : : 1.02 0.03 0.30 , 8.75 95.63 'LO~,F~~~CII-~~ 174b02-3 45.55 , 0.32 . 35.92 + 1.51 , 0.03 0.55 , 0.04 0.64 , 6.97 ' 91.46 'Ïnchl%e ------, : . 174b02-41 46.16 0.61 33.15 7.22 - - 1.09 0.08 , 0.36 . 7.21 ' 91.34'~chlorite, ------174b02-5- 46.17 0.24 36.75 1.68 0.10 0.47 0.01 0.90 , 7.~2 93.73 ln chloite - --. - - - - - 1 : : : : : : . -- 174b03-3-' 47.76 0.18 38.39 . 0.73 , 0.04 0.33 , 0.05 0.99 . 7.38 , 95.84 :Mat& A- . - --- , -- - . -- . -. , Fcken Me~nber SlqI.nycr *- -- . - .- - 1 4ppendix- -. - B Microprobe Anaiyses,.. Weighî % Oxide-. - Muscovite (cont.) - 1------, I - -- -. -- I - Awrir 502 ' Ti02 A1203 Fe0 ' Mn0 Mg0 Ca0 Na20 K20 Total :~otes - --. -. * : : : : : - -

el- ken- - .~etnber. . . Slrity- Lqw- (conr$ 49.30 0.22-. - 29.12 369 ' 0 O1 ' 2.73 ' : 0.19 : 8.15 .' 93.91. 'ln, chlorite- 47.97 0.73 . 33.91 1 52 O 03 1 77 O 46 9.02 , 95.26 , Lighter core of matrix grain 47.70-. '. 37.93 O 52 O 51 : 1.15 8.40 96.56 ~arker.- - &e of Girix gain 49.80 1.23 29.52 3 58 0.10 2.30 0.27 8.68 95 39 i in chlorite porphyroblast . - .. 47.69 0.37 36 74 ' I 05 ' 0.64 ' 0.91 871 96.12 '~atrix 47.70 0.14 38.37 071 O 29 1 09 7.86 96.01- t Fabnc--: // .- - - - - . : , - - . 1 ..-

0.1 1 . 37.88 + 068 . 0.20 0 08 0.76 . 7.62 94.75. Matrix-. - , 0.87 34 O0 3 26 O 80 O 05 O 47 7.61 , 93.32- (---In chlorite porphyrob-st

030 37.17 ' 0.76 ' : : 0 42 1 0.08 : 1.06 1 7.87 . 94.24 ,Matrix- - . - -ineplar -- . grab - , 1.20 32.21 1.23 , , t , - 1 63 . 0.01 0.18 9.40- ' 96 54 Matrix - lath 164~01-11 ' 38.23 ' 0.73 ' 036 ' , -0.76 , 7.43 , --94 85- - .'~at&,-- - &bric /l 3-. ' 164~01-2' 47.53 ' 39.04 0.48 .*.- . -.. - .. , - 0.25 ., 0.95. . , 7.43...- . . . 95.68~-..-.- .. ,:Matrix,-- . .- - .fabric.-- .- //.. - . . ------.--

a 164~02-1 47.58 ; 37.88 0.59 0.39 , I w/ ~ - - core -,~.. -- , '. -- 0.83 1 7.35 ,, 94.61 P-blast chlorite on edee ~

- , -~ - , 4 1 ~ 38.35 0.75 7.S4 164~02-2.. - 47.5- 1 , y 0.66 1 94.80 iP-blast- - -w/ - . ---.chlorite .- on edge_--- rim-- - - . .. I ' 164~02-31 49.76 36.83 0.66 0.29 ...... -.. - .. . - - - . .... ; 0.72 , 7.67 - 1-9192- - !fabric- . - .Il-. - (darker)-. .-. - - ...... 7 - - . . . , , . 164~02-41 49.70 : 32.53 7.15 1.29 0.32 8.93 1 95.50 ,Fabric l/ (li~hter).Ba0=.585 0 mie-omm -2- 9 O or400 o 000000 X088

\3 ci ~i m - m u 9 o. C Z 2 O4 0 0 C i 8 ".$ ...... $ ...... gC.u,~c ? ---~L-Q.à 2 g ~1$,~:~1~$1::1 ~,%.RI~,c ;:: n ; - - - le. ------+ + . + - -- m F atm a,~/-::=#m TI~ inlaimlm 2 w N m a ii Cf la z a10 ,I3 a- r- * m,mlrim 0 mlmlm ' VIN O. : 01 210 6 6 6 o ch16l~~m918 o!~01,-i- - - O " ~5,mt.c@lim4mim m m~m!.zim~m,mm- mlm~n-lm ntmim r~1 2 el 1 ~-C-C--+--- - * ,-, .- -c --. + * ---.. I ppendix- - B Microprobe Aidysrs, Weight % Oxide - Tourmaline I I .-. - - -- - * ' 1 1 --. t 1 1 1 l 1 1 ~n&& 1 Si02 1 Ti02 ' AI203 Fe0 ' Mg0 \ Ca0 Na20 i K20 j Total :Notes * - : 't 1---, - I -- 1-, 1- l I ' ~isser's knîli M;ntber - San@ L.o& I i 36.66 ' 84.46 i~atrix , - .- 1 34.39 ' 8.22 ' 4.09 1 Y 110 ' T~ncoukMemher; ~pper*iant&~ttir (TJ) - SRnrlJl ~a,~er .- - -- l , . . -- r- - C 35.63 r, --0.82 ; 30.48 ; 9:70 6-22 0.26 1 2.40 i i 85.52 cor! 1 35.57 : 0.69 30.68 1 9.71 ' 6.35 : 0.40 / 227 : 1 85.67 Iini 1 - 1------1 35.42 1.25 ; 30 13 9.24 ' 6.56 0 61 : 2.07 ' 85 28 l Rim - 9 ' -- .- - 1 -- 7901-7- - 30.50 j I 37 a 25 92 1 9.45 ' 5.36 0.54 Ï.64 i Rim,- - poor- analysis- , -- , , 74.78. - . 7901-8- - , 35.19 1.03-- . 30.25 9.89 6.12 0,33 1 2.16 1 84.96 Rim - t , -- .$miJ~Unit (T3) ,~lut~ ,~me&& -- - ~enther, U' - 1.qw r - r -- , - i I 1Gb0l-6- - ; 36.19 33.64 10.48 3 53 I 1.70 1 85.04 ,Matrix f - --- 1 [ 1 , Cunard Mernbcr - Slntv Lrrrer 1 Appendix- - . - B. Microprobe- - . Anaiysas, Weight U/O Oxide - Zircon 7------7 - I l l 1 i I ?- P~nilris ~OZ-Ti02 / A1203 ' Fe0 Mn0 ' My0 : Ca0 I Na20 K2O : Ni0 z*? ! P?OS / Tool ' N&V Harbour Member - Sanrb Iqer 1 1 1 1 ' 0.07 --1~01-3 -- -*-i 32- 27- i 1 0.04 O 07 O 05 O 07 0.11 6633' ; 98 60 1 . -1 - f 1 -- - -- . Saiiuij~-,- - - - 1 Risserl.s kmch ~&er. - LRJW I -----122102-11 131.17-003 ' 4.53 I 149 : 053 013 014 074 ' 0.21 '4923' 2.07-1 8990---- t---- . 1705-1 1 30.07 O 10 O 17 ' 035 008 O 17 ' ' O 14 ; 61 I7 .- ---

1 . . ~ .- . 7 - 3.

49aOl-5~ -,------.-- 1 32.17- ~.. / 0.11 . .~ j 0.03 : 0.38. . ! 67.33. . ,: 0.02. .. i 96.98. . .. . i Felrzen Mernbcr - ,Silry Lqcr ------. ,- -. .. - - ., . - - , .--.- y -t t i 74a02-4.- . - -.. . - . ' 36.00 i 0.10 I 5.55 0.77 0.17 ' 0.07 , O?? , -.1,23 t 0.17 55.27i i ... .. - , .99.20 - - -- 74b03-4 41.99 19 0.225 0.61 : 0.42 1 0.02 ' 0.14 1 0.09 ; 0 12 I 0.14 ; 0.13 i 53.09 i 0.45 96.63 I 4ppendix C Reciilciilnted Cherniciil Forniuliic 1 411 recalculations perfornied by Minpci for Windows, version 2, O L Ridiard

Biotite - Bascd on 24 Onygens, 2 OH Groiips (akr Decr et HI. 1972)

35 ?d'si 2 09'~i 17 14'~l Cr 23 91:~s? Fe3 0 15'~n 7.14'~~, -

'Ba 0.000l Ba0 'Ba O.OO'C~ 0 21'~a 886'~ AlIV AlVI v.0- Wi 0,looo CI CI CI' rppendix- - C Recdculated Cheinicnl Formulac (continued)

:hlorite (rontinued) - Bnsd on 28 Oxygcns, 16 OH Croups (rfier Deer et HI. 1972)

23.35'si 33 26 Si O 14:~i 0.29'~i 21 97.~1 22.82'Al -t - t Cr 'Cr 2'1.37 Fe? 27.49'~& Fe3 O ?s'Mn IO 87'~~ O:OO'C~ 0.01'NR O OO'K Al IV AlVI

Appendin-. C -Recrilcutated Cheniicrl Formuliic (continued)

I

CYhlorite -.- (continuedl - Baseci on 28 Oxygcns, 16 OH ~rouis(iifter ~crret al. 1972) I H

l

34 23 Si 24 3tT~i 0.08'~i O ioi*ïi 20 85:~l 2 1 071 AI

Cr l Cr 31 15'~e2 79 431~e2 Fe3 , Fe3

O. 16'~" O 15iMn. ,- - IO 30'~~ 11 07'~~ O.OO'C~ 0.03 '~a 0.27'Na O 2 I 'NA O 07'~ 008;~ Al IV AllV AlVl AlVl

t

t

1 Appendix C Recnlculnted Cheniicnl Formulne (continiied)

Bnsed an 28 0x&ns. 16 OH ~rniips(nfler Drer (1 II. 1972) , - - . -

23.43'~i O OO'T~ 22.18'~l Cr 29.54'~e2 -3 2.00t~n 9 071~~ O OO'C~ O 00;Na 0.00 K AllV : AIVI ,

I t-lrncw,, ?> -z-G-T.G.E*E*z>z*+-z*g.7-7+ a09 OQ azooo mom a ce 000 ppendix-*- C Reciilciiliited Chernical Formulaie (conliniied)

'hl&ite (coniinued)- - - Barrd on 28 Orygens, 16 OH rouis (aher ~ieret nl. 1972)

73 41 Si 33 13'si O 05'Ti O OO~T~ 22 ~S'AI 23 71 Al : 1 Cr ,Cr 1 ?873:~e? 30 27:~e2 ' Fe3 Fe3 2 71'~n I 74'~n 9 18'~~ 8 65'h1g 0.03'~a O 01jc* O 12'~a O 10lNa 0.00:~ O II~K Al 1V AllV AlVl AlVl I Morite--- (continu&) - Based on 28 0xygens, 16 OH Groiips (arter Deer et ri. 1972)

13 93 'si Z,US'S~ 33 76Si 5.131 O OO'T~ O OO'T~ O 05'~i oooe 72 71'AI 72 59 Al 73- 34'~lt 5.9k Cr Cr Cr

79 4 1 Fe3 79 . 55 ,Fe2 - 27 ~O'F~Z--. 5.035 Fe3 Fe3 Fe3 0.00~ 1 68'~n 1.41'Mn 1 44'~n 0.361 10 37'~~ 9 34;~~ i O, 76'~~ 3.461 O.OO'C~ O.OO'C~ O OO'C~ 0.001 0.00'~a O OO'N~ O 20'~a 0.08L

0.00'~1 - O.OO'K O OO'K O.OO(.- AlIV AllV AllV 3.865 AlVl AlVI AlVl 3 06; Appendix- .- C Recnlcul~tcdChemicnl Forniulrte (coniinued) . - T

C:hloriie .-- (roniinued) - Bastd an 28 Oxygens, 16 OH Croups (alter ?ter ei al. 1972)

6 S

-1

S 2-1 80'~i T O 13'~i 21.19IAl Cr 29.37 Fe? Fe3 I M'M~ 10 19'~~ O OO'C~ O ?d'Na O 00:~ AlIV Al VI Lppendix C Recaleulated Cheniicd Formulne (continiied) I 1

:hl&iic.- -,(iontinued) - Bmd an 28 0r&eiii. 16 -.OH ~mu@efter Dssr el al. 1972)

'>4,59'si 23 86'si O 03'~i O 06:~i 23 74'~l 73 70iA1 Cr \Cr !O 08; F!? 77 5 1 '~122 Fe3 Fe3 1 13'~" O 92'~n 15 77'~~ 9 77'~~ O OO'C~ OOI'C~ O 35'~a O 19'~a 0 04:~ O 13'~ AllV Al IV AlVl AlVl .,.-- ,Q~,E œ G,> .m.t..~-~.Lt~.=EEEuUz*~I~*~. OOm \D -Cl1OrnV. mol- a OO\OOCl- Troc1 al oalooo' CI PI PI qpendix- C- Recrlculrled Chernical Forniulre (coniinued) t

I 1 :hlorite (continuid)- - Based in 28 0&ens. 16 OH Croups (afier Deer (i al. 1972) - -- 7

l 7233 #Si O 08'~i 1 23.53 Al 73 88 1 AI Cr Cr 30 82 Fe? 3 1 42'Fe2 Fe3 ' Fe3 0.85:~" 0.98 IM~ 8 36'~~. . 8 39\hlg O O4 Ca o.ooica O ?4'~a O 23 Na O 06'~ O OO'K

AllV 1 AllV

AlVl I AIVl

l

l rppendir. -- C Rec~lciil~ted. . Chemical Formulrie (contiriiied) , - 1

~hlorite-- - Foiitinued) .. - Bnsed .n 28 Oxygens, 16 OH rouir. (after- Deer et ni. 1972)

22.83 Si 22 70'si 0.00'Ti O 17'Ti 23.3- - 1 :AI 23 73:~l

I Cr Cr 30.28 Fe2 31 ??,Fe2 - 1- ' Fe3 Fe3 1 .02'Mn I~s'M~ 8.54~~ 8 X'M~

'O.OO'C~ O 00'ca O 00 Ca O--. 000-. O. 10:~a O 28:Na O OO~N~ O OOC 0.04[~ O 03'~ 0 ooi~ O ooc :AIIV AllV AllV 3 8% AlVl A1V1 AlVl 3 309 ippendix C Rcrnlc~ilrtedCheniicnl Forniulnc (coniiniied)

'eldspr'- Bnscd on 32 Oxygeiis (aîter ~eerei 11: 1966) :

Andcsiiie Appeiidix C RCCHICUIR~C~Cheniical Forinulric (contiiiiied) rppendix-. C Recalculrted Chemicrl.. - Formuiiie. (conciniied) -. , - -

f,

l 5.99: 1 0.008 ' 600t t --- 37 06'~~i 36 03'Tsi 4 081 1 O 13.~~1 O TA TAI O.OO( 30 86'~urnT 6.000' 30 45'~uiiiT 20 87;~ur?i T O Olt : , -- l l.~~~AIVI , 3.996' IO O~:AIVI io ~AIVI I 1 -- Fe3 O 000: Fe3 Fe3 4 091 1 - Ti 0.076 Ti Ti ,a: t 37.43 Cr 28 9l '~r 38.03'~; 0.075 0.32'~uni. - - . A : 4 071' O 18'~uniA O 32i~uniA 1 3.9%-. 3.74 Fe? 1 565' 1 57 Fe7 3.461~e2 O 00;~~ O 078 O 09'~~ O 04 'M& Mn 3 804' Mn 1 Mn I : t Ca . 0.481' Ca Ca Na 0.000: Na 'Na Sum B 5 928 Suni B I Suiii B 1 - :SU~I Cal 16 000: Sum Cat Sun1 Cai

1 Alni : 26408: Alni Alni And O O00 And And Gross 8 110 Gross Gross

,Pyrope + 1318 Pyrope +Pyrope Spess 64 164' Spess Spess Uvaro O O00 Uvaro Uvaro Chcniicnl- --

36.57'~~i 36 86'~~i 0.17TAI O I I 'TAI 20:60 ' Sum T 20 67'~uiiiT 10 ~~:AIVI 36 51'~1\~1 Fe3 Fe3 Ti Ti 29- -09'~r 13 53'~r 023:~umA 1 10'SurnA 2 24,Fe2 I 06i~e2 0.09; M$ O 06:M$ Mn Mn Ca Ca Na Na Sum B Suin B Sum Cat . - Sum Cat

Alni Al ni And And Gross Gross Pyrope Pyrope Spess Spess Uvaro Uvaro Appendix- - C Recrlculntcd Chemicnl Forniulne (conlinued)

l&ovi,e - ~n;ed'on-. 24 0xY~enn,4 OH Groupr (wfter ~eiret al. 1972)

, 47.101Si o.o~/T~ 35.78'~l 1 Cr ?.3I1Fe? Fe3 0.18:Mn 0.28i~~ O.OO'C~ 0.30'~a 8.96:K , AIIV AlVl O 48.53'si 48 39:si t 'i02 , 037,Ti O 18'~i --il203 - , 33 39j~1 34 981~1

MO3 , Cr Cr + 2.61 lFe2 1 48l~e2 1 'e203 ; Fe3 Fe3

-An0 .. , . ---O 00j~ii O OO'M~ 480 - , 143j~~ 091'~~ 0.52'~~ 3a0 OOO~C~ O OO'C~ O ooica da20 O 20j~a O 43'~a O 52!~a (70 848:~ 8 46i~ 8 291~ AlIV AllV : AIIV I 1 AlVl AlVl 'ANI t 1 bpendix C Recdculated- . .- - Chcmical. . Formulne. - (coiitiiriied)

1 .- - 1 Iiscovilr (ioain;ed) on 24 ~&~enî,4 OH ~roikr(nfter Der et rl. 1972) i - .- - . . - - - - ~nrc

R- S 3 f

I1 S 47 02'si 47 78'si 5 1 22 Si T 03l*~i O 50'~i 028;~i A 34.951~1 34 ~S'AI 3 1 G'AI

C- 1Cr Cr 8 Cr F 1.85:~e2 1 35 Fe3 2 78I~e2t - -7 F ' Fe3 Fe3 Fe3 h 0.09'~n O. I I '~n O.OO'M~, - h 0.87'~~ O 85'hlg 2.33 ML~ C O.OO'C~ O oo'ca O.OO'C~ pl 0136'~a.. O 43;Na O 30'Na K 8.02 K 9 42'~ 7 81'~ Al IV AllV AlIV AlVl AlVl AlVl 1

f rppeiidix C Recalculated Chen~icalPormulne (continued) I I 1 -. I 1 &covik (continued) Bnsed on 24 Oxygens, 1OH ~roibr(iifler ~eercl al. 1972) - - -- Y - - - -

1

46 44'si 48 63;si O Z'T~ O 15l~i t 35 67:~l 32.81 ,Al , - Cr l Cr t 1 28 Fe? 2 53 \Fe2 Fe3 Fe3 0.08i~n O OO~M~ 0 64'~~ i 53'~~ O OO;C~ O 0o1cà 05i'Na o IIha 9 H'K 8 87:~ AllV AllV AlVl AlVl . -

1

1

1 Appendix-. - - C . -Recrlculated - -. . Chemicrl Formulre (contiiiiied) . , - - - 1

1 , AIIV Àivi .1 - .-.*--.*-.-- .*.+-&O-- * . - - ...... -70 FJSJW. aooa SQ** Y-?. -==t-J=-rJr.P c. aow. o00000--~ r-a iz ..4i ...... -......

rirncqma 25 vj ----.C - 6-2-E. -~~~b_~-~+?_7. c~*O O or~wmrl qcia ? q~oar- boa OOOOCI 3 m - Appendix- - --. C Recnlciilnled-- Chemicnl Formulne (continiied) - -

i i ~"scovite(contint!ed) - Bnsed on 24 ~&~ens,4 OH ~roiibs(ufter Deer et al. 1972) l ----* -- t

, .-.-O 140 O 000 . . -.. . . 0.010

, oiioA -- , 0.000 7- -- - 0.065

'; 1.E4 , I ,748 3.9;s .. ... Chernical. + - -~ - Formulae (continiied) Recrlcul~ted , ...... - 1 1 I t 1 1

&scovite. (continved) - ~atdon 21 0&ps. 40~~roibr (rftrr Deer et al. 1972) -7 - -

-.

I 1 l I 4731'si 48 I l'si 46 58;si O.OO'T~ 0.32'Ti 0.25i~i 36 06;~l 33 62;Al 37 O~;AI Cr Cr Cr 1 8or~e2 3.42 Fe2 I 0gi~e',, -

'~e3 Fe3 I Fe3 O.OO'M~ O. I 1 'Mn 0.02:~n O.& ;M$ 1 28'~~ 0.371~~ O OOlCa O.OO'C~ O OO;& O 3giiVa 031'Na O 53'~; 8 45'~ 8 OS'K. .

1

t CI Cr, C =O( L Y; F_aw 212zlz V 2 YLZ :=y"-, -' *"* -*~,.,'o-~-", CIO m O~OCIF a - o'ooor- ,ppendin C Recalculnied Chemicnl Formulre (coniinued) luscmjte-- (coniiniied)-- - ~lisedoii 24 oxygens, 1OH croups (~fier~eer et ail. 1972)

46 74 Si 6.201 O 07'~i 0.00' 38.41'~l 5.77i Cr

O 46:Fe2 O- O41 - i Fe3 Fe3 O.OO(

O.OO:M~ 001'~n --0.001 .- 0.33~~~ O 20;~~ 0.05: 0.00 Ca O o~;cA O ooi 1.14:ia I 96:~~ 1.18iNa 0.391 7.67:~ 7O~'K 7.83 !K 1-30. 9 - AllV AllV AllV 1.79: AlVl AlVl i AIVI 3 971 Appendix- - - - . C- Recrlculrted.. - - Cheniicrl. - - - Formulne.- (continued)- -

lluscovite (continuedl Bnsed on 24 Oxygeits,-. 4 OH Groiips (rfter. . Deer- et al. 1972) - - , -

. ,-

.-. ? 1 46.96;si 47 08'si 48 26i~i

0.46tï'i~ .-.. O 07*~i O 03 l~i 35.96 Al . ~, 37 -14.~1 38 321~1

. . . ..'Cr Cr Cr 3. I 1 Fe2 O ~o'F~L' O 561~12 - ...... - ! Fe3 Fe3 IF@ 0112i~n 0.04'~n O 07:~"t - -- . . - . .. - - 03'~~ ..0.43, .- Mg 0 O 32iMg 0.OOTca O 05'ca O ooici 0I66i~a 99'~a . . .. , . . . O O 73:& 8.01. . ,-iK 7 27'~ 6 96'~- , AIIV AllV AllV ; AlVI AIV1 AlVl

7

!

f Pl0 =.*Ya 55 cf; 2 E'u2 Y,? 7

The choice of XRD illite-muscovite crystalIinity index is the most critical factor in studies of this kind. The most popular today is the Kübler index although its use is not universal. Several authors have devised conversion methods to equate the Weber index wîth the Kiibler index and coal rank but these are not entirely satisfactory. The recommended method is the Kiibler index with anchizone lirnits set at 0.42 and 0.25

"A28 (Kisch, 199 1). Illite-muscovite crystallinity studies should also use the <2 pm (clay) size Fraction although Pollastro ( 1994) raised the point that Iirniting the sample to this size hction may bias results. The proportion of a particular mineral or group of minerals may change with depth, and reported illite-muscovite crystallinity results do not reveal the correlation between whole rock mineralogy and that particular size Fraction with its mineralogical changes. Pollastro (1994) states that "a fair representation of the bulk sample deserves at least as much attention as that of the clay fraction." Unfortunately, illite-muscovite crystallinity studies are restricted to clay-size samples.

There are serious concerns regarding physical preparation methods and although the IC workshop group made no specific recommendations, certain precautions should prevail until more information is available. Samples should be crushed so as to apply as littie heat and stress as possible. Hammers and jaw crushers can partially commute the sarnple, sometimes releasing enough of the fine grain size fraction for separation. Swing or disc mills and ultrasonic disaggregation may be used if necessary but only for durations of 30 seconds or less. Techniques for separating the c2 prn fraction include sieving, gravimetric

settling and centrifuging techniques, none of which seem to alter the degree of

crystallinity of a sample.

The proportion of interlayered smectite can be determined by expanding the

interlayer spacing by a specific amount. Ethylene glycol (HOCH,CH,OH),- - inserted

around the cation-water complexes of each layer, gives a characteristic overail interlayer

repeat distance of 16.9A (Velde, 1992).

There are other suggestions regarding the thickness of the prepared sample (at

least 3 mg cm' thickness is recommended) and X-ray difffactometer settings. The cost of

adapting or changing equipment to fit a standard is prohibitive in many instances but it is

critical that studies be very clear about equiprnent and settings used to enable useful

comparison of results between studies.

For this study, samples were fitst broken into smaller pieces with a hammer and a

small ceramic jaw crusher. The chips were then passed through a rotating disk mil1 for a

duration of only a few seconds and the resuIting powder was sieved through a 45 mesh cloth. Samples were then sieve separated into >180 Fm, 189-90 Pm, 90-45 pm and <45

pm size fractions. Five grams of the finest size fraction fiom each sample were reserved

for analysis. Some samples were large enough to produce enough fine grained material without using the disk mill, a few had to be passed through the disk mil1 a second time, again for a duration of only a few seconds. A swing miIl was used on some samples

instead of the disk miIl for a maximum of 30 seconds. Sixty-three samples were prepared and sent to Birkbeck College at the University of London, UK for analysis and sixtysne

am-ved intact.

Further sample preparation at Birkbeck College involved disaggregating

fragments in an ultrasonic bath, isolating the < 2 pm fraction by settling techniques, and

removing the liquid containing the desired fraction with a pipette and centrifuging the

clay particles out of suspension. The clay fraction of each sample was smeared on two

glas slides to a unifom density and air dned at 20 OC. Samples were analysed on a

Philips PW 1710 X-ray diffractometer using Ni-filtred Cu-& radiation, 40 kV, 30 mA,

scanning through 2-35 "20 at 0.5 O20 per minute. AAer examining the XRD traces,

representative samples were scanned over the range 1519 O10 to establish the presence

or absence of paragonite. The Kübler index (KI) was determined by scanning the 10 A

peak twice ffom 7.5-10 O20 in the case oFmost of the samples, and scanning From 6-1 1

'28 in the case of diaçenetic sarnples. Following the recommendations of Kisch ( 1%IO),

other machine conditions were: dits 0.5 O divergence, 1 scatter, 0.1 mm receiving, with a chart speed of 1 "28 = 40 millimetre on paper and scan speed of 0.5 O20 per minute, and ratemeter I x 1O' c.p.s. at time constant 5.

Widths of the 10 A peaks at half height were measured to the nearest O. I mm, averaged and converted to degrees 28. Maximum variation due to fluctuations in machine conditions were c 0.02O 28 with s.d.= 0.003 ( i O). Samples yielding diagenetic

Ki were glycolated and heated to ascertain the proportion of any interlayered smectite present. -ndix 1 XRD Illite-Muscovite Crvstallinitv (KI)Results and Mineral Analvses I 8"38 ic Zong; heral Anab

93-RH0 1 Cunard 0.38 Low Anchizone 2M, K-mica, chlorite with lesser quartz, discrete paragonite and NaIK mica. R93-RH03a Feltzen Mixed-layer vermiculite-mica with tesser mica, chlorite, quartz with minor albite and NaK mica. 1 O A peak too small. 2M, peaks indicate metamorphic grade was at least low anchizone. 2M, K-mica with lesser quartz, chlorite and paragonite. 10 A peak too small. Epizone (or Contact 2M,K-mica, chlorite with lesser quartz and albite. Unresolved peak at Beach Metamorphism) 3.57 A normally corresponds to kaolinite but grade is too high. P3-RH?O I~isreh Epizone (or Contact 2M, K-mica, chlorite with lesser quartz and albite. Beach Metamorphism) P-RH~~I~osher's Epizone (or Contact 2M, K-mica, chlorite with lesser quartz and rninor albite. lsland Metamorphism) - -- 2M,~-mica. chlorite with lesser quartz, discrete parago& and~& mica. Epizone (or contact I~M, K-mica and chlorite with lesser quartz and albiie. Metamorphism) 2M, K-mica and paragonite with lesser chlorite, quartz and some NaK mica. Large paragonite peak inierferes with 10 A peak, 93-RH52a Cunard DiagenetidLow ?M, K-mica with lesser chlorite, quariz, paragonite and NdK mica, Anchizone Amendix E XRD Illite-Muscovite Crvstallinitv (KI) Results and Mineral Analvses (continuedl

Cunard 0.24 Epizone (or Contact Mica with lesser chlorite, quartz, jarosite and mixed-layer smectite-mica. Metamorphism) The presence of jarosite and mixed-layer smectite-mica indicates low temperature hydration, possibly weathering, Mosher's 0,22 Epizone (or Contact 2M, K-mica and chlorite with lesser quartz and albite. Island Metamorphism) West 0.16 Epizone (or Contact Mica and mixed-layer verrniculite-mica with lesser chlorite, quartz and IDublin Metamorphism) albite. Some ininor mixed-layer smectite-mica is indicated. 93-RH69 Mosher's 0.25 High Anchizone Chlorite and SM,K-mica with lesser quartz and albite. 1 llslrnd / / 93-RH7 1 a Cunard ZM, K-mica with lesser chlorite, paragonite, quartz and Na/K mica. 10 A = 0.44 but is invalid due to paragonite interference. %RH81 a Tancook 0.2 Epizone (or Contact 2M, K-mica and chlorite with lesser quartz. 2 Metamorphism) 93-RH90b Tancook 0.21 Epizone (or Contact 2M,K-mica and chlorite with lesser quartz. 1 12 1 IMetamorphism) 93-RH97 Mosher's 0.17 Epizone (or Contact 2M, K-mica and chlorite with lesser quartz and minor albite. Very minor Island Metamorphism) tnixed-layer smectile-mica may indicate some late stage retrogression. 93-RH112b Mosher's 0.19 Epizone (or Contact 2M, K-mica and chlorite with lesser quartz. Island Metamorphism) 93-RH 12 1a Cunard 0.33 Low Anchizone ?MlK-mica with lesser chlorite, quartz, discrete paragonite, NaK mica and minor lepidocrocite. Paragonite may be interfering with 10 A peak. Illite-Muscovite Crvstallinitv (KI) Results and Mineral Aoalvses (continuedl

Lu!&uz c Zone meral hdyw

- - - Mosher's Epizone (or Contact 2Ml K-mica and chlorite with lesser quartz. Peaks at 2.91 A and 2.82 A lsland Metamorphism) may represent ankerite and hydroxyapatite respectively. Mosher's Epizone (or Contact 2Ml K-mica and chlorite with lesser quartz and minor albite, Island Metamorphism)

- ~ ~- Tancook Epizone (or Contact 2M1K-mica with lesser chlorite and quartz. 2 Metamorphism) 1 Tancook Epizone (or Contact 2M, K-mica and chlorite with lesser quartz and albite. 1 Metainorphism) Mosher's Epizone (or Contact Chlorite and 2M, K-mica with Iesser quartz and albite. Small peak at Island Metamorphism) 2 1 .O3 A represents some mixed-layer mica-smectite expandable material. This may represent cold reworking - faulting? or hydrothennal activity. Fel tzen High Anchizone 2M, K-mica with lesser chloriie, quartz and NaK mica. Mosher's Epizone (or Contact Chlorite and 2M, K-mica wiih lesser quartz and ininor albite, Na/K inka Island Metamorphism) and possibly hyroxyapatite. Mosher's Epizone (or Contact 2M, K-mica with lesser chlorite, quartz and albite. lsland Cunard 2M, K-mica with lesser chlorite, quartz, discrete paragonite and NaK mica. Paragonite definately interferes with IO A peak. - Cunard Low Anchizone 2M,K-mica with lesser chlorite, quartz, discrete paragonite and NdK mica, '- XRI Illite-Muscovite Crystallinitv CH)Results and iMineral Analvses (continued) 1 m bl~tamomhicZone WralAnab

-~ Mosherts 0.25 digh Anchizone 2M, K-mica with lesser chlorite, quartz and NaK mica. Island Feltzen 0.22 Epizone (or Contact 2M, K-mica with lesser chlorite, quartz and Na/K mica. Metamorphism) - Cunard 2M, K-mica with lesser chlorite, quartz, discrete paragonite and NaK mica. Paragonite interferes with 10 A peak. Feltzen 0.24 Epizone (or Contact 2M, K-mica with lesser chlorite, quartz, Na/K mica and minor albite. Metamorphism) Mosher's Epizone (or Contact Chlorite with lesser 2M,K-mica, and quartz. Island Metamorphism) -- Cunard Low Anchizone Mixed-layer vermiculite-mica with lesser mica, chlorite, quartz, paragonite and minor NaK mica. Possible paragonite interference on the 10 A peak. Feltzen Epizone (or Contact 2M, K-mica and chlorite with lesser quartz, NaJK mica and minor albite. Metamorphism) Cunord High Anchizone Chlorite and 2M, K-mica with lesser quartz, discrete paragonite and minor NafK mica. Mosher's Epizone (or Contact 2M, K-mica and chlorite with lesser quartz and minor albite. Island Metamorphisin) Mosher's Epizone (or contact I~M, K-mica with lesser chlorite, quartz and minor albite. Island Metamorphism) I7-rAmendix E XR. Illite-Muscovite Crvstallinitv (KI)Results and .Mineral Analvses (continuedl

Chlorite, 2M, K-mica with lesser quartz, discrete paragonite, hematite and minor NaK mica, Paragonite interferes with 10 A peak. 94-RH202 Mosher's 0.2 1 Epizone (or Contact 2M, K-mica and chlorite with lesser quartz and minor albite. / IIsland 1 Metamorphism) Epizone (or Contact Chlorite and 2M, K-mica with lesser quartz and albite. Metamorphism) Epizone (or Contact 2M, K-mica with lesser chlorite, quartz and minor albite. Metamorphism) ------Low-High Chlorite and 2M,K-mica with lesser quartz and ininor NaK mica. Anchizone 2M, K-mica with lesser paragonite, chlorite, quariz and NaK mica, Possible trace of albite. Paragonite interferes with 10 A peak. 1;tinard oOr5 Low-High 2M, K-mica with lesser chlorite, quartz, discrete paragonite and NaK Yzo71 Anchizone mica. 94-RH208 Cunard High Anchizone 12~,K-mica with lesser chlorite, quartz, discrete paragonite and Na/K [mica with minor mixed-layer smectite-mica. High Anchizone 2M, K-mica and chlorite with lesser quartz, discrete paragonite and Na/K mica with a trace of albite. ~~iu>ne

0.36 High Anchizone Mica with lesser chlorite, quartz and paragonite with minor NaIK mica and mixed-layer smect ite-mica. %RH2 1 2 Cunard 0.28 High Anchizone 2M, K-mica, chlorite and quartz with lesser paragonite and NaK mica. +94-RH2 1 3 Cunard Vial broken in shipping. 0.28 High Anchizone Chlorite, 2M, K-mica and quartz with lesser paragonite and Na/K mica. Possibly some minor paragonite interference on the 10 A peak, Low Anchizone 2Ml K-mica with lesser chlorite, quartz, paragonite and Na/K mica. Some paragonite interférence on the 10 A peak. -- - -- [2~,K-mica with lesser mica andqua& 10 A l= 0.46 but is invalid due to arag go ni te interference. p~2l7l~elken Vial broken in shipping, 94-RH2 1 8 Cunard High Anchizone 2M, K-mica with lesser chlorite, quartz and NdK mica. -- -- Tcatcite and amphibole (hornblende). LOW Anchizone 2Ml K-mica with lesser chlorite, quartz, paragonite and NaK mica. Possible paragonite interference on the 10 A peak. 94-RH22 1 Cunard Epizone (or Contact Mica, chlorite and quartz with lesser paragonite. r-t-I Metamomhism)

A~~endixC Stemheatine schedule for 40Arl39Ar dating t , --.

O , A C. tnV39 1 % 39 : Age (Ma) % ATM 37/39 ! 36/40 39/40- .- % IC 1 - 7-- -

Sample-.- 93-RH1300- (muscovile) ,. i ...... -.. - -. I600 8.3 '0.8 i534.7 * 32.8 1 12.5 0.03 :0.000426 :0.006415 !O Aoaendix G Steo-hea* schedule for 40ArL39Ar datiin (concinuedl 1. .- - l - ...... A .. .. 7----- , Pr. - - - -- O C. : mV 39 . % 39 A~c(MI) i % ATM 37/39 i 36/40 ..-... - - - -- ~ .~-- - - .- . - 39/10 % IC - .. -. .... - .. -. Sample..... 93-RH1 0 7b (inuscovite). contùiued ...... - 1300 i2.2 iO.1 '555.2 i 74.6 70.9 o. 18 0.002399 :o.ooi871 i0.02 ...... - . - - ~ - * ------~- --* -- --- * - -- gas age = 553.2 Ma ...-..Total ......

--- - -.- - - . - - . C ------Sample 93-RH42b- - --(muscovite) ------. 550 2.1 -- - - 0.2 '336.2* 35. 1 -37.7 0.06 0.001276 0.00705 i 600 5.2 0.5 '407.2* 10.5 '21.3 0.1 -0.000723 0.00720 i -- - --. - 650 11.8 1.2 395.3 4.3 8.8 0.05 0.000300 0.008625..... -- .- .--~-- . .~- ho-% 2.7 386.1i2.3 6.8 0.01 '0.000231 0.009055 O

------* ------. .------0.2 7 18.0 * 150.3 '62.6 O. 15 0.002 120 0.00 177 1 0.0 I ------A ------Total gas age = 499.1 Ma -- .- - - .- -

Samp le-.. 93--- RH 70 (muscovite) -- - - .--- * - - I600 !6.8 1-6 459.2 * 30.8 14.1 0.02 '0.000477 0.006871 O

~ . - .~ . -~ -...... - . 800 '56.0 13.9 424.6 * 1.0 i 1.8 O j 0.000062 - -- --~.* -.*. - --- 830 ~42.5 10.6 i448.5 1.7 j2.0 -0.01 10.000069 -- - -.- - .. - - --. - -* .------&------. .- .. -+ ------. 1350 i218.0 , - . - ~.-! - , - - - ~~- ~p - - - (Sample--.- accidentally baked out.) - - - y- - A~aendixC Stem-hea tine schedule for 40Arl39Ar datine (continuedl -. . .-*-. . .. -- - .--.-

------C-. -. A~ . * -- L - -- - - age = 407.5 i 1 .-! ...... * .-....- -.., ..-..-.-. .-- .-.-... J = 0.002533 1 ...P. ~.-c~ ...... L L ---. Amendix G- ..--Stepheatinr scheduie for 40ArB9Ar datinl (continuedl --. .

O C. mV 39 1 % 39 1 Age (Ma) % ATM 37139 1 36/40 i 39/40 I % ICI 1 --A-- - -A------.-A-A----p-

. -+ ------. - - . + - - - . - - - Sample 93-RH62c (muscovite) - -- . ------600 -4.9 0.5 336.1 19.9 -20.3 0.04 0.000689 -0.009842 'O

650 '6.5 0.7 - - 393.5*8.2 12.3 0.04 ,0.000418 0.009102 O .- - - - - i Amendix G Step-heatine schedule for 40Ar139Ardating Iroalinued) : I I- l ! ! ! I I - >------y-I------& - - O C. mV 39 % 39 ie(Ma) I % ATM 37/39 36/40 39/40 % IC ------. - .-- C l Sample 93-RH62c (muscovite) continued I ..... - ...... - ... -. ... .-..- I ...... : ......

I~otalgas age = 393.1 Ma -a------* ------.------~------~- - -- - . - . . -

Sample 93-RH1 12b (whole rock, clay fraction present) , - I450 26.2 0.9 257.6 & 2.0 37.1 0.02 0.001258 0.009489 O

840 -206.0 '7.5 383.6 k 0.9 2.4 O 0.000082 0.009548 O ------+ ------AL- - -- - 870 154.1 5.6 387.5 0.9 2.0 O 0.000069 0.009480 O . - .-. - --- - * ---- 900 107.1 3.9 393.7 * 1.0 1.7 0.01 0.000059 0.009343 O 930 -82.1 -2.9 402.4 It 1.3 1.7 0.02 0.000059 0.0091 16 O ------960 181.7 2.9 399.1*1.1 1.9 0.03 0.000065 0.009186 O -- - -.- - - . - -- - 1000 195.1 '3.4 388.5k1.1 ,l.6 0.03 0.000057 0.009488 -- .-O - -- - .+ ------1050 ' 122.5 4.4 383.9 * 0.9 1.0 0.04 0.000035 0.009677 O - - . - 1100 -53.1 '1.9 382.7I1.1 2.1 -- .- - . . - - - - - . - -- .- . - - -0.19-- - .--'0.00007 1 .'0.009606 - 0.02 1150 2.9 O. 1 484.6 * 26.5 27.6 9.6 0.000935 0.005444 1.17 ------.--a - -- - - 1350 '1.1 O 590.5 * 182.3 76.7 4.94 0.002597 0.00 1391 0.54 - -- -- a A ------. - Total gas age = 383.4 Ma - - .- - -- ...... - - 1 = 0.00232 - -. . ------.- I , Amendix G Stcp-heahe schedule for 40Arf39Ar datina (continued) --.-; I i mV 39 % 39 1 Age (Ma) ' % ATM 37/39 / 36/40 , 39/40 % IC I _ I - - - Sample 93-RH2 226 (wtiole rock, clav fraction removedl

------*------Sample 93-RH59a (muscovite) -? - -- - -. -- - . - - - - A ------. -- - - 600 29.1 2.2 352.2 * I .7 4.9 0.01 O.OOOI67 0.01 1268 O A~oendkG Stepheatinp schedule for 40ArB9Ar datin~(continued) I

I I t I I ------a--+ ------. O C. i mV 39 1 % 39 -i Age (Ma) i % ATM 37/39 36/40 1 39/40 --% ICC

.- - --. -- .. . - . - - - .. ~ 1200 ,[.O O 1191.9*1844!54.2 0.17 ,0.001834 '0,001250 '0.01 -. ..- - --- . - rotal gas age = 376.7 Ma

A - ~ . . .- - - . -- . - .- . - - . ------. - - I = 0.002556 Amendix EI Critical Value Method for Defininp an *&PAr Plateau

In an "~r/~~Arspectnim, a plateau is deterrnined by the following method.

For each adjoining two age "steps", calculate the following:

Criticai Value (CV)= 1.96 d(error from step 1 )' + (error from step 2)' .

If (age fiom step one - age From step two) is greater than the CV, the two age steps are considered to be different. [f (age korn step one - age fiom step two) is the same or less than the CV, within error, the two ages are considered to be the same.

The above is calculated for every adjoining two steps in the spectrum. A plateau is defined as when 50% or more of the spcctrum is composed of steps that are detennined to be the sarne age by the critical value method (Fleck et al. 1977). References Cited

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