Western Washington University Western CEDAR

WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship

Winter 1986

Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington

Gregory Joseph Reller Western Washington University, [email protected]

Follow this and additional works at: https://cedar.wwu.edu/wwuet

Part of the Geology Commons

Recommended Citation Reller, Gregory Joseph, "Structure and Petrology of the Deer Peaks Area Western North Cascades, Washington" (1986). WWU Graduate School Collection. 726. https://cedar.wwu.edu/wwuet/726

This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. STRUCTURE AMD PETROLOGY OF THE

DEER PEAKS AREA iVESTERN NORTH CASCADES, WASHIMGTa^

by

Gregory Joseph Re Her

Accepted in Partial Completion of the Requiremerjts for the Degree

Master of Science

February, 1986

School

Advisory Comiiattee

STRUCTURE AiO PETROIDGY OF

THE DEER PEAKS AREA

WESTERN NORTIi CASCADES, VC'oHINGTON

A Thesis

Presented to

The Faculty of

Western Washington University

In Partial Fulfillment of the requirements for the Degree

Master of Science

by

Gregory Joseph Re Her

February, 1986 ABSTRACT

Dominant bedrock mits of the Deer Peaks area, nortliv/estern Washington, include the Shiaksan Metamorphic Suite, the Deer Peaks unit, the Chuckanut

Fontation, the Oso volcanic rocks and the Granite Lake Stock. Rocks of the

Shuksan Metainorphic Suite (SMS) exhibit a stratigraphy of meta-basalt, iron/manganese schist, and carbonaceous phyllite. Tne shear sense of stretching lineations in the SMS indicates that dioring high pressure metamorphism ttie subduction zone dipped to the northeast relative to the present position of the rocks. Exposures of the SMS along Coal Mountain are consistent with interpretation of folding as an isoclinal anticline though discrimination between an F or an F structure is not possible. 1 2 The Deer Peaks unit (DPu) (age unknown) consists of transitional calcalkaline tuffaceous andesite with minor interbedded dacite and less abundant slate and chert, all of v^ich is intruded by diabase dikes. Trace element geochemistry is interpreted to indicate a transitional-to-arc back arc basin origin for the igneous protolith of the DPu. During rnetamorphism, a penetrative foliation (S ) was developed parallel to primary layering. S is 1 1 folded into northeast-souti'iwest trending F folds \jhich are in turn folded 2 about a south-southwest trending F axis. Metamorphic mineral assemblages 3 recognized in the DPu are (in addition to quartz and albite):

1) Chlorite + Punpellyite + Epidote + Actinolite

2) Pumpellyite + Calcium Carbonate + Actinolite

3) Epidote + Calcium Carbonate + Actinolite

Calcium carbonate is present as both aragonite and calcite. Metamorphism of o the DPu is of high-P/low-T type, occurring at temperatures between 330 C and o 350 C, and pressures between 7 and 11 Kbar. Rocks of the Deer Pea]

rocks in the study area. The Chuckanut Formation is intruded by quartz-diorite

of the Higgins Mountain and Granite Lake stocks, and unconformably overlain by

the 43.2 _+ 1.9Ma Oso volcanic rocks. The Chuckanut Formation is folded into

north\vest trending open folds. Two northwest trending high angle faults

juxtapose the Chuckanut Formation with metamorphic rocks in the area: the

Higgins Mountain-Day Lake fault and the Segelson Lake shear zone. The Higgins

Mountain-Day Lake fault is a sinistral strike slip fault. ACKNCWLEDGEJyiENTS

Ned Brown pointed out the thesis topic, taught me metamorphic petrology,

and provided financial support for this thesis. Scott Babcock furnished many

useful references as well as good advice throughout my career at Western, and

taught me about geochernistry. Dave Engebretson contributed to a broadening in

my perspective on botli geology and mathematics. I wish to thank these members

of my thesis conmittee for their patience and understanding during my career at

Western.

Many of the students in the graduate program contributed indirectly to

this project through discussions of related topics. I would like to thanJc David

Black\>)ell, Brad Carkin, Mike Gallagher, Jeff Jones, Mo Smith, and Chuck Ziegler

especially.

The Vfeasels, vyyn Hill and David Silverberg, provided intellectual

stimulation, moral support, and lots of fun during this study, which \irauld not

have been completed without acquaintance with them. Many fruitful discussions

of North Cascades geology were held with them.

Roger Nichols of the U. S. Forest Service provided access to air photos,

and valuable advice during this study. This study also benefited from

discussions with Rowland Tabor, of the U. S. G. S.

In the field season of 1984 I was ably assisted by Dana Bayuk. During the

field season of 1985 Mike Hylland accompanied me without a complaint through

rain or shine, over waterfalls and through the jungle. I also enjoyed the

company of Arthur Morrill and Shirley Sanchez, two friends from a drier clime, during the 1985 field season, and Bemie Dougan experienced and epic or two with me during the su:nmer of '85 .

Special thanks to April Gacsi for emotional support in a time of great need, and to Ken Clark ;\^ose advice and dialogue have assisted me in a multitude of dilemma.

Financial support for this thesis was provided by a mapping grant fron the state of Washington, a Forest Service contract through Ned Brown, a National

Science Foundation grant to Ned Brcwn, and a teaching assistantship fron the

Geology Department. TABLE OF CONTE^^^S

Abstract...... i

Acknowledgenents...... iii

Table of Contents...... v

List of Figures...... vii

List of Tables and Plates...... ix

Introduction...... 1

Geologic Setting...... 1

Statement of Problem...... 7

Lithologic Units...... 9

Oso volcanic rocks...... 9

Quartz Diorite...... 10

Chuckanut Formation...... 11

Shuksan Metamoirphic Suite...... 12

Shuksan Greenschist...... 13

Ferruginous Schist...... 13

Darrington Phyllite...... 14

Deer Peak unit...... 14

Pyroxene Tuff...... 14

Dacite and Rhyolite Tuff...... 19

Chert and Argillite...... 24

Diabase...... 24

Metamorphism...... 26

Recrystallization History...... 26

Tenperature of Metamorphisra...... 27

Pressure of I-fetamorphism...... 28 Comparison witii other Western North Cascade Rocks...... 30

Geochemistry...... 34

Introduction...... 34

Classification...... 34

Tectonic Discrimination...... 44

Vftiole Earth Normalized Elemental Abundance Diagrams...... 44

Cortparison with otlier North Cascades rock units...... 49

Structure...... 50

Structures within the Shuksan Metarnorphic Suite...... 50

Foliation...... 50

Folds...... 51

L Lineations...... 54 1 Comparison with regional structural elements...... 55

Structures observed within tlie Deer Peak unit...... 57

Bedding and Foliation...... 60

Folds...... 60

L Lineations...... 62 1 Deer Peaks fault...... 62

High angle faults...... 64

Higgins Mountain-Day Lake Fault...... 64

Segelson Lake shear zone...... 66

Folds within the Cliuckanut Formation...... 66

Conclusion...... 69

References...... 74

Appendix-1...... 83 LIST OF FIGURES

Figure Page

1 Regional Geologic Map...... 2

2 Location of the Study Area...... 3

3 Tectonic stratigraphy...... 4

4 Photomicrograph of sheared clinopyroxene...... 16

5 Photomicrograph of sheared vesicle...... 16

6 Photomicrograph of vesicle filling...... 18

7 Photomicrograph of epidote...... 18

8 Photomicrograph and sketch of aragonite...... 20

9 Photomicrograph of resorbed quartz...... 21

10 Photomicrograph of pumpellyite beard...... 21

11 Photomicrograph of clinozoisite...... 22

12 Photomicrograph of relict textiare in ferrogabbro...... 25

13 Photomicrograph of relict granophyric texture...... 25

14 T-X epidote graph...... 28 FE 15 T-X curve...... 29 Fe 16 Petrogenetic grid for Deer Peak unit...... 31

17 A-C-F diagram for Deer Peak unit...... 32

18 A-C-F diagrams in P-T space...... 33

19 Variation diagrams with linear trends...... 36

20 Vciriation diagrams v/ith ^xxDrly defined linear trends...... 37

21 Variation diagrams with no observable trend...... 38

22 Log-log trace element plots...... 39

23 Log-log plots showing scatter...... 40

24 Ne'-Ol'-Q' plot of Deer Peak unit...... 42 25 SiO -Fe*/f4gO diagram and Jensen Cation Plot...... 43 2 26 Island Arc WENEA diagram...... 46

27 Back Arc Basin IVE3S1EA diagram...... 47

28 NDRB WENEA diagram...... 48

29 Ni-Zr plot...... 45

30 Ti/100-Zr-Yx3 diagram...... 49

31 Outcrop map along Coal Mountain...... 52

32 Pi-diagram of Shuksan Suite foliation...... 53

33 Projection of F and L axes of Shuksan Suite...... 51 2 2 34 Projection of L lineation of tlie Shuksan Suite...... 56 1 35 Sketch of asymmetrically sheared epidote porphyroclast...... 56

36 Map of regional lineation directions in the Shuksan Suite..... 57

37 Photomicrographs of variable metamorphic fabric...... 58

38 Map of structural elements observed in the Deer Peak unit..... 59

39 Sketch of incipient S in the Deer Peak unit...... 60 2 40 Projection of F axes of the Deer Peak unit...... 61 2 41 Sketch of F fold in Deer Peak unit...... 61 2 42 Projection of L of the Deer Peak unit...... 62 1 43 Map of major structures in the study area...... 65

44 Illustration of relationship bets.'?een a stretching lineation and fault motion...... 67

45 Schematic tectonic stratigraphy...... 70 LIST OF TABLES AND PLATES

Table Page

I Geochemical Analyses...... 35

II Elemental Abundances...... 44

Plate

I Geologic Map...... Back Pocket

II Geologic Cross Sections...... Back Pocket INTRODUCTION

The study area comprises 70 square miles of rugged, heavily forested land south of the Skagit River in the western North Cascades (Figures 1 & 2). Total relief in the area is about 3400 feet. The area lies on portions of the U. S.

G. S. Oso 15 minute, Finney Peak 7.5 minute, and Fortson 7.5 minute quadrangles. Good access is generally provided by logging roads. Structure and petrology of the bedrock geology of the area are the subjects of the study.

GEOLOGIC SETTING

Misch (1966, 1977) interpreted the structural stratigraphy of the western

North Cascades as shown in Figure 3a. The rocks of interest in this study are part of an imbricated complex on the western flank of the North Cascades,

Washington, of v^ich the Shuksan Metamorphic Suite (SMS) has been interpreted by Misch (1966, 1977), to be the highest structural unit. Immediately beneath the SMS is a thrust fault and thick imbricate zone (the Shuksan Thrust) containing exotic Precambrian and Paleozoic rocks, directly above the

Chilliwack Group. According to Misch (1966, 1977) the Chilliwack Group is in thrust contact with the underlying Nooksack Group v^ich was unconformably deposited upon the Wells Creek Volcanics. Misch (1966) determined that the

Wells Creek Volcanics is the lowest exposed structural unit in the western

North Cascades, Washington. Whetten et al. (1980) suggested the presence of an additional thrust above the SMS, v^iich they named the Haystack Thrust. Whetten et al. (1980) hypothesized that an ophiolitic terrane was emplaced above the

Haystack Thrust and subsequent work by Cruver (1983) resulted in recognition of the Haystack Mountain Unit, which may be thrust over the SMS. A slightly different interpretation of the tectonic stratigraphy of the south-central portion of the North Cascades by Ziegler (1985) is that the Wells Creek

Volcanics and Nooksack Group are also imbricated with other units along the

1 GEOF TOTOLITH [Q^QUATERNARY SEDIMENTS O o [^QUATERNARYVOLCANIC ROCKS N O TgJ TERTIARY GRANITE z UJ o um TERTIARY SAN DSTON E 49^0 O ISED. AND VOLC. ROCKS O C=CULTUS FM, N=NOOKSACK FM N O H= HAYSTACK MTN.UNIT cn UJ jSHUKSAN METAMORPHIC SUITf!.

SAMtSH BAY

SED AND VOLC. ROCKS, CHILLIWACK GROUP y ^AMPHIBOLITE, O VEDDER COMPLEX

rn SCHIST AND GNEISS, S_J SKAGIT SUITE Q. »«=ipYROXENITE, GABBRO, DIORITE

45 = FAULT WITH DIP < 45

121°30 Figure 1, Regional geologic map of the western North Cascades, Washington, from Brown (1983) , based on work by Vance (1957), Monger (1966), Misch (1966 & 1977), Bechtel (1979), Vance and others (1980), Rady (1981) , Frasse (1981), R- Lawrence (personal communication, (1981), Johnson, (1982) , Brown et al. (1982), Balckv\ell (1983), and unpublished mapping by E. H. Brown, J.T. Jones, J. H. Sevigny, and P. A. Leiggi, all of Western Washington University. IM = Iron Mountain, MB = Mount Baker, TS = Twin Sisters, MS = Mt. Shuksan, GP = Gee Point, WC = White Chuck Mountain.

2 Figure 2, Irx:ation of the study area, previously mapped areas are ruled in the enlarged area.

3 Shuksan Greenschlst Shuksan Greenschlst

Barrington Phyllite Barrington Phyllite ST'P’

Chilliwack Group

nMTf

Nooksack Group

Wells Creek Volcanics

3A 3B

Figxore 3, Schematic tectonic stratigraphy of the western North Cascades, Washington. 3A after Misch (1966); 3B after Ziegler (1985). Note the absence of the Church Mountain Thnast Fault, and thickened imbricate zone in figure 3B. PDY = PreDevonian Yellow Aster Group, UPC = paleozoic Chilliwack Group, JRN = Jurassic Nooksack Group, Jw = Weill Creek Volcanics, Pkbs = PreCretaceous Baker Lake blueschist, STF = Shuksan Thrust Fault, CMTF = Church Mountain Thrust Fault, IZ = Imbricate Zone.

4 Shuksan Thnist (Figure 3b).

The oldest rocks found in the western North Cascades belong to the Yellow

Aster Conplex (YAC) of Misch (1966). Misch (1977) described the YAC as consisting of slices of metamorphosed gabbroic to trondhjemitic rocks, including possible granulite-facies pyroxene gneisses. By dating zircons,

Mattinson (1972) interpreted the protolith of the YAC to be at least 1452 Ma.

An amphibolite facies metamorphic event in the YAC is interpreted to have occurred at approximately 415 Ma, based on a date obtained from metamorphic sphene by Mattinson (1972). Subsequent work has shown that some rocks previously correlated with the YAC are in fact younger, and belong to tlie

Vedder Conplex of Armstrong et al.(1983). Misch (1977) interpreted the YAC to represent geochemically immature continental crust v^ich has been uplifted along deep thrust fault zones of the North Cascades.

The Vedder Conplex was described by Armstrong et al.(1983) as consisting of high-pressure metamorphic rocks (amphibolite to blueschist), occixring as tectonic fragments in the western North Cascades of Washington and southern

British Columbia. Using Rb-Sr and K-Ar dating techniques Armstrong et al.

(1983), determined that the Vedder Conplex is Late Paleozoic in age (219-279

Ma). Armstrong et al.(1983) suggested that the Vedder Complex may be correlative with rocks of the Garrison Schist, v^ich crcp out on the San Juan

Islands.

Rocte of the Chilliwack Group crop out extensively throughout the western

North Cascades (Figure 1). Misch (1966,1976) described the Chilliwack Group as consisting of interbedded limestone, graywacke (with minor interbedded arkose and quartzite), shale, siltstone, minor conglonerate, ribbon chert, massive volcanic graywackes, and basaltic to andesitic volcanic rocks, metamorphosed in the prehnite-pumpellyite facies. Brown et al.(1981) assigned rocks of the

Chilliwack Group to the low temperature blueschist facies, based on mineral

5 as'-emblages and mineral compositions. Fossils from interbedded limestone indicate that the Chilliwack Group is Devonian through Permian in age (Danner,

1957; Liszack, 1982; Monger, 1966). Brown et al. (1981) reasoned that the

Chilliwack Group was metamorphosed after the Early Jurassic, viien the Cultus

Formation was disconformably deposited above it (and subsequently metamorphosed) but before the Eocene, vdien the Chuckanut Formation was deposited. Misch (1976) , interpreted the Chilliwack Group as representing an

island-arc on the basis of tlie association of lithologies it exhibits.

Cruver (1983) and Whetten et al.(1980) described the Jurassic Haystack

Mountain Unit (K>uJ) as consisting of basalts, basaltic andesites, gabbro, diorite, argillite (with minor interbedded graywacke), chert, and chert breccia, metamorphosed in the blueschist facies. The HMU was interpreted to have formed in a back-arc basin based on Isasalt geochemistry (Cruver, 1983).

VJhetten et al.(1980) proposed that the HMU could be correlated with ophiolitic

rocks in the San Juan Islands to the west of tiie North Cascades. Cruver (1983) did not favor correlation of the HMU with these ophiolitic rocks because of differences in metamorphic grade and metamorphic history, but suggested that

the HMU may be correlative with similar rocks in the Elbow Lake area, described by Blackwell (1983).

The Upper Jurassic to Lower Cretaceous Nooksack Group, according to Misch

(1966), disconformably overlies the Middle Jurassic Wells Creek Volcanics and

is separated from the overlying Chilliwack Group by the mid-Cretaceous Church

Mountain Thrust (Figure 3a). Misch (1966) described the Wells Creek Volcanics

as consisting of metamorphosed volcanic rock ranging in composition from

andesite to dacite intercalated with slates and graywackes. The Nooksack Group

was described by Msch (1966) as a metamorphosed accumulation of flysch-type

sediments. Sondergaard (1979) concluded that the Nooksack Group represents a

6 metamorphosed medial sutxnarine fan deposited in a magmatic arc environment, based on the vertical succession of lithologies it exibits. Brown et al.(1981) assigned rocks of the Nooksack Group to the prehnite-pumpellyite facies, based on mineral assemblages and mineral compositions.

Rocks of the SMS crop out extensively throughout the western North

Cascades (Figure 1). Misch (1966, 1977), described the SMS as consisting of the

Barrington Phyllite, a carbonaceous phyllite intercalated with minor phylIonite, and unconformably overlain by a thick meta-k3asaltic section: the

Shuksan Greenschist, metamorphosed in the blueschist facies. Misch (1977), interpreted the Shuksan Suite to represent deposition in an ensialic-arc setting. Haugerud et al.(1981), noting the presence of Fe/Mn metasediments between the Shuksan Greenschist and Barrington Phyllite, suggested that the

Barrington Phyllite was originally deposited on a basement of Shuksan

Greenschist and that the sequence was overturned by folding or repeated by low angle faulting. Haugerud et al. (1981) concluded that the Shuksan Metamorphic

Suite had a sea-floor origin based on the presence of associated rock types and metamorphic history. Dungan et al.(1983) presented geochemical data suggesting that the Shuksan Greenschists had a MORE protolith.

STATEMENT OF THE PROBLEM

Rock units exposed within the study area belong chiefly to the Shuksan

Metamorphic Suite and a metavolcanic unit of lancertain affinity, here informally named the Beer Peaks unit. Some previous workers have correlated the Deer Peaks unit with the Paleozoic Chilliwack Group (Misch, 1966, 1976;

Bechtel Report, 1979), and others have suggested it is correlative with the

Jurrasic Hr^U (Whetten et al., 1981; Cruver, 1983; Brown, 1983).

Rocks of the SMS and the metavolcanic unit are juxtaposed by a fault in the study area. This fault has been interpreted as the western "limb" of the

7 Shuksan Thrust by Misch (1966) and the Bechtel Report (1979), based on correlation of the metavolcanic unit with the Chilliwack Group and assuming a northward dip of the fault. An alternative interpretation is that the fault dips south, under the metavolcanic unit (Brown et al., 1982), that the metavolcanic unit is not correlative with the Chilliwack Group, and therefore the fault is not the Shuksan thrust. If the latter hypothesis is correct, then a new thrust fault, above the Shuksan Suite, must be recognized.

8 LITHOLOGIC UNITS

OSO VOLCANIC ROCKS

The Oso volcanic rocks, named informally by Vance ( oral communication

1980, in Cruver 1981), unconformably overlie the Chuckanut Formation in the

central portion of the study area (Plates I and II). These rocks range in

composition from rhyolite to basalt, and are interbedded with volcanic

sandstones. Ten thin sections of the Oso volcanic rocks were examined

including: one rhyolite, five tsasalts, three volcanic sandstones, and one

tuffaceous rock.

In hand specimen the crystal lithic tuffs are v^ite on fresh surfaces and

tan on weathered surfaces. The tuff contains quartz and feldspar crystal

fragments up to 3mm, and partially collapsed pumice fragments up to 5cm in an

ash matrix. In thin section the tuff contains quartz and plagioclase crystal

fragments, collapsed pumice fragments, and trachytic textured volcanic

fragments in a felsitic matrix containing stretched glass shards. Many of the

plagioclase laths are partially replaced by calcite.

The rhyolite in hand specimen is pink iDecause of selvages of hematite

oriented parallel to flow bands. White lithophysae bearing rhyolite was also

observed in the field. Crystals of feldspar and quartz up to 3mm occur in the

flow bands. In thin section, quartz and sanidine crystals are present in a

microgranitic matrix in v^ich flow bands are visible in plane light. Many of

the qi:iartz and sanidine crystals are surrounded by a felsite reaction rim. Mats

of sericite and epidote replace plagioclase cores.

The basalt in hand specimen is black to dark green on fresh surfaces. Red

hematite + quartz + calcite veins and veinlets cut the basalt in most outcrops.

Vesicular basalt is rare in the study area. No Ijasalt columns were observed in

the area. Basalt dikes cutting rocks of the Chuckanut Formation were observed

in the vicinity of Hawkins Lake (Plate-I). Both rare vesicular flows and more

9 common fine grained dikes of basalt are present in the study area- In thin section, the basalt is seen to contain normally zoned plagioclase and less abundant pyroxene (pseudomorphed by chlorite) as phenocryst phases, in a matrix of plagioclase microlites, opaque minerals, and chlorite pseudomorphs of mafic minerals. In two of the thin sections all the plagioclase phenocrysts and some microlites are replaced by calcite, and the opaque mineral is altered to sphene. In orie specimen a prehnite-biotite veinlet is present. The anorthite content of a plagioclase phenocryst in one sample was determined to be approximately 40% using the A-normal method. This value may be low, as the core of the crystal is altered. Groundmass textures observed in the basalt range from trachytic to felty.

The volcanic sandstone occurs interbedded with basalt flows in the

Segelson Lake-Deer Creek Pass area on the southeast boarder of the area (Plate-

I). In outcrop and hand specimen it resembles a tuffaceous rock. In thin-

section it is composed of angular to subrounded clasts of zoned plagioclase,

clinopyroxene, partially resorbed quartz, pumice fragments, subtrachytic volcanic rock, and porphyritic volcanic rock in a fine grained matrix

containing ash shards. These sandstones may have been derived in part from the

Oso volcanic rocks, with viiich they are interbedded.

A zircon age of 43.2 1.9 Ma was obtained from a sample of the Oso

volcanic rocks in the study area (Vance, oral communication in Cruver, 1981).

QUARTZ DIORITE

Granitic textured rocks crop out in two localities witliin the study area:

In the vicinity of Granite Lake ( the Granite Lake Stock), and along upper

Higgins Creek in the cirque north of Higgins Mountain (the Higgins Mountain

stock), (Plate-I). In hand specimen these rocks are gray on fresh surfaces and

vary from red to gray on weathered surfaces. The quartz diorite is coarse

10 grained, and contains: 60 to 70%, 1 to 5mm, subhedral to euhedral, blocky plagioclase; 10 to 15%, 2 to 7mm, subhedral to euhedral, lath shaped hornblende; 5 to 10%, 1 to 3mm, subhedral to anhedral biotite; and 5 to 10%, 1 to 3nm, anhedral quartz. In thin section, the hornblende is observed to be partially replaced by chlorite and biotite. Plagioclase exhibits normal and oscillatory zoning. Both hornblende and plagioclase occur as subhedral to

euhedral crystals. Biotite occurs as subhedral crystals and as an interstitial

phase with quartz and opaque minerals. Biotite is altered to chlorite along

cleavage traces. The quartz is often poikilitic, containing fine plagioclase

crystals. Apatite and zircon are present as accessory minerals.

The Granite Lake Stock has yielded a hornblende age of 53 (Bechtel

Report, 1979). Sonewhat younger K-Ar ages were obtained from hornblendes of

the the Granite Lake Stock by Tabor (personnal conmunication, 1986): 45.5 +

10.9, 31.5 + 6.2, and 32.7 + 6.0 Ma. The Higgins Mountain stock is intrusive

into the Chuckanut Formation, causing contact metamorphism as discussed in

Cruver (1981). The Granite Lake and Higgins Mountain stocks may be related to

the Oso volcanic rocks, but more work is required to test this hypothesis.

CHUCKANUT FORMATIOSI

Rocks of the Chuckanut formation occur either in high angle fault contact

with or nonconformably deposited above older metamorphic rocks in the area.

The Oso volcanic rocks appear to unconformably overlie the Chuckanut Formation.

In most of the area the Chuckanut Formation consists of interbedded arkosic

sandstone and siltstone. Locally, coal seams and conglomerate beds are

present.

In hand specimen the arkose is conposed of: 30 to 40% angular to

subrounded feldspar (mostly plagioclase); 35 to 45% angular to subroianded

quartz; and 20 to 30% angular lithic fragments. Lithic fragments in the arkose

11 have tile same composition as conglonerate clasts: greenstone, vein quartz, phyllite, schist, and rare serpentinite. Quartz pebble conglomerates are common in the study area. Plant fossils, and sedimentary structures such as cross bedding, graded bedding, ripple marks, channel cut-and-fill structures, and laminated bedding are well preserved throughout the area. Contact metamorphism of the Chuckanut Formation in the vicinity of the Higgins Mountain stock was described by Cruver (1981).

A palynological study by Reiswig (1982), indicated that the Chuckanut

Formation was deposited from the middle Paleocene to the late Eocene. Johnson

(1982) obtained radiometric ages of 55 Ma from a tuff clast taken from a conglomerate layer and 45 Ma from a tuff layer in the Chuckanut Formation.

Johnson (1982) concluded that the Chuckanut Formation was deposited in a meandering stream environment in tectonically formed basins. Detailed studies of portions of the Chuckanut Formation in the present study area were performed by Cruver (1981), and Robertson (1981).

SHUKSAN METAMORPHIC SUITE

Rocks belonging to the Shuksan Metamorphic Suite (SMS) crop out along Coal

Mountain, adjacent to the western margin of the study area. For thorough descriptions of the SMS the reader is referred to Brcwn (1986), Brown

(1974); Haugerud et al., (1981); Jones (1959); Misch, (1966); and Morrison,

(1977). Three lithologies belonging to the SMS are present along Coal

Mountain: Shuksan Greenschist overlain by a transitional facies conprising quartzite, chloritic schist, and ferruginous schist, in turn overlain by

Carrington Phyllite. This stratigraphy was cited by Morrison (1977), as evidence supporting a sea-floor origin for the SMS. Geochemistry reported by

Dungan, et al., (1983) and Bernard!, (1977), indicate that the Shuksan

Greenschist had a tORB protolith. The protolith of the SMS is thought to be

12 Jurassic in age, based on preliminary Rb-Sr isotopic studies by Armstrong

(1980), and U/Pb zircon dating by Walker (Brown, 1986). K-Ar studies indicate that the SMS has been metamorphosed twice; a localized event in the

Gee Point area at 144 to 164 Ma, and a regional event at approximately 120-130

Ma (Brown, in press).

Shuksan Greenschist The Shuksan Greenschist crops out as isolated knobs surrounded by Barrington Phyllite. The only primacy structure preserved within the greenschist are relict basaltic pillows. Two metamorphic mineral assemblages were observed in the Shuksan Greenschist;

1) Actinolite + Chlorite + Epidote

2) Na-amphibole + Chlorite + Epidote + Fe-oxide

Quartz and albite are ubiquitous. Additional minerals observed in some specimens include sphene, calcite, pumpellyite, v^ite mica, and stilpnomelane.

Assemblages 1 and 2 are similar to those discussed by Brown et al. (1981). Two generations of epidote are present; Fe-rich pre-tectonic epidote, and Fe-poor syn-kinematic epidote. Haugerud et al. (1981) interpreted the pretectonic epidote as evidence for a pre-kinematic metasomatic event, possibly sea-floor metamorphism. The amount of Na-amphibole increases significantly in the vicinity of ferruginous schist, in good agreement with the observations of

Misch (1959), and Brown (1974), that the stability of Na-amphibole requires an

Fe-rich environment.

Ferruginous Schist The ferruginous schist occurs as a discontinuous layer overlying the Shuksan Greenschist and underlying the Barrington Phyllite.

Where present, it is an excellent stratigraphic marker. A gradational contact from Shuksan Greenschist to chloritic schist to ferruginous schist to quartzite to Barrington Phyllite is present on the ]

1/4 of section 29, T. 34 N, R. 7 E., Plate-I. The ferruginous schist is often

13 tightly folded with greenschist and phyllite, as along Forest Service Road 1765 on tlie west edge of section 18, T. 34 N, R. 7 E. Minerals observed in thin sections of ferruginous schist include: quartz, albite, chlorite,. stilpnomelane, garnet, epidote, Na-amphibole, magnetite, hematite, sphene, and in sample 109-38 cymrite (BaAl Si O . HO). 2 2 8 2 Darrington Phyllite The Darrington Phyllite overlies the ferruginous schist.

It is a shiny black carbonaceous phyllite with local intercalations of metagraywacke (type II-B phylIonite). In hand sample the phyllite contains alternating layers of v^ite-mica + graphite and quartzo feldspathic material.

Graphite and mica give this rock a distinct sheen on foliation surfaces. These compositional layers (S ) are contorted by F folds which transpose S . 12 1 Minerals observed in thin section include: quartz, albite, Fe-poor epidote, chlorite, actinolite, stilpnomelane, Wnite mica, and sulfide.

DEER PEAK UNIT

Rocks of the Deer Peaks unit (DPu) comprise a metamoiphosed deposit of andesitic pirroxene tuff interbedded with minor argillite, chert, and rhyolite- dacite, and intruded by diabase dikes and sills. Detailed mapping has revealed no useful stratigraphic markers; the rare argillite and chert layers are traceable along stride for only a few meters and are truncated by diabase dikes at most locales. A crude layering or bedding in pyroxene tuff is the most obvious relct structure in the DPu.

Pyroxene tuff The pyroxene tuff is the most abundant lithology of the DPu in the study area. It forms prominent cliffs, occurs along roadcuts, in quarries, and as outcrops along ridges. Weathered surfaces are pale v^itish green and may contain pits, resembling vesicles, from which pyroxenes have been weathered out. Foliation in the pyroxene tuff is well develo^Ded, except near baked contacts with diabase where the rock is massive. On fresh surfaces the

14 pyroxene tuff is translucent pale apple green with relict black pyroxene phenocrysts from .5 to 2 mm. Plagioclase, quartz, and hornblende may occur as minor accessory relict phenocrysts. Rare dark green relict vesicles filled with epidote and/or pumpellyite and/or calcium carbonate were also observed in the pyroxene tuff. Discrete relict bedding planes are rare in the pyroxene tuff. Contacts between pyroxene tuff and more felsic tuff apppear to be gradational.

In thin section the pyroxene tuff ranges in texture fran slightly sheared to thoroughly sheared with the iTXDSt thorough recrystallization occurring in the more highly strained rocks. Relict features observed in slightly strained pyroxene tuff include: pyroxene, plagioclase, and hornblende, phenocrysts; felty and variolitic alignments of groundmass plagioclase microlites; and vesicles. In thoroughly recrystallized samples the mafic grains are replaced by chlorite, actinolite, pumpellyite, and epidote, as discussed below.

Metamorphic minerals show evidence for two deformational episodes: D 1 responsible for the formation of S vAiich is defined by the alignment of 1 metamorphic minerals; and D viiich caused folding of S (F ) and was not 2 12 accompanied by recrystallization.

Tiiree metamorphic assemblages are present in the pyroxene tuff:

1) Chlorite + Pumpellyite + Epidote

2) Pumpellyite + Calcium Carbonate

3) Epidote + Calcium Carbonate

Actinolite is ubiquitous, albite and quartz are present in many of the sanples; stilpnomelane, vAiite-mica, sphene, and opaque minerals are common groundmass constituents; both calcite and aragonite are present.

In moderately recrystallized rocks actinolite heals fractures in and forms beards on relict pyroxene phenocrysts (Figure 4). Actinolite is also present as very fine grained needles defining S in the matrix of poorly recrystallized 1

15 Figure 4, Pyroxene tuff of the DPu, showing a sheared relict clinopyroxene phenocryst with an actinolite beard, bright lenticles in the matrix are actinolite. Abbreviations used in this and the following photomicrographs: act = actinolite, ar = aragonite, cpx = clinopyroxene, cc = calcium carbonate, chi = chlorite, cz = clinozoisite, ep = epidote, plag = plagioclase, pp = pumpellyite, qtz = quartz.

Figure 5, Pumpellyite and Calcite in a sheared vesicle. This figiire also shows the typical texture of a moderately recrystallized pyroxene tuff of the DPu.

16 rocks. In well recrystallized rocks, actinolite replaces mafic phenocrysts with chlorite, and defines S as abundant needles in the matrix. 1 Quartz and albite occur, along with epidote and calcium carbonate replacing plagioclase phenocrysts and also as very fine grains in the matrix in poorly recrystallized rocks. In thoroughly recrystallized rocks quartz and albite occur as fine grains in recrystallized matrix, and as elongate patches parallel to S . Quartz veins are common in the specimens examined. 1 Fe-rich chlorite occurs in pressure shadows around relict pyroxenes and relict plagioclase crystals in poorly recrystallized samples, and as relict vesicle fillings with pumpellyite, epidote, quartz, and albite. In thoroughly recrystallized rocks Fe-rich chlorite occurs with pumpellyite vrtiite mica, and epidote replacing mafic relict phenocrysts in aggregates elongate parallel to

S . Fe-poor chlorite occurs with quartz and albite replacing relict 1 plagioclase phenocrysts. In many samples Fe-rich chlorite rims Fe-poor chlorite v^ich in turn surrounds quartz or albite.

Fe-Pumpellyite occurs as relict vesicle fillings with epidote and chlorite

(Figure 5), and in pressure shadows with chlorite around relict phenocrysts in

poorly recrystallized rocks. In thoroughly recrystallized rocks pumpellyite

occiors with chlorite, epidote, and vhite mica in patches elongate parallel to

S . 1 Epidote occurs in vesicles with pumpellyite and chlorite in poorly

recrystallized rocks (Figiire 6). In thoroughly recrystallized rocks epidote

occurs as granules throughout the recrystallized matrix. Epidote also occurs as

pre-tectonic grains viiich have been strained and are now composite, and as

syntectonic rods in thoroughly recrystallized rocks. Fe-poor rims on Fe- rich

epidote cores are present in most samples examined (Figure 7).

Stilpnonelane occurs as very fine plates along thin brcsvn selvages

subparallel to S in both poorly and thoroughly recrystallized rocks. 1

17 Figure 6, E)etail of intergrown epidote and pumpellyite fron a vesicle filling in a DPu flow rock.

Figure 7, Epidote on plagioclase showing Fe-poor rim on Fe-rich core.

18 Calcium carbonate is present as calcite and aragonite (Figure 8).

Aragonite was identified by x-ray and optical techniques. Calcium carbonate is both pre— and post— tectonic. It cuts many samples in post-tectonic veinlets.

Pre-tectonic calcium carbonate occurs as irregular masses parallel to S in 1 sample 109-142. Calcium carbonate is common in relict vesicles, and with quartz replacing relict plagioclase phenocrysts. Calcium carbonate also occurs as patches in the recrystallized groundmass of both poorly and thoroughly recrystallized pyroxene tuff.

Sphene occurs as fine granules in trains parallel to S in the matrix of thoroughly recrystallized pyroxene tuff.

Dacite and Rhyolite Tuff The felsic tuff occurs as .5 to 3 m thick layers

interbedded with pyroxene tuff. The felsic rocks occur as tuff layers and

less often as layers of pillow breccia. On weathered surfaces it is chalky v^ite with 1 to 5mm relict quartz crystals protruding fron the rock surface.

Plagioclase, from 1 to 5mm is a common accessory relict phenocryust, and

locally may be as or more abundant than quartz. Relict mafic phenocrysts are

rare in the felsic tuffs.

The felsic tuffs range from unstrained to extremely strained as seen in

thin section, with the most complete recrystallization having occured in the

more highly strained rocks. Unstrained felsic tuff contains plagioclase,

hornblende, and partially resorbed quartz as relict phenocrysts (Figure 9).

Relict cimulophyric grains of plagioclase and quartz are common in less

strained specimens. Relict groundmass textures observed in felsic tuff

include: microgranitic, spherulitic, felsitic and subtrachytic. Skeletal

opaque grains, and euhedral pyrite cubes are present in many samples.

Metamorphic mineral assemblages in the felsic tuff are identical to those

discussed above in the pyroxene tuff. Stilpnomelane and v^ite mica are more

abundant in the felsic tuff. Quartz and albite are ubiquitous in the felsic

19 Figure 8, Photomicrograph and sketch of aragonite embayed by calcite, in a vesicle in pyroxene tuff of the DPu, scale is the same in photo and sketch.

20 Figure 9, Relict partially resorbed quartz grain in felsic tuff of the DPu.

Figure 10, Pumpellyite-epidote beard on a relict plagioclase crystal in felsic tirff of the DPu. Pumpellyite also occurs on the plagioclase.

21 Figure 11, Clinozoisite grains associated with quartz in felsic tuff of the DPu.

22 tuff.

In highly strained felsic tuff, actinolite occurs as fine needles in anastOTOsing bands defining S . In less strained felsic tuff, actinolite 1 occurs as very fine randomly oriented needles in tlie matrix and along small veinlets with stilpnomelane. Actinolite also replaces relict hornblende with chlorite and pumpellyite, and beards relict plagioclase phenocrysts.

Quartz and albite are abundant in the groundmass and replacing relict

plagioclase phenocrysts. Quartz veinlets are common.

Fe-rich and Fe-poor chlorite occur in the felsic tuff. Where they occur

together, Fe-rich chlorite rims Fe-poor chlorite. In highly strained felsic

tuffs chlorite occurs with punpellyite and epidote replacing relict hornblende

phenocrysts.

Fe- rich pumpellyite occurs in less strained felsic tuff as well developed

blades replacing hornblende phenocrysts, and as beards on plagioclase

phenocrysts in sample 109-130ABV (Figure 10). Fe-poor pumpellyite occurs with

actinolite replacing relict plagioclase phenocrysts.

Epidote ocCTors as pre-D Fe-rich grains with Fe-poor rims in moderately 1 strained felsic tuff. The grains are often fan shaped and composite. Sample

109-93 contains strained clinozoisite grains (Figure 11). Epidote occurs with

chlorite and pumpellyite replacing relict hornblende phenocrysts in unstrained

felsic tirff.

Stilpnomelane occurs as spindle shaped aggregates throughout the matrix

and phenocrysts of unstrained felsic tuff and as fine fibrous grains along

brownish yellow selvages in highly strained felsic tuff.

Vihite mica occurs in anastcxiXDsing layers parallel to S in highly strained 1 felsic tuff. In less strained felsic tuff v^ite mica occurs as patches in and

around relict plagioclase phenocrysts.

Calcium carbonate occurs as veinlets, and with quartz replacing relict

23 plagioclase grains.

Chert ^ Argillite Chert and argillite are exceedingly rare in the DPu.

A 25 cm thick chert lens was found in a stream bottom interbedded with pyroxene tuff in the northwest comer of section 34, northeast of Little Deer Peak

(Plate-I), but was not traceable out of the stream. The chert lens has a sheared contact with surrounding pyroxene tuff, v^ich does not appear to be silicified. The chert is dark brown and has a fine granular texture, caused by recrystallization.

Argillite, slightly more abundant than chert, was observed in a cliff face, v^iere it is tmncated by diabase dikes, and in road cuts on the South flank of Big Deer Peaks (Plate-I), interbedded witli pyroxene tuff. Neither of the argillite layers are laterally extensive. In hand specimen the argillite

is black, friable, and smells of sulfur due to the breakdown of disseminated

sulfides.

Diabase The diabase is common in the DPu occurring as sills, dikes, and a large

irregular intrusive body on Deer Peaks. The diabase crops out in the same

manner as the pyroxene tuff. It is intrusive into all other lithologies of the

DPu. On weathered surfaces it may resemble the pyroxene tuff or weather to a

pale reddish tan color. On fresh sirrfaces the diabase has a granular

appearance caused by an intergrowth of .5 to 1.5 mm grains of dark green

pyroxene and pale green plagioclase. Quartz occurs as an accessory mineral.

The diabase is generally massive, showing a poorly developed foliation near

shear zones. The diabase shows only slight strain in thin section, and exhibits

excellent relict subophitic and granophyric textures (Figures 12 and 13).

Fractured relict plagioclase and pyroxene and quartz crystals with imdulatory

extinction are evidence for slight strain during metamorphism.

24 .3.5mrn

Figure 12, Relict texture of the Diabase, DPu.

,0Smm

DPu.

25 Metaiporphic assemblages in the diabase are identical to those observed in the pyroxene-tuff. Albite, quartz, and actinolite are ubiquitous, vArite mica and stilpnomelane are rare, calcium carbonate is common.

Actinolite occurs as very fine grained needles healing fractures in, and bearding, relict pyroxene crystals, and intergrown with chlorite or pumpellyite in mats on tlie edges of relict pyroxene and plagioclase crystals.

Albite and quartz occur together replacing relict plagioclase crystals.

Quartz also occurs as primary grains v^ich appear to be unaltered by metamorphism. Quartz veinlets are common in thin-section.

Fe-rich chlorite occurs as fine plates on relict plagioclase crystals and

in patches with actinolite on relict pyroxene and plagioclase crystal boundaries.

Tabular Fe-rich pumpellyite occurs in patches with or without actinolite

around the edges of relict pyroxene crystals, and as fine plates on relict

plagioclase crystals.

Epidote occurs as plates and rods with chlorite replacing plagioclase in

sample 109-471TDP. Most of the epidote is strained and has Fe-rich cores

surrounded by Fe-poor rims.

Stilpnomelane occurs as fibers, bundles and blades in relict plagioclase

crystals in sample 109-131.

White mica occurs in patches along a pre-shearing quartz veinlet in sairple

109-514, yiich was in the vicinity of a shear zone.

Calcium carbonate occurs as patches on relict plagioclase crystals and

along veinlets in the diabase.

Metamorphism

Recrystallization History: Two episodes of recrystallization are evident in

the DPu. The first episode is deduced frcxn the presence of Fe-rich pre­

26 foliation epidote grains. These epidote grains may be evidence for a static sea-floor hydrothermal metamorphic event, similar to that proposed by Haugerud et al. (1981) for the Shuksan Greenschist; or for contact metamorphism in the vicinity of diabase dikes.

The second episode of recrystallization was syntectonic with the deformation (D ) that produced the foliation (S ) as shown by the alignment of 1 1 actinolite, chlorite, pumpellyite, and muscovite parallel or subparallel to S^.

The Syn-D assemblage also crystallized in unstrained rocks, v^ere metamorphic 1 minerals have a random orientation. The amount of strain, and consequently the development of S , varies with lithology. Tuffaceous rocks are generally the 1 most highly strained and recrystallized, flow rocks and dike rocks are generally unstrained to slightly strained and are only partially

recrystal1ized.

D structures, mainly F folds, deform all metamorphic and primary 2 2 minerals. In a few samples S is incipiently developed by transposition of S . 2 1 Recrystallization appears not to have accorpanied D .

Temperature of Metamorphism: Nakajima et al. (1977) established that X - Fe epidote varies with teirperature (Figure 14) in rocks containing the reaction

assemblage:

Punpellyite + Chlorite + Quartz = Clinozoisite + Actinolite + Water

Brown and O'Neil (1982) calibrated the curve of Nakajima et al. (1977) (Figure

15) using experimental results from various sources and oxygen isotope data,

they also suggested that this geothermometer is pressure independent.

27 #90 ■

decrease of Fe content of epidote with increasing temperature. From Nakajima et al. (1977)

The temperature of metamorphism for the DPu was determined by estimating the mole fraction of ferric iron in epidote from birefringence. The mole fraction of ferric iron varies from .17 to .25, and averages .21 in rocks of

the DPu vAiich contain the full reaction assemblage. These epidote compositions o o indicate a range of temperature from 330 C to 350 C, and an average temperature o of metamorphism for tlie DPu of approximately 340 C. No systematic variation in

temperature was observed within the DPu.

Pressure of Metamorphism: High pressure during metamorphism is demonstrated by

the presence of aragonite. Using the calcite-aragonite transition curve of

Johannes and Puhan (1971), and the average temperature of metamorphism for the

DPu, determined above, a pressure in excess of 7.5 Kbar is obtained. The

maximum pressure is constrained by the presence of albite v^ich breaks down to o jadeite + quartz at approximately 11.1 Kbar at 340 C. The absence of

metamorphic pyroxene in rocks of the DPu precludes more precise estimation of

pressure during metamorphism of this unit. Figure 16 shows the location of the

Dpu in P-T space, in relation to high P-T reactions, the Haystack Mountain

unit, and the Shuksan Metamorphic Suite.

28 ^Ep^Fe

Figure 15, T-XFe-epidote curve from Brown and O'Neil (1982). The range of epidote canpositions from t±ie Deer Peaks unit, the Haystack Mountain unit (Cruver, 1983), and the Shuksan Suite (Brown, 1986) are shown.

29 Comparison with other western North Cascade metamorphic Rocks Figure 17 is a generalized ACF diagram showing the metamorphic assemblages observed within the

DPu. In figure 18 this diagram is compared in P-T space with ACF diagrams constructed for metamorphic assemblages observed by Brown et al. (1981) in other units of the North Cascades. It appears that assemblages for the

Chilliwack Group, Haystack Mountain Unit-chert basalt unit, Deer Peaks unit, and Shuksan Metamorphic Suite, form a sequence of units metamorphosed in progressively higher grade environments. The Deer Peaks unit was metamorphosed at the same temperature as lower grade Shuksan Metamojq^hic Suite rocks, but contains no Na-amphibole because of its low iron content.

30 Figure 16, P-T diagram showing metamorphic reactions pertaining to Deer Peaks unit metamorphism. Approximate locations in P-T space of the Deer Peaks unit, Shuksan Metamorphic Suite (Brown, 1986), and Haystack Mountain unit(Cruver, 1983) are also shewn. Sources for reactions: (1) Nakajima et al. (1977); (2) Johannes and Puhan (1971); (6, 7, 8, & 9) Liou (1971); (10,11, & 11) calculated using data from Newton and Smith (1967) , and Holland (1983).

31 A1 Paragonite

+3 Figure 17, Al-Ca-Fe projection diagram for assemblages observed in the Deer Peaks unit, * = assemblage observed in the Deer Peaks unit

32 +3 Figure 18, Al-Ca-Fe projection diagrams for the Chilliwack Group (Ch), chert basalt unit (CB) , Deer Peaks unit (DP) , and Shuksan Suite (SMS) , in P-T space, modified from Brown et al. (1981). Experimental reaction lines are from various sources; Jd + Q = Alb, calculated from data in Newton and Smith (1967), and Holland (1983); Ar = CC, Johannes and Puhan (1971) and Crawford and Hoersch (1972); Pump = Cz + Act from Nitsch (1971). Mineral abbreviations as in Figure 4. Dashed on the Deer Peaks diagram show phases present in the low grade Shuksan Suite.

33 CHEMICAL COMPOSITION OF ROCKS IN THE DEER PEAK UNIT

INTRODUCTION

Five pyroxene tuff, four diabase, and tliree dacite samples all belonging to the DPu were analyzed for major elements and the trace elements Rb, Sr, Zr, Sc,

V, Ba, Y, Cr, and Ni. Analyses were performed at Washington State University by X-ray fluorescence under the direction of Dr. Peter Hooper. The analyses are listed in Table-1. Samples were screened for weathering and alteration effects by tliin-section examination.

The analyses of these samples were carried out for the purpose of providing data relevant to determination of the tectonic environment of formation and correlation of the Deer Peaks unit with other rocks in the western North Cascades.

CLASSIFICATIOI

To provide evidence as to whether the DPu rocks form a comagmatic suite

SiO variation diagrams were constructed. Plots of Fe* (total Fe as FeO), I'lgO, 2 and Na 0 against SiO all shav linear trends with two clusters: one in the 50% 2 2 to 60% SiO , and one in the 70% to 75% SiO (Figure 19). Plots of A1 0 , CaO, 2 2 2 3 P 0 and TiO against SiO (Figure 20) show less well defined trends. A plot of 2 5 2 2 K 0 against SiO shows wide scatter, and a P 0 -TiO plot shows three separate 2 2 2 5 2 fields (Figxore 21). Linear trends are also prominent on the log-log plots

(Figure 22). Three samples plot off the trends on the Sc-Zr, Cr-Sc, TiO -V, 2 arxi Ni-Sc plots, these are the three silica rich (>70% silica) samples. The

TiO -Zr plot shows no trend but the diabase and dacite plot in distinct groups 2 and the pyroxene-tuff is scattered. Rb-Sr, and Ba-Sr log-log plots are scattered (Figure 23).

34 Table I

Geochemical Analyses (Major elements in wt. %, Trace elements in ppm)

109- 109- 109- 109- 109- 109- 109- 109- 109- 109- 109- 109- 42 124 126 127 131 L32 135 141 143 80 96 130

Pt Pt Di Di Di Di Pt Pt Pt D D D

SiO 53.66 60.56 55.07 57.46 56.67 57.26 53.64 57.47 47.61 72.57 71.57 72.47 2 A1 0 16.91 14.88 15.12 15.75 15.27 15.57 14.28 17.21 14.89 13.62 13.28 12.86 2 3 TiO 0.75 0.46 0.68 0.67 0.73 ' 0.65 0.45 0.97 0.65 0.26 0.29 0.25 2 FeO 9.08 6.44 10.35 9.12 9.58 8.95 8.86 8.75 10.59 2.22 2.80 2.68

MnO 0.12 0.13 0.11 0.12 0.12 0.15 0.14 0.15 0.13 0.06 0.09 0.07

CaO 8.67 12.87 7.68 6.56 6.82 7.14 8.78 1.37 6.54 1.72 0.22 4.61

MgO 5.68 3.90 5.27 4.53 4.93 3.99 9.27 4.70 7.35 0.60 2.31 0.89

K 0 0.35 0.00 0.39 0.15 0.14 0.03 0.00 1.24 2.41 2.22 0.62 0.37 2 Na 0 2.70 1.38 2.43 3.41 3.22 3.15 1.86 3.34 1.09 2.98 2.73 2.80 2 P205 0.155 0.128 0.073 0.081 0.070 0 .072 0.123 0.115 0.132 0.060 0.057 0.068

Total 98.54 101.05 97.68 98.31 98.03 97.39 97.85 95.74 91.91 96.53 94.12 97.20

(Totals are volatile free)

Rb 14 0.00 12 3 10 4 3 13 46 0.00 0.00 0.00

Sr 327 49 153 88 139 98 565 80 945 132 20 126

Zr 97 38 41 44 39 38 92 60 127 55 57 49

Sc 35 26 40 32 40 41 39 33 40 9 10 13

V 276 191 305 255 363 278 254 364 283 50 36 67

Ba 61 20 124 141 209 121 63 220 467 276 375 162

Y 22 11 15 18 14 20 11 16 22 8 9 6

Cr 167 42 80 69 85 78 370 37 168 34 36 21

Ni 62 42 51 42 44 47 100 31 52 26 25 19

Pt = Pyroxene tuff , Di = Diabase, D = Dacite

35 7.50, A

6.00.

Figure 19, Variation diagrams showing linear trends. Note the separate grouping of rocks containing 70% silica. All values are in weight percent. pyroxene tuff; 0= ferro-gabbro; ©= dacite in this and succeeding figures.

36 20

18 AI2O3 A A 16 QlI# A A 14

12

10 ~T" T" "I 40 50 nr60 70 80 SiO

0.20

0.15 A A A ^ ¥5 A 0.10 - Q

0.05 -

0.00 To lo 6^ ^0 80

Si02 Figure 20, Variation diagrams with poorly defined trends, all values in v/eight percent. Scatter on CaO diagram is caused by alteration. Symbols as in Figure 19.

37 0.20

A 0.15 A 5 A 0.10 S QB 03

0.05

O.OQ___ "T" “I 0.0 0.5 1 .0 TiO^

Figiare 21, Variation diagrams showing no trends, all values in weight percent. Symbols as in Figure 19.

38 400,

1 oa.

Or 100.

Ni

@ ± 0

10 4-<----- —f 9 Sc 50

50 Sc

Figure 22, Log-log plots of selected trace elements (in ppm unless noted otherwise) . Syriibols as in Figure 19.

39 0.00 A "T 1 0 1.5 3.0

Figijre 23, Log-log plots showing scatter, symbols as in Figure 19. The linear trends observed on most of the variation diagrams are interpreted to show that pyroxene tuff and diabase of the DPu have similar compositions and could be considered a comagmatic suite. However, separation of the diabase and pyroxene tuff on tiie P 0 -SiO and P O -TiO diagrams is evidence for separate 2 5 2 2 5 2 magmatic origins for these two lithologies and the intrusive nature of the diabase is more evidence in support of this interpretation. The separation between the dacites and other DPu lithologies observable on the Na 0 vs. SiO 2 2 diagram, and the TiO -V, Cr-Sc, Ni-Sc, Sc-Zr, and TiO - Zr log-log plots is 2 2 interpreted as evidence that these rocks form a separate group of igneous rocks. The scatter observed on the variation diagrams of figirres 20 and 21, and the Ni-Sc, and TiO -Zr log plots of Figure 22, may represent mobilization 2 during metamorphism, lithic contamination of the tuffaceous rocks, or both.

Rocks of the DPu plot in subalkaline fields on the Ne'-Ol'-Q' triangle

(Figure 24). On a plot of SiO against FeO/MgO (Figure 25A), after Miyashiro 2 (1974), most DPu rocks plot in the calcalkaline field near the discriminant line, a characteristic of andesitic rocks called " Transitional Calcalkaline rocks"(TCA) by Kay and Kay (1985). Therefore pyroxene tuff and diabase of the

Deer Peaks unit are classified as a 'Transitional Calcalkaline Suite'. Rocks of the DPu plot in the calcalkaline field on a Jensen cation plot (Figure 25B), and are classified as basalts on this diagram. However the silica content of

Deer Peaks unit rocks is generally within the range used to define andesites

(54 to 62 weight %), proposed by Chayes (1969). The high silica content of the diabase is due to tlie granophyic intergrowths, that of the pyroxene tuff may be caused by lithic contamination. SiO and TiO content of Deer Peaks unit rocks 2 2 also matches the average andesite conpositions better than the average basalt compositions of Lei4aitre (1976). The rocks containing more than 70% silica are classified as rhyolite or dacite on Figure 25B. Mobilization of the alkali elements prevents their use to classify rocks of the Deer Peaks unit.

41 Figure 24, Ne'-Ol'-Q' plot of DPu rocks illustrating their subalkaline character, symbols as in Figure 19.

42 80

70 Calcaikaline ^^Tholelitlc

SiO^

60 . /

A M / 50 ' A /

Figure 25, A: Si02 vs. Fe*/MgO diagram, after Miyashiro (1974). B: Jensen Cation Plot, after Jensen (1976). Fe* = FeO; R = rhyolite; D = ddacite; A = andesite; B = basalt; HMT = high Mg-tholeiite; HFT = high Fe-tholeiite; Symbols as in Figure 19.

43 TECTONIC DISCRIMINATIOSI

Whole Earth Normalized Elemental Abundance (WENEA) Diagrams WENEA diagrams were constructed using element abundance estimates of Shaw (1980) , shown in Table

II. Most of the alkali elements were not used on these diagrams as they were probably mobilized during metamorphism, as discussed above. Before being used all data were screened using a T-test(values outside of two standard deviations

froia the average analysis of a particular element in the same suite of rocks were excluded), any values failing the test were rejected. Ranges of

normalized values are shown in the WENEA diagrams instead of averages because

the average trends may be misleading with respect to the precision with which

discrimination may be made.

Table-II Elemental Abundances (Ppm)

Ba 12

y 1.1

Sc 6.2

Zr 15

V 36

Cr 3100

Mn 900

Ni 2385

P 205

WENEA diagrams were constructed frcm published analyses of back arc basin

volcanic rocks (BAB), and island arc volcanic rocks (lA). WENEA plots of lA

rocks are depleted in Cr and Ni, and slightly enriched in Y compared to rocks

of the DPu (Figure 26). Abundances for all elements fall within the rather

44 broad ranges of the BAB diagram (Figure 27) . The protolith of the DPu may have

formed in a back arc basin. However, according to Hawkins and Melchior (1985)

BAB are in general similar to MORB. Hawkins and Melchior (1985) and Saunders

and Tarney (1979), observed rocks apparently transitional between tholeiitic

BAB rocks and more evolved island arc tholeiites, v»^ich were erupted at the

beginning of back arc spreading. Ni and Cr contents of the DPu are

intermediate between those of MORB and island arc tholeiites (coirpare figures

26 and 28), and on a Ni-Zr plot most DPu rocks plot near the transitional-to-

arc point of Hawkins and Melchior (1985), (Figure 29). Therefore rocks of the

DPu are interpreted as being transitional-to-arc type volcanic rocks formed

during the early stages of back arc spreading.

Figure 29, Ni-Zr plot shoing transitional nature of the Deer Peaks unit rocks. Arrow points to transitional-to-arc point of Hawkins and Melchior (1985). Symbols as in Figure 19.

45 100

Figure 26, WENEA diagram showing island arc volcanic rocks and the Deer Peak: unit. Saipan, Bougainville and Fiji (Taylor et al, 1969) [ Viti Levu, Fiji (Frey et al., 1980)

Deer Peaks unit

46 100

10-

1.

0.1. I —r —T“ —r- T- -- 1— ~T“ —I------Ba Y Sc Zr V Or Mn Ni P XI 00 XI 00

Figure 27 , WENEA diagram showing back arc basin volcanic rocks and the Deer Peaks unit. South Sandwich (Saunders and Tarney, 1979)

Sarmiento (Saunders and Tarney, 1979)

South Shetland Islands (Weaver et al., (1979)

Deer Peaks unit

47 10.

1 -

0.1 _T- “T“ —I— ■nr I I --- 1— "T~ Ba Sc Zr V Or Mn Ni p XI 00 XI 00 Figure 28, WENEA diagram showing PDRB rocks and th Deer Peaks unit.

Atlantic Ridge (Sun et al., 1979)

Indian Ocean (Frey et al., 1980)

FAMOUS Basalts (le Roex et al., 1981) □ Deer Peaks unit 48 CayiPARISON WITH OTHER NORTH CASCADES ROCK UNITS

A Ti/100-Zr-Yx3 digram (Figure 30) was constructed to compare geochemical characteristics of the Chilliwack Group, the Haystack Mountain unit, and the

Deer Peak unit. On this diagram rocks of the Chilliwack Group and Deer Peak unit plot in the same area, and Haystack unit rocks plot in a separate field.

The distrubution of points on figure 30 may indicate that the Chilliwack Group and Deer Peaks unit are related. Figure 30 is a representative example of

several other plots on vAiich the Deer Peaks unit shews an affinity for

Chilliwack Group rocks and slight separation from Haystack Mountain unit rocks.

Ti/lOO

Figure 30, Ti/100-Zr-Yx3 plot of rocks fron the Chilliwack Group, Haystack Mountain unit(unpublished data fron Brown), and the Deer Peaks unit.

49 STRUCTURE

Structures observed or inferred to exist within the study area are shown in cross section on Plate-II, and include: a pre-Tertiary fault v^ich juxtaposes rocks of the Deer Peaks unit and the SMS (the Deer Peaks fault); metamorphic fabrics within the Deer Peaks lanit and Shuksan Metamo2:phic Suite; folds within the Chuckanut formation; and high angle faults active in the Tertiary. An angular unconformity separates pre-Tertiary metamorphic rocks from the overlying Paleocene to Eocene Chuckanut Formation.

STRUCTURES WITHIN THE SHUKSAN METAMORPHIC SUITE

Orientations of foliation planes, fold and crenulation axes, and lineations do not vary between the Darrington Phyllite and the Shuksan

Greenschist in the study area. Therefore metamorphic structures within different lithologies of the Shuksan Metamorphic Suite are treated together below.

Misch (1966) interpretd the depositional stratigraphy of the SMS to be

Shuksan Greenschist deposited on top of Darrington Phyllite. Morrison (1977) and Haugerud et al. (1981) interpreted the original stratigraphy to be Shuksan

Greenschist on top of Darrington Phyllite based on the similarity of the greenschist to seafloor basalts and the additional observation of hydrothermal

Fe-Mn deposits between the greenschist and phyllite. Structural interpretations in this study are based on field observations of an SMS stratigraphy of greenschist-ferruginous schist-phyllite fron the bottom up, and the assunption, after Haugerud et al. (1981), that the SMS is a metamorphosed sea floor sequence.

Foliation The most prominent structure within the SMS is a metamorphic foliation surface S . Primary layering, S , is observed only at contacts 1 0 between the Shuksan Greenschist and Darrington Phyllite and is always parallel

50 to S . In the Darrington Phyllite, S is defined by alternating quartz-albite 1 1 . . . w and muscovite-graphite layers. In the Shuksan Greenschist, S is defined by 1 epidote layers and albite porphyroclast or amphibole rich layers as well as the alignment of the platy minerals chlorite and muscovite. At many localities

(i. e. locations 1(109-33) and 2(109-5), Figure 31), S is transposed parallel

to the axial plane of F , forming S . Axial planar cleavage developed at the 2 2 hinges of F folds also defines S . In the field, S is recognizable only at 2 2 2 the hinges of F folds. S is the most prevalent planar structure in the SMS 2 1 of the study area. Figure 32 shows equal area plots of poles to S for A: the

paTTington Phyllite, B; the Shuksan Greenschist, and C: A and B ccxnbined. These

plots show that S has been folded about a North-northwest South-southeast 1 trending horizontal axis.

Folds F folds were not observed in the Shuksan Metamorphic Suite of the 1 study area. F folds trend North-northwest South-southeast, vary from tight to 2 . . ^ isoclinal, and have a variable plunge (Figure 33). F folds range in size from 2 crenulations of a few millimeters to folds v/ith amplitudes of several hundred

meters. Development of axial planar cleavage or crenulation cleavage is

conmon. Most of the F folds verge to the northeast.

Figure 33, Projections of F2 and L2 axes from the SMS along Coal Mountain, n = 69, + = F , * = L 2 2

51 Figure 31, Map showing t±ie out­ crop pattern of the Shuksan Suite on Coal Mountain. KG = Shuksan Greenschist; KDP = Darrington Phyllite; = out­ crop of greenschist; ^ = outcrop of phyllite; ^ - direction of upper plate motion fron stretching lineations, arrow indicates direction of plunge; Deer Peaks fault; DPu = Deer Peak unit;A = outcrop of Deer Peak unit; TCS = Chuckanut Formation; X = synclinal axis;

] Mile

52 N N X X

N

Figure 32, Pi-digrams of poles to foliation planes in the Shuksan Metamorphic Suite on Coal Mountain, A: Darrington Phyllite; B: Shuksan Greenschist; C: Shuksan Suite (A + B). All Pi-diagrams in this and following figures are lower hemisphere, equal area projections.

53 Rare F folds trend north-northeast and are open. The variable plunge of 3 F axes in figure 33 is caused by folding around F axes. 2 3 Anticlinal folding is supported by stratigraphy of the SMS and the outcrop pattern along Coal Mountain illustrated in figure 31. I'tiere observable in the study area the sequence greenschist-ferruginous schist-phyllite, from the bottom up, is observed. Thus, the occurrence of Shuksan Greenschist topographically above Darringbon Phyllite implies an anticlinal fold. Field observations support interpretation of folding along Coal Mountain as an isoclinal anticline overturned to the northeast (Plate II): the outcrop of

Shuksan Greenschist in the west flowing stream in section 32, east of Day Lake

(Figure 31) has a gradational contact upv/ards into overlying phyllite v^biich o dips approximately 50 to the southwest (Plate-I); the occurrence of isolated outcrops of Darrington Phyllite and ferruginous schist at the top of the knob in the center of the North-half of section 29, Plate-I, also supports isoclinal folding if they are interpreted as occurring because of tight second order folding. Isoclinal folding is also supported by the lack of northeast\\ard dipping S surfaces along the northeast flank of Coal Mountain, the observation 1 that most of the northeast dipping S planes occur on the limbs of low 1 amplitude folds, and the northeast vergence of most of the low amplitude folds.

Available exposure along Coal Mountain does not reveal vdiether S is axial 1 planar to the anticline or folded by it, thus the fold may be either an F or 1 an F structure. 2 LI Lineations L lineations in the SMS are of two types: stretching lineations 1 defined by deformed epidote and albite porphyroclasts (L C); and metamorphic 1 lineations defined by syntectonically crystallized amphibole (L M). L C and 1 1 L M lineations are not everywhere parallel in the study area. Two L lineation 1 1 directions are present in the SMS of the study area (Figure 35). The first is defined by L C and L M lineations and trends oblique to F axes. The second 11 2

54 direction is parallel to subparallel to F axes, and is defined by L 2 1C lineations- L lineations form a girdle due to folding about F axes, (Figure 1 2 34). Most of the L C and L M lineations observed trend west-southwest east- 1 1 northeast. Three of these L C-L M lineations observed in oriented thin 1 1 section yielded a sense of shear indicating upper plate motion to the southwest using the criteria of Sinpson and Schmidt (1983) (Figure 35). Two northwest- southeast trending L C lineations shov/ed ambiguous shear sense in oriented thin

Comparison with Regional Structural Elements: According to Brown (1986) regionally consistant L orientations indicate the direction of plate 1 convergence in v^ich the SMS was metamorphosed. Figure 35 is a sketch of parallel L C and L M lineations used to determine the direction of plate 11 convergence during SMS metamojrphism. Data in this study are in agreement with those of Brown (1986) that indicate a northeast dipping subduction zone during

SMS metamorphism (Figure 36A).

F axes along Coal Mountain are parallel to regional L lineations in the 2 2 SMS described by Brovm (1986) as late metamorphic lineations formed by late metamorphic compression (Figure 36B).

The lineation data can be interpreted only in relation to the present position of the rocks, and do not take into account possible rotations related to their emplacement.

55 1 N

Figure 34, Equal area plot of LI lineations observed in the Shuksan Suite along Coal Mountain, L C lineations not parallel to L M lineations are circled. 1 1

Figure 35, Asymmetrically sheared epidote grain indicating dextral shear. Notff that • amphibole needles and albite grains parallel the stretching lineation. Ab = albite; Q = quartz; A = amphibole; Ep = epidote; sample number 109-9A.

56 Figiare 36, Lineation directions observed in the Shuksan Suite after Brown (1986). A: early metamorphic lineations; B: late metamorphic fold axes and lineations; data fran Morrison (1977), Haugerud (1980), Leiggi (1983), Silverberg (1985), Brown (unpublished), and this study (CM). Shuksan Suite is stippled, TS is the Twin Sisters.

STRUCTURES OBSERVED WITHIN THE DEER PEAK UNIT

MetanxDrphic structural elements within the Deer Peaks unit are variably

developed (compare Figures 37 A and B) and poorly exposed. In many outcrops

rocks of the Deer Peaks unit are so massive or so covered by vetetation as to

nearly preclude meaningful structural observations. No systematic relationship

between metamorphic fabrics and the Deer Peaks fault was observed.

The most obvious structures present in the Deer Peaks unit are primary

layering of interbedded tuffaceous rocks (S ) and parallel metamorphic

foliation (S ). Rare F folds are visible in a few localities. Stretched 12 vesicles and relict phenocrysts form L lineations, measurable at only a few 1

57 Figure 37, Photonicrographs demonstrating the variably developed metamorphic fabric in the Deer Peaks unit. A: unstrained rock; B: strained rock. Pyx = pyroxene, all other abbreviations as in figure 4.

58 Figure 38, Map showing structures of the Deer Peaks unit, and the Deer Peaks fault./ = strike and dip of SI; / = F2 axis;»/= LI indicating sinistral shear;^ = LI showing upper plate motion, arrow points in direction of plunge approximate contact between surficial deposits 1 Mile and bedrock,*X= synform. Other symbols are the Contour Interval 250 m. same as those in figure 29.

59 lcx:alities in the field (Figure 38). Rocks of the Deer Peaks unit are folded into an open south-southwest plunging synform.

Bedding and Foliation Relict bedding (S ) in the Deer Peaks unit is defined by 0 layers of dacite and p^TTOxene tuff and rare chert and argillite. Prominent benches in tlie vicinity of location 1 (Figure 38) are parallel to S . ^iflierever 0 both are observable, S and S are parallel. 0 1 i-tetamorphic foliation (S ) is defined by selvages of chlorite and less 1 commonly by flattened vesicles or breccia fragments, as at location 1 (Figure

38). S defines a broad, gentle synform (Figure 38). S is apparently dragged 1 1 into the Higgins Mountain-Day Lake fault zone (Figure 38)-

In thin-section an incipient S was observed, parallel to crenulation axes 2 (Figure 39).

Figure 39, Sketch of incipiently developed S in the Deer Peaks unit. 2

Folds F folds were not observed in the Deer Peaks unit. 1 F folds vary in amplitude from a few millimeters to a few tens of meters, 2 and generally trend northeast-southwest (Figure 40). Crenulations and minor

folds verge toward axes of larger folds (Figure 41). Large amplitude folds are

open, and lower air^Jlitude folds are tight. Crenulation cleavage is locally

developed.

60 Figure 40, Pi-diagram of F2 axes in the Deer Peaks unit, n 19

Figure 41, Sketch of F2 fold in pyroxene tuff of the Deer Peaks unit

61 F folding is represented by the large south-southwest plunging synform, 3 (Figure 38)• The synform is defined by the variation in S attitudes. The 1 variable plunge of F axes is caused by folding about the synformal axis. 2 LI Lineations L stretching lineations are defined by stretched relict 1 phenocrysts and vesicles. The lineations are not readily observable in the field. Examination of oriented thin-sections allowed determination of shear sense on a local scale, using the criteria of Sirrpson and Schmidt (1983). No regionally consistent orientation of L was observed. Lineations for v^iich a 1 sense of shear was determined are plotted on (Figure 38), an equal area plot of

L lineations observed in the Deer Peaks unit are shown in (Figure 42). 1

Figure 42, Equal area plot of L lineations observed in the Deer Peaks unit. 1

DEER PEAKS FAULT

The Deer Peaks fault separates the Shuksan Metamorphic Suite from structurally higher Deer Peaks unit rocks. The trace of this fault is shown on Figure 38 and Plate-I; it runs along the northwest flank of the Deer Peaks massif, crosses Little Deer Creek, and then taends to the southeast and runs

62 along the base of the prominent northwest-trending ridge between Little Deer

Peak and Gee Point. The Deer Peaks fault is not exposed but is inferred to exist because the change in rock units v/hich occurs across its proposed trace cannot be attributed to any other type of contact relation. Map control on the

Deer Peaks fault is based on outcrop bracketing.

Three interpretations of the Deer Peaks fault have been proposed: 1) it dips northwest and represents a folded portion of the Shuksan Thrust Fault

(Misch,1966; Bechtel Report, 1979); 2) it is a combination of high angle faults

(Tabor, oral communication to Brcwn, 1985); 3) it is a folded low angle fault vAiich emplaces rocks of the Deer Peaks unit above those of the SMS (this thesis).

The dip of the Deer Peaks fault is constrained by outcrops to be to the soutlieast (Figure 38) and Plate I, rendering interpretation (1) above unfeasible. A tiiree point geometrical solution of the fault plane yielded a o 51 easterly dip, however different strikes and dips are obtained \>^en different control points are used, indicating that the Deer Peaks fault is nonplanar.

The trace of the of the Deer Peaks fault in Figure 38 requires that it be divided into at least four segments to support interpretation (2) above because of its non-linear trend. The marked change in strike of the Deer Peaks fault occurs in tlie vicinity of the hinge of the synform discussed above.

Coincidence of the hinge of the synform and the change in strike of the Deer

Peaks fault supports interpretation (3) above. The Deer Peaks fault is concluded to be a folded tiirust fault based on its non-linear map trace, nonplanar attitude, and near coincidence with the F synform discussed above. 3 The maximum age of the Deer Peaks fault is constrained by the 120 Ma age of the

metamorphic fabric of the Darrington Phyllite (Brown, 1986), viiich it cuts.

Minimum age control on the Deer Peaks fault is provided by the 50-60 Ma

63 Chuckanut Fonnation (Johnson, 1982) \vhich overlies the fault in sections 31 and

32, T. 34 N, R. 8 E (Plate-I).

HIGH ANGLE FAULTS

Higgins Mountain-Day Lake fault The Higgins Mountain-Day Lake (HM-DL) fault

trends northwest across Higgins Mountain, vAiere it cuts rocks of the Chuckanut

Formation. The fault trace is expressed as a topographic lineament along

Higgins Mountain, vdiere attitudes of bedding in the Chuckanut Formation change

drastically across its trace (Plate-I). This fault is projected to the

northwest through an outcrop of sheared serpentinite v^ich contains

metavolcanic fragments, located in the NE 1/4, SE 1/4, section 24, S of Granite

Lake (Plate-I). The HM-DL fault may be part of a large fault system inferred

to run down the Day Creek valley on the western boundary of the present study

area. The Day Creek fault zone is inferred from scattered outcrops of

serpentinite with northijest trending foliation, a fault contact between

Darrington Phyllite and serpentinite in the center of the W 1/2, section 14, T.

34 N, R. 6 E (Plate I), and the occurrence of a sliver of rocks of the Vedder

Complex associated with serpentinite on the ridge in section 31, S of Day Lake

(Plate-I). The HM-DL fault zone is shown on Figure 43.

Three earthquakes recently occurred along the HM-DL fault zone. The

epicenter is located near the southeast end of Day Lake (Zelwig, personnel

communication,1986). One of the fault-plane solutions yields a strike of N60W

and a dip of 70SVV (Zelwig, personnel communication, 1986) , in good agreement

with tlie attitude of the HM-DL fault zone (Plates I and II). Preliminary first

motion studies indicate that the slip was dominated by reverse motion

(soutliv/est plate up) , (Zelwig, personnel communication, 1986) .

Siiiistral motion along the HM-DL fault is indicated by assymetric

stretching lineations present in phylIonite associated with a sliver of rock

64 55 belonging to the Vedder Complex, and drag of the S surface of the DPu South of 1 Big Deer Peaks into the fault zone, location 2 (Figiare 38). Figure 44 is a sketch of a stretching lineation used as evidence for sinistral motion along the HM-DL fault, and its spatial relationship to the HM-DL fault.

Segelson Lake shear zone The Segelson Lake shear zone was traced northwest from Segelson Lake to Chute Cree)c, vhere it appears to die out in tiie SHS

(Figure 43). In the Segelson Lake area, the shear zone is marked by the following features: linear topography; serpentinite and exotic metavolcanic rocks; and jujctaposed Chuckanut Formation rocks and Shuksan Greenschist. The

Segelson Lake area also contains andesite of the Oso volcanic rocks, v^ich appears to be cut by the shear zone. To the northwest the shear zone is marked by the juxtaposition of Shuksan Greenschist with sandstone of the Chuckanut

Formation in the following locations: a roadcut southwest of the boundary of sections 10 and 11, T. 33 N, R. 8 E; at the intersection of sections 2,3,10, and 11, S of Finney Peak; and along the nortlieast trending ridge southv/est of

Finney Peak(Plate-I). This fault exhibits brittle deformation where it cuts rocks of the Chuckanut Formation.

All the major high angle faults discussed above cut the Eocene Chuckanut

Formation aind thus must have been active post 40 Ma; they may also have been active prior to the Tertiary.

FOLDS WITHIN THE CHUCKANUT FORi4ATION

Folds within the Chuckanut Formation generally trend northwest-southeast and are open with horizontal to subhorizontal axes. Amplitudes vary frcsn tens to hundreds of meters. Along Deer Creek, east of the mouth of Higgins Creek an overturned anticline was observed (Plate I); folds in this area trend nearly east-west, (Figure 43). An open syncline, described in detail by Robertson

66 Figure 44, Location and spatial relationships of a stretching lineation in phylIonite indicating sinistral shear along the Higgins Mountain-Day Lake fault zone; A = location of sample 109-153; B = oriented sample 109-153; C = asymmetric pressure shadow indicating sinistral shear. Ga = garnet; Q = quartz; A = actinolite; = phylIonite outcrop.

67 (1981), was observed on the southwest flank of the northwest end of Coal

Mountain (Figure 43). An open syncline West of Granite Lake coincides with the

synform discussed above, in the Deer Peaks mit (Figure 43). Three northeast­

trending open folds are present north of Deer Creek across frcm the moutli of

Higgins Creek (Figure 43). These folds increase in amplitude and wavelength to

the southeast.

Deformation recorded in rocks of tne Chuckanut Formation is not observable

in pre-Tertiary metamorphic rocks of the area. Alignment of fold axes in the

Chuckanut Formation and underlying metamorphic rocks, as along Coal Mountain

may be responsible for this. Another explanation is that the Chuckanut

Formation became detached at its base during folding. Evidence for this

hypotiiesis is visible at location 1 (Figure 43), Wnere a fault parallel to the

to the Chuckanut Formation-Darrington Phyllite contact was observed.

68 CONCLUSION

Rocks of tlie area belonging to the Shuksan Metamorphic Suite are similar to those described in other areas of the North Cascades by previous workers

(i. e. Misch, 1966; Brown, 1986) . The ocean floor stratigraphy comprising meta-basalts overlain by ferruginous schist overlain by phyllite observed in this area was recognized by Morrison (1977), in the Finney PeaJc area. Pre- D 1 epidote has also been interpreted as evidence of a sea-floor origin (and metamorphism) for rocks of the Shuksan Suite by Haugerud et al. (1981).

Metamorphic mineral assemblages indicate tliat recrystallization of the Shuksan

Suite took place in a high-P/low^T environment, perhaps a subduction zone.

Stretching lineations observed in three oriented thin sections demonstrate upper plate motion to the southwest, during metamorphism. Since the Shuksan

Suite was metamorphosed at approximately 120-130 Ma (Brcwn, 1986) the existence of a northeast dipping (relative to the present position of the rocks)

Cretaceous subduction zone is inferred. Folding of the Sf/IS along Coal Mountain is constrained to be anticlinal by field observations though v^ether the fold

is an F or an F structure is not clear. 1 2 The Deer Peaks unit is emplaced above the Shuksan Metamorphic Suite by the

Deer Peaks fault (Figure 45). The Deer Peaks fault is interpreted as a folded

thrust fault because of its non-linear map trace, coincidence with a synform,

and demonstrably non-planar attitude. The Deer Peaks fault is younger than 120

Ma, as it truncates the metamorphic fabric of the Darrington Phyllite, and

older than Eocene as it is covered by the Chuckanut Formation.

The age of the Deer Peaks unit is currently unknown. Geochemistry

indicates tliat protolith igneous rocks of the Deer Peaks unit are dacite and

transitional calcalkaline andesitic tuff and dike complex v^ich probably

represent three separate magmatic groups. The DPu is interpreted here to have

69 Shukuun Creenuchlut Shukaun Cruanauhiut

Darrlngton Phyllita Darrlngton Pliyllite ______STF 1 *^PDY

Chilliwack Group m UPC

Pkbs Nookaack Group j

Wella Craek Volcanioa

A. B.

Figure 45, Schematic tectonic stratigraphy of the southwestern Nortli Cascades, Washington, modified after Misch (1966, inset A), and Ziegler (1985, inset B). PDY = PreDevonian Yellow Aster Group, UPC = Paleozoic Chilliwack Group, = Jurrassic Nooksack Group, Pkbs = PreCretaceous Baker Lake blueschist, STF = Shuksan Thrust Fault, DPf = Deer Peaks fault, CMTF = Church Mountain Thrust Fault. IZ = Imbricate Zone. formed at the early stages of spreading in a back arc basin. Metamorphic mineral assemblages indicate tiiat the Deer Peaks unit was metamorphosed in a

high-P/low-T environment at the same temperature as lower temperature rocks of

the Shuksan Metamorphic Suite. Pretectonic epidote may indicate either an

early pretectonic sea-floor metamorphism or contact metamorphism in the

vicinity of diabase dikes.

Poor exposure and variable development hinder interpretation of

structures in the Deer Peaks unit. Apparently northeast-southwest trending F 2 folds have been folded about a South-southwest trending F synformal axis. The 3 regional significance of L stretching lineations in the Deer Peaks unit is 1 presently unclear.

Correlation of the Deer Peaks unit with other units of the North Cascades

is difficult. Metamorphism of the Deer Peaks unit is similar to, though of

higher temperature than, that of the Haystack Mountain unit of Cruver (1981).

Protolith material of the Haystack Mountain unit consists of abundant pillow

basalts and metasediments, neitner of v^ich are common in the Deer Peaks unit.

The separation of the Deer Peaks unit and the Haystack Mountain unit on the Ti-

Zr-Y diagram(Figure 30) argues against correlation of these two units. Relict

textures are canmon in the Deer Peaks unit and exceedingly rare in the Shuksan

Metamorphic Suite v^ich also has a more ccmple>< textural history than the Deer

Peak unit. Street-Martin (1981), and Dungan et al. (1983) presented geochemical

evidence that the protolith of the ShuJ^san Greenschist is MOPvB. Protolith

materials in the Deer Peaks unit are similar to those described in the

Giilliwack Group by Blackwell (1983) , in the Locanis Mountain area, and both

units plot in the same area on the Ti-Zr-Y diagram (Figure 30). However,

regional metanx)rphism of the Chilliwack Group produced calcium carbonate + Fe-

oxide instead of arnphibole (Brovvn et al., 1981) and actinolite is abundant in

tile Deer Peaks unit, though this difference may be caused by higher metamorphic

71 temperature in tlie Deer PeaJcs area. It is presently not clear witli which, if any, of the otlier units in the North Cascades the Deer Peaks unit is correlative though similarities to the Chilliwack Group can not be discounted.

Rocks of the Eocene Chuckanut Formation nonconformably overlie those of the Shuksan Metamorphic Suite and Deer Peaks unit witliin the study area, but also occur jujitaposed with metamorphic rocks by high angle faults. The

Chuckanut Formation has been folded into northwest trending open folds in most of the area.

The Chuckanut formation is intruded by quartz-diorite of the Granite Lake and Higgins Creek stocks, and unconformably overlain by the Oso volcanic rocks.

K/Ar hornblende ages range from 31 6 to 53 8 Ma for the Granite Lake stock

(Bechtel Report, 1979; Tabor, personnel communication, 1986). A fission-track zircon age of 43.2 jh 1.9 Ma was obtained fron the Oso volcanic rocks (Vance, oral communication in Cruver, 1981). The Oso volcanic rocks range in conposition fron rhyolite to basalt. It is possible that the intrusive diorite and the Oso volcanic rocks are comagmatic, but geochemistry is required to verify this hypotliesis. Both the intrusive rocks and the Oso volcanic rocks are confined to a northwest trending area between two high angle faults (Plate-

I).

Two northwest trending high angle faults occur in the study area. Both cut rocks of the Chuckanut Formation indicating tiiat they were active later than the mid-Eocene. The Segelson Lake shear zone juxtaposes rocks of the

Shuksan Metamorphic Suite with the Chuckanut Formation, and dies out to the northwest in Chute Creek as a series of shear zones within the ShuJisan Suite.

The Higgins Mountain-Day Lake fault is expressed as a topographic lineament along Higgins Mountain v^ere it cuts the Chuckanut Formation. Sinistral strike slip motion along the Higgins Mountain-Day Lake fault is demonstrated by drag of the S surface in tlie Deer Peaks unit into the fault zone, and stretching 1

72 lineations in phylIonite in the fault zone.

73 REFEREL'JCSS CITED

Armstrong, R. L., 19^ ., CGCclironology of the Shuksan ^fetaITlorphic Suite, North

Cascades, vvashington: Geological 3(x:iety of America, Abstracts with

Programs, v. 12, p.94.

Armstrong, R. L., Karakal, J. E., Sro n, E. H., Bernardi, M. L., and Rady, P.

M., 1983, Late Paleozoic high-pressure metamorphic rocks in nortliwestern

Washington and southwestern British Columbia: The Vedder Complex:

Geological Society of America Bulletin, v. 94, p. 451-458.

Bechtel Report, 1979, Report of Geologic investigations in 1978-79: Skagit

Nuclear Power project for Puget Sound Power and Light Company, Seattle,

Washington, v. 1 & 2.

Bernardi, M. L., 1977, Petrology of the Crystalline Rocks of Vedder Mountain,

British Columbia[M. S. Thesis]:Bellingham, Western Washington University,

13 7p.

Blackwell, David L., 1983, Geology of the Park Butte-Loomis Mountain Area,

Washington (Eastern Margin of the Twin Sisters Dunite)[M. S. Thesis]:

Bellinghara, Western Washitigton University, 253p.

Brown, S. H., 1974, Comparison of the mineralogy and phase relations of

blueschists from the North Cascades, Washington, and greenschists from

Otago, New Zealand: Geological Society of America Bulletin, v. 85, p. 333-

344. Brown, E. H., Bemardi, M. L., Christenson, B. W., Cruver, J. R., Haugerud, R.

A., Rady, P. M., and Sondergaard, J. N., 1981, Metamorphic facies and

tectonics in part of the Cascade Range and Puget Lowland of northv/estem

Washington: Geological Society of America Bulletin, Part 1, v. 92, p. 170-

178.

Brown E. H., and O'Neil, J. R., 1982, Oxygen isotope geothermometry and

stability of lawsonite and pumpellyite in the Shuksan Suite, North

Cascades, Washington: Contributions to Mineralogy and Petrology, v. 80, p.

240-244.

Brovm, E. H., Wilson, D. L., Armstrong, Richard Lee, and Harakal, J. E., 1982,

Petrologic, structural, and age relations of serpentinite, amphibolite,

and blueschist in the Shuksan Suite of the Iron Mountain-Gee Point area.

North Cascades, Washingi:on: Geological Society of America Bulletin, v. 93,

p. 1087-1098

Brovvn, E. H., 1983, Field guide to the Shuksan Metamorphic Suite: Penrose

Conference on Blueschist and Related Eclogites, Geological Society of

America, Department of Geology, Western Washington University, Bellingham,

29p.

Brown, E. H., 1986, Geology of the Shuksan Suite, North Cascades, Washington,

U. S. A.: Geological Society of America Memoir, in press.

Chayes, F., 1969, The Chemical Conposition of Cenozoic Andesite, in.

Proceedings of the Andesite Conference: Oregon Department of Geology and

Mining Industry Bulletin, v. 65, p. 1-11.

Crawford, W. A., and Hoersch, A. L., 1972, Calcite-Aragonite equilibrium from o o 50 C to 150 C: American Mineralogist, v. 57, p. 440-471.

75 Cruver, S. K., 1981, The geology and Mineralogy of Bentonites and associated

rocks of the Chuckanut Formation, Mt. Higgins area. North Cascades,

Washington [M. S. Thesis]: Bellingham, Western Washington University,

10 5p.

Cruver, J. R., 1983, Petrology and geochemistry of the Haystack Mountain unit,

lower Skagit Valley, Washington [M. S. Thesis]: Bellingham, Western

Washington University, 149p.

Danner, W. R., 1957, Stratigraphic reconnaissance in the Northwestern Cascades

and San Juan Islands of Washington[Ph. D. thesis]: Seattle, University of

Washington, 562 p.

Dungan, M. A., Vance, J. A., and Blanchard, D. P., 1983, Geochemistry of the

Shuksan greenschists and Blueschists, North Cascades, Washington: Variably

fractionated and altered metabasalts of oceanic affinity: Contributions to

Mineralogy and Petrology, v. 82, p. 131-146.

Frasse, F. I., 1981, Geology and structure of the western and southern margins

of the Twin Sisters Mountains, North Cascades, Washington[ M.S.

Tnesis]: Western Washington University, Bellingham, 87p.

Frey, F. A., Dickey, J. J., Thampson, G., Bryan, W. B., and Davies, H. L.,

1980, Evidence for heterogeneous primary MORB and Mantle sources,

nort^R^?est Indian Ocean: Contributions to Mineralogy and Petrology, v. 74,

p. 387-402.

Gill, J. B., 1970, Geochemistry of Viti Levu, Fiji, and its evolution as an

island arc: Contributions to Mineralogy and Petrology, v. 27, p. 179-203.

76 Haugerud, R. A., 1980, The Shuksan Metaitiorphic Suite and Shuksan Thrust, Mt.

Watson area. North Cascades, Washington[M. S. Thesis]: Bellingham, Western

Washington University, 125p.

Haugerud, R.A., Morrison, M.L., and Brown, E. H., 1981, Structural and

metamorphic history of the Shuksan Metamorphic Suite in the Mount Watson

and Gee Point areas. North Cascades, V7ashington: Geological Society of

America Bulletin, v. 92, p. 374-383

Hawkins, J. W., and Melchior, J. T., 1985, Petrology of Mariana Trough and Lau

Basin Basalts: Journal of Geophysical Reasearch, v. 90, p. 11431-11468.

Holland, T. J. B., 1979, Reversed hydrothermal determination of jadeite-

diopside activities: EOS, Transactions of the American Geophysical Union,

V. 60, p.405.

Holland, T. J. B., 1983, Experimental determination of activities in Disordered

and Short-Range ordered Jadeite-Pyroxenes: Contrihrutions to Mineralogy

and Petrology, v. 82, P. 214-220.

Irvine, T. N., and Baragar, W. R. A., 1971, A guide to the chemical

classification of common volcanic rocks: Canadian Journal of Earth

Science, v. 8, p. 523-548.

Jensen, L. S., 1976, A new cation plot for classifying subalkalic volcanic

rocks, in Miscellaneous paper 66: Ontario Division of Mines and Ministry

of Natural Resources, p. 22.

Johannes, W., and Puhan, D., 1971, The calcite-aragonite transition re­

investigated: Contributions to Mineralogy and Petrology, v. 31, p. 28-38.

77 Johnson, S. Y-, 1982, Stratigraphy, aedimentology and tectonic setting of the

Eocene Chuckanut Fonnation, northwest Washington [Ph.D. Dissertation]:

University of Washington, Seattle, 191p.

Jones, R. W. ,1959, Geology of tlie Finney Peak Area, Northern Cascades,

Washington[Ph. D. Thesis]:Seattle, University of Washington, 185p.

Kay, S. M., and Kay, R. W., 1985, Aleutian tholeiitic and calc-alkaline magma

series I: The mafic phenocrysts: Contributions to Mineralogy and

Petrology, v. 90, p. 276-290.

Leiggi, P. A., 1983, Structure and Petrology along a segment of the Shuksan

Thrust Fault, Mount Shuksan area, Washington[M. S. Thesis]: Bellingham,

l-festern Washington University, in progress.

LeMaitre, 1976, The chemical variability of some common ingeous rocks: Journal

of Petrology, v. 17, p. 589-637.

le Roex, A. P., Erlank, A. J., and Needham, H. D., 1981, Geochemical and

mineralogical evidence for the occurrence of at least three distinct magma

types in the FAi^DUS region: Contributions to Mineralogy and Petrology, v.

77, p. 24-38.

Liou, J. G., 1971, P-T stability fields of alumontite, wairakite, lawsonite and

related minerals in the system CaAl Si 0 -SiO -H 0: Journal of Petrology, 2 2 8 2 2 V. 12, p. 379-411.

Liszack, J.L., 1982, The Chilliwack Group on Black Mountain, Washington[M.S.

thesis]: Bellingham, Western Washington University, 104 p.

78 Mattinson, J. M., 1972, Ages of Zircons from tlie Nortliern Cascade

Mountains, Washington: Geological Society of America Bulletin, v. 83, p

3769-3784

Misch, P., 1959, Sodic amphiboles and metamorphic facies in Mount Shuksan belt.

North Cascades, Washington: Geological Society of America Bulletin, v.70,

p.1736-1737.

, 1966, Tectonic Evolution of the Northern Cascades of Washington

State-A west-Cordilleran case history: Canadian Institute of Mining and

Nfetallurgy Special Volume 8, p. 101-148.

, 1976, Remarks on the geology of the Northern Cascades:

University of British Columbia, Department of Geological Sciences, Report

number 17, 7p.

, 1977, Bedrock geology of the North Cascades, in Brown, E. H.,

and Ellis, R. C., Geological excursions in the Pacific Northwest:

Geological Society of America Annual Meeting Guidebook, Bellingham,

Western Washington University, p. 1-62

Miyashiro, A., 1974, Volcanic Rock Series in Island lures and Active Continental

Margins: American Journal of Science, v. 274, p. 321-355.

Monger, J. V7. H., 1966, The Stratigraphy and Structure of the type-area of the

diilliwack Group, southwestern British Columbia[Ph. D. thesis]: Vancouver,

University of British Columbia, 173p.

Morrison, M. L., 1977, Structure and Stratigraphy of the Shuksan Metamorphic

Suite in the Gee Point-Finney Peak Area: North Cascades[M. S.

Tnesis]:3ellingham. Western Washington University, 69p.

79 Nakajima, T-, Banno, S., and Suzuki,T., 1977, Reactions leading to the

Disappearance of Pumpellyite in low—grade [■tetamorphic Rocks of the

Sanbagawa Metainorphic Belt in Central ShiJcoku, Japan: Journal of

Petrology, v. 18, p. 263-284.

Nevrtion, R.C., and Smith, J.V., 1967, Investigatioiis concerning the breakdown of

Albite at Depth: Journal of Geology, v. 75, p. 268-286.

Nitsch, K. H., 1971, Stabilitatsbeziehungen von prehnit- und pumpellithaltigen

paragenesen: Contributions to Mineralogy and Petrology, v. 30, p. 240-260.

Pearce, J. A., and Cann,J. R., 1973, Tectonic setting of basic volcanic rocks

determined using trace element analyses: Earth and Planetary Science

Letters, v. 19, p. 290-300.

Rady, P. M., 1981, Structure and petrology of the Groat Mountain area. North

Cascades, Washington[ M. S. Thesis]: Western Washington University,

Bellingham, 133p.

Reiswig, K. N., 1982, Palynological differences between tiie Chuckanut and

Huntingdon Formations, northivestem Washington[M. S. Thesis]: Bellingham,

Western Washington University, 6Ip.

Robertson, C. A., 1981, Petrology, sedimentology, and Structure of the

Chuckanut Formation, Coal i4ountain, Skagit County, Washington[ M. S.

Thesis]: University of Washington, Seattle, 4Ip.

Robie, R. A., Hemingway, 3. S., and Fisher, J. R., 1978, Thermodynamic

Properties of Minerals and Related Substances at 298.15 K and 1 Bar (105

Pascals) Pressure and at Higher Temperatures: Geological Survey Bulletin

1452, 456 p.

80 Saunders, A. D., and Tamey, J., 1979, The Geochemistry of basalts fran a back-

arc spreading centre in the East Scotia Sea: Geochimica et Cosmochimica

Acta, p. 555-572.

Shaw, D. M., 1980, Development of the early continental crust part III,

Depletion of incompatible elements in tlie mantle: PreCambrian Research,

no. 10, p.281-299.

Silverberg, D. S., 1985, Structure and Petrology of the Whitechuck Mountain-

Mount Pugh area. North Cascade Range, Washington, Washington[M. S.

Thesis]: Bellingham, Western Washington University, 173p.

Simpson, C., and Schmid, S. M., 1983, An evaluation of criteria to deduce the

sense of movement in sheared rocks: Geological Society of America

Bulletin, v. 94, p. 1281-1288

Sondergaard, J. N., 1979, Stratigraphy and Petrolog of the Nooksack Group in

the Glacier Creek—Skyline Divide Area, North Cascades, Washington[M. S.

Thesis]: Bellingham, Vfestern Washington University, 103 p.

Street-Martin, L. V., 1981, The Chemical Composition of the Shuksan Metarrtorphic

Suite in the Gee Point-Finney Peak area. North Cascades, VJashington[M. S.

Thesis]: Bellingham, Western Washington University, 76p.

Sun, S. S., Nesbitt, R. W., and Sharaskin, A. Y., 1979, Geochemical

characterstics of mid-ocean ridge basalts: Earth and Planetary Science

Letters, v. 44, p.119-138,

Taylor, S. A., Capp, A. C., Graham, A. L., 1969, Trace Element Abundances in

Andesites, II. Saipan, Bougainville and Fiji: Contributions to Mineralogy

and Petrology, v.23, p. 1-26.

81 Vance, J. A., 1957, The geology of the Sauk River area in the northern Cascades

of Washington[Ph. D. Dissertation]: University of Washington, Seattle,

313p.

Vance, J. A., Dungan, M. A., Blcinchard, D. P., and Rhodes, J. M., 1980,

Tectonic setting and trace element geochemistry of Mesozoic ophiolitic

rocks in v/estem Western Washington: American Journal of Science, v. 280~

A, p. 359-388.

Ifeaver, S. D., Saunders, A. D., Pankhurst, R. J., and Tarney, J., 1979, A

geocheraical study of magmatism associated with tlie initial stages of back-

arc spreading: Contributions to Mineralogy and Petrology, v. 68, p. 151-

169.

Whetten, J. T., Zartmann, R. E., Blakely, R. J., and Jones, D. L., 1980,

Allochthonous Jurassic ophiolite in nortliwest Washington: Geological

Society of America Bulletin, v. 91, p. 359-368.

Ziegler, C., 1985, Geology of the Swift Creek area. North Cascades,

Washington[M. S. Thesis]: Bellingham, Western VJashington University,

82 APPEMDIX-I

Compilation of thin section petrography of the metamorphic rocks

Key to abbreviations:

Rock type: Unit : c = chert DPu = Deer Peak unit bs = blueschist FS = Ferruginous Schist d = dacite FZ = Fault zone fg = ferro-gabbro KDP = Darrington Phyllite fs = ferruginous schist KG = Shuksan Greenschist gs = greenschist Vc = Vedder Complex p = phylIonite ph = phyllite pt = pyroxene tuff

83 Sample # 109-1 109-2 109-5A 109-5B 109-7 109-8B 109-8C

Quartz X X X X X X

Albite X X X X X

Plagioclase X

Epidote X X X X X

Pumpellyite

Chlorite X X X X X X X

White Mica X X X X X X

Stilpncmelane

Actinolite X X X

Hornblende

Na-amphibole X

C1inopyroxene

Garnet X

Carbonate X X

Graphite X X X

Sphene X X X X

Fe-oxide X X X X X

Opaque X X X

Lithic fragment

Rock name gs gs ph ph ph gs gs

Unit KG KG KDP KDP KDP KG KG

84 SaTiple # 109-9 109-12B1O 109-13 109-14B 109-15B

Quartz X X X X X

Albite X X X X X

Plagioclase X

Epidote X X X X X

Pumpellyite X

Chlorite X X X X

White mica X X X

Stilpnomelane X X

Actinolite X X X

Hornblende

Na-amphibole X

C1inopyroxene

Garnet X

Carbonate

Graphite

Sphene X X

Fe-oxide X X

Opaque X X

Lithic fragment

Other

fs Rock name gs gs fs gs

Unit KG KG FS KG FS

85 Sample # 109-17A 109-17B 109-18 109-18A 109-19

Quartz X X X X X

Albite X X X

Plagioclase

Epidote X X X X X

Pumpellyite

Chlorite X X X

White mica X X

Stilpnomelane X X

Actinolite X X X

Hornblende

Na-aitphibole X

Clinopyroxene

Garnet X X

Carbonate X

Graphite

Sphene X X

Fe-oxide X X

Opaque

Lithic fragment

Other

Rock name gs gs fs gs gs

Unit KG KG FS KG KG

86 Sample # 109-20 109-21A 109-28 109-32 109-3

Quartz X X X X

Albite X X X

Plagioclase

Epidote X X X

Pumpellyite

Chlorite X X X

White mica X X X X

Stilpnomelane X X

Actinolite X

Hornblende

Na-amphibole X X

C1inopyroxene

Garnet X X X

Carbonate X X

Graphite

Sphene X X

Fe-oxide X

Opaque X X

Lithic fragment

Other(Lawsonite) X X

Rock name bs dp fs dp fs

Unit KG KDP FS KDP FS

87

I Sample # 109-34E 109-35 109-38 109-53 109-59

Quartz X X X

Albite X X X X

Plagioclase

Epidote X X X

Pumpellyite

Chlorite X X X X

White mica X X X

Stilpnomelane X X

Actinolite X X X

Hornblende

Na-amphibole X X

Clinopyroxene

Garnet X

Carbonate X

Graphite X X

Sphene X X X

Fe-oxide X X

C^que X

Lithic fragment

Other (Cymrite) (Lawsonite)

Rock name gs gs fs ph gs

Unit KG KG FS KDP KG

88 Sample # 109-62 109-71 109-75 109-99 109-136 109-137

Quartz X X X X X X

Albite X X X

Plagioclase X X X

Epidote X X X X X

Pumpellyite X X

Chlorite X X X X X

White mica

Stilpnomelane X X

Actinolite X X X X X

Hornblende

Na-amphibole

C1inopyroxene

Garnet

Carbonate X

Graphite

Sphene X X X

Fe-oxide X X X

Opacjue X X

Lithic fragment

Other X

Rock name gs ph gs gs gs gs

Unit KG KDP KG KG KG KG

89 Sample # 109-138 109-138 109-139 109-140 109-147

Quartz X X X X

Albite X X

Plagioclase X

Epidote X

Pumpellyite

Chlorite X X X X

Vtiite mica X X X

Stilpnomelane

Actinolite X X X

Hornblende

Na-amphibole

C1inopyroxene

Garnet

Carbonate

Graphite X X X

Sphene X X

Fe-oxide X X

Opaque X

Lithic fragment

Other

Rock name ph gs fs ph ph

Unit KDP KG FS KDP KDP

90 Sample # 109-148 109-184 109-186(2660) 109-185 109-187

Quartz X X X

Albite X X X X

Plagioclase

Epidote X X X

Pumpellyite

Qilorite X X X X

White mica X X X X

Stilpnomelane

Actinolite X X

Hornblende

Na-amphibole

C1inopyroxene

Garnet

Carbonate

Graphite X X X

Sphene X X

Fe-oxide X X

Opaque X

Lithic fragment

Other

Rock name fs ph ph gs ph

Unit FS KDP KDP KG KDP

91 Sample # lOSI-9A 109-17C 109-21 109-153 109-153A

Quartz X X X X

Albite X X

Plagicxlase

Epidote X X X

Pumpellyite

Qilorite X X X

White mica X X X X

Stilpnomelane X

Actinolite X X X

Hornblende

Na-amphibole X X

C1inopyroxene

Garnet X X

Carbonate X

Graphite X

Sphene X

Fe-oxide X X X

Opaque X

Lithic fragment

Other

Rock name gs fs bs c P

Unit KG FS KG FZ FZ

92 Sample # 109-;L54 109-155 109-156 109-157 109-160

Quartz X X X X X

Albite X X

Plagioclase X X X

Epidote X X X X

Purnpellyite

Chlorite X X X X

White mica X X X X

Stilpnomelane X

Actinolite X X X X

Hornblende X X

Na-amphibole

Clinopyroxene

Garnet

Carbonate X

Graphite X

Sphene X X X

Fe-oxide X X X

Opaque

Lithic fragment

Other(Barroisite) X X

Rock name VC VC P VC p

Unit FZ FZ FZ FZ FZ

93 Sample # 109-3 109-24 109-24' 109-29 109-29b 109-30

Quartz X X X X X X

Albite X X X X

Plagioclase X X X X

Epidote X X X X

Pumpellyite X X X X

Chlorite X X X X X X

V'Jhite mica

Stilpnonelane

Actinolite X X X

Hornblende

Na-amphibole

C1inopyroxene X

Garnet

Carbonate X X X

Graphite

Sphene X

Fe-oxide

Opaque

Lithic fragment

Other

Rock name pt d d d d pt

Unit DPu DPu DPu DPu DPu DPu

94 Sample # 109-23B 109-30' 109-31 109-40 109-41 109-42

Quartz X X X X X X

Albite X X X

Plagioclase X X X X

Epidote X X X X X

Punpellyite X X X

Chlorite X X X X X

White mica X

Stilpnomelane X X

Actinolite X X X X

Hornblende

Na-amphibole

C1inopyroxene X X

Garnet

Carbonate X X

Graphite

Sphene

Fe-oxide X X

Opaque X X X

Lithic fragment

Other

Rock name d d d d pt pt

Unit DPu DPu DPu DPu DPu DPu

95 Sample # 109-79abv 109-80 109-80* 109-81 109-81'' 109-82

Quartz X X X X X X

Albite X X X

Plagioclase X

Epidote X X X X X X

Pumpellyite X X X

Chlorite X X X

I'lhite mica X X

Stilpnonelane X X X X

Actinolite X X X X X X

Hornblende X

Na-amphibole

Clinopyroxene X X

Garnet

Carbonate X

Graphite

Sphene X

Fe-oxide X X X

Opaque

Lithic fragment

Other

Rock name d d d Pt vs pt

Unit DPu DPu DPu DPu DPu DPu

96 Sample # 109-82' 109-83* 109-84 109-84* 109-85 109-87

Quartz X X X X X X

Albite X X X X X

Plagioclase X

Epidote X X X X X X

PLimpellyite X

Chlorite X X X X X

White mica X X X

Stilpnomelane X X

Actinolite X X X X X X

Hornblerde

Na-amphibole

Clinopyroxene X X X X

Garnet

Carbonate X X

Graphite

Sphene

Fe-oxide X XXX

Opaque X

Lithic fragment

Other

Rock name Pt pt pt pt pt pt

Unit DPu DPu DPu DPu DPu DPu

97 Sample # 109-■79blo 109-90 109-91 109-93 109-94 109-96 109-100

Quartz X X X X X X X

Albite X X X X

Plagicxilase X X X X

Epidote X X X X X X

Pumpellyite X X

Chlorite X X X X X

White mica X X

Stilpnomelane X

Actinolite X X X X X X X

Hornblende

Na-amphibole

C1inopyroxene X

Garnet

Carbonate X X

Graphite

Sphene X

Fe-oxide X X X X

Opaque X

Litiiic fragment

Other

Rock name Pt d pt pt pt d d

Unit DPu DPu DPu DPu DPu DPu DPu

98 Sample # 109-121 109-122 '-123 109-124 109-125 109-126blo

Quartz X X X X X X

Albite X

Plagioclase X X X X

Epidote X X X X X X

Pumpellyite X X X X X

Chlorite X X X X X

White mica X X X

S t i Ipncsne lane

Actinolite X X X X

Hornblende

Na-amphibole

Clinopyroxene X X X X X

Garnet

Carbonate X X X

Graphite

Sphene X X

Fe-oxide X

Opaque X X X

Lithic fragment

Other

Rock name af Pt pt pt fg fg

Unit DPu DPu DPu DPu DPu DP

99 Sample # 109-126 109-127 109-128 109-130abv 109- 130'bio

Quartz X X X X X

Albite

Plagioclase X X X X X

Epidote X X

Pumpellyite X X X X X

Chlorite X X X X

White mica

StilpnoTielane

Actinolite X

Hornblende

Na-amphibole

C1inopyroxene X X X

Garnet

Carbonate

Graphite

Sphene X

Fe-oxide

Opaque X

Lithic fragment

Other

Rock name fg fg fg d d

Unit DPu DPu DPu DPu DPu

100 Sample # 109--130'in 109-131 109-131* 109-132 109-133 109-134

Quartz X X X X X X

Albite X X

Plagioclase X X X X X

Epidote X X X X

Pumpellyite X X X X X

Chlorite X X X X

White mica X X

Stilpnomelcine X X X

Actinolite X X X X X

Hornblende

Na-amphibole

Clinopyroxene X X X X

Garnet

Carbonate X

Graphite

Sphene X X

Fe-oxide X X

Opaque X X X

Lithic fragment

Other xl

Rock name d fg pt fg fg b

Unit DPu DPu DPu DPu DPu DPu

101 Sample # 109-135 109-135a 109-141 109-142 109-143 109-145

Quartz X X X X X

Albite X X

Plagioclase X X

Epidote X X X X X X

Pumpellyite X X X X X

Chlorite X X X X X

White mica

Stilpnomelane

Actinolite X X X X X

Hornblende

Na-amphibole

C1inopyroxene X X X X

Garnet

Carbonate X X X

Graphite

Sphene X X

Fe-oxide X

Opaque

Lithic fragment

Other

Rock name c pt d pt pt pt

Unit DPu DPu DPu DPu DPu DPu

102 Sample # 109-161 109-174 109-250 109-444 109-448 109-450

Quartz X X X X X X

Albite X X X X X X

Plagioclase X X X

Epidote X X X X X

Puinpellyite X X

Oilorite X X X X X

White mica X X

Stilpnomelane

Actinolite X X X X

Hornblende

Na-amphibole

C1inopyroxene X

Garnet

Carbonate X X X X

Graphite * Sphene

Fe-oxide X X X

Opaque X X X X

Lithic fragment

Other

Rock name pt pt pt pt d pt

Unit DPu DPu DPu DPu DPu DPu

103 Sample # 109-451 109-465 109-466 109-467 109-468 109-471

Quartz X X X X X X

Albite X X X X X X

Plagioclase X X X X

Epidote X X X X X X

Pumpellyite X X X X X

Chlorite X X X X X X

V^hite mica X X

Stilpnomelane

Actinolite X X X X

Hornblende X

Na-amphibole

C1inopyroxene X X X X X

Garnet

Carbonate

Graphite

Sphene

Fe-oxide

Opaque X X X X

Lithic fragment

Other

Rock name pt d pt fg fg fg

Unit DPu DPu DPu DPu DPu DPu

104 Sample # 109-473 109-474 109-477tdp 109-478 109-479 109-502

Quartz X X X X X X

Albite X X X X

Plagioclase X X

Epidote X X X X X

Pumpellyite X X X

Oilorite X X X X X X

White mica X X

Stilpnomelane

Actinolite X X X X X

Hornblende

Na-artphibole

Clinopyroxene X X X X

Garnet

Carbonate X

Graphite

Sphene X X X X

Fe-oxide X X X

Opaque X X X X

Litliic fragment

Other

Rock name Pt pt fg fg fg d

Unit DPu DPu DPu DPu DPu DPu

105 Sample # 109-535 109-536

Quartz X X

Albite X X

Plagioclase

Epidote X X

Pumpellyite X

Gilorite X X

I'Jhite mica X

Stilpnomelane X X

Actinolite X X

Hornblende

Na-amphibole

C1inopyroxene

Garnet

Carbonate X

Graphite

Sphene X

Fe-oxide

Opaque X

Lithic fragment

Other

Rock name d d

Unit DPu DPu