Bedrock Geology and Geochemical Analysis of the Bowdoinham 7.5' Quadrangle, Southwestern Maine

Bedrock Geology and Geochemical Analysis of the Bowdoinham 7.5’ Quadrangle, southwestern Maine

Joel Frank Cubley

Submitted in Partial Fulfillment of the Requirements for the Degree of Bachelor of Arts Department of Geology Middlebury College Middlebury, Vermont

April 2005

Bedrock Geology and Geochemical Analysis of the Bowdoinham 7.5’ Quadrangle, southwestern Maine

Joel Cubley, Department of Geology Middlebury College, Middlebury, Vermont 05753

The Bowdoinham 7.5’ quadrangle, located in southwestern Maine, is situated along the boundary between the regionally extensive Liberty-Orrington and central Maine lithotectonic belts. Detailed 1:24,000 scale bedrock mapping in the northern half of the quadrangle has resulted in the delineation of the following lithologic units (described from west to east): (1) interlayered biotite granofels and calc-silicate gneisses of the Silurian-Devonian Vassalboro Formation (central Maine sequence), (2) a previously unrecognized, deformed and recrystallized Devonian metagranitoid pluton hereby named the Hornbeam Hill Intrusive Suite, (3) migmatitic biotite gneisses and other subordinate lithologies (e.g. amphibolites, rusty schists) associated with the Ordovician Falmouth-Brunswick sequence (Liberty-Orrington belt), and (4) several small but mappable granitic pegmatite bodies of both Devonian and Permian age. The Hornbeam Hill Intrusive Suite is significant because it stitches the contact between the Vassalboro Formation and Falmouth-Brunswick sequence rocks. Thin dikes and sills of Mesozoic diabase are found in the study area, but cannot be mapped at this scale. Stratified rocks in the quadrangle have been penetratively deformed, folded, and metamorphosed to upper amphibolite conditions during the Acadian orogeny. A pervasive east-dipping foliation (generally <45º) can be found in rocks of both lithotectonic belts, as well as the Hornbeam Hill Intrusive Suite, implying that the dominant episode of deformation in this region occurred after the emplacement of that pluton. This foliation is axial planar to inclined isoclinal folding in the field area. A reconnaissance geochemical study of amphibolites from the Falmouth- Brunswick sequence shows subalkaline, tholeiitic basalt compositions with slight LREE enrichment. Tectonic diagrams show a mixture of MORB and IAT signatures suggestive of a back-arc basin environment. The geochemical characteristics of the Falmouth- Brunswick sequence amphibolites are similar to previously published geochemical studies from rocks of the Spring Point Formation of the Casco Bay Group (exposed in other parts of the Liberty-Orrington belt) and rocks of the Bathurst Supergroup in the Miramichi Highlands of New Brunswick. The Hornbeam Hill pluton is characterized by significant petrographic and geochemical variability, ranging from coarse-grained granitic gneisses to syeno-dioritic gneisses (SiO2 ranges from 54 to 72%). New U-Pb zircon (SHRIMP) dates from the intrusion yield an average metamorphic recrystallization age of 390 ± 3 Ma, and igneous crystallization appears not to be significantly older, with core ages falling within analytical uncertainty of rim ages. This age is important for two reasons: (1) it implies that no significant movement occurred along the boundary between the central Maine and Liberty-Orrington lithotectonic belts in this region subsequent to ~390 Ma, and (2) the deformational event responsible for the pervasive foliation and associated folding in the field area must be younger than ~390 Ma.

i Acknowledgements

This project was funded by support given to Dave West by the Maine Geological Survey (through the StateMap program). Additional funds were provided by the National Science Foundation (Grant# EAR-0207263).

First and foremost, I would like to thank Dave West for giving me the opportunity to battle the mosquitoes and humidity of southwestern Maine and from it derive this entire project. Without his continued guidance and support this thesis would have never come to fruition.

I would also like to express my deepest gratitude to Ray Coish for patiently answering my unending geochemical questions day in and day out, and helping me sift through the piles of diagrams to find the strongest argument possible.

The hospitality of Art Hussey in welcoming Dave and me into his home during the field season was extremely generous, and his continued input on the local geology was a valuable asset. The advice and constructive criticism of Spike Berry at the Maine Geological Survey was also critical in the development of this project.

The rest of the geology department faculty at Middlebury, including Jeff Munroe, Pete Ryan, Patricia Manley, and Tom Manley were extremely supportive throughout the year, and all lent valuable insights at different points during the evolution of this thesis project. I would also like to thank Bill Hegman and Lee Perlow in the geography department for their continued assistance with the GIS analyses and displays presented within.

Many thanks must be extended to Gianina Farrugia, Levi Doria, Katharine North, and Trevor Cloak for their camaraderie during those late nights on the geology wing, and their humorous fatalism each and every morning. It has been a great pleasure to work with each and every one of them this year.

I would like to also acknowledge the efforts of Colin Kikuchi, Brendan Condit, Nick Benjamin, John Hanley, Chris Farina, Charlie Bettigole, Mike Hennessy, Dan Stone, and Max Jones in forcing me to disregard the joys of glacial striations every once in a while, and teaching me what it really means to be a Prankster 4 Life.

I must express my deepest gratitude to my mother, Cindy Cubley, for her love and support of all my endeavors, past, present, and future.

Finally, I would like to thank Lauren Armstrong for being the fabric of this entire year. Without her constant encouragement, unending patience, and selfless love this thesis, and my entire senior year, would have been a much less gratifying experience.

To Dad

So was I once myself a swinger of birches; And so I dream of going back to be. It's when I'm weary of considerations, And life is too much like a pathless wood Where your face burns and tickles with the cobwebs Broken across it, and one eye is weeping From a twig's having lashed across it open. I'd like to get away from earth awhile And then come back to it and begin over. May no fate willfully misunderstand me And half grant what I wish and snatch me away Not to return. Earth's the right place for love: I don't know where it's likely to go better. I'd like to go by climbing a birch tree, And climb black branches up a snow-white trunk Toward heaven, till the tree could bear no more, But dipped its top and set me down again. That would be good both going and coming back. One could do worse than be a swinger of birches.

-Robert Frost

iii Table of Contents

Abstract i Acknowledgements ii Dedication iii Table of Contents iv List of Figures vi Chapter I—Introduction 1 Chapter II—Regional Geology 4 Stratigraphy 4 Structure 19 Metamorphism 23 Geochemistry 25

Previous Work in the Bowdoinham 7.5’ Quadrangle 30 Chapter III—Methods 32 Fieldwork 32 Geochemical Analyses 34 Petrographic Analyses 36 Chapter IV—Results 37 Metamorphic Stratigraphy 37 Reconnaissance Petrography 47 Structure 59 Geochronology 62 Geochemistry 64 Chapter V—Discussion 81 Mapping 81 Metamorphism 87 Structure 87 Geochemistry 89

Chapter VI—Conclusions 98 Works Cited 101

iv Appendix I—Field Stations 107

Appendix II—Geochemical Sample Data Table 139

Appendix III—ICP Standards Data 142 Appendix IV—Falmouth-Brunswick Amphibolites ICP Data 143

Appendix V—Hornbeam Hill Intrusive Suite ICP Data 144

Appendix VI—Mineralogy of Thin Sections 145 Appendix VII—Fold Axis and Mineral Lineation Measurements 148

v List of Figures

1. Generalized Bedrock Geology of southwestern Maine 3 2. Regional Geology and Lithotectonic Terranes of New England 5 3. Southwestern Maine Lithotectonic Terranes 7 4. Liberty-Orrington Belt Structural Interpretation 9 5. Stratigraphic Cross-Section of the Bath 1:100,000 Map Sheet 10 6. Summary of Stratigraphic Nomenclature, southwestern Maine 12 7. Maine Pegmatite Bodies Map 15 8. Brunswick Pegmatite Field Map 15 9. Topsham Granite REE pattern 19 10. Metamorphic zones of Maine 24 11. Spring Point Formation REE and Spider Diagrams 26 12. Ordovician Tectonic Model for the Iapetus Ocean Basin 27 13. Bathurst Supergroup-Spring Point Formation Geochemical Comparison 29 14. Newberg (1984) map of northern Bowdoinham 7.5’ Quadrangle 30 15. Geochemisty sampling sites 33 16. Geochemistry sites within northern half of Bowdoinham 7.5’ Quadrangle 34 17. Field photograph of the Vassalboro Formation 39 18. Field photograph of the Unnamed Gneiss Member 41 19. Field photograph of Mixed Rocks Member 42 20. Field photograph of Hornbeam Hill pluton, garnet gneiss variant 44 21. Field photograph of Hornbeam Hill pluton, porphyritic feldspar variant 44 22. Field photograph of Devonian tourmaline-bearing pegmatite 45 23. Field photograph of Permian pegmatite 46 24. Field photograph of Mesozoic dike 47 25. Photomicrograph of Vassalboro Formation 49 26. Photomicrographs of Rusty-Schist and Coticule Member, Vassalboro Fm. 50 A. Sillimanite-rich gneiss 50 B. Coticule-rich gneiss 50 27. Photomicrograph of mafic hornblende gneiss, Hornbeam Hill pluton 52 28. Photomicrograph of poikilitic garnet gneiss, Hornbeam Hill pluton 53 29. Photomicrograph of alkalic granitic gneiss, Hornbeam Hill pluton 53 30. Photomicrograph of rusty schist, Unnamed Gneiss Member 54 31. Photomicrograph of homogenous Falmouth-Brunswick amphibolite 56 32. Photomicrograph of banded Falmouth-Brunswick amphibolite 57 33. Photomicrograph of titanite-rich Falmouth-Brunswick amphibolite 58 34. Equal Area Stereonet Projection—Fold Axes 59 35. Equal Area Stereonet Projection—Lineations 60 36. Equal Area Stereonet Projection—Foliations of stratified rocks 61 37. Equal Area Stereonet Projection—Foliations of Hornbeam Hill pluton 61

vi 38. Cathodoluminesence image of Hornbeam Hill zircon crystals 63 39. 206Pb/238U plot of Hornbeam Hill U/Th zircon analyses 63 40. Falmouth-Brunswick amphibolites Zr/TiO2-SiO2 diagram 64 41. Falmouth-Brunswick amphibolites AFM diagram 65 42. Falmouth-Brunswick amphibolites Zr-Ti diagram 66 43. Falmouth-Brunswick amphibolites Ti-Zr-Sr diagram 67 44. Falmouth-Brunswick amphibolites Ti-V diagram 68 45. Falmouth-Brunswick amphibolites Ta/Yb-Th/Yb diagram 69 46. Falmouth-Brunswick amphibolites REE diagram 70 47. Falmouth-Brunswick amphibolites Spider diagram 71 48. Hornbeam Hill pluton SiO2-Alkalis diagram 72 49. Hornbeam Hill pluton SiO2-ASI diagram 73 50. Hornbeam Hill pluton Harker diagrams 75 51. Hornbeam Hill pluton REE diagram 77 52. Hornbeam Hill pluton Spider diagram 78 53. Hornbeam Hill pluton Y-Nb diagram 79 54. Hornbeam Hill pluton alkali-lime index diagram 80 55. Swanson positive flower structure model 89 56. Revised Ordovician tectonic model 91 57. Regional Correlatives REE diagram 93 58. Regional Correlatives Spider diagram 94 59. Mariana Trench Correlation REE diagrams 95 A. Mariana Trench REE diagram 95 B. Falmouth-Brunswick – Mariana Trench Correlation diagram 95 60. Mariana Trench Correlation Spider diagrams 97 A. Mariana Trench Spider diagram 97 B. Falmouth-Brunswick – Mariana Trench Correlation diagram 97

vii

I. INTRODUCTION

The process of orogenesis, or mountain building, can have serious implications

for the rocks involved, including physical deformation, metamorphism, and partial

melting. While the characteristics of the original protolith are often obscured by these

processes, subtle evidence remains in the petrology, geochemistry, and stratigraphy of the

deformed and metamorphosed units. Keying in on variations in these properties,

geologists can often determine the pre-metamorphic environment in which rocks formed,

and from this information make educated inferences concerning the geologic and tectonic

history of the region. Over time, erosional processes gradually wear away post-orogenic

stratigraphy, opening up windows into the progressively deeper levels of old mountain

belts. These belts, despite overprinting by structural and metamorphic deformation, can

play a central role in establishing ancient tectonic relationships, relationships that might

otherwise be beyond determination.

The Liberty-Orrington belt of coastal Maine represents an Ordovician sequence of

allochthonous origin (Gondwanan affinity) that is juxtaposed against rocks of Laurentian

affinity. The rocks of the Falmouth-Brunswick sequence, contained within this belt, have

the potential to serve as important sources of information on the pre-metamorphic

tectonic evolution of the region. During the Silurian-Devonian Acadian Orogeny (~420-

380 Ma), rocks of Gondwanan affinity collided with North America. They remained

juxtaposed until the Mesozoic, when rifting caused Pangaea to split, leaving small peri-

Gondwanan terranes (e.g. Gander terrane), plastered against the margin of the Grenville basement terrane (Robinson et al., 1998). This massive orogenic event has obscured much of the pre-Silurian history of the region (Dorais, 2000).

This pre-Silurian history centers on the Iapetus Ocean, which was situated between the North American and Gondwanan continents. It is accepted knowledge that sediment accumulated in the Iapetus basin, and subduction produced igneous rocks within and along the margins of this complex ocean basin (West et al., 2003).

Unfortunately, much deformation and metamorphism has obscured these processes, making reconstructions difficult. A thorough geologic study of the Falmouth-Brunswick sequence would yield valuable information regarding the setting of these rocks in relation to tectonic events surrounding the ultimate destruction of the Iapetus Ocean.

It is the purpose of this study to further efforts in deciphering the pre-Silurian tectonic history of the Maine Coast, in particular the Ordovician rocks of the Falmouth-

Brunswick sequence. This will be achieved through a detailed, multi-faceted geologic investigation involving the following components: bedrock mapping, metamorphic petrography, structural analysis, and meta-igneous whole-rock geochemistry. Fieldwork was concentrated in the northern half of the Bowdoinham 7.5’ Quadrangle, located 15 km north of Brunswick in southwestern Maine (Figure 1). Extensive amphibolite facies metamorphism and regional penetrative deformation associated with the Acadian orogeny has obscured many of the obvious clues as to the nature of the original protolith for rocks in this area, but detailed fieldwork and laboratory analysis can help to overcome this impediment and allow a greater understanding of Ordovician tectonics along the

Maine Coast and in the Applachians as a whole.

Figure 1: Generalized Bedrock Map of the Casco Bay region of the Maine Coast. The Liberty-Orrington Belt, which includes the Falmouth-Brunswick sequence, is shaded in gray, while the central Maine sequence is located to the west of that belt. The Fredericton Trough is located to the east of the Liberty-Orrington belt. The location of the Bowdoinham 7.5’ Quadrangle is indicated by the black rectangle.

II. REGIONAL GEOLOGY

STRATIGRAPHY

Liberty-Orrington Belt

The non-Grenvillian, peri-Gondwanan rocks of coastal Maine have been divided into 8 distinct lithotectonic terranes separated generally by major fault and shear zones

(Berry & Osberg, 1989). The two terranes with which this study is primarily concerned are the central Maine and Liberty-Orrington belts (Figures 1 & 2). Ordovician rocks of the Liberty-Orrington belt extend nearly 170 km along strike and are flanked by younger rocks of the central Maine sequence (west) and the Fredericton belt (east). Rocks with volcanic and volcanogenic affinities characterize the Liberty-Orrington Belt along its length (Hussey, 1988; Hussey & Berry, 2002; West et al., 2003). Due to geological complexity and the wide range of researchers working along its length, stratigraphic nomenclature within the Liberty-Orrington Belt has been inconsistent and confusing (see

a discussion of this in West et al. (2003)). However, in this thesis the nomenclature of

Hussey & Berry (2002) will be followed because of the proximity of this work to the

study area.

Initial mapping of the Liberty-Orrington belt, incorporated in the 1:500,000

Geologic Map of Maine (Osberg et al., 1985), groups all the units of the Liberty-

Orrington belt into two main formations, the Cushing Formation and the Cape Elizabeth

Formation. At the time of publication of this map, the Cushing Formation was believed

to be late Precambrian-Ordovician in age (based on what are now considered to be

unreliable Rb-Sr dating methods) and stratigraphically below the Cape Elizabeth

Formation (Osberg et al., 1985). More recent dating using high precision U-Pb zircon

dating methods (Hussey et al., 1993; Tucker et al., 2001) indicate that all the stratified rocks in the Liberty-Orrington belt are Ordovician in age.

Figure 2: Regional Geology and lithotectonic terranes of New England. The central Maine sequence referred to in this paper is identified as the Merrimack Belt, and the Liberty-Orrington Belt is shown as the Casco Bay Belt of Medial New England (Robinson et al., 1998).

In an overview of the geological relationships of the Casco Bay portion of the

Liberty-Orrington belt, Hussey (1988) introduced the first major reorganization of the

Liberty-Orrington belt’s stratigraphic nomenclature (Figure 3). The members of the former Cushing Formation west of the Flying Point fault, namely the Nehumkeag Pond,

Mount Ararat, Torrey Hill, and Richmond Corner members, were divorced from the

Casco Bay Group and assigned to the Falmouth-Brunswick sequence. This subdivision was based on major lithologic differences and a contrast in metamorphic grade on opposite sides of the Flying Point fault (one of the major strands of the Norumbega fault zone). More recently, all of the above-mentioned members of the Falmouth-Brunswick sequence have been raised to the formational level (Hussey & Berry, 2002). The

Nehumkeag Pond and Mount Ararat Formations underlie the vast majority of the

Falmouth-Brunswick sequence in the southern portion of the belt.

East of the Flying Point Fault, Hussey (1988) introduced the Saco-Harpswell sequence and within it assigned the remainder of the former Cushing Formation, namely the Peaks Island, Yarmouth Island, Bethel Point, Mere Point, and Wilson Cove members, as well as the overlying formations in the Casco Bay Group (Cape Elizabeth, Spring

Point, Diamond Island, and Scarboro Formations). However, recently Hussey (in Hussey

& Berry, 2002) has abandoned the term “Saco-Harpswell Sequence” and has now assigned rocks east of the Flying Point fault to two sequences: the Casco Bay Group and the East Harpswell sequence. Because all of these rocks are east of the Norumbega fault system and the Bowdoinham 7.5’ Quadrangle is west of the Norumbega, details of these sequences will not be provided here, but the interested reader is referred to Hussey &

Berry (2002) for those details.

Figure 3: Southwestern Maine lithotectonic divisions, from Hussey (1988). Note the presence of the newly established Falmouth-Brunswick sequence west of the Flying Point Fault. The Saco-Harpswell sequence (a term that has recently been abandoned) contains the remainder of the old Cushing Formation and the Casco Bay Group. The approximate location of the Bowdoinham 7.5’ Quadrangle is shown by the black rectangle.

In a study focused on the central portion of the Liberty-Orrington belt, Tucker et al. (2001) suggest that the eastern part of the Liberty-Orrington belt is contained within

an east-verging allochthonous thrust sheet (Figure 4). This interpretation is based on

southwest-plunging isoclinal upright folds in the Bucksport Formation (Fredericton belt),

which lies structurally below the Liberty-Orrington sequence. While the Liberty-

Orrington belt consists of Ordovician rocks, the Bucksport Formation is Silurian,

establishing an older-over-younger relationship characteristic of a thrust fault. Based on its emplacement prior to 419 Ma (sealed by the Lincoln shonkonite pluton) and an eastward vergence, Tucker et al. (2001) suggest that the Liberty-Orrington thrust sheet formed in the early Silurian period coincident with the closing of the Taconian back-arc basin. While the Casco Bay Group and Cushing Formation in the eastern part of the

Liberty-Orrington belt are interpreted as being allochthonous, Tucker et al. (2001) describe the Falmouth-Brunswick sequence in the western part of the belt as being autochthonous.

Figure 4: Structural interpretation of a Rome-Camden transect across the central portion of the Liberty-Orrington belt (northeast of the present study area).The Casco Bay Group and Cushing Formation (Hussey, 1988) are indicated as the Liberty-Orrington allochthonous thrust sheet, while the Falmouth-Brunswick sequence is included under the relatively autochthonous Lake Messalonskee thrust sheet (Tucker et al., 2001).

As mentioned earlier, Hussey & Berry (2002), in an overview of the bedrock geology of the Bath 1:100,000 map area, significantly revise the stratigraphic nomenclature of this region. Of particular relevance to this study is the reassignment of two thin units (Richmond Corner and Torrey Hill Formations) formerly assigned to the western-most portion of the Falmouth-Brunswick sequence into the younger Late

Ordovician-Early Devonian central Maine sequence (Hussey & Berry, 2002). The reassignment of the Richmond Corner Formation is of particular interest because it was

originally defined by Newberg (1984) in the present study area and new mapping associated with this study (to be discussed later) sheds light on this issue.

A schematic cross section through the Bath Map Sheet (Figure 5) provides a good illustration of the general stratigraphy and possible large-scale structural relationships in the vicinity of the study area of Hussey & Berry (2002). Figure 6 presents a correlation diagram summarizing the rather confusing evolution of stratigraphic nomenclature associated with the Liberty-Orrington belt.

Figure 5: Schematic cross section from across the Bath 1:100,000 Map Sheet (this line of section is approximately 17 km south of the present study area). Cross section begins from the northwest corner of the map sheet and continues southeast to the edge of the Phippsburg synform at Phippsburg village. CM: Central Maine Sequence; FB: Falmouth- Brunswick Sequence; CB: Casco Bay Group; HC: Hutchins Corner Fm.; RC: Richmond Corner Fm.; TH: Torrey Hill Formation; MA: Mount Ararat Fm.; NP: Nehumkeag Pond Fm.; NPM: marble/schist/amphibolite unit within NP; CE: Cape Elizabeth Fm.; PI: Peaks Island member of Cushing Fm.; UCB: Upper Casco Bay Group (Spring Point, Diamond Is., Scarboro Fms.). The approximate location of the present study area is shown by the black box. Note that this location lies along the boundary between rocks of the central Maine sequence and the Falmouth-Brunswick sequence.

The Hussey & Berry (2002) report also presents several new radiometric ages for different units within the Falmouth-Brunswick sequence. The Mount Ararat Formation was dated to 458 ± 3 Ma using U-Pb TIMS dating, while the Nehumkeag Pond

Formation was assigned a U-Pb zircon (SHRIMP) age of ~460 Ma (no uncertainty is provided for this age). A U-Pb zircon age of 469 ±3 Ma on the Spring Point Formation

(Tucker et al., 2001) suggests rocks of the Casco Bay Group are Middle Ordovician in age. The combination of these age relationships supports the interpretation that the

Falmouth-Brunswick sequence is not part of the Cushing Formation, and may represent a basement to the central Maine sequence (Hussey & Berry, 2002).

berty-Orrington belt and i ngs for individual formations, s of the L ck e for the ro r bove. a hown s s in ages and overarching groupi raphic nomenclatu xamples e te change o e stratig sland I armouth Y and Corner re presents a summary of th is figu ichmond h R T the as Figure 6: westernmost portion of the central Maine belt. N such

Central Maine Sequence

While the majority of this study is concerned with rocks of the Falmouth-

Brunswick sequence and their implications for the Ordovician tectonic history of the region, it is also important to briefly discuss the central Maine sequence, as it is juxtaposed next to the Falmouth-Brunswick sequence in the western portion of the

Bowdoinham 7.5’ Quadrangle. The definitive paper on the central Maine sequence by

Osberg (1988) provides a broad overview of the stratigraphy, structure, and metamorphism within the sequence. Deposited in a broad basin, the central Maine sequence is late Ordovician- early Devonian in age, and consists of “flyschoid metamorphosed wackes” (Hussey & Berry, 2002), in addition to shales, limestones, and lenticular conglomerates (Osberg, 1988). These rocks are interpreted to be mainly turbidite deposits from flows on the edge of a continental margin, with input mainly from the west (Grenville province) during the Silurian (Moench et al., 1995) and from the east

(Avalon and Gander Zones) during the Devonian (Roy & Mencher, 1976).

Unfortunately, similar to the Liberty-Orrington belt, there exists confusion in the stratigraphic nomenclature within the central Maine sequence. In addition to the recent inclusion of the Torrey Hill and Richmond Corner Formations into the central Maine sequence (Hussey & Berry, 2002—discussed above), the oldest unit within this sequence has seen a name change. This unit, the Vassalboro Formation of Osberg (1968),

Newburg (1984), and Osberg et al. (1985) or the Hutchins Corner Formation of Osberg

(1988) and Hussey & Berry (2002) is represented by metamorphosed calcareous greywacke interlayered with thinly bedded phyllite and quartzite (Osberg, 1988; Hussey

& Berry, 2002). Because of the high metamorphic grade in the Bowdoinham 7.5’

Quadrangle, this unit is represented locally by interlayered biotite granofels and calc- silicate gneisses. Justification will be provided later, but in this thesis “Vassalboro

Formation” will be used rather than Hutchins Corner Formation.

According to Osberg (1988), the Hutchins Corner Formation is placed conformably beneath the Early Silurian Waterville Formation of the central Maine sequence and unconformably above the Nehumkeag Pond member (now Formation) of the Falmouth-Brunswick sequence (then part of Osberg’s (1985) Cushing Formation).

However, Hussey and Berry (2002) suggests these rocks (Hutchins Corner or Vassalboro

Formation) conformably overlie the Richmond Corner and Torrey Hill Formations of the central Maine sequence (see Figure 6).

Intrusive Bodies

Pegmatites

Granitic pegmatite intrusions are ubiquitous within the southern coastal Maine region and demand a closer inspection. Wise & Francis (1992), in an overview of pegmatites in Maine, divide these occurrences into two major fields (Figure 7). The present study area falls within the Brunswick field of Wise & Francis (1992), which is further subdivided into the Waldoboro, Topsham, Georgetown, and Edgecomb series, with the Topsham series located closest to this study area (Figure 8). The most diversified of any series within the Brunswick pegmatite field, the Topsham series lies in a “1.5-km long northeast-trending belt, 5-10 km north and south of the towns of Topsham and Brunswick” (Wise & Francis, 1992). Hussey & Berry (2002) extend this field to a belt extending from Brunswick northeastward through the village of Bowdoinham,

singularly restricted to the Falmouth-Brunswick sequence. Unlike the other series in the

Brunswick field, the Topsham series is located west of the Norumbega fault (Wise &

Francis, 1992).

Figure 7: Location map of the two major pegmatite fields in Maine, the Oxford and Brunswick Fields. The Topsham series of the Brunswick field lies to the northwest of the Norumbega Fault system that runs diagonally through the NW corner of the field (Wise & Francis, 1992).

Figure 8: Map showing the distribution of the four major series of the Brunswick Pegmatite Field: 1) Waldoboro, 2) Topsham, 3) Georgetown, 4) Edgecomb. The different symbols represent the most important geochemical feature of the respective pegmatite bodies (Wise & Francis, 1992).

The Topsham pegmatites are typically lens-shaped, discordant bodies trending N-

NE, and generally intrude middle-upper amphibolite gneisses that have been previously intruded by larger granitic bodies. Poor to moderate internal zonation includes a wall zone rich in graphic potassium feldspar, biotite and magnetite, with a core consisting mainly of quartz (Wise & Francis, 1992; Tomascak et al., 1999). The pegmatites are poorly to moderately fractionated, and common accessory minerals include garnet, beryl, columbite, monazite, and samarskite. Other accessory minerals are rare, and include lepidolite, microlite, tourmaline montebrasite, hydroxylherderite, stibiotantalite, and topaz, as found in the Fisher Quarry outside of Topsham by Francis (1987) (Wise &

Francis, 1992; Tomascak et al., 1999; Hussey & Berry, 2002). The most notable mineralogical feature of the Topsham pegmatites is their abundance of REE-bearing minerals, namely monazite and samarskite, which are not found in significant quantities anywhere else in the state (Wise & Francis, 1992). Also of note is the large contribution of K-feldspar to the bulk mineralogical composition. Wise & Francis (1992) place the

Topsham pegmatites in the rare-earth class of rare-element pegmatites (Cerny, 1991),

based on the mineral assemblages and textures observed. Overall, the Topsham

pegmatites seem to come from a geochemically primitive source (Wise & Francis, 1992),

and a set of U-Pb monazite ages by Tomascak et al. (1996) yields a mean ages ranging

from 275-268 Ma.

Granites

There are a large number of granitic bodies in southwestern to south-central

Maine, ranging in age from Early Ordovician to Permian. These include the

Carboniferous Sebago batholith, located 20 km to the southwest, and the Devonian

Waldoboro pluton located 40 km to the east (Osberg et al., 1985). Both the Sebago and

Waldoboro plutons are large, well-studied bodies, and the reader is referred to Tomascak et al. (1996) for detailed petrologic information on the Sebago Batholith and Barton &

Sidle (1994) for similar information on the Waldoboro pluton. However, due to their geographic proximity to the current study area, it is granites found in the Topsham-

Brunswick area (Tomascak et al., 1999) that are thought to have the greatest significance relative to the current project, and these granites are described below. The relationship between intrusive units found in the Bowdoinham 7.5’ Quadrangle and other Paleozoic intrusive units in southwestern Maine is discussed in more detail in the discussion section of this paper.

The Topsham-Brunswick area granitic bodies are almost exclusively concordant lenses of two-mica granite (Hussey & Berry, 2002). A 207Pb/ 235U monazite mean age of

278 +/- 1.5 Ma was recorded by Tomascak et al. (1996), indicating that the granites were emplaced just before the related pegmatite bodies (Hussey & Berry, 2002). While two- mica leucogranites dominate the lithology, the Topsham granites are still slightly bimodal, with spatially confined biotite leucogranite. While the major element compositions of these two members overlap considerably, the biotite leucogranite has a lower degree of

alumina saturation. They are weakly peraluminous, low in phosphorous (<0.07 wt%), and

contain only very low proportions of apatite (Tomascak et al., 1999). In regard to trace

elements (Figure 9), the two-mica leucogranites are LREE enriched, with large negative

Eu anomalies, while the biotite leucogranites have prominent Eu anomalies and very high concentrations of HREEs, as based upon a Y proxy (>120 ppm) (Tomascak et al., 1999).

No coeval mafic rocks or siliceous rocks with primitive bulk compositions (such as granodiorites or diorites) are found within the area, lending evidence against any significant mantle input into the Topsham granites.

According to Tomascak et al. (1999), the Topsham-Brunswick leucogranites are derived principally, if not wholly, from sources in the middle to lower crust. Nd isotope values for the granites (-3.7 to -5.2 ‰) are considerably different than those for the migmatized country rock (-2.6 to +.08 ‰), effectively ruling out their in situ derivation from the exposed host country rock (Tomascak et al., 1999). The Topsham leucogranite

Nd isotope values most closely affiliate themselves with values from Brookville and

Gander zone (Medial New England) basement terranes in Nova Scotia (Barr & Hegner,

1992) and values from granites found on the Gander-Avalon boundary in southeastern

Newfoundland (Kerr et al., 1995).

Figure 9: Nakamura (1974) Rare Earth Element (REE) plot for the Topsham-Brunswick leucogranites, adapted from Tomascak et al. (1999). Note HREE enrichment in the biotite leucogranite and consistently large negative Eu anomalies throughout.

STRUCTURE

Liberty-Orrington Belt

The rocks of the Liberty-Orrington belt have been folded and thrust faulted in multiple deformational episodes associated with the Acadian Orogeny. In addition, these rocks have been subjected to dextral transpressive movement associated with the

Norumbega fault system during Middle-Devonian-Early Carboniferous time (Hussey &

Berry, 2002; West & Hubbard, 1997).

Northeast of the study area, rocks of the Casco Bay Group record a complicated history of multiple folding events. According to West et al. (2003), a F1 set of folds, the result of D1 deformation, is characterized by “shallow-plunging, northeast-trending upright isoclinal folds.” D2 deformation is characterized by “northerly-trending,

relatively open asymmetric Z-folds.” These folds deform compositional layering, as well as D1 deformational features. Fold axes associated with D2 deformation tend to plunge steeply, with axial surfaces trending between 005º and 025º, and a weak crenulation cleavage parallel to the axial surface is often present (West et al., 2003).

South of the study area, Hussey (1988) and Hussey & Berry (2003) describe a different sequence of folding within the Casco Bay Group. F1 folds are nearly isoclinal recumbent folds, joined by additional parasitic minor recumbent folds, with D1 deformation also producing schistosity, spaced cleavage, and mineral lineations, as well as downward-facing stratigraphy (Hussey & Berry, 2002). The younger F2 fold system consists of upright to slightly overturned tight to open folds, with a strong axial planar schistosity (Hussey, 1988). These F2 folds significantly deform the F1 folds, with the only obvious evidence for those earlier folds being a folded spaced cleavage (Hussey &

Berry, 2002). This D2 system of Hussey (1988) and Hussey & Berry (2002) is probably equivalent to the D1 system of West et al. (2003).

Similarities do exist between the areas to the north described by West et al.

(2003)) and those to the south described by Hussey (1988) and Hussey & Berry (2002).

This is particularly with regard to D3 deformation, which consists of dextral shear bands, asymmetric boudinage (West et al., 2003), crenulation cleavages of prior schistosity, and sinistral vertical kink bands (Hussey & Berry, 2002). West et al. (2003) associate this D3 deformation with the post-peak metamorphism, dextral- transpressive tectonic activity along the Norumbega Fault System, as described by West & Hubbard (1997).

To date, no detailed structural studies have been completed in rocks of the

Falmouth-Brunswick sequence. In the Nehumkeag Pond Formation near Topsham,

Hussey & Berry (2002) do note the presence of strongly overturned, recumbent antiforms and synforms that plunge gently to the north-northeast, with axial planes dipping 35-40 degrees southeast.

Central Maine Sequence

While Hussey (1988) remarks that the fold systems of the Falmouth-Brunswick sequence are not well known, mostly due to a scarcity of outcrops, he notes F2 folding in the sequence appears to be congruent with F2 fold systems in the central Maine sequence.

According to Osberg (1988), F1 folding in the central Maine sequence consists of isoclinal folds, often with abnormally steep plunges (65º to 80º). The orientation and nature of D1 deformation is very vague in the central Maine sequence as a result of limited outcrops and considerable overprinting by D2 deformation. F2 folding consists of large, upright isoclinal folds that are the most prominent fold elements in the region.

Most folds plunge shallowly (<35º) to the northeast, with a penetrative schistosity in pelitic beds that is parallel to the axial surface. Massive wacke and limestone beds exhibit pressure solution cleavage. The most recent F3 folding consists of small (10-20 cm), generally open asymmetrical folds that deform bedding, schistosity, and the cleavages of D1 and D2. Axial surfaces plunge steeply towards the NE (~10ºNE), and a spaced cleavage roughly parallel to the axial surfaces is well developed, with micaceous minerals and at higher grades sillimanite growing along those surfaces.

Hackmatack Pond Fault

The nature of the important contact between the central Maine sequence and the

Falmouth-Brunswick sequence continues to be the subject of considerable dispute.

Pankiwskyj (1996) conducted a detailed structural analysis of the contact between the two sequences in Kennebec and Waldo Counties northeast of the Bowdoinham

Quadrangle, and concluded that the boundary is a thrust fault, affirming the previous interpretations of Hussey (1988), Osberg and Berry (1991), and Newberg (1984). This fault, called the Hackmatack Pond fault, is interpreted to be a NW-dipping thrust fault, displacing the younger rocks of the central Maine sequence over the Ordovician

Falmouth-Brunswick sequence. Further evidence for the existence of this fault is given by Stewart et al. (1991), who present geophysical results indicating a “strong seismic reflector” originating at the mapped fault trace with a boundary dipping at 25ºNW to a depth of 10 km. Hussey (1988) identifies a similar fault between the central Maine and

Falmouth-Brunswick sequences in southwestern Maine that he correlates with the

Hackmatack Pond Fault. Hussey (1988) extends this fault as far south as Portland, where it is cut off by the Flying Point fault.

Tucker et al. (2001) disagree with the fault hypothesis, describing the boundary between the central Maine sequence and the Falmouth-Brunswick sequence as

“conformable or possibly with mild disconformity.” This is based upon conformable map patterns of the Beaver Ridge Formation of the Liberty-Orrington belt and the Hutchins

Corner Formation of the central Maine sequence. On an opposite note, a paper by

Osberg (1988) identifies the contact as an unconformity, with the Silurian Hutchins

Corner Formation unconformably overlying the Ordovician Nehumkeag Pond Formation.

This interpretation is based upon the stratigraphic interpretation of basal beds of the

Hutchins Corner Formation.

METAMORPHISM

Work by Guidotti (1989) led to a geographical delineation of large scale metamorphic zones within the state of Maine (Figure 10). The rocks of the Casco Bay region of southwestern Maine are dominated by amphibolite to upper-amphibolite conditions, though slightly less intense greenschist facies metamorphic conditions are found in the Portland area to the southwest. No detailed metamorphic studies have been performed in the Bowdoinham 7.5’ Quadrangle, but the reconnaissance relationships established by Guidotti (1989) suggest that the rocks achieved upper amphibolite facies metamorphic conditions.

Hussey & Berry (2002) provide a good overview of metamorphic characteristics within the southern portion of the Liberty-Orrington belt. The rocks of the Casco Bay

Group (east of the Flying Point Fault) have been metamorphosed in low-pressure,

Buchan-type metamorphism, ranging from middle greenschist to upper amphibolite facies. In suitably pelitic rocks, the result ranges from staurolite grade to sillimanite + k- feldspar grade, with the majority falling within sillimanite-grade metamorphism. Rocks in the Falmouth-Brunswick sequence are generally higher grade, having been similarly metamorphosed to a sillimanite or sillimanite + k-feldspar grade but showing evidence of significantly more migmatization (Hussey & Berry, 2002).

The central Maine sequence has undergone chlorite zone greenschist facies (north) to sillimanite-grade amphibolite facies (south) metamorphism in three phases of

metamorphism beginning in the middle Devonian (394 Ma) and concluding in the

Carboniferous (Dallmeyer & Van Breeman, 1981; Lux & Guidotti, 1985; Osberg, 1988).

40Ar/39Ar dating performed by West et al. (1993) suggests a Late Paleozoic thermal event reset hornblende ages to ~280 Ma and left an overprint on early metamorphic textures. This metamorphic phase does not involve any structural deformation, and is proposed to be a contact metamorphic event associated with the

Carboniferous emplacement of the Sebago Batholith. The batholith, which dips shallowly to the northeast, may be structurally located only a few kilometers below the rocks exposed in the Bowdoinham 7.5’ Quadrangle (West et al., 1993).

Figure 10: Generalized map of regional metamorphic zones within the state of Maine. Notice the position of the Bowdoinham 7.5’ Quadrangle study area in a zone of upper amphibolite facies metamorphic conditions.

GEOCHEMISTRY

A recent paper by West et al. (2004) uses major, trace, and isotopic geochemical analyses of amphibolites from the Casco Bay Group to infer information on the tectonic setting for that portion of the Liberty-Orrington belt. The authors also attempt to correlate

these results with geochemistry reported from the Miramichi belt and Bathurst

Supergroup of eastern Maine and New Brunswick, described in studies by Rogers & van

Staal (2003) and van Staal et al. (2003).

Taking samples from the metavolcanic felsic gneisses and amphibolites of the

Casco Bay Group’s Spring Point Formation, West et al. (2004) conducted major element,

trace element, and rare earth element (REE) analyses. A bimodal suite of rocks is

revealed within this formation, with mafic rocks plotting as sub-alkaline basalts and

basaltic andesites and felsic rocks plotting as dacites and rhyolites. Rare earth element

diagrams for both felsic and mafic samples show elevated but nearly flat patterns, with a

slight enrichment of LREE elements in felsic samples. Distinct negative Nb (Ta), Eu, P,

and Ti anomalies are clearly evident in extended spider diagrams (Figure 11).

Figure 11: REE and extended spider diagrams reported by West et al. (2004) for trace element analyses performed on the metavolcanic Spring Point Formation of the Casco Bay Group. Open markers indicate felsic samples, while closed markers indicate mafic samples. Note relatively flat REE patterns with a significant negative Eu anomaly in felsic samples, as well as negative Nb (Ta), P, and Ti anomalies in the spider diagram.

Neodymium isotope analyses returned low concentrations (relative to chondrite) for both mafic and felsic samples, indicating an evolved source component within the

Spring Point Formation. The negative εNd values found in the Spring Point Formation place these rocks in the peri-Gondwanan Gander Zone, excluding them from formation in the Avalon terrane (Whalen et al., 1996; West et al., 2004).

The negative Nb anomalies in mafic samples are representative of a subduction component (Green, 1995), and the moderate nature of these anomalies suggests a back- arc basin setting, as opposed to a volcanic arc (Fretzdorf et al., 2002). The overall chemistries of the rocks are also best explained by a mantle source enriched by a crustal and/or subduction component (West et al., 2004). Figure 12 shows West et al. (2004)’s interpretation of the tectonic setting of the Liberty-Orrington belt prior to the closure of the Iapetus Ocean, circa 470 Ma. It is suggested that the Falmouth-Brunswick sequence represents volcanic arc rocks related to continued arc magmatism on the trench side of the Gander-zone back-arc basin in which the Casco Bay Group formed.

Figure 12: Tectonic model for the Early-Middle Ordovician evolution of the Casco Bay Group (West et al., 2004). Early volcanic arc formation and related volcanism occurs on the Gander continental margin around 485-475 Ma, with later rifting forming a back-arc basin in which the younger members of the Casco Bay Group (Diamond Island and Scarboro formations) are deposited.

The last main component of the West et al. (2004) paper is an attempt to correlate the geochemistry of the Spring Point Formation with that of the Bathurst Supergroup, which overlies the Miramichi Group in eastern Maine and western New Brunswick (van

Staal et al., 2003). Geochemical comparisons, shown in Figure 13, are suggestive of a correlation, with similar elevated REE levels relative to CHUR and matching spider diagram patterns for both felsic and mafic samples. The same Eu, Nb (Ta), P, and Ti anomalies are evident in both sample sets (West et al., 2004; Rogers & van Staal, 2003).

εNd values for the Bathurst Supergroup published by Whalen et al. (1998) are, like those for the Spring Point Formation, negative, indicating a Gander Zone source. A U-Pb zircon age for the Little River Formation of the Tetagouche Group of the Bathurst

Supergroup, 459 +/- 3 Ma (Sullivan & van Staal, 1996), is relatively close to Tucker et al.

(2001)’s age of 469 +/- 3 Ma for the Spring Point Formation of the Casco Bay Group.

Figure 13: These extended spider diagrams from West et al. (2004) show the close geochemical similarities in trace elements between rocks of the Spring Point Formation (Casco Bay Group of the Liberty-Orrington belt) and the Bathurst Supergroup.

While there are numerous similarities between the Casco Bay Group and the

Bathurst Supergroup, both West et al. (2004) and van Staal et al. (2003) believe that

direct correlation is unlikely, based on a complex formation history for the Bathurst

Supergroup in which a number of widely separated and distinct blocks were later

juxtaposed during Acadian orogenesis. This is in addition to a significant along-strike

distance between the Casco Bay Group and the Bathurst Supergroup (van Staal et al.,

2003; West et al., 2004).

PREVIOUS WORK IN THE BOWDOINHAM 7.5’ QUADRANGLE

To date, no detailed work has been done specifically within the Bowdoinham 7.5’

Quadrangle. The only reconnaissance bedrock mapping in the quadrangle was performed by Newberg (1984), who recorded 33 bedrock stations in the northern half of the quadrangle while compiling his larger 1:62,500 scale map of the Gardiner 15’

Quadrangle (for comparison, this study incorporated information from 441 stations).

Ordovician units are placed in the “blanket” Cushing Formation of the 1985 1:500,000

state bedrock map (Osberg et al., 1985), but in what is now the Falmouth-Brunswick

sequence (Hussey, 1988). Newberg’s lithologic boundaries for the northern half of the

Bowdoinham Quadrangle are shown in a cut-out from his 1982 map, Figure 14.

Figure 14: Bedrock geology of the northern portion of the Bowdoinham Quadrangle, as mapped in the Gardiner 15’ Quadrangle by Newberg (1984). OSv: Vassalboro Formation of central Maine sequence; EOcma: Mount Ararat member of the Cushing Formation; EOcr: Richmond Corner member of the Cushing Formation; EOcm: marble unit within Cushing Formation lithologies. Note the west-dipping thrust fault boundary between the Vassalboro and Cushing Formations.

There are a number of key features in the mapping and analysis of Newberg (1984) that demand further mention. The four major units delineated within the northern

Bowdoinham Quadrangle are the following: OSv, EOcma, EOcr, and EOcm. OSv represents the Vassalboro Formation of the central Maine sequence, renamed the

Hutchins Corner formation by Osberg (1988), a unit of calcareous metasedimentary turbidites. EOcma represents the Mt. Ararat member of the Cushing Formation which consists of biotite granofels interlayered with hornblende-rich amphibolite layers, while

EOcr represents the Richmond Corner member of the Cushing Formation, comprised of garnet-biotite granofels with coticule and minor hornblende. As discussed earlier,

Hussey & Berry (2002) place this unit in the central Maine sequence, conformably underlying the Hutchins Corner Formation. A narrowly constrained, impure marble unit

(EOcm) appears to be a “refolded fold.” The presence of this unit will be discussed later in this study.

Structurally, the boundary between the central Maine sequence and the Richmond

Corner member of the Cushing Formation (pre-division by Hussey (1988)) is mapped by

Newberg (1984) as an east-verging thrust fault. This is similar to the relationships

portrayed for the Hackmatack Pond fault contact along strike to the northeast

(Pankiwskyj, 1996; Stewart et al., 1991). In addition to this major faulting, Newberg

(1984) identifies 3 distinct episodes of folding. The first episode, F-1, involves large- scale recumbent folds that are not visible in the quadrangle but are regionally accepted, while F-2 folds are smaller upright to isoclinal folds. F-3 folds are crenulation of F-2 cleavages (Newberg, 1984).

Newberg assumes sillimanite-grade, amphibolite facies metamorphism for the entire Gardiner 15’ quadrangle, based on the presence of abundant sillimanite crystals found in suitably pelitic lithologies within the Nehumkeag Pond member of the Cushing

Formation and portions of the Cape Elizabeth Formation of the Casco Bay Group.

Evidence of local retrograde metamorphism is suggested by the partial replacement of garnet porphyroblasts, biotite, and amphibole by chlorite (Newberg, 1984).

III. METHODS

FIELDWORK

Mapping of the northern half of the Bowdoinham 7.5’ Quadrangle and sample collection for this study took place in late July- early September 2004. Using a handheld global positioning system (GPS), the latitude and longitude of each outcrop station and geochemical sampling locality were entered in Universal Transverse Mercator coordinates (NAD83, Zone 19). Based on these coordinates, each station was plotted in the field on a copy of the USGS 7.5’ Bowdoinham quadrangle. Each evening, stations plotted in the field were transferred to a full topographic base map of the entire quadrangle. At each of 441 field stations lithologic descriptions were made, and when possible, structural measurements were taken of bedding/foliation planes, joints, and smaller-scale structural features such as fold axes (Appendix I).

At locations seemingly representative of particular units, hand samples were taken for reference and petrographic analysis. Geochemical samples of amphibolites, gneisses, and granitoids were collected at 18 stations, using a hammer and chisel, and stored in plastic grocery bags sealed with duct tape. These bags were labeled in the field with the

station number. It is important to note that some of these stations (e.g. FT-73) were outside of the Bowdoinham Quadrangle and hence are not included in Appendix I. The locations and general descriptions of these geochemistry sampling localities are presented in Appendix II, and their geographic distribution is shown in Figure 15. A detailed map of the location of geochemistry sampling sites within the northern half of the quadrangle, overlaid upon the finished bedrock map of this study, is shown in Figure 16. Samples representative of the variations in mineralogy within units were cut for petrographic thin section analysis (see Appendix II).

Figure 15: Geographical distribution of geochemistry sampling localities within the Ordovician Liberty-Orrington belt. Note that some of these localities are outside the northern quadrangle boundary. Six amphibolite samples were taken from the I-295 Richmond interchange, and two amphibolite samples (GC5 & GC6), as well as one Hornbeam Hill pluton sample (B274), were collected in the southern half of the quadrangle.

Figure 16: Geochemistry sampling locations within the northern half of the Bowdoinham 7.5’ Quadrangle. Nine samples were taken from the Hornbeam Hill Intrusive Suite, as well as three amphibolites from the Unnamed Gneiss unit of the Falmouth-Brunswick sequence.

GEOCHEMICAL ANALYSES

Twenty-three samples were analyzed for major and trace element compositions by

Inductively-Coupled Argon Plasma spectrometry (ICAP), using a Thermal Jarrell Ash

1000 at Middlebury College. Following standard Middlebury College procedures (Coish,

2004), yttrium (Y) was used as an internal standard for major element analyses, and germanium (Ge) was used as an internal standard for trace elements. Rocks were prepared for ICAP analysis in the following manner: First, samples were cut into small chips using a standard diamond-blade rock saw. Weathered and oxidized portions of each sample were removed from the sample to be analyzed, as to minimize contamination.

Second, these chips were run through a porcelain jaw crusher and then a tungsten-carbide shatter box, yielding a powdered sample. Third, these powdered samples were analyzed for loss on ignition (LOI) by weighing one gram of each sample into a carbon crucible and then igniting that sample for 15 minutes at 1050ºC in a Thermolyne 47900 Muffle

Furnace. Loss on ignition percentages were recorded for each sample.

Using these ignited samples, nitric acid rock dissolution was performed, based on standard Middlebury procedures developed by Coish (2004). First, 0.8 grams of Lithium

Metaborate flux was weighed out into a carbon crucible, to which was added 0.20 grams of the ignited sample. Precise weight measurements of both constituents were recorded, and then the crucible was placed in a 1050ºC oven for 14 minutes, fusing the flux and sample. To make the trace element solution, this fused sample was dissolved into 60 ml of 10% nitric acid (HNO3), diluted to 100ml using 10% HNO3, and then filtered to remove any particulate matter, mainly residual carbon particles from the crucible itself.

From this trace element solution, major element solutions were made by pipeting 5ml of

the trace element solution into an Erlenmeyer flask and then diluting this solution to

100ml with 10% HNO3. Both major and trace element solutions were finally stored in polypropylene containers.

Standards were run with all sample ICP runs to assess sample preparation and ICP accuracy. Standard MRG-1 was used for amphibolite samples and standard AGV-2 was used for pluton samples. Appendix III shows geochemical results for these standards.

Whole-rock geochemical analysis, including rare earth element analysis, was performed on 11 powdered samples (Appendices IV, V) using ICP-MS technology at

Activation Laboratories in Ancaster, Ontario. These data provided an additional check on the accuracy of the ICP-AES analyses at Middlebury College.

PETROGRAPHIC ANALYSES

Thirty-one thin section chips were sent to Burnham Petrographics in Rathdrum,

Idaho for the preparation of thin sections for petrographic analyses. Chips were cut at an approximate size of 1.5 cm thick by 5 cm long and 3 cm wide, and the resulting thin sections have a thickness of 0.03 mm. All thin sections were prepared using standard procedures, and were analyzed using a Nikon Eclipse E600 POL petrographic microscope.

IV. RESULTS

METAMORPHIC STRATIGRAPHY

Bedrock mapping in the northern half of the Bowdoinham 7.5’ Quadrangle led to a major revision of the previous work of Newberg (1984) in his mapping of the Gardiner

15’ Quadrangle. Four main lithologic units were identified in the quadrangle: 1) migmatitic biotite gneisses and related subordinate lithologies (i.e. amphibolites and rusty schists) of the Ordovician Falmouth-Brunswick sequence, 2) calc-silicate gneisses and biotite granofels of the Late Ordovician – Devonian (?) central Maine sequence, 3) a previously unrecognized, deformed Devonian intrusive body of variable composition, hereby called the Hornbeam Hill Intrusive Suite, and 4) several small granitic pegmatite bodies (of both Devonian and Permian age). Field relationships suggest the Hornbeam

Hill Intrusive Suite provides a minimum age for the timing of last movement between the central Maine and Falmouth-Brunswick sequences in this area. The narrow, refolded marble unit (EOcm) described by Newberg (1984) was not located in the field. The lithologic units found in the quadrangle are described below, with stratified, deformed intrusive, and undeformed intrusive units described separately. Within each category, the units are discussed from west to east across the quadrangle. The spatial distribution of these units is illustrated in the bedrock map for the northern half of the Bowdoinham 7.5’

Quadrangle (West & Cubley, in review), shown in Plate 1.

Stratified Rocks

Vassalboro Formation (Sv): The Vassalboro Formation (believed to be Late

Ordovician to Early Silurian in age) of the central Maine sequence underlies the western

half of the Bowdoinham 7.5’ Quadrangle. These rocks have been referred to by Hussey

& Berry (2002) as the Hutchins Corner Formation, a formation that at its type locality in

south-central Maine has been characterized as being stratigraphically below the

Waterville Formation (Osberg, 1988; Tucker et al., 2001). As the relative stratigraphic

position of the these rocks within the central Maine sequence could not be established in

the Bowdoinham 7.5’ Quadrangle, the name Vassalboro Formation was adopted from the

precedent of older maps of the area (Newberg, 1984; Osberg et al., 1984).

The Vassalboro Formation in the study area consists of medium-gray to purplish- gray, fine to medium-grained quartz-plagioclase-biotite granofels and schist interlayered with greenish-gray-fine-grained, plagioclase-quartz-actinolite-diopside±biotite granofels.

Layer thickness ranges from 3 to 25 cm, with the calc-silicate layers clearly subordinate, generally thinner, and often discontinuous along strike. These metasedimentary rocks often weather to a slabby appearance, and rusty weathering is common on foliation surfaces. Within the Vassalboro Formation are numerous pegmatite dikes and sills, which present sharp contacts with the country rock. Figure 17 shows a typical outcrop of the Vassalboro Formation.

Figure 17: Photograph of a pavement exposure of the Vassalboro Formation. Note the greenish calc-silicate bands, darker colored biotite granofels, and slight rusty weathering.

Rusty schist and coticule member (Svr): This member of the Vassalboro

Formation is located on the contact between the main body of the Vassalboro and

the Hornbeam Hill Pluton in the southern portion of the field area (see plate 1).

The rusty schist unit is the more common constituent of this member, and is

comprised of medium to dark gray, moderately to extensively rusty weathering,

sulfidic and locally graphitic, quartz-plagioclase-muscovite-biotite±sillimanite

schist and granofels. A lighter gray, fine to medium-grained plagioclase-quartz-

biotite granofels is also be present within the unit, in minor amounts. The coticule

unit of this member is decidedly subordinate, found in very few outcrops, and

consists of medium gray, quartz-plagioclase-biotite-garnet±sillimanite gneiss and

granofels, with locally abundant, discontinuous layers of coticule. The garnets

within both the schist/granofels unit and the coticule unit are fine grained (<1mm

in diameter).

Falmouth-Brunswick Sequence

Unnamed Gneiss unit (Oug): The Unnamed Gneiss unit of the Falmouth-

Brunswick sequence, believed to be Ordovician in age, is located in the eastern

half of the quadrangle. The unit contains a number of lithologies, but is

dominated by a light-gray, medium to coarse-grained, non-rusty to slightly rusty

weathering, plagioclase-quartz-biotite gneiss (Figure 18). These gneisses often

display evidence of migmatization and pegmatite dikes, sills, and boudins are

found throughout the unit. There are two main subordinate lithologies, the first

being a dark gray, fine to medium-grained, locally biotite-bearing amphibolite.

Within this amphibolite lithology, greenish-gray, fine-grained discontinuous calc-

silicate lenses (up to 3 cm thick) are present locally. The second subordinate

lithology consists of a medium gray, medium-grained, slightly to moderately rusty

weathering, quartz-plagioclase-biotite±muscovite±sillimanite schist and gneiss.

This lithology may locally contain coarse-grained garnet.

Figure 18: This outcrop of the Unnamed Gneiss unit of the Falmouth-Brunswick sequence displays migmatitic gneiss textures and coarse quartzofeldspathic segregations.

Mixed Rocks subunit (Ougm): Mapped separately within the unnamed Gneiss

unit of the Falmouth-Brunswick sequence is a subunit termed the Mixed Rocks

subunit, which consists of a thin band of variable lithologies. The constituent

lithologies within this subunit cannot be separated from each other on a 1:24,000

mapping scale, due to their poor exposure and relatively thin nature. There are 5

rock types included within the Mixed Rocks subunit: The first rock type is a dark

gray, fine to medium-grained, very rusty weathering, sulfidic and graphitic

quartz-muscovite-biotite-sillimanite±garnet schist and gneiss. The second

lithology is a medium gray, medium to coarse-grained, slightly to moderately

rusty weathering plagioclase-quartz-biotite±garnet gneiss. In localities of this

lithology including garnet, those garnets are coarse grained (up to 3 cm diameter)

and are poikilitic. The third rock type is a dark gray, medium-grained, garnet-

bearing amphibolite, which is characterized by consistent, thick (up to 4 cm)

layering, and coarse poikilitic garnets (up to 2 cm diameter). The fourth lithology

is a greenish-gray, medium to coarse-grained plagioclase-diopside±hornblende

granofels and gneiss (Figure 19), while the fifth lithology is a light gray, medium-

grained, moderately to strongly foliated quartz-K-feldspar-plagioclase-

biotite±muscovite granitic gneiss.

Figure 19: This photograph shows the calc-silicate hornblende gneiss lithology of the Mixed Rocks subunit of the Falmouth-Brunswick sequence.

Deformed Intrusive Units

Hornbeam Hill Intrusive Suite (Dhh): The Hornbeam Hill Intrusive Suite, unrecognized in the original mapping of Newberg (1984), consists of deformed and metamorphosed metagranitoid rocks of at least 4 different types. These constituent types cannot be spatially separated on a 1:24,000 scale. Individual exposures, while typically dominated by a single rock type, can be comprised of multiple lithologies. Contacts between the constituent lithologies are clouded by post-intrusive deformation and

metamorphism, and at no locality is one lithology observed to cross-cut another. The

four main rock types are described below, in order of decreasing abundance. The most

abundant rock type contained within the intrusion is a light to medium gray, medium to

coarse-grained, plagioclase-quartz-K-feldspar-biotite-garnet±hornblende gneiss, with

garnets that are relatively coarse-grained (up to 2 cm diameter) and poikilitic (Figure 20).

This rock type is thought to represent deformed and metamorphosed tonalite or

granodiorite.

The second rock type is a light gray, medium to coarse-grained K-feldspar-quartz-

plagioclase-biotite±garnet gneiss, which is interpreted to represent deformed and

metamorphosed granite. The third lithology is a light gray, medium-grained, porphyritic

K-feldspar-quartz-plagioclase-biotite gneiss, which is characterized by coarse grained (up

to 3 cm in length) K-feldspar crystals that are commonly aligned (Figure 21). This unit is

interpreted to represent deformed and metamorphosed porphyritic granite.

The final and least abundant constituent of the pluton is a dark gray, fine to

medium-grained, plagioclase-hornblende-biotite-quartz gneiss, which is interpreted to

represent deformed and metamorphosed diorite.

Figure 20: This photograph shows an outcrop of the biotite-garnet unit of the Hornbeam Hill Intrusive Suite. Notice the abundant poikilitic garnets and the relative abundance of biotite.

Figure 21: This photograph shows an outcrop of the porphyritic K-feldspar unit of the Hornbeam Hill Intrusive Suite. Notice the roughly parallel alignment of the coarse feldspar crystals, and a more felsic composition than that seen in the biotite-garnet unit (Figure 20).

Non-deformed Intrusive Units

Tourmaline-bearing granite pegmatite (Dtp): These pegmatite bodies appear to be restricted to the country rocks of the central Maine sequence, and consist of light gray to white, very coarse-grained to pegmatitic, tourmaline-bearing±muscovite±biotite±garnet granite pegmatites (Figure 22). They are assigned a Devonian age based upon a U-Pb zircon age of 367 ± 1 Ma that was recorded for a lithologically similar pegmatite body located in the adjacent Gardiner 7.5’ Quadrangle (Tucker et al., 2001).

Figure 22: The photograph shows an outcrop of the Tourmaline-bearing granitic pegmatite (Dtp). Notice the coarse feldspar crystals and the abundant black tourmaline.

Moderately foliated to non-foliated, biotite-bearing granite and granite pegmatite (Dp): Located in both the Ordovician rocks of the Falmouth-Brunswick

sequence and the Silurian-Devonian rocks of the central Maine sequence, these rocks

consist of light gray, coarse-grained to pegmatitic, moderately foliated to non-foliated,

biotite bearing ±muscovite±garnet±tourmaline granite and granite pegmatite. As with the

tourmaline-bearing granite pegmatite (Dtp), these pegmatites are assigned a Devonian age based on comparison with the Devonian intrusion age-dated by Tucker et al. (2001).

Muscovite-bearing, graphic, granite pegmatite (Pp): These pegmatite bodies, found on hilltops within the Unnamed Gneiss unit of the Falmouth-Brunswick sequence, are comprised of light gray to white, very coarse grained to pegmatitic, muscovite bearing

±biotite±garnet graphic granite pegmatite (Figure 23). Along the margins of these pegmatite bodies, xenoliths are commonly found, with sizes of up to several meters across. These pegmatites are lithologically similar to granite pegmatites in the Topsham area of the adjacent Brunswick 7.5’ Quadrangle (Hussey & Berry, 2002). Tomascak et al.

(1996) report Permian U-Pb monazite ages for the Topsham pegmatites that range from

268-275 Ma.

Figure 23: Permian pegmatite from the southeastern part of the Bowdoinham 7.5’ Quadrangle. Note graphic quartz textures. Width of photo is 6cm.

Mafic Dikes (Mzd): These dikes are found throughout the quadrangle, crosscutting all the major lithologies, but are too thin to be mapped on a 1:24,000 scale. The dikes consist of dark gray to black, fine-grained diabase (Figure 24) and are Mesozoic in age, based on comparisons with lithologically similar rocks to the south that have been radiometrically dated (West & McHone, 1997).

Figure 24: This photograph shows a thin Mesozoic diabase dike cutting rocks of the Falmouth-Brunswick sequence.

RECONNAISSANCE PETROGRAPHY

While a detailed study of the metamorphic petrology within the Bowdoinham

Quadrangle was not within the scope of this project, reconnaissance-level petrographic

analyses were performed in order to 1) generally characterize units, most importantly the

previously unrecognized rocks of the Hornbeam Hill Intrusive Suite, and 2) lend support

to the conditions of metamorphism established for the area by Guidotti (1989). The section that follows outlines the general mineral compositions of a number of units, highlighting variability within, and comments on the implications of these metamorphic mineral assemblages. Please note that thin sections were not made for the pegmatite units, hence petrographic descriptions are not available. The order of the following descriptions follows a transect from west to east (refer to Plate 1 for spatial distributions).

Detailed descriptions of all thin sections are presented in Appendix VI.

Vassalboro Formation (Sv): One sample from the Vassalboro Formation, B125, was analyzed in thin section, and a photomicrograph from that sample (Figure 25) clearly shows the calc-silicate and biotite granofels banding that is so characteristic of the

formation. The upper part of the photomicrograph shows a distinct calc-silicate band

with the mineral assemblage quartz-plagioclase-hornblende-diopside, while the biotite-

rich lower part is characterized by the assemblage quartz-plagioclase-biotite. An

equigranular, granofelsic texture is common to both bands, the boundary between which

is very sharp and distinct.

Figure 25: Nearly a full thin section view of a thin section from a typical Vassalboro Formation rock showing the contact between biotite granofels (Quartz+Plagioclase+ Biotite assemblage shown in the lower portion of the photo) and calc-silicate granofels (Quartz+Plagioclase+Hornblende+Diopside assemblage shown in the upper portion). Note the equigranular texture (granofelsic) and the very distinct and sharp boundary between the two rock types.

Vassalboro Formation, rusty schist and coticule member (Svr): Two samples from the rusty schist and coticule member, B207 and B209, were analyzed in thin section.

B207 (Figure 26A) contains the mineral assemblage quartz-plagioclase-biotite- sillimanite-garnet±apatite±zircon±ilmenite, with sillimanite comprising roughly 20% and garnet only 15%. This presence of sillimanite in this pelitic sample lends strong support to the determination of Osberg et al. (1985) that the Bowdoinham area has been subjected to amphibolite facies metamorphism. B209 (Figure 26B) contains nearly 75% coticule garnet, with considerably less quartz, plagioclase, and biotite than B207. Although sillimanite is only observed in small amounts, this is most likely due to differences in bulk rock composition.

B Figure 26A) Plane-light photomicrograph of B207, showing abundant sillimanite and biotite, with garnet porphyroblasts. B) Photomicrograph of B209 in cross-polarized light, showing a composition dominated by small garnets (coticule) with smaller amounts biotite and quartz/feldspar.

Hornbeam Hill Intrusive Suite: As was observed in field observations, there is considerable mineralogical and textural variation within the Hornbeam Hill Intrusive

Suite. The most mafic samples, e.g. B259 and B296, have the mineral assemblages quartz-plagioclase-hornblende-biotite-apatite-titanite-ilmenite±zircon. Hornblende is modally the most abundant mineral, comprising 30-40% of the minerals in both samples.

Biotite ranges from ~10% in B259 to ~35% in B296. B296 (Figure 27) shows an abundance of large euhedral apatite crystals and coarse titanite that is typically cored by ilmenite. The relative size and abundance of these titanium-bearing minerals reflects the high percentage of titanium found in this sample, 2.69% as compared to the pluton samples’ average of 1.29% (Appendix VI). Apatite is also abundant in B259, constituting ~2% of the overall composition.

Intermediate samples in the intrusive suite (e.g. GC11, GC12) have mineral assemblages typically represented by quartz-plagioclase-biotite-garnet- allanite±apatite±titanite ±zircon±calcite±chlorite. Hornblende is occasionally observed unaltered, but is generally in various stages of secondary replacement by chlorite.

Garnets are large and poikilitic, and constitute a significant percentage of the overall mineralogy, i.e. 15% in B132 (Figure 28). Biotite constitutes 20-35% of the overall composition, and allanite can be present up to 1%.

The most felsic samples within the intrusive suite, characterized by sample B299

(Figure 29), contain 90-95% quartz and feldspar, with both plagioclase and K-feldspar present (both microcline and orthoclase). Alkali feldspar appears to be more abundant than plagioclase, especially microcline, and the grain size of feldspar and quartz is considerably larger than that found in more mafic and intermediate samples. There is

very little biotite, and garnets are small (<1.0mm) and euhedral, if present. The overall mineral assemblage for the felsic samples is quartz-Kfeldspar-plagioclase-biotite- garnet±allanite±apatite±titanite±ilmenite±zircon±muscovite±chlorite.

Thus, reconnaissance petrography suggests rocks in the intrusive suite range from hornblende-bearing mafic gneisses to intermediate composition garnet-bearing gneisses to granitic gneisses rich in quartz and K-feldspar.

Figure 27: Plane light photomicrograph of B296, a mafic end member of the Hornbeam Hill Intrusive Suite. Notice the large, euhedral apatite crystals and coarse titanite that is cored by ilmenite. Hornblende, biotite, quartz and plagioclase feldspar dominate the mineralogy.

Figure 28: This photomicrograph shows sample B132, an intermediate biotite-garnet gneiss from the Hornbeam Hill Intrusive Suite under crossed polars. Notice the large poikilitic garnet in the upper left, as well as abundant biotite in the center of the slide. Small allanite crystals can be seen in the bottom center of the thin section.

Figure 29: This photomicrograph shows a felsic Hornbeam Hill intrusive sample, B299, under crossed polars. Notice the coarse grain size of the quartz and feldspar, as well as the presence of K-feldspar (microcline variety), which was not seen in as great abundance in more mafic samples. Smaller subgrains are characteristic of recrystallization. Biotite is no longer a major constituent of the overall mineralogy.

Falmouth-Brunswick Sequence: Samples were petrographically analyzed from both the amphibolite and rusty schist lithologies within the Falmouth-Brunswick sequence. The rusty schists, observed in samples from B6 and B7, are characterized by the assemblage quartz-plagioclase-biotite-opaques±apatite. Quartz and plagioclase typically make up 45-

65% of the overall composition, with biotite adding 25-30%. It is assumed that the opaque minerals, which make up 15-25%, depending on the thin section, are dominated by sulfide minerals (most likely pyrite and pyrrhotite). Coarse pyrite is clearly seen in hand sample and hence this appears to be a well-founded conclusion. Rusty schist sample B6 is shown in plane light in Figure 30, below.

Figure 30: This photomicrograph shows sample B6 of the rusty schist lithology of the Mixed Rocks subunit of the Falmouth-Brunswick sequence under plane light. Notice the abundant sulfide minerals, which appear as opaques, as well as biotite and quartz/plagioclase feldspar.

Falmouth-Brunswick Sequence Amphibolites: Reconnaissance petrographic analyses were conducted on amphibolite samples from the Unnamed Gneiss unit and Mixed Rocks subunit of the Falmouth-Brunswick sequence, as well as the Mount Ararat Formation of the Falmouth-Brunswick sequence, from just outside the northeast corner of the quadrangle in the adjoining Richmond 7.5’ Quadrangle. Despite having a spatially confined distribution (Figure 15), the amphibolite samples show considerable variation in the mineral assemblages. In samples collected just outside of Bowdoinham in the Mount

Ararat Formation, (e.g. R1-3 and FT-73: see Figure 15), and some samples collected in the middle of the Unnamed Gneiss unit, (e.g. B41), the mineral assemblage is typically hornblende-plagioclase-apatite-titanite-ilmenite±biotite±clinopyroxene. There is little in the way of compositional banding in these rather homogenous, hornblende-dominated samples, which are illustrated in a photomicrograph of sample R2 seen in Figure 31.

Figure 31: This photomicrograph shows sample R2, of the relatively homogenous and mineralogically simple amphibolite variant found within the quadrangle. Notice the abundance of hornblende but also the presence of clinopyroxene in the middle of the slide. Colorless minerals are plagioclase feldspar—quartz is not present.

A well-represented mineralogical variation, characterized by sample GC6 (Figure

32) in the southern part of the Bowdoinham 7.5’ Quadrangle (outside the northern half),

consists of alternating bands of hornblende and clinopyroxene. Hornblende makes up

thin bands within samples, while pyroxene bands are considerably thicker in thin section.

Two types of clinopyroxenes are present: a colorless, nonpleochroic variety and a light

green, slightly pleochroic pyroxene. Ilmenite is abundant, and titanite is coarse and lenticular. Quartz is present in trace amounts. The overall mineralogy is plagioclase- hornblende-clinopyroxene-titanite-ilmenite±quartz±calcite±apatite. The distinct small-

scale banding and abundance of clinopyroxene (probably diopside) in some of the layers suggests a possible sedimentary origin to these amphibolites.

Figure 32: This plane light photomicrograph shows the boundary between hornblende and pyroxene bands in amphibolite sample GC6. Notice the two types of pyroxene: a nonpleochroic, colorless type and a slightly pleochroic, light green type. Lenticular titanite and opaques are relatively abundant within.

A third amphibolite variant is a garnet-bearing amphibolite with the general assemblage hornblende-plagioclase-titanite-ilmenite-garnet±apatite. Hornblende comprises a relatively high percentage of the amphibolite (75%), and ilmenite is plentiful, between 4-5%. In one sample, GC13 (Figure 33), titanite (CaTiSiO5) is found in high concentrations (5% of the mineralogy), which reflects the elevated levels of titanium in that sample (3.85% weight percent as opposed to an amphibolite average of 1.73%). This

increased titanium is most likely responsible for the increased amounts of ilmenite

(FeTiO3) as well. Again, this abundance of titanium-bearing minerals could be indicative

of a sedimentary origin—perhaps more ilmenite-rich sands or placer-type deposits.

Figure 33: This plane light photomicrograph of sample GC13 shows a mineralogy dominated by hornblende but also containing garnets and a high concentration of titanite and ilmenite.

STRUCTURAL RESULTS

The rocks of the Bowdoinham Quadrangle have all been subjected to multiple phases of pervasive structural deformation. Poor exposure limited the ability to recognize and quantitatively analyze structural features, and only 3 fold axis and 6 lineation measurements were taken in the field. These measurements are shown in

Appendix VII. Stereonets showing these limited measurements are displayed in Figures

34 and 35, respectively. Fold axes trend between 013-035º and plunge between 14-27º.

Most observed folds are isoclinal and significantly reclined, with no evidence of the large-scale upright isoclinal folding that is so characteristic of other parts of the Liberty-

Orrington and central Maine belts (Osberg, 1988; Hussey & Berry, 2002; West et al.,

2003). The majority of the lineations (recorded as rakes on foliation surfaces) trend from

030-067º, at an average rake of 74º to NW-striking foliation planes.

Figure 34: Equal area stereonet projection of the 3 fold axes measured in the field. Axes trend to the NE between 013-035º, and plunge shallowly from 14-27º.

Figure 35: Equal area stereographic projection of the 6 mineral foliation lineations measured in the field. The majority of these lineations trend 030-067º, at an average rake of 74º to the foliation planes, but one outlier lineation trends 245º.

The most visible evidence of structural deformation in the quadrangle is a

pervasive foliation that is prominent in all lithologies, aside from the Permian pegmatite

bodies. In the stratified rocks of the Vassalboro Formation and Falmouth-Brunswick

sequence, the average strike of this foliation is 351º, with an average dip of 36.5º to the

northeast (Figure 36). The Hornbeam Hill pluton yields foliation measurements (Figure

37) that closely mirror those recorded in the surrounding country rock. The average

strike is 349º, with an average dip of 37º to the northeast. This similarity suggests that

the main deformational event causing this major foliation took place after the

emplacement of the Hornbeam Hill pluton.

Figure 36: Equal area stereographic projection of poles to foliation planes for 153 samples from the Vassalboro Formation and Falmouth-Brunswick sequence. The average of these orientations (shown by the great circle) is 351º, 36.5ºNE.

Figure 37: Equal area stereographic projection of poles to foliation planes for 38 samples from the Hornbeam Hill Intrusive Suite. The average strike (indicated by the great circle) is 349º, with a dip of 37ºNE, and the overall pattern of foliation measurements closely mirrors that of the surrounding country rock (Figure 34). This suggests that penetrative ductile deformation occurred after the intrusion of the Hornbeam Hill intrusive complex.

GEOCHRONOLOGY

A sample of the Hornbeam Hill pluton (garnet-biotite gneiss variety - locality 131) was collected in an attempt to obtain the intrusive age of these rocks. Numerous elongate and euhedral zircons characteristic of an igneous origin (see Figure 38) were separated from this sample and analyzed (by Dave West) using the U-Pb dating method with the

Sensitive High Resolution Ion Micro Probe (SHRIMP) at Stanford University.

Cathodoluminescence images of these zircons (Figure 38) reveal relatively low

U/Th ratio oscillatorilly zoned igneous cores surrounded by relatively high U/Th ratio metamorphic overgrowths. Sixteen individual analyses of various portions of these grains were completed using the SHRIMP and individual ages ranged from 365 to 395

Ma. Curiously, ages from the cores of these grains were generally slightly younger than the rims – but within analytical uncertainty. The best estimate of the rim ages is provided by a 206Pb/238U plot of eight high U/Th analyses (Figure 39). This age of 390 ± 3 Ma (2

sigma uncertainty) is interpreted to represent the timing of metamorphic recrystallization

in this rock. Because the core ages obtained were slightly younger than the rim ages

(although within analytical uncertainties), more analyses are needed to confirm the timing

of original igneous crystallization. However, given that the core ages obtained thus far

are similar to the rim ages, it is doubtful that the igneous crystallization age would be

significantly older than 390 Ma. One additional point to note, no visual

(cathodoluminescence images) or geochronological evidence was found for older

inherited zircons within this sample.

Figure 38: Cathodoluminescence image of zircon crystals from the Hornbeam Hill Intrusive Suite analyzed using the SHRIMP. Note the lighter colored (low U/Th ratios) oscilliatorilly zoned cores that are characteristic of igneous zircon growth and the darker colored (high U/Th ratios) rims that are characteristic of growth during metamorphism. The width of the photos is approximately 500 µm.

Figure 39: 206Pb/238U plot of eight high U/Th analyses for zircons from the Hornbeam Hill Intrusive Suite. Zircon rim ages, indicative of the age of metamorphic crystallization, were averaged to 390 ± 3 Ma with 2-sigma uncertainty.

GEOCHEMICAL RESULTS

Falmouth-Brunswick Amphibolites

Eleven samples of amphibolite from the Unnamed Gneiss unit (Oug) and Mixed

Rocks (Ougm) subunit, as well as the Mount Ararat Formation in the Richmond

Quadrangle, were analyzed in an attempt to gain greater understanding as to the tectonic setting of the Falmouth-Brunswick sequence at the time of its deposition. Geochemical data from these analyses is given in Appendix IV. Initial classification of these metavolcanic rocks was achieved by using a Zr/TiO2 vs. SiO2 diagram, in which all of the amphibolite samples fall within a subalkaline basalt field (Figure 40). This diagram was used instead of other classification diagrams, i.e. Na2O+K2O vs. SiO2, because zirconium and titanium are less mobile during metamorphism than are alkalis, and hence their concentrations provide a more reliable measure of initial abundances.

Figure 40: Plot of Zr/TiO2 versus SiO2 (wt%) clearly shows that the 11 amphibolite samples collected from the Falmouth-Brunswick sequence plot as subalkaline basalts.

To further subdivide these subalkaline basalts, the samples were plotted on a

t triangular AFM diagram, using FeO , MgO, and Na2O+K2O as the three indices (Figure

41). The sample points plot in a rough line trending towards the FeOt apex, a pattern which more closely follows the upper, or tholeiitic trend. The rocks are distinctly alkali- poor compared to the concentrations of iron and magnesium. Consequently, the amphibolite samples are consistent with initial subalkaline, tholeiitic basalt compositions.

Caution must be taken in making this determination, however, again due to the mobility of alkalis under metamorphic conditions.

Figure 41: This triangular AFM diagram displays a trend towards increasing FeOt with fractional crystallization, indicating a tholeiitic rather than calcalkaline basalt.

In many tectonic discriminant diagrams, the Falmouth-Brunswick amphibolites show geochemical signatures that encompass both island arc tholeiite (IAT) and within-

plate basalt (WPB) fields. A good example of this pattern is a Zr-Ti diagram (Figure 42), which shows samples evenly split between the two fields. What is important to notice, however, is that the majority of these samples fall within the mid-ocean ridge basalt

(MORB) field that overlaps with both the IAT and WPB. This MORB signature becomes the common element in all tectonic diagrams.

Figure 42: Plot of Zr versus Ti shows the amphibolite samples distributed evenly between island-arc tholeiite (IAT) and within-plate basalt (WPB) fields. Most importantly, the majority of the samples plot within the MORB overlap field that incorporates parts of both the WPB and IAT.

In both a triangular Ti-Zr-Sr diagram (Figure 43) and a Ti-V diagram (Figure 44), there is a clear exclusion of WPB basalt, and the decision was made to rule out that environment as a tectonic setting. In the Ti-Zr-Sr diagram, there is a clear dichotomy between the ocean floor basalt (MORB) and low-K tholeiite (IAT), with roughly equal numbers in both fields. In a Ti-V diagram, however, 9 of the 11 samples plot in the

MORB and BABB field, while only two plot in the IAT field. While MORB/BABB is dominant, the continued presence of IAT samples hints at a subduction zone environment with a back-arc spreading center that emulates the MORB chemical signature.

Figure 43: Triangular Ti-Zr-Sr plot showing the Falmouth-Brunswick amphibolite samples plotting evenly between the ocean floor basalt (OFB) and low-K tholeiite (LKT) fields. There is no evidence of a within-plate (WPB) signature. Note that strontium is very mobile under metamorphic conditions, and thus this diagram must be interpreted with caution.

Figure 44: Plot of Ti versus V showing 9 of the 11 samples plotting within the MORB/BABB field, with only 2 samples plotting with a distinct arc signature. There is no within-plate component. Sample G13, plotting with extremely high levels of titanium, may represent an amphibolite with more evolved, sedimentary origins.

A plot of Ta/Yb versus Th/Yb was constructed to show two subgroups of amphibolite samples (Figure 45). One group plots squarely in the MORB field, while the second group plots just barely outside the MORB field in a subduction-influenced calcalkaline field. While these two samples in the second group, R3 and AFT-73, are not the two samples plotting as IAT in the Ti-V diagram (Figure 44), they were collected in very close proximity to the two samples that did plot as IAT, R1 and R2 (Figure 15). Rare earth element analyses were not performed on those samples.

Figure 45: Plot of Ta/Yb versus Th/Yb showing two distinct groups within the four analyzed samples. The first group plots with a distinctly MORB signature, while the second group shows the slight influence of subduction processes.

The rare earth element pattern (Figure 46) for the Falmouth-Brunswick

amphibolites is elevated 30-100x relative to chondrite, and each of the four samples

shows essentially the same pattern. The light rare earth elements (LREEs) are enriched

relative to the heavy rare earth elements (HREEs), with a gently sloping downward trend

((La/Lu)N = 4.1). A spider diagram joining the rare earth elements with select trace

elements (Figure 47) shows relative enrichment of large ion lithophile (LILE) elements.

The whole pattern is enriched in comparison to N-MORB, except for the strongest high

field strength (HFS) elements, i.e. Cr and Ni. There are small negative zircon (Zr) and

ytterbium (Yb) anomalies.

Two samples, FT-73 and R3, collected very close to each other in the Richmond

Quadrangle, display very slight niobium (Nb) anomalies (Green, 1995), while the other two samples, B41 and GC13 (from inside the Bowdoinham Quadrangle), do not show anomalies. These pairings correspond with the groupings shown in Figure 45. Samples

FT-73 and R3 plot with a slight island arc signature in Figure 45 and also have a very slight Nb anomaly in the spider pattern. Similarly, B41 and GC-13 plot as MORB in

Figure 45 and do not show any Nb anomaly in the spider diagram. FT-73 and R3 may be showing subduction zone influences while B41 and GC13 might have formed in a more evolved MORB setting, eliminating the negative Nb subduction signal.

Figure 46: REE pattern for the Falmouth-Brunswick amphibolite samples. Notice general enrichment in samples relative to chondrite and the gently downward-sloping pattern, indicating LREE enrichment over HREEs. Adapted from Sun and McDonough (1989).

Figure 47: Trace element spider diagram for the Falmouth-Brunswick amphibolites displaying relative enrichment in LILE elements. The amphibolites are enriched relative to N-MORB for everything but the strongest high field-strength (HFS) elements. Note the very slight Nb anomalies in two samples, while the other samples do not show this subduction zone influence. Dotted lines predict the pattern without Nb anomalies. Adapted from Pearce (1983).

Pluton Geochemistry

Analysis of the Hornbeam Hill Intrusive Suite geochemical data was conducted in a manner similar to that for the amphibolite samples, with results first used for rock classification purposes, and then to identify a tectonic environment for their magma generation. Pluton geochemical data from ICP analysis is presented in Appendix V.

A SiO2 versus Alkalis (Na2O + K2O) plutonic rock classification diagram (Figure

48) was used to classify the Hornbeam Hill samples. What becomes immediately

obvious in this diagram is the wide range in compositions within the pluton, a fact

supported by both the field and petrographic findings. Samples range from alkali granite

to borderline gabbro, with most spread throughout the syeno-diorite field. The majority

of the samples plot as being slightly subalkaline, though three samples are distinctly

alkaline in nature. While this diagram is effective in displaying the wide geochemical variations present within the pluton, it is important to realize that alkalis are mobile under metamorphism, and since these rocks have been recrystallized, caution must be exercised when making interpretations. This is especially true when assessing whether the samples are alkaline or subalkaline.

Figure 48: Alkali versus SiO2 classification diagram clearly illustrating the wide geochemical variation present within the Hornbeam Hill Intrusive Suite. Samples range in composition from syeno-diorites to alkali granites. Adapted from Wilson (1989).

To determine whether the Hornbeam Hill pluton had been derived from the melting of igneous or sedimentary source material, the silica was plotted against the alumina saturation index, or ASI, which is equal to Al/Na+K+Ca (Figure 49). All samples except one, the alkali granite (B299), plot as metaluminous I-type granites. This classification suggests that the magma was derived from the partial melting of “mafic

mantle source material,” most probably subcontinental underplating (Winter, 2001).

While it does fall in the margin of error between the two zones, sample B299 does exhibit a weak S-type signature, suggesting that it was produced from the partial melting of sedimentary source rocks (Winter, 2001). One sample, that plotting closest to the gabbro field in the classification diagram (Figure 48), doesn’t fall within the silica range of this diagram, but also plots as a metaluminous, I-type sample. Similar to above, because alkalis are involved in the plot, the findings should be integrated with some degree of caution.

Figure 49: This diagram plots SiO2 percentage versus Alumina Saturation Index (ASI). All samples except for one, B299, plot as I-type, which indicates their origin from a mafic, mantle protolith. B299 may be derived from a more aluminum-enriched, sedimentary source.

Major element geochemical data appears to suggest that lithologic variation

within the Hornbeam Hill Intrusive Suite is the result of varying degrees of fractional

crystallization (Figure 50). Distinct trends are seen in the calcium, iron, magnesium,

manganese and titanium content with increasing silica content. Calcium decreases

sharply within increasing SiO2, as it is incorporated in hornblende and plagioclase

feldspar, early-crystallizing major constituents of the more intermediate members of the

intrusive suite. Calcium is taken up preferentially before sodium in high temperature

plagioclase crystallization, quickly depleting the relative abundance of the element.

The weight percentage of iron oxide also decreases with increasing SiO2. Iron, like calcium, is contained in hornblende and garnet, but more importantly, is also a major constituent element in biotite. Biotite comprises a large percentage of the mineralogy in more intermediate syeno-dioritic intrusive samples, but by the time of the crystallization of the alkali granite sample, at a lower temperature, most of the available iron may have been used up, for biotite appears only in trace amounts.

The relative concentration of potassium increases gradually with increasing silica percentage. Potassium is not typically incorporated into the structures of minerals crystallizing at higher temperatures, as are elements like calcium, and doesn’t become incorporated in any minerals in large amounts until biotite is crystallized at intermediate temperatures. Consequently, its relative concentration rises in the lower temperature, more felsic melts occurring at late stages in the fractional crystallization process, and it is taken up in K-feldspar. Magnesium, on the other hand, decreases quickly with increasingly felsic magmas, as magnesium is preferentially incorporated over iron at higher temperatures into hornblende and biotite, and is found in much smaller abundances in later bodies of more felsic composition.

Titanium also shows a steady decline. It is crystallized at high temperatures into ilmenite, which is often present as cores for the abundant titanite in many of the pluton samples (Figure 27). Titanium is also incorporated into biotite, and as it is progressively

crystallized, its relative abundance decreases by the time of the crystallization of the felsic samples. Manganese substitutes for Fe2+ and Mg2+ in common Fe-Mg silicate minerals such as garnet, hornblende, and biotite, with the largest amount crystallized in spessartine garnet. The relative concentration of manganese decreases with increasing silica content, as does the concentration of the Fe-Mg silicate minerals.

Figure 50: Harker variation diagrams for major element data from the Hornbeam Hill Intrusive Suite. Linear patterns in Ca, Fe, K, Mg, Mn, and Ti suggest progressive fractional crystallization during the emplacement of the pluton.

Rare earth element analyses were obtained for seven of the Hornbeam Hill pluton

samples. The downward-sloping REE pattern (Figure 51) shows overall enrichment of

10-400x relative to chondrite, with LREE elements significantly enriched relative to

HREE elements. The pattern flattens out in the HREE elements, implying that garnet is

not involved in producing the LREE enrichment.

The REE pattern shown can not be the result of simple fractional crystallization, as lines from different samples’ patterns intersect each other, and it appears that there are two groups within the pluton. The first group, shown in blue, has a steeper slope in the

LREE elements ((La/Sm)N = 4.6) and a distinct negative europium anomaly. The second group, shown in red, has a much gentler slope in the LREE ((La/Sm)N = 2.8) and does not have the significant europium anomaly seen in the first group. This grouping and crossing of patterns stipulates that either 1) the two groups came from different magma sources or 2) the two groups came from the same magma source but during emplacement were subjected to differing degrees of contamination from the overlying crust. The first group contains samples B104, B113, GC11, B185, and B299, while the second group is comprised of samples B259 and B296 (see Figure 16 for locations). Group 1 sample

B299, located very close to Group 2 sample B296, is 100x more enriched in La relative to

MORB, which indicates that there is significant geochemical variation over small distances.

Figure 51: REE plot for the Hornbeam Hill Intrusive Suite. Note the two groups within: 1) a more LREE enriched, steeply dipping group with a significant Eu anomaly and 2) a gently dipping, less LREE enriched group with little to no Eu anomaly. Adapted from Sun & McDonough (1989).

Figure 52 shows a trace element spider diagram for the Hornbeam Hill Intrusive

Suite. Notice significant negative scandium, titanium, phosphorous, and barium

anomalies, as well as a cesium peak. The most important feature of this pattern is the

niobium-tantalum negative anomaly. This anomaly rules out the possibility of the pluton

being derived from solely a mantle source, and suggests that the pluton was either 1)

emplaced in a subduction environment, or 2) derived through the partial melting of

continental crust that may have been formed or modified by subduction processes—thus

the granitic rocks inherit this signature.

Figure 52: Trace element spider pattern for the Hornbeam Hill Intrusive Suite. Notice negative Nb, P, Ti, Sc, and Ba anomalies, and a positive Ce anomaly. Adapted from Pearce (1983).

Granite tectonic discriminant diagrams were utilized to attempt to identify an environment of magma generation and eventual emplacement for the Hornbeam Hill

Intrusive Suite. These tectonic discriminations were based heavily upon trace elements, including REE, for 7 samples. Results point to the conclusion that some pluton samples were emplaced in a within-plate basalt environment, while others were emplaced in a volcanic arc setting. Figure 53 shows a plot of Y versus Nb, where points are split between within-plate granite (WPG) and volcanic arc/syn-collisional granite (VAG+syn-

COLG) fields. The majority of samples plot as within-plate granite. Other tectonic diagrams, e.g. Y+Nb vs. Rb consistently exclude any syn-collisional component, however due to the mobility of rubidium the accuracy of these diagrams is greatly reduced. Tectonic discrimination via granites is problematic because while granites may actually have the signature of a certain tectonic environment, this environment could just be a relic signature gained from partial melting of tectonically inactive crustal basement.

Figure 53: This Y-Nb tectonic discriminant diagram for the Hornbeam Hill Intrusive Suite shows a split of samples between the within-plate granite (WPG) and volcanic-arc granite (VAG) – syn-collisonal granite (syn-COLG) fields.

The most important evidence used to identify a tectonic setting for the

emplacement of the Hornbeam Hill Intrusive Suite is not a determinant diagram at all, but

a simple plot of (Na2O+K2O) and CaO vs. SiO2, shown in Figure 54. (Na2O+K2O) and

CaO are plotted as two separate data series, and a mean trendline is assigned to each series. The point of intersection of these two trendlines is significant, as its silica content

(or “alkali-lime index”) is indicative of a certain magmatic type, and by extension a tectonic environment. For the Hornbeam Hill Intrusive Suite, the intersection of these two data series falls at a silica content of ~57.2%. According to the work of Peacock

(1931), an alkali-lime index falling between 56-61 is “calc-alkalic.” The position of the

Hornbeam Hill pluton samples within this range places them closer to alkali-calcic (51-

56%) than calcic (>61%). According to Wilson (1989) and Winter (2001), a calc-

alkaline magma series will not be emplaced in within-plate tectonic settings, and is essentially restricted to convergent, subduction-related processes. This determination correlates well with the 390 ± 3 Ma U-Pb zircon age for the pluton, as well as the negative Nb anomaly observed in the spider pattern (Figure 52), because all these results suggest syn-collisional emplacement during the Acadian orogeny.

10.00 8.00

9.00 7.00 8.00 6.00 7.00

t%)

5.00 ) w 6.00 % t O (

5.00 4.00 w K2

O ( + 4.00 a 3.00 C

Na2O 3.00 2.00 2.00 1.00 1.00 Na2O + K2O (wt%) CaO (wt%) 0.00 0.00 50.00 55.00 60.00 65.00 70.00 75.00 SiO2 (wt %)

Figure 54: Plot of (Na2O+K2O) and CaO versus SiO2. The intersection of the two trendlines represents the “alkali-lime index” of Peacock (1931), and its SiO2 value (~57.2%) falls into a “calc-alkalic” magmatic composition field. This strongly suggests emplacement in a subduction zone (Wilson, 1989).

V. DISCUSSION

The rocks exposed in the Bowdoinham 7.5’ Quadrangle reflect a complex geologic history spanning over 250 million years of tectonic processes. This history began in the Ordovician with the deposition of the rocks of the Falmouth-Brunswick sequence (~460-470 m.y.a.) and ended in the Mesozoic with the intrusion of post- tectonic mafic dikes (~200 m.y.a.). The following section will provide a discussion of the major aspects of the geologic history of the Bowdoinham 7.5’ Quadrangle. It will be divided into sections that correspond to the major aspects of this study (Mapping,

Metamorphism, Deformation, and Geochemistry).

MAPPING

The bedrock mapping component of this project provides considerably more detail and significant modification to the only existing geologic map of the region (the

1:62,500 scale map of the Gardiner 15’ Quadrangle: Newberg, 1984). The modifications include a major change in the location of the central Maine-Liberty-Orrington belt boundary and the recognition of an extensive deformed and recrystallized plutonic suite.

In addition, the stratigraphic nomenclature was adjusted to reflect the currently accepted naming schemes in southwestern Maine.

Falmouth-Brunswick Sequence

The Unnamed Gneiss unit (Oug) of the Falmouth-Brunswick sequence exposed in the eastern part of the quadrangle (Plate 1) may correlate with portions of the Nehumkeag

Pond and Mount Ararat Formations of Hussey & Berry (2002). However, comparisons

of the lithologic characteristics of the Unnamed Gneiss unit and those descriptions published for the Nehumkeag Pond and Mount Ararat Formations reveal significant differences. Consequently, it is best not to attempt a direct correlation (hence the name

“Unnamed Gneiss unit”). However, based on the position of the Unnamed Gneiss unit in the Liberty–Orrington belt east of the Flying Point Fault, it can be confidently correlated with the Falmouth-Brunswick sequence as defined by Hussey (1988) and Hussey &

Berry (2002).

Rocks previously mapped in the quadrangle as the Richmond Corner member of the Cushing Formation by Newberg (1984) are now mapped as a mixed-lithology subunit

(Ougm = “Mixed Rocks subunit”) within the Unnamed Gneiss unit of the Falmouth-

Brunswick sequence. This was done because the significant lithologic variability observed in the Mixed Rocks subunit is more characteristic of rocks within the Falmouth-

Brunswick sequence than the relatively homogenous central Maine sequence.

Unfortunately, south of the study area Hussey & Berry (2002) have used the name

Richmond Corner Formation to describe a thin metasedimentary unit, and assigned this unit to the central Maine sequence. It should be noted that the Richmond Corner

Formation of Hussey & Berry (2002) does not correlate with the Unnamed Gneiss unit

(despite the fact that this unit is exposed at Richmond Corner).

Central Maine Sequence (Vassalboro Formation)

The thick assemblage of biotite granofels and calc-silicate gneisses that underlie the western half of the field area are without question members of the central Maine sequence. Newberg (1984) first made this distinction, and grouped these rocks in the

Vassalboro Formation (a designation also used by Osberg et al., 1985). However, beginning with the work of Osberg (1988), similar rocks along the eastern margin of the central Maine belt have been reassigned to the Hutchins Corner Formation. This formation was defined by Osberg (1988) as being a unit located southeast of (presumably beneath) the Waterville Formation, with its type locality located 45 km to the northeast of the Bowdoinham Quadrangle. Tucker et al. (2001) revived the name “Vassalboro

Formation” and used it to refer to biotite granofels and calc-silicate gneisses of unknown stratigraphic position. As the stratigraphic position of these rocks relative to the

Waterville Formation is unknown, the name Vassalboro Formation (OSv) is maintained.

The rusty schist and coticule member of the Vassalboro Formation (Svr), located along the eastern margin of this unit, may correlate with the Torrey Hill and Richmond

Corner Formations descried by Hussey (1988) and Hussey & Berry (2002) to the south.

The Torrey Hill Formation is characterized by very rusty weathering sulfidic biotite schist with sillimanite and garnet, while the Richmond Corner Formation is characterized by migmatitic biotite gneisses and granofels with sillimanite and garnet (Hussey & Berry,

2002). Both these lithological assemblages can be found within the rusty schist and coticule member of the Vassalboro Formation. Unfortunately, exposures of this unit are limited in the Bowdoinham Quadrangle and this hinders attempts to make a direct correlation.

Hornbeam Hill Intrusive Suite

A previously unrecognized suite of intrusive rocks, here termed the Hornbeam

Hill Intrusive Suite (named for a prominent hill in the south-central portion of the quadrangle) was mapped, and at a reconnaissance level, petrographically and geochemically characterized. Although the northeastern and southwestern limits of the intrusion extend past the study area, the plutonic body is a minimum of 8 km long and up to 1.6 km in width. The map pattern of this suite of intrusive rocks indicates that it “seals the contact” between the Falmouth-Brunswick and central Maine sequences, and therefore provides a minimum age for the juxtapositioning of these two important lithotectonic terranes into their current positions. Although the U-Pb (SHRIMP) work performed on zircons from this suite did not yield a solid igneous crystallization age, it did suggest that original crystallization was not significantly older than ~390 Ma.

Consequently, any movement along this contact between the Falmouth-Brunswick and central Maine sequences in this region must have occurred prior to ~400 Ma.

The Hornbeam Hill Intrusive Suite is also significant because it is penetratively deformed and thoroughly recrystallized. In addition, the map pattern of the pluton is highly elongated roughly parallel to the strike of the other lithologic boundaries in the region. This has the implication that the dominant episode of deformation and metamorphism in the Bowdoinham Quadrangle postdated the emplacement of the

Hornbeam Hill pluton. An additional constraint is provided by a U-Pb (SHRIMP) age of

390 ± 3 Ma on metamorphic overgrowth rims on zircons from the Hornbeam Hill pluton

(see Figures 36 & 37). This Middle Devonian age is consistent with the timing of high-

grade regional metamorphism and deformation associated with the Acadian orogeny

(Tucker et al., 2001).

Numerous plutons of Early-Middle Devonian age are found in the state of Maine

(Osberg et al., 1985), however the ones temporally and spatially most closely related to the Hornbeam Hill pluton are the Togus (378 ± 1 Ma) and Threemile Pond (381 ± 1 Ma) plutons which are located 22 km to the northeast. Although to date no detailed petrographic or geochemical studies have been performed on these plutons, their compositions seem to overlap with the range of compositions found in the Hornbeam Hill pluton, and, perhaps more importantly, they are similarly located along the eastern margin of the central Maine belt close to the contact with the Liberty-Orrington belt.

Given the at least 10 million-year difference in age, it is assumed that the magmas could not have been generated from the same magma source, and hence their chemical and mineralogical compositions are likely to be different.

Descriptions of the Togus and Threemile Pond plutons (Osberg, 1988) indicate that rocks in their central cores are slightly foliated while rocks along the margins of these intrusions have been more intensely foliated. These differences may provide insight into the timing of deformation in the eastern part of the central Maine belt. It is hypothesized that the timing of intense deformation in the region may be bracketed by the age differences of these plutons—a lower age limit is provided by the slightly deformed,

~380 Ma Togus and Threemile Pond plutons, and an upper age limit is provided by the strongly deformed Hornbeam Hill pluton. An alternative explanation would be that the differences in deformational styles of these intrusions is a function of the differences in rheological properties due to pluton size differences. The Togus and Threemile Pond

plutons are significantly larger, thus deformation may have been deflected around the margins of these intrusions while the smaller Hornbeam Hill pluton absorbed the full brunt of deformational forces. A detailed comparative structural study of the two plutons would be necessary to accurately assess these two hypotheses on deformational variation.

Pegmatites

The muscovite-bearing, graphic granitic pegmatites found in the northeastern portion of the Bowdoinham Quadrangle correlate well with the Topsham-Brunswick area leucogranites described by Tomascak et al. (1999) and Hussey & Berry (2002). The pegmatites in the Topsham-Brunswick area were U-Pb monazite-dated to a mean age range of 275-268 Ma by Tomascak et al. (1996). Thus the correlation of pegmatites in the Bowdoinham Quadrangle with those in the Topsham-Brunswick area establishes that the Permian aged pegmatites extend as far north as the northern part of the Bowdoinham

Quadrangle, significantly further than was previously realized.

Mafic Dikes

The post-tectonic dikes found in the Bowdoinham Quadrangle are relatively small and cannot be mapped at a 1:24,000 scale. These dikes are correlated with dikes all along the southern coast of Maine including the Christmas Cove dike (Hussey & Berry, 2002).

The Christmas Cove dike has a tholeiitic diabase composition similar to those found the

Bowdoinham Quadrangle and itself has been correlated with other larger dikes in New

England as well as coeval basalt flows in the Hartford and Fundy Mesozoic Basins (West

& McHone, 1997). The age range for the regionally extensive Christmas Cove dike is

196.4-204.8 Ma, based on 40Ar/39Ar dates recorded by West & McHone (1997).

Consequently, while mafic dikes are relatively minor within the Bowdoinham

Quadrangle, they do record tectonic events associated with extensional processes related to early stages of the rifting of Pangaea in the Mesozoic and the opening of the Atlantic

Ocean basin.

METAMORPHISM

Field observations and reconnaissance petrographic investigations confirm the findings of Guidotti (1989) who suggested that rocks in the Bowdoinham 7.5’

Quadrangle were subjected to upper amphibolite facies metamorphism. Abundant prismatic sillimanite is found in rocks of pelitic bulk composition (e.g. the rusty schist unit within the Vassalboro Formation), and the assemblage hornblende+clinopyroxene+plagioclase is found in metamorphosed mafic rocks

(amphibolites) of the Falmouth-Brunswick sequence. In addition, the presence of extensive migmatization within quartzofeldspathic rocks of the Falmouth-Brunswick sequence is consistent with partial melting due to the high temperatures associated with amphibolite facies metamorphism.

STRUCTURE

The structural features of the rocks within the Bowdoinham Quadrangle are dominated by a gentle, east-dipping foliation that appears to be axial planar to minor, inclined isoclinal folds. These folds appear to be west verging. There is no evidence in the field area of upright isoclinal folds that are so typical elsewhere in central and

southwestern Maine (Hussey, 1988; Osberg, 1988). In addition, there is no evidence of the Norumbega fault zone-style dextral shear deformational features that are also pronounced in other parts of the Liberty-Orrington and central Maine belts (West &

Hubbard, 1997; Swanson, 1999).

These observations fit well into the model of Swanson (1999), which proposes

that the area around Norumbega Fault System represents a positive transpressional flower

structure (Figure 55). The nature of movement within this structure results in west-

verging oblique thrusting and reclined folding along the northwest side of the Norumbega

fault system. Most of the Liberty-Orrington belt is located within the region of dextral

transpressive movement in the center of the flower structure, and consequently contains

vertical foliations and dextral shear deformational features. The postulated position of

the Bowdoinham Quadrangle, on the other hand, lies outboard of the vertical components

of the Norumbega system in this model (Figure 55). While the Bowdoinham 7.5'

Quadrangle is located north of the cross-section illustrated by Swanson, it occupies the

same structural position as the Sebago Pluton relative to the fault system. Notice the

reclined folding in this region of Swanson’s flower structure, correlating well with fold

and foliation orientations observed in the field.

Figure 55: This model shows the positive transpressional flower structure proposed for southwestern Maine by Swanson (1999). The observed cross-section runs along a H- H’’’’ transect taken from the Maine Bedrock Geologic Map (Osberg et al., 1985) which is approximately 29 km south of the present study area. Notice the approximate position of the Bowdoinham Quadrangle on the NW flank of the system, in an area of reclined folding and west-vergent thrusting.

GEOCHEMISTRY

Falmouth-Brunswick Tectonic Discrimination

Based upon the amphibolite geochemical data presented previously, it is believed that amphibolites within the Falmouth-Brunswick sequence represent basaltic magma generated from an evolved back-arc basin spreading ridge. While most of the amphibolite samples plot consistently within MORB or MORB-overlap fields in tectonic discriminant diagrams (e.g. Figures 42, 44), there is also a small but distinct subduction- zone, IAT component best illustrated in Figures 44 and 45. This component is seen in a spider diagram (Figure 47) as very small negative niobium anomalies for 2 of 4 samples

analyzed, the legitimacy of which is strengthened by the grouping of those two samples just inside a subduction-influenced field in a Ta/Yb vs. Th/Yb diagram (Figure 45). The

REE pattern (Figure 46), with moderate LREE enrichment and a negative slope, fits well between an island arc setting (more LREE enrichment, steeper slope) and a MORB setting (negative enrichment of LREEs to a flat pattern).

It is proposed that the Falmouth-Brunswick samples formed in a back-arc spreading region that had progressed beyond the initial rifting stage, evidenced by the very small magnitude of the niobium subduction signature. However, the spreading center had not quite reached a fully evolved MORB stage, as indicated by the continual presence of IAT signatures and the enrichment of LREE relative to HREE in the REE pattern. It is of note that those samples plotting as IAT in the Ti-V (Figure 44) and the

Ta/Yb-Th/Yb diagrams (Figure 45), and those displaying a Nb anomaly in Figure 47 are from the suite of samples collected at the Richmond Quadrangle interstate interchange just outside the northeast corner of the Bowdoinham Quadrangle. Taking into consideration the complex lithotectonic history of the area, one cannot assume that all amphibolite bodies sampled are the same age, were formed in their current relative positions, or were even necessarily formed in the same tectonic environment. However, the evolved back-arc determination represents the most appropriate tectonic environment if a similar depositional setting is assumed for all amphibolites.

Figure 56 (below) shows the Falmouth-Brunswick sequence’s position in the

Ordovician tectonic model proposed by West et al. (2004). Instead of being an arc volcanic group, as was originally proposed, the Falmouth-Brunswick sequence, along with the Upper Casco Bay Group (Cape Elizabeth, Spring Point, Diamond Island, and

Scarboro Formations), appears in a back-arc spreading zone that rifts the older Cushing

Formation volcanic arc.

Figure 56: This diagram shows the tectonic model of West et al. (2004) for the formation of Liberty-Orrington Belt rocks along the Iapetus Ocean- Gander subcontinent margin. Note the change of the Falmouth-Brunswick sequence’s position from that of a volcanic arc sequence to a younger back-arc basin sequence.

Regional Correlations

The two closest regional correlatives for back-arc basin spreading in northern

New England and southern Canada are the Casco Bay Group's Spring Point Formation and the Bathurst Supergroup of New Brunswick. While there are doubts whether the

Spring Point and Bathurst can themselves be positively correlated, based on complex tectonic history and along-strike distance (van Staal et al., 2003), they are part of the same lithotectonic terrane as the Falmouth-Brunswick sequence, and hence comparison is

appropriate. The Spring Point Formation geochemistry represents the closest regional work done on amphibolites in the Liberty-Orrington belt.

Rare-earth element and spider diagrams comparing geochemical data from the

Falmouth-Brunswick, Spring Point, and Bathurst lithologies are shown in Figures 57 and

58, below. Data shown is an average of multiple samples. For the Spring Point

Formation, data results from 5 mafic (SP3-6, SP8) metavolcanic samples were analyzed, while felsic samples were not considered for lack of a clear correlative within the

Falmouth-Brunswick sequence (West et al., 2004). As West et al. (2004) compare the

Spring Point Formation with the Tetagouche and California Lake Groups of the Bathurst

Supergroup, those groups were the Bathurst members used in this analysis as well. Five

basalt samples were averaged from the two groups, and only tholeiitic basalt samples

were considered, in order to provide the most even comparison with the tholeiitic basalts

of the Falmouth-Brunswick sequence.

The REE pattern of the Falmouth-Brunswick sequence is generally similar to that

of the Spring Point Formation and Bathurst Supergroup, though it is more LREE enriched

and generally has a steeper slope, indicating a greater relative difference between the

abundance of LREE and HREE elements (Figure 57). In the HREE elements, the

patterns of all three groups are essentially identical.

In the spider diagram (Figure 58), the patterns for all three groups are again very

similar, with identical patterns in the LILE elements. There is a common negative barium

anomaly for all groups, however the niobium-anomaly arc signature that one might

expect from all back-arc basin lithologies is only present in the Spring Point samples.

This suggests that the Spring Point Formation may have formed in a less-evolved back-

arc environment that was still undergoing rifting of the arc itself, while the Bathurst

Supergroup and Falmouth-Brunswick sequence were formed in a more-evolved, spreading ridge back-arc system. It is important to keep in mind, however, that averaging samples might eliminate lesser niobium signals. This is illustrated by the fact that the slight Nb anomalies in two of the Falmouth-Brunswick samples (Figure 47) are not represented in the Falmouth-Brunswick average spider pattern (Figure 58).

Figure 57: This REE diagram compares averages from the Falmouth-Brunswick, Spring Point, and Bathurst lithologies. Notice Falmouth-Brunswick LREE enrichment relative to the two other groups, but the identical patterns in the HREE elements. Adapted from Anders & Ebihara (1982).

Figure 58: This trace element spider diagram comparison shows relatively similar patterns in all three groups, with overall LILE enrichment. In the LFS elements, the patterns match almost perfectly. A negative barium anomaly is a common feature, however the Nb-Ta anomaly indicative of arc processes is only viewed in the Spring Point samples. Adapted from Pearce (1983).

The Falmouth-Brunswick sequence's trace and rare-earth element pattern similarities with the established back-arc settings of the Spring Point Formation and

Bathurst Supergroup lend support to the tectonic determination of this paper and to the regional correlation of these member groups within the Liberty-Orrington Belt.

Current Evolved Back-Arc Spreading

In order to test the evolved back-arc discrimination for the Falmouth-Brunswick sequence, the amphibolite geochemical results of this study were compared with those collected by Gribble et al. (1998) for evolved "back-arc spreading ridge” samples in the

Northern Mariana Trough. Gribble et al. (1998) identify a progression of back-arc

magmatic evolution in the Northern Mariana Trough, from a magmatic rift in the north to

an amagmatic rift and then eventually a spreading axis in the south. Six basalt and basaltic-andesite samples collected from the southern spreading axis or “spreading ridge” zone of the northern Mariana Trough were averaged for this comparison.

The REE pattern (Figure 59) for the Mariana Trough basalts has a pattern significantly different than that of the Falmouth-Brunswick sequence. Instead of being

LREE enriched, with a moderate negative slope, as is the Falmouth-Brunswick sequence, the Mariana Trough basalts show a LREE-depleted pattern that is more characteristic of full-blown MORB spreading.

B) Figure 59A) A rare-earth element plot for Mariana BABB shows a generally flat pattern with slight depletion in LREE elements in a number of the samples. This is typical of a MORB signature. B) This comparison REE plot clearly shows the differences in patterns between the Falmouth-Brunswick sequence and the Mariana Trough basalts. The Falmouth-Brunswick sequence has a moderate negative slope while the Mariana pattern has a slight positive to zero slope. (Adapted from Anders and Ebihara, 1982)

A multivariable, trace element spider diagram for the Mariana Trough samples, as well as a comparison of that data with that of the Falmouth-Brunswick sequence, is shown in Figure 60. The Mariana pattern is slightly LILE enriched, with a large positive strontium anomaly. In the high field strength (HFS) elements, the pattern is essentially flat, and relative to MORB, it is enriched only in the LILE elements. In comparison with the Mariana Trough pattern, the Falmouth-Brunswick pattern has a slightly steeper negative slope through the LILE elements, but the two patterns are very similar for the high field strength elements. The Falmouth-Brunswick pattern is consistently enriched relative to the Mariana pattern (further from MORB composition), though the gap closes in the HFS elements.

Figure 60A) This spider plot for the evolved Mariana Trough BABB shows a slightly LILE enriched pattern with a large positive strontium anomaly. B) This spider diagram comparison shows the Falmouth-Brunswick pattern’s consistent enrichment relative to the Mariana pattern, as well as its steeper negative slope and its greater LILE enrichment relative to HFS elements. Adapted from Hofmann (1982).

In general, the evolved back-arc samples from the Mariana Trough plot much

closer to MORB than do the proposed back-arc samples of the Falmouth-Brunswick

sequence. The negative enrichment of LREE elements relative to HREE elements in the

Mariana samples (Figure 59A) is very characteristic of MORB, as is the lower

enrichment relative to the N-MORB standard of Pearce (1983). This may suggest that the

back-arc spreading environment in which the Falmouth-Brunswick sequence formed had not reached the same degree of back-arc evolution now present in the Mariana Trough, and still possessed more of an arc signature.

One must take caution making this claim, however, by considering the limits of

comparing a current area of spreading with a paleoenvironment. While the basaltic

glasses sampled in the Mariana Trough back-arc are non-metamorphosed, the

amphibolites of the Falmouth-Brunswick sequence have been subjected to upper-level

amphibolite facies metamorphism. This may have numerous implications on the

geochemistry of the rocks. For instance, metamorphism can cause increased mobility in

the LILE elements, leading to enrichment or depletion not characteristic of the tectonic

setting. If the Falmouth-Brunswick sequence had in fact been diagenetically enriched in

LILEs during metamorphism, their original REE and spider patterns may have been

much more similar to the modern day pattern of the Mariana Trough.

VI. CONCLUSIONS

Despite high-grade metamorphism, ductile deformation, poor outcrop exposure,

and small scale lithologic variability, this study has yielded a better picture of the original

stratigraphy and geological history of this region of the Liberty-Orrington Belt. The

Bowdoinham 7.5’ Quadrangle is of regional significance because it encompasses the boundary between the Falmouth-Brunswick sequence of the Liberty-Orrington Belt and the Vassalboro Formation of the central Maine sequence. Detailed geologic mapping in the northern portion of the quadrangle has resulted in the delineation of the following lithologic units: (1) migmatitic gneisses and other subordinate lithologies (e.g.

amphibolites, rusty schists) associated with the Ordovician Falmouth-Brunswick sequence, (2) calc-silicate gneisses and biotite granofels associated with the Late

Ordovician (?) – Devonian central Maine sequence, (3) a previously unrecognized deformed Devonian intrusive body of variable composition – here termed the Hornbeam

Hill Intrusive Suite, and (4) several small granitic pegmatite bodies (likely both Devonian and Permian in age). Careful field observations of unit relationships reveal that the

Hornbeam Hill Intrusive Suite “seals the contact” between the Falmouth-Brunswick and central Maine sequences in this region. Crystallization of this plutonic rock body appears to have occurred at ~390 Ma.

The Hornbeam Hill Intrusive Suite contains a range of deformed and metamorphosed plutonic rocks which, based on whole-rock geochemical results appear to be either: 1) derived from a single magma source with differing levels of crustal contamination or 2) derived from multiple magma sources. Compositions of this deformed and recrystallized intrusive suite range from quartzofeldspathic alkali granites to hornblende-bearing syeno-diorites. Future studies should further examine the small- scale spatial distributions of the main lithologic types within the pluton, and additional zircon age dating should be employed to determine if there are any differences in

emplacement ages across the body. As this pluton is newly recognized, mapping its full

extent in the southern Bowdoinham and adjoining quadrangles is a first priority.

The Unnamed Gneiss unit (Oug) which underlies much of the eastern portion of

the field area can confidently be assigned to the Falmouth-Brunswick sequence of the

Liberty-Orrington belt. However, a direct correlation with rocks of the Mount Ararat and

Nehumkeag Pond Formations cannot be made due to lithologic differences. Interestingly,

the Richmond Corner Formation (central Maine sequence) as described by Hussey &

Berry (2002) is not present in the original type locality of this unit (as defined by

Newberg (1984). Instead, exposed at Richmond Corner is a sequence of mixed

lithologies (Ougm) that are best associated with the Falmouth-Brunswick sequence.

However, rocks that may correlate with the Richmond Corner Formation of Hussey &

Berry (2002) are found to the west and are included as a member of the Vassalboro

Formation (Svr).

Ductile deformation of the stratified rocks in the quadrangle is characterized by

overturned isoclinal folds and an associated axial planar schistosity that generally strikes

N-NW and dips gently to the east. Metamorphic mineral assemblages from a range of

bulk compositions are all consistent with upper amphibolite facies conditions.

Preliminary geochemical results for amphibolites from the Falmouth-Brunswick sequence reveal sub-alkaline basaltic compositions with trace element patterns that are consistent with derivation in a back-arc tectonic setting. These geochemical results allow for a loose correlation with similar findings in other parts of the Liberty-Orrington belt as well as likely correlative rocks of the Bathurst Supergroup in the Miramichi Highlands of

New Brunswick.

100

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Appendix I

Lithologic Descriptions of Bedrock Outcrop Stations, Bowdoinham 7.5’ Quadrangle

Location (lat & Station Joints Foliations Other Structures Lithology Comments long)

Garnet-bearing felsic gneiss (popcorn in places), also a N44 06.064 4 315,27 FelGn, MzD massive Mesozoic mafic dike on W69 53.612 west side of road, slight rust- weathering

N44 05.950 5 FelGn Felsic Gneiss W69 53.551

N44 06.230 Very rusty weathering sulfidic 6 RustSch W69 53.668 Schist

N44 06.249 Very rusty weathering sulfidic 7 136,79 240,22 RustSch W69 53.627 Schist

Feldspathic biotite gneiss and N44 06.249 8 314,46 FelGn schist -- some coarse grained W69 53.583 garnet in more schtose layers

N44 06.245 Rusty schist, similar to stations 6 & 9 RustSch W69 53.552 7

95% Muscovite-bearing graphic N44 04.779 10 028,57 Peg textured pegmatite, minor W69 53.083 feldspathic biotite gneiss

N44 04.827 Muscovite-bearing, graphic 11 Peg W69 53.109 textured pegmatite

N44 04.854 Muscovite-bearing, graphic 12 Peg W69 53.160 textured pegmatite

N44 04.898 Feldspathic biotite gneiss with 13 FelGn W69 53.301 some tiny pink garnets

N44 05.064 Muscovite-bearing, graphic 14 Peg W69 53.486 textured pegmatite

N44 05.111 Muscovite-bearing, graphic 15 Peg W69 53.539 textured pegmatite

N44 05.162 Muscovite-bearing, graphic 16 Peg W69 53.540 textured pegmatite

N44 05.197 Muscovite-bearing, graphic 17 Peg W69 53.565 textured pegmatite

107

Gas Line boulders, lots of N44 05.028 18 FelGn, Peg migmatitic felsic gneiss and some W69 53.334 pegmatite

Gas Line boulders, mostly N44 05.066 19 FelGn feldspathic felsic gneiss, some W69 53.296 Pegmatite and < 5% amphibolite

Gas Line boulders, mostly N44 05.070 feldspathic felsic gneiss with some 20 FelGn W69 53.214 amphibolite blocks and some pegmatite

Gas Line boulders, 60 to 70% N44 05.061 pegmatite but lots of felsic gneiss, 21 Peg, FelGn W69 53.148 some with dime-sized garnets, < 5% amphibolite

N44 04.866 Pavement outcrop, felsic gneiss 22 FelGn W69 53.026 and amphibolite, some pegmatite

N44 04.889 Muscovite-bearing, graphic 23 Peg W69 53.123 textured pegmatite

95% pegmatite, but not muscovite- N44 05.309 24 Peg bearing or graphic textured. 5% W69 53.034 felsic gneiss

N44 04.071 Muscovite-bearing, graphic 25 Peg W69 53.126 textured pegmatite

N44 04.063 Muscovite-bearing, graphic 26 Peg W69 53.187 textured pegmatite

N44 04.087 Muscovite-bearing, graphic 27 Peg W69 53.221 textured pegmatite

N44 04.058 Muscovite-bearing, graphic 28 Peg W69 53.296 textured pegmatite

N44 04.190 Muscovite-bearing, graphic 29 Peg W69 53.289 textured pegmatite

N44 04.514 Muscovite-bearing, graphic 30 Peg W69 53.671 textured pegmatite

N44 04.597 Gas line, pegmatite, some biotite 31 Peg W69 53.679 and garnet

N44 04.673 Muscovite-bearing, graphic 32 Peg W69 53.709 textured pegmatite

108

Quartz- rich biotite gneiss, both N44 05.842 rusty & nonrusty weathering - - 33 FelGn W69 53.811 also some more typical feldspathic felsic Gneiss, minor pegmatite

Variable gneisses - - mostly felsic 80degree NW N44 05.902 gneiss but some darker colored 34 347,35 rake of min. lin FelGn W69 53.772 biotite-rich gneisses with garnets, on fol. "popcorn" gneiss, some rusty

Slightly rusty weathering, biotite garent-bearing (probably N44 05.949 sillimanite too) gneiss with 35 FelGn, MzD W69 53.730 popcorn feldspars. Dike on east side of Rd - lines up with station 4 and strike would be about 030.

Migmatitic-looking "popcorn" N44 05.947 36 023,54 FelGn biotite gneiss. Nonrusty W69 53.771 weathering

Migmatitic felsic gneiss with N44 05.779 popcorn feldspar and some fine- 37 350,33 FelGn W69 53.855 grained biotite layers - rusty weathering on foliation surfaces

Some fine-grained biotite gneiss N44 05.685 with some "popcorn" migmatitic 38 351,54 FelGn W69 53.789 gneiss - - minor pegmatite (non- muscovitic, non-graphic)

Slightly rusty weathering on N44 05.706 39 005,25 FelGn foliation surfaces - "popcorn" W69 53.830 migmatitic gneiss

Moderately rusty weathering biotite N44 05.698 "popcorn" gniess - - thin whisps of 40 344,34 FelGn W69 53.874 biotite separating feldspathic layers

Moderately rusty weathering biotite N44 05.655 "popcorn" gneiss with some nice 41 345,43 FelGn, Amph W69 53.894 black biotite-bearing amphibolite; no calc-silicates

Black hornblende-biotite N44 05.578 granofelsic amphibolite flanked by 42 Amph W69 53.979 2 pegmatites rich in garnet & biotite

109

N44 05.559 Biotite gneiss (not popcorn) with 43 002,42 FelGn W69 54.032 some pegmatite

N44 05.580 Biotite gneiss and amphibolite 44 FelGn, Amph W69 54.090 (small woods outcrop)

Rather uniform looking granitic- N44 05.521 looking felsic gneiss. Very slightly 45 FelGn W69 54.093 rusty weathering. Minor pegmatite.

N44 05.496 Pegmatite - no muscovite or 46 Peg W69 54.097 graphic texture

N44 05.467 Biotite Gneiss--very slight rust 47 010,67 FelGn W69 54.077 weathering. Minor Pegmatite

N44 05.534 48 344,25 FelGn Biotite Gneiss W69 53.982

"Popcorn" texture, feldspathic N44 05.537 49 330,31 FelGn biotite gneiss with thin whispy W69 53.916 biotite layers

N44 05.499 Non-rusty weathering, migmatitic, 50 327,33 FelGn W69 53.822 "popcorn" biotite gneiss

N44 05.477 51 FelGn Migmatic "popcorn" biotite gneiss W69 53.724

Whispy biotite layers in garnet- N44 05.435 bearing, "popcorn" Felsic gneiss - 52 335,39 FelGn W69 53.669 just to east is a "calc-silicate" bearing amphibolite

N44 05.421 50-50 Popcorn biotite gneiss and 53 353,40 FelGn W69 53.671 pegmatite

N44 05.416 Migmatitic gneiss with some 54 148,46 FelGn W69 53.929 garnet

Migmatitic, "popcorn" gneiss - N44 05.416 55 149,44 FelGn some garnet and slightly rusty W69 53.879 weathering

N44 05.426 56 Peg Muscovite pegmatite W69 53.797

N44 05.566 57 001,37 FelGn Migmatitic "popcorn" felsic gneiss W69 53.951

Very dark gray to black biotite N44 06.485 58 034,37 FelGn schist in with biotite gneiss, slight W69 53.311 popcorn feldspar texture.

110

Biotite gneiss, garnet rich N44 06.446 "Quartzite", hornblende garnet 59 HblGn W69 53.363 gneiss - - some garnets up to dime sized

N44 06.486 60 Peg Small pegmatite - no muscovite W69 53.235

Calc-silicate gneiss - - some diopside rich layers - weathering N44 06.563 pits, quartz segregations, black 61 018,54 CalSil W69 53.488 hbl-plag granofels layers, slight rusty weathering on foliation surfaces

Slabby amphibolite, slightly rusty N44 06.567 on foliation surfaces - biotite and 62 336, 41 Amph W69 53.443 diopside layers - - looks like sedimentary amphibolite.

N44 06.565 Small pavement outcrop - biotite 63 FelGn W69 53.361 gneiss

Variety of lithologies: rusty sulfidic N44 06.572 schist, garnet-hbl-qtz gneiss 64 010,60 RustSch, HblGn W69 53.307 (similar to 59), ribbed weathering amphibolite

N44 06.548 Biotite gneiss with some 65 351,36 FelGn W69 53.205 feldspathic rich segregations

Mostly felsic "granitic looking" 85 degree rake N44 06.890 gneiss - rusty weathering in places 66 340,36 of min lin to SE FelGn W69 54.558 - - also migmatitic gneiss, granitic on fol. pegmatite pods

N44 06.006 Very rusty weathering sulfidic 67 009,44 RustSch W69 53.862 Schist/Granofels

N44 05.997 Non-rusty weathering biotite 68 FelGn W69 53.844 gneiss, intensely folded

Similar to 59& 64 - garnet bearing N44 06.068 hornblende gneiss along with calc- 69 328,41 HblGn W69 53.855 silicate gneiss and garnet bearing biotite schist

Biotite gneiss, slightly rusty on N44 05.968 70 349,46 FelGn foliation surfaces, minor black W69 53.936 amphibolite with little calcsilicate

65 deg rake of Biotite gneiss with occasional N44 04.263 71 329,29 min lin to NW on FelGn garnet, thin pegmatite sills (non- W69 54.265 fol. popcorn texture)

111

N44 04.239 50/50 Felsic biotite gneiss and 72 Peg W69 54.281 pegmatite

N44 04.214 Biotite gneiss (no popcorn or 73 004,29 fold axis 035,27 FelGn W69 53.891 migmatite); minor pegmatite

N44 04.045 Biotite Gneiss (no popcorn). Minor 74 356,46 FelGn W69 54.016 pegmatite sill.

Slightly rusty on foliation surfaces, N44 04.020 75 122,79 315,19 FelGn but good biotite gneiss with some W69 54.038 more schistose layers

Lichen covered pavement - but N44 04.150 76 FelGn looks to be biotite gneiss and W69 54.366 minor pegmatite

N44 04.354 "Swirly Qtz-Felspar-Biotite gneiss - 77 FelGn W69 54.853 - some minor garnet. Peg

Slabby garnet-biotite amphibolite N44 04.360 78 311,14 Amph with some garnet-bearing biotite W69 54.963 schist and gneiss

Lots of slabby garnet amphibolite N44 04.410 79 008,42 Amph float. In places is dark gray, fairly W69 54.899 massive biotite schist/gneiss

Sheared "grantitic looking" felsic N44 03.787 gneiss with some biotite garnet 80 115,85 FelGn, RustSch W69 55.081 schist interlayers, also some rusty sulfidic schist

Lots of rusty weathering sulfidic 75 degree rake N44 03.777 schist, lesser amounts of 'granitic 81 341,34 of min lin to NW FelGn, RustSch W69 55.064 looking" garnet-bearing felsic on fol gneiss and some pegmatite

Hornblende calc-silicate gneiss, N44 03.813 some felsic gneiss and some clean 82 CalcSil, HblGn W69 55.044 black amphibolite, rusty mineralized pegmatite

N44 03.829 Felsic gneiss and coticule football. 83 FelGn W69 55.044 Minor pegmatite.

Large exposure of well jointed N44 03.810 jointing is very muscovite-biotite garnet foliated 84 110,79 358,30 FelGn W69 55.017 well developed granite. Minor rusty weathering schist

112

Rusty weathering sulfidic schist N44 03.843 85 RustSch, FelGn and lesser amounts of biotite W69 55.145 gneiss

Unusual, foliated hornblende N44 03.766 bearing gabbro-diorite. 86 FolHblGabb W69 55.160 Hornblende is both porphyritic and in matrix

Foliated granitoid rock - ranging N44 04.047 87 Peg, FolGr from pegamtite to coarse grained W69 55.061 granite. Minor garnet.

N44 04.073 Pegmatite - no muscovite or 88 Peg W69 55.071 graphic texture

Rusty mica schist - most of rusty N44 03.872 weathering is on foliation surfaces, 89 325,31 RustSch W69 55.147 good bit of garnet & discordant pegmatite

High strain plutonic gneiss - some N44 06.640 hornblende-biotite diorite, biotite- 90 004,59 PltGn W69 54.481 garnet gneiss & some pegmatite boudins

N44 06.598 91 351,31 PltGn Granitic gneiss W69 54.421

Deformed granitic rock with some N44 06.615 92 PltGn darker mafic layers within which W69 54.346 have slight rusty weathing.

"Popcorn-texture" biotite gneiss - - N44 06.530 some minor garnet-biotite gneiss 93 FelGn W69 54.232 with large garnets, boudins of pegmatite.

Biotite gneiss (small garnets) and N44 06.562 sheared pegmatite with minor 94 FelGn W69 54.298 muscovite - - some minor biotite schist

Poikilitic garnet biotite granitoid N44 07.114 95 011,54 PltGn gneiss - - possible hornblende; W69 53.927 pegmatite dike with garnets.

minor late brittle Granitic to dioritic biotite gneiss, N44 07.143 96 007,50 fault oriented PltGn feldspar boudins, epidote in high W69 53.898 021,82 angle fault plane.

Granitic to dioritic biotite gneiss, N44 07.237 97 PltGn feldspar boudins, hornblende in W69 53.857 feldspar-rich layers

113

Generally a more "meta- N44 07.181 sedimentary looking" felsic gneiss 98 349,55 FelGn W69 53.954 than previous two stops - - some late pegmatite

N44 06.227 Slabby, biotite granofels and calc- 99 034,80 BtGran/Calc W69 55.304 silicate gneiss; minor pegmatite

N44 06.314 Slabby, garnet-bearing biotite 100 BtGran/Calc W69 55.274 granofels and calc-silicate gneiss

"Metasedimentary " slabby, biotite N44 06.403 101 006,46 BtGran/Calc granofels and calc-silicate gneiss; W69 55.246 minor pegmatite.

N44 06.457 Slabby, biotite granofels and calc- 102 295,83 001,36 BtGran/Calc W69 55.190 silicate gneiss

N44 06.535 Slabby, biotite granofels and calc- 103 014,48 BtGran/Calc W69 55.117 silicate gneiss

Garnet-biotite-plagioclase-quartz N44 05.897 fold axis 104 109,68 344,24 PltGn gneiss - - looks metaplutonic with W69 54.610 oriented 013,22 large poikilitic garnets.

Somewhat slabby weathering, N44 05.872 105 359,50 BtGneiss somewhat rusty on foliation W69 54.624 surfaces, biotite gneiss

Pavement in snowmobile trail, N44 05.582 106 PltGn garnet-biotite gneiss -- looks W69 54.410 metaplutonic; minor pegmatite

N44 05.688 Very dark colored, biotite (possible 107 349,39 PltGn W69 54.454 hbl) gneiss. Looks metaigneous.

Similar to 106, dark colored, N44 05.712 108 112,71 343,37 PltGn dioritic composition, foliatied W69 54.467 gneiss; late pegmatite

Similar to previous 2 stops, dark colored biotite rich gneiss (slight N44 05.727 109 104,72 356,35 PltGn rusty weathering on foliatons), also W69 54.505 some lighter colored plagioclase rich gneiss

N44 05.724 Mostly pegmatite, minor biotite 110 Peg W69 54.582 gneiss

Light gray, garnet-bearing biotite gneiss - - rusty on some foliation N44 05.602 111 100,76 009,34 PltGn surfaces. Possible W69 54.742 pseudotachylyte discordant to foliation.

114

50-50 pegmatite and light gray N44 05.566 plagioclase rich biotite gneiss; 112 PltGn, Peg W69 54.790 rusty weathering on foliation surface

Poikilitic garnet biotite granitoid N44 05.535 113 PltGn gneiss - - possible hornblende; W69 54.824 pegmatite boudins.

Poikilitic garnet biotite granitoid N44 05.507 114 PltGn gneiss - - possible hornblende; W69 54.841 pegmatite boudins.

Slightly rusty weathering on N44 05.399 115 011,48 BtGneiss foliation surfaces - slabby biotite W69 54.930 gneiss; late pegmatite.

Similar to 107, dark colored biotite N44 05.310 rich gneiss and some salt&pepper 116 125,78 356,43 PltGn W69 55.099 textured biotite gneiss, some rust on fol.

Small outcrop of pegmatite and N44 05.219 117 014,52 BtGneiss, Peg biotite gneiss, rust weathering on W69 55.228 foliations.

Pavement outcrop of mostly N44 05.166 granitic gneiss with coarse aligned 118 PltGn W69 54.954 feldspars (not garnet bearing, but metaplutonic)

N44 05.097 Late, fine-grained mafic dike - at 119 MzD W69 54.977 least 2 meters wide

Poikilitic garnet biotite granitoid N44 05.065 gneiss - - also some darker more 120 358,57 PltGn, Peg W69 55.020 mafic material along with Peg and a small Mez dike

Darker colored biotite gneiss, N44 05.014 121 016,63 BtGneiss slight rust weathering on foliation W69 55.160 surfaces, late pegmatite.

Somewhat slabby, slightly rusty N44 04.953 122 BtGneiss weathering, somewhat schistose W69 55.049 biotite gneiss

Biotite schist to gneiss, somewhat N44 04.933 123 349,35 BtGneiss rusty weathering on foliation W69 54.995 surfaces

N44 05.584 Quarry exposure, biotite granofels 124 334,22 BtGran/Calc W69 54.878 and calc-silicate gneiss

115

Biotite granofels and calc-silicate N44 05.577 gneiss - - also some darker biotite 125 018,60 BtGran/Calc W69 54.866 gneiss; coarse pegmatite sills; possible amphibolite.

Biotite granofels and calc-silicate gneiss - - seems to be more N44 05.584 126 021,40 BtGran/Calc feldspathic that previous 2 stops; W69 54.854 musc-pegmatite; rusty weathering on some foliation surfaces.

Mostly biotite granofels and gneiss N44 05.568 - little to no calc-silicate. Quite 127 019,44 BtGran/Calc W69 54.861 felspathic, minor rust weathering on foliation planes.

Biotite granofels and schist - biotite N44 05.461 looks coarser grained than typical 128 BtGran/Calc W69 54.937 Vassalboro; minor rust on weathinerg surfaces.

N44 04.197 Granitic gniess with large aligned 129 PltGn W69 55.525 feldspars; very minor garnet

N44 04.222 Granitic gneiss with large aligned 130 PtlGn W69 55.545 feldspars; very minor garnet

Poikilitic garnet biotite granitoid N44 04.122 131 PtlGn gneiss - - possible hornblende; W69 55.431 also coarse pegmatite.

N44 04.104 Poikilitic garnet biotite granitoid 132 PtlGn W69 55.461 gneiss - - possible hornblende

Mixture of lithologies, some biotite N44 04.130 133 346,39 Pt.Gn,BtGn schist and gneiss mixed in with W69 55.503 poikilitic garnet granitoid gneiss

Granitic Gneiss - some layers N44 04.091 contain poikilitic garnets, other 134 PtlGn W69 55.404 layers are more felsic and don't contain garnet; coarse feldspar

Poikilitic garnet granitoid gneiss and somewhat slabby biotite N44 04.081 135 PtlGn,BtGn gneiss and schist which has minor W69 55.445 rusty weathering on foliation planes.

116

Poikilitic garnet granitoid gneiss N44 04.078 along with more slabby weathering 136 290,26 PtlGn,BtGn W69 55.466 biotite gneiss; massive garnet- pegmatite

N44 06.151 Biotite granofels and calc-silicate 137 BtGran/Calc W69 55.359 gneiss with discordant pegmatites

Biotite granofels and calc-silicate N44 06.102 138 117,77 034,68 BtGran/Calc gneiss (minor garnet) with W69 55.415 discordant pegmatites

Biotite granofels and calc-silicate N44 06.077 139 BtGran/Calc gneiss (grossularite garnet) with W69 55.455 discordant pegmatites

Small outcrop of biotite granofels N44 05.622 and calc-silicate---minor rust 140 356,37 BtGran/Calc W69 55.633 weathering on foliation surfaces; some pegmatite

Granitic pegmatite and coarse N44 05.370 141 Gran/Peg grained biotite granite - moderately W69 55.591 foliated

Granitic pegmatite and coarse N44 05.328 biotite granite - - lots of slabby 142 Gran/Peg W69 55.605 biotite granofels float, but nothing in place

Light gray to white coarse grained N44 05.357 143 Gran/Peg foliated biotite granite; feldspar W69 55.432 >>quartz

Light gray, to white, coarse N44 05.364 144 Gran/Peg grained very feldspar rich W69 55.388 grainitoid - foliated

Biotite granofels and calc-silicate N44 05.150 145 007,43 BtGran/Calc gneiss; minor rust weathering; W69 55.470 pegmatite dikes & sills

N44 05.168 Slabby biotite granofels and calc- 146 BtGran/Calc W69 55.498 silicate; minor rust weathering

N44 05.283 Pegmatite and moderately foliated 147 Gran/Peg W69 55.627 coarse grained granite

N44 05.405 Not definitely in place but lots of 148 Gran/Peg W69 55.816 large boulders of coarse granitoid

N44 05.503 50-50 biotite granofels and calc- 149 345,76 BtGran/Calc W69 55.838 silicate and pegmatite

117

Granitic pegmatite and moderately N44 05.572 150 Gran/Peg foliated, coarse grained biotite W69 55.989 granite - < 5% granofels

Biotite granofels and calc-silicate N44 05.560 gneiss and deformed granitic 151 BtGran/Calc.,Gran/Peg W69 56.079 pegmatite to coarse-grained granite

Biotite granofels and calc-silicate N44 05.502 152 BtGran/Calc gneiss with some discordant W69 56.132 granitic/pegmatite dikes

Biotite granofels and calc-silicate N44 05.385 153 295,28 BtGran/Calc gneiss; slight rusty weathering; W69 56.173 pegmatite

N44 05.308 154 009,27 BtGran/Calc Biotite granofels and calc-silicate W69 56.213

N44 05.182 Weakly foliated granitic pegmatite 155 Gran/Peg W69 56.050 - muscovite bearing

N44 05.209 Biotite granofels and calc-silicate 156 295,21 BtGran/Calc W69 55.977 gneiss

N44 05.266 Biotite granofels and pegmatite 157 BtGran/Calc W69 56.076 with tourmaline

N44 05.200 158 95,82 338,31 BtGran/Calc Biotite granofels and calc-silicate W69 56.304

Coarse grained to mostly N44 05.311 159 Gran/Peg pegmatitic granite with minor W69 56.346 tourmaline

N44 05.631 Biotite granofels and calc-silicate 160 270,34 BtGran/Calc W69 56.121 gneiss with some minor pegmatite

N44 05.825 Biotite granofels and calc-silicate 161 BtGran/Calc W69 56.119 gneiss

N44 05.669 Biotite granofels and calc-silicate 162 BtGran/Calc W69 55.885 gneiss

Moderately rusty weathering, N44 04.442 163 016,40 BtGn feldspathic biotite gneiss, in places W69 55.749 popcorn feldspar texture.

Slightly rusty weathering biotite N44 04.463 164 350,32 BtGn gneiss with abundant quartz W69 55.726 segregations (40%)

Quite rusty in places, feldspathic N44 04.418 165 357,27 BtGn biotite gneiss - - quartz rich W69 55.765 segregations

118

Biotite granofels and possible calc- N44 04.633 166 356,22 BtGran/Calc silicate - - a bit rusty in places; W69 56.088 discordant pegmatite

N44 04.646 Biotite granofels and possible calc- 167 356,24 BtGran/Calc W69 56.171 silicate; cross-cutting pegmatite

N44 04.707 Biotite granofels and calc-silicate 168 BtGran/Calc W69 56.246 gneiss

Slabby weathering biotite N44 04.781 granofels and calc-silicate gneiss; 169 BtGran/Calc W69 56.305 bands of coarse feldspars. Mesozoic dike float.

On top of hiss is coarse grained N44 04.839 granite to pegmatite, granofels 170 BtGran/Calc., Gran/Peg W69 56.252 float on the way up, 20 meters south is granofels crop

Pegmatite on top of hill, 20 meters N44 04.734 171 349,42 BtGran/Calc., Gran/Peg down is good outcrop of biotite W69 56.028 granofels and calc-silicate gneiss

Coarse grained, poikilitic garnet, N44 04.505 172 PltGn biotite granitic gniess with some W69 55.964 popcorn feldspars

Poikilitic garnet, biotite granitic N44 04.402 173 002,54 PltGn gneiss - garnets up to dime size; W69 56.078 pegmatite boudins

20% poikilitic garnet biotite gneiss N44 04.054 174 276,19 PltGn with slight rust weathering - - the W69 55.586 rest is pegmatite

Mostly foliated coarse grained N44 04.001 175 PltGn granite to pegmatite, but some W69 55.635 garnet-biotite granitic gneiss

N44 04.009 Mostly pegmatite, but 10 to 20 176 PltGn W69 55.714 percent is big garnet-biotite gneiss

N44 03.884 Foliated granitoid rock - minor 177 288,23 PltGn W69 55.846 garnet, large quartz crystals

Coarse-grained, poikilitic garnet N44 03.840 178 287,22 PltGn biotite granitoid gneiss; pegmatite W69 55.882 sills

119

Garnet-biotite granitoid gneiss, N44 03.914 179 PltGn coarse-grained popcorn feldspars, W69 55.904 sample collected for geochemistry

N44 03.987 Granitic to dioritic biotite gneiss - 180 341,27 PltGn W69 55.905 some containing garnet

Very porphyritic biotite granite N44 04.043 181 PltGn gneiss - - no garnet, just beautifully W69 55.829 aligned coarse grained feldspars

Granitic to granodioritic gneiss - N44 04.134 182 PltGn some coarse feldspar variety. W69 55.732 Little to no garnet

Foliated, coarse grained biotite N44 04.288 granite, abundant popcorn 183 PltGn, MzD W69 55.823 feldspars, 3 Mesozoic dikes with chilled margins

Foliated garnet bearing granitic N44 04.303 184 BtGn,PltGn gneiss along with some slightly W69 56.153 rusty weathering biotite schist

Mostly coarse garnet granitoid N44 04.317 185 358,28 PltGn gneiss but some slabby biotite W69 56.237 schist (< 10%)

Granitic gneiss, some small N44 04.314 186 355,36 PltGn garnets, but mostly rather felsic W69 56.330 granitic gneiss

Large exposures of foliated, rake of mineral N44 04.288 coarse grained biotite granite 187 345,24 lineation is 77 PltGn W69 56.364 gneiss and some sheared NW on fol pegmatite

Very rusty weathering sulfidic N44 04.337 188 104,73 276,18 RustSch Schist, some granite to pegmatite W69 56.388 sills

Slabby weathering biotite granofels and possible calc- N44 04.140 189 314,22 BtGran/Calc silicate, "metasedimentary" W69 56.352 appearance, slight rusty weathering

Slabby weathering biotite N44 04.144 granofels and definite calc-silicate 190 322,33 BtGran/Calc W69 56.295 gneiss, "metasedimentary" appearance

120

N44 04.144 Biotite granofels and calc-silicate 191 350,21 BtGran/Calc W69 56.254 gneiss, extremely slabby

Poikilitic, coarse-grained garnet, N44 04.138 192 354,41 PltGn granitoid gneiss (between stations W69 56.204 191 & 192 is contact)

Mixture of lithologies, some coarse N44 04.091 grained garnet, biotite granitoid 193 342,37 PltGn W69 56.153 gneiss, some porphyritic feldspar rich granite gneiss

Complex exposure with garnet N44 04.080 Mesozoic dike granitoid gneiss "sills" in calc, 194 348,27 PltGn,RustSch W69 56.122 oriented 219,60 structurally overlain by rusty schist, overlain by garnet granitoid gneiss

Large fine-grained mafic Mesozoic N44 04.007 195 MzD dike - at least 10 meters across; W69 56.127 pegmatite

Nothing in place for sure but lots of N44 06.333 196 PltGn very large boulders of foliated W69 54.451 granite

Dark gray dioritic gneiss, no garnet N44 06.329 197 005,41 PltGn observed, metaigneous W69 54.296 appearance

N44 06.438 Dark gray dioritic gneiss, no garnet 198 PltGn W69 54.293 observed, possible hornblende

N44 04.250 Mostly pegmatite, but some biotite 199 BtGran/Calc,Peg W69 57.670 granofels and calc-silicate

Slabby biotite granofels and calc- N44 04.205 silicate gneiss - - slightly rusty 200 277,84 003,37 BtGran/Calc W69 57.421 weathering on foliation surfaces; musc-pegmatite

Slabby biotite granofels and calc- N44 04.206 201 BtGran/Calc silicate gneiss, muscovite- W69 57.260 pegmatite

N44 04.177 Biotite granofels and schist - some 202 113,85 351,36 BtGran/Calc W69 57.206 calc-silicate boudins/blebs

Slabby, slightly rusty weathering N44 04.146 203 109,86 324,24 BtGran/Calc on foliation surfaces, biotite W69 57.079 granofels and calc-silicate gneiss

Biotite granofels and calc-silicate N44 04.104 204 119,82 295,21 BtGran/Calc gneiss, slight slabby rusty W69 56.977 weathering

121

N44 04.031 Biotite granofels and calc-silicate 205 343,32 BtGran/Calc W69 56.883 gneiss; minor pegmatite

Slightly rusty weathering on N44 03.763 foliation surfaces, biotite granofels 206 BtGran/Calc W69 56.712 and calc-silicate gneiss; sharp discordant pegmatite

Rounded exposure of meta- N44 04.111 207 PltGn granitoid gneiss - - some large W69 56.315 garnets observed

Gas line "exposure" but large N44 04.264 amounts of blasted rusty 208 RustSch W69 56.477 weathering sulfidic schist - - looks like 188

Gas line exposure of very N44 04.253 garnetiferous biotite sillimanite 209 CotGn W69 56.556 schist/gneiss. Coticule, lots of very tiny garnets

Gas line exposure, slabby slightly N44 04.257 210 BtGran/Calc rusty weathering biotite granofels W69 56.632 and calc-silicate

Slabby, slightly rusty weathering N44 04.251 211 BtGran/Calc on foliation surfaces, biotite W69 56.750 granofels and calc-silicate gneiss

About 50 meters thick but very N44 04.247 212 RustSch rusty and sulfidic schist and W69 56.820 granofels

N44 04.239 213 BtGran/Calc Biotite granofels and calc-silicate W69 56.922

N44 04.167 Biotite granofels and calc-silicate 214 114,78 001,26 BtGran/Calc W69 56.996 gneiss

Slabby weathering, slighly rusty weathering on foliation surfaces, N44 04.317 215 341,34 BtGran/Calc biotite granofels and schist, minor W69 57.001 calc-silicate; sharp discordant pegmatite

Slabby, biotite granofels and schist N44 04.496 216 290,30 BtGran/Calc and minor calc-silicate, slight rust W69 56.966 weathering

N44 04.534 Slabby biotite granofels, no calc- 217 009,34 BtGran/Calc W69 57.155 silicate. Sheared pegmatite sills

N44 04.560 Cruddy, slightly rusty weathering 218 011,37 BtGran/Calc W69 56.935 biotite granofels

122

Slabby biotite granofels - - slight N44 04.688 219 345,33 BtGran/Calc rust weathering--small woods W69 56.994 exposure

Biotite granofels and minor calc- N44 04.574 220 325,26 BtGran/Calc silicate--slight rust weathering - - W69 56.617 large pegmatite sill

Biotite granofels and calc-silicate N44 04.624 gneiss - - some slightly rusty 221 121,90 316,20 BtGran/Calc W69 56.656 weathering horizons; discordant pegmatite

N44 04.658 Biotite granofels and calc-silicate; 222 328,18 BtGran/Calc W69 56.671 minor pegmatite

N44 04.750 223 333,31 BtGran/Calc Biotite granofels and calc-silicate W69 56.757

N44 04.824 224 350,37 BtGran/Calc Biotite granofels and calc-silicate W69 56.752

N44 04.860 225 345,34 BtGran/Calc Biotite granofels and calc-silicate W69 56.760

N44 04.936 226 330,33 BtGran/Calc Biotite granofels and calc-silicate W69 56.763

N44 04.959 227 344,31 BtGran/Calc Slabby biotite granofels W69 57.018

N44 04.881 228 336,19 BtGran/Calc Biotite granofels and calc-silicate W69 57.072

N44 04.777 Biotite granofels, more quartz and 229 348,36 BtGran/Calc W69 57.112 feldspar rich than typical

Biotite granofels and calc-silicate N44 04.709 230 109,90 009,24 BtGran/Calc gneiss; discordant coarse W69 57.141 quartz/feldspar stringers

N44 04.538 Slabby biotite granofels and calc- 231 085,84 336,28 BtGran/Calc W69 56.568 silicate; discordant pegmatite

Mixture of foliated biotite granite - N44 04.514 232 Gran/Peg medium grained, and foliated W69 56.489 granitic pegmatite

N44 04.489 Slabby biotite granofels and calc- 233 343,38 Bt/Gran/Calc W69 56.450 silicate with some pegmatite

Very rusty weathering and sulfidic N44 04.438 234 338,34 RustSch quartz rich granofels and schist. W69 56.437 Some muscovite rich layers

123

Moderately rusty weathering biotite N44 04.485 235 348,19 BtGran/Calc granofels and some minor calc- W69 56.418 siliate

10% rusty schist and granofels, N44 04.488 the rest is extremely rusty 236 Gran/Peg, RustSch W69 56.329 weathering coarse grained granite to pegmatite

Biotite granofels and calc-silicate N44 04.545 knobs - - about 50m up trail is a 237 349,33 Bt/Gran/Calc, Rust W69 56.222 small patch of very rusty weathering schist

N44 05.049 Knobby Biotite granofels and calc- 238 92,90 328,33 BtGran/Calc W69 56.564 silicate

N44 05.061 Biotite granofels and calc-silicate 239 316,24 BtGran/Calc W69 56.608 gneiss (large calcsilicate knobs)

20% biotite granofels and the rest N44 05.144 240 320,27 Gran, BtGran/Calc is sheared coarse grained granite W69 56.574 to pegmatite

N44 05.166 Biotite granofels and some calc- 241 309,46 BtGran/Calc W69 56.539 silicate, minor pegmatite

N44 04.936 Biotite granofels and highly 242 BtGran/Calc W69 57.225 discordant thin pegmatite dikes

Rather thinly layered, salt&pepper N44 04.151 textured biotite gneiss - - slightly 243 341,39 BtGn W69 55.293 rusty weathering (20m up hill is foliated granite)

Foliated biotite granite (30%), thin N44 04.610 244 PtlGn layers of garnet bearing darker W69 55.364 material (20%), pegmatite (50%)

Foliated granitoid, some N44 04.566 245 PtlGn porphyritic feldspar rich granitic W69 55.303 rock - similar to 181

Migmatitic biotite gneiss. Lots of N44 04.757 swirled up "partially molten 246 FelGn W69 55.639 looking" gneiss, pegmatite pods, possible granofelsic amphibolite

N44 04.747 Fine-grained biotite gneiss, 247 BtGn W69 55.589 relatively homogeneous

124

Poor exposure, but not meta- N44 04.804 248 BtGn intrusive rock. Migmatitic looking W69 55.515 biotite gneiss; minor pegmatite.

Range of deformed plutonic rocks N44 05.030 - - some poikilitic garnet-biotite 249 PtlGn W69 54.824 gneiss, some more felsic biotite gneiss; pegmatite cap

Range of deformed plutonics - - N44 04.977 some poikilitic garnet-biotite 250 019,67 PtlGn W69 54.819 gneiss, some coarse feldspar granite gneiss, some mafic gneiss

Deformed granitic rock - quite N44 05.133 251 PtlGn felsic - no poikilitic garnets; W69 54.787 pegmatite

N44 05.210 "Typical" poikilitic garnet-biotite 252 PtlGn W69 54.810 granitoid gneiss

N44 05.237 Foliated granite - no garnet and 253 PtlGn W69 54.722 very little biotite

Foliated granite- a bit more mafic N44 05.179 than previous stop - but still 254 PtlGn W69 54.723 granitic. Some small euhedral garnets

Foliated granite gneiss, some N44 05.140 255 PtlGn small euhedral garnets (not W69 54.755 poikilitic)

Range of deformed plutonics - some poikilitic garnet gneiss, some N44 05.318 256 PtlGn "granite" gneiss and minor W69 54.787 granofels; pegmatite; Mesozoic dike emplacement

Mixture of migmatitic "popcorn" N44 05.345 gneiss with granite pods - also 257 007,26 PtlGn W69 54.829 some poikilitic garnet gneiss (contact area?)

Poikilitic garnet-biotite granitoid N44 05.403 258 009,34 PtlGn gneiss - and some more felsic W69 54.790 granite gneiss

Mafic gneiss (collected for N44 05.425 geochemistry) - weathers 259 PtlGn W69 54.624 salt&pepper but dark on fresh surfaces, some granitic gneiss too

125

Large boulders, probably in place, N44 04.464 260 PltGn of foliated biotite granitoid rock - W69 55.289 no garnet observed

Deformed granitoid rock - some N44 04.465 261 PltGn coarse poikilitic garnet granitoid W69 55.219 gneiss; pegmatite

Foliated granite - some with large N44 04.527 262 PltGn aligned feldspars - biotite but no W69 55.173 garnet observed

Slabby weathering, feldspathic N44 03.836 263 314,25 BtGn biotite gneiss - abundant W69 55.491 pegmatite

Complex exposure with poikilitic N44 03.795 garnet migmatitic gneiss, some 264 BtGn W69 55.567 layered biotite gneiss and discordant pegmatite

Slabby, feldspathic biotite gneiss N44 03.725 (slightly rust weathered) and 265 300,25 BtGn, Peg W69 55.602 coarse grained granite to pegmatite - moderately deformed

Migmatitic looking, very coarse N44 03.719 266 005,26 BtGn feldspar and large garnet (not W69 55.777 poikilitic) gneiss

Poikilitic garnet-biotite granitoid N44 03.923 267 PtlGn gneiss exposures all the way down W69 55.693 to the creek

Somewhat slabby weathering, N44 03.693 268 BtGn somewhat rusty on foliation W69 55.692 surfaces, biotite gneiss

Garnet-bearing biotite gneiss with N44 03.766 269 BtGn minor calc-silicate (Millay Rd. W69 55.010 sandpit); hornblende bands

Migmatitic biotite gneiss and schist N44 02.930 270 346,25 BtGn - - no garnets or calc-silicate W69 56.633 observed

Slabby weathering, nonrusty N44 03.259 weathering biotite righ 271 BtGn W69 56.783 granofels/schist - - no garnets or calc-silicate

N44 03.430 Minor granofels, but mostly cruddy 272 Peg, BtGn W69 56.807 and rusty weathering pegmatite

126

Mostly pegmatite but 20% is biotite N44 03.508 273 PtlGn gneiss with a few medium sized W69 56.811 garnets - - looks metaplutonic

Huge outcrops of meta-plutonic mineral lineation N44 03.553 biotite gneiss - felsic to 274 325,21 rakes 75 PtlGn W69 56.786 intermediate in composition - - no degrees NW garnets observed

Beautiful exposure of more mafic N44 03.541 fold axis = (dioritic) gneiss - weathers 275 318,26 PtlGn W69 56.719 035,14 somewhat slabby - also more felsic varieties (high strain)

N44 03.555 Foliated dioritic gneiss--lower 276 PtlGn W69 56.698 strain (fewer strung-out feldspars)

Mixture of poikilitic garnet-biotite N44 03.594 277 325,22 PtlGn granitoid gneiss and some foliated W69 56.746 dioritic gneiss

N44 03.632 Foliated granitic to granodioritic 278 PtlGn W69 56.775 gneiss

Somewhat slabby weathering, but N44 03.706 dark colored biotite rich gneiss - - 279 PtlGn W69 56.762 looks like high-strain metaplutonic rock

Very felsic and very coarse N44 03.742 280 PtlGn grained and heavily foliated biotite W69 56.729 granite gneiss and pegmatite

Huge exposures of felsic and N44 03.700 281 PtlGn coarse grained biotite granite W69 56.674 gneiss

N44 03.656 Coarse-grained biotite granite 282 PtlGn W69 56.694 gneiss; small euhedral garnets

N44 03.758 Coarse-grained biotite granite 283 PtlGn W69 56.650 gneiss

N44 03.795 Coarse-grained biotite granite 284 PtlGn W69 56.559 gneiss, large feldspars

Poikilitic garnet-biotite granitoid N44 03.828 285 PtlGn gneiss; garnets in both euhedral W69 56.590 and poikilitic forms

N44 03.809 Relatively felsic granite gneiss - no 286 PtlGn W69 56.641 garnets observed

127

Complex exposure, sill of foliated N44 03.671 biotite granite but mosly very 287 BtGran, PtlGn W69 56.822 biotite rich schist and more slabby biotite granofels

Biotite granofels and calc-silicate - N44 03.614 some schistose layers and some 288 BtGran/Calc W69 56.919 boudinaged layers of foliated biotite granite

Intermediate to felsic, foliated N44 03.551 granitoid gneiss - no garnet. 289 PtlGn W69 56.959 Some slabby biotite rich zones nearby

Very dark, schistose biotite rich N44 03.539 rock some quartzofeldspathic 290 BtGn W69 57.045 layers - - could be highly sheared metaplutonic

N44 03.539 Biotite granitic gneiss in direct 291 BtGran, PtlGn W69 57.127 contact with calc-silicate gneiss

Slabby weathering, biotite N44 03.555 granofels - - looks 292 BtGran W69 57.230 metasedimentary but no calc- silicate observed

One outcrop is poikilitic garnet- N44 03.603 biotite granitoid gneiss while 293 BtGran, PtlGn W69 57.261 another close by is slabby biotite granofels

Rusty weathering on foliation N44 03.544 294 BtGran/Calc surfaces, slabby biotite granofels, W69 57.465 some coarse feldspars

N44 06.310 Coarse-grained, poikilitic biotite 295 005,40 PtlGn W69 54.531 granitoid gneiss

Blasted from house foundation, N44 04.875 296 PtlGn fairly uniform bioite gneiss - - looks W69 55.238 dioritic

N44 04.700 Coarse-grained, poikilitic biotite 297 PtlGn W69 55.354 granitoid gneiss

N44 04.792 Coarse-grained, poikilitic biotite 298 PtlGn W69 55.187 granitoid gneiss

Relatively felsic granite gneiss - no N44 04.830 299 PtlGn garnets observed (sample W69 55.172 collected)

N44 04.761 Coarse-grained, poikilitic biotite 300 PtlGn W69 55.242 granitoid gneiss

128

Coarse grained garnet-bearing N44 04.098 gneiss/schist with abundant 301 FelGn W69 54.391 pegmatite. Garnets up to dime sized - metaplutonic look?

N44 04.043 Migmatitic gneiss with abundant 302 FelGn W69 54.442 pegmatite

N44 07.189 Biotite granofels and calc-silicate 303 BtGran/Calc W69 55.202 with some discordant granitic dikes

"Rough weathering" - bumpy, N44 07.167 304 352,34 BtGran/Calc biotite granofels and calc-silicate W69 55.107 with abundant pegmatite

Biotite granofels and calc-silicate N44 07.299 305 015,54 BtGran/Calc gneiss with some rusty weathering W69 55.213 horizons

Slightly rusty weathering on N44 07.353 306 354,44 BtGran/Calc foliation surfaces, biotite granofels W69 55.192 and calc-silicate gneiss

N44 07.395 Biotite granofels and calc-silicate 307 008,51 BtGran/Calc W69 55.212 gneiss

N44 07.463 Somewhat rusty weathering biotite 308 350,57 BtGran/Calc W69 55.242 granofels and calc-silicate gneiss

N44 07.477 Biotite granofels and calc-silicate 309 006,49 BtGran/Calc W69 55.176 with some discordant granitic dikes

Slightly rusty weathering on N44 07.467 310 007,46 BtGran/Calc foliation surfaces, biotite granofels W69 55.101 and calc-silicate gneiss

Slightly rusty weathering on N44 07.266 311 003,29 BtGran/Calc foliation surfaces, biotite granofels W69 55.360 and calc-silicate gneiss

Slightly rusty weathering on N44 07.263 312 BtGran/Calc foliation surfaces, biotite granofels W69 55.443 and calc-silicate gneiss

N44 07.282 Biotite granofels and calc-silicate 313 91,90 001,37 BtGran/Calc W69 55.545 gneiss

N44 07.203 Biotite granofels and calc-silicate 314 BtGran/Calc W69 55.931 with some discordant granitic dikes

N44 07.275 Biotite granofels and calc-silicate 315 048,76 BtGran/Calc W69 56.075 gneiss

129

N44 07.345 Biotite granofels and calc-silicate 316 010,32 BtGran/Calc W69 56.184 with some discordant granitic dikes

N44 07.315 Biotite granofels and calc-silicate 317 BtGran/Calc W69 56.293 gneiss

N44 07.319 Slightly rusty weathering biotite 318 019,43 BtGran/Calc W69 56.380 granofels

Moderately to heavily rusty N44 07.345 weathering biotite granofels, 319 BtGran/Calc W69 56.455 sulfide rich in places. Not much calc-silicate - - heavily folded

Slightly rusty weathering swirled N44 07.395 320 BtGran/Calc biotite granofels and calc-silicate W69 56.552 gneiss

N44 07.456 Slightly rusty weatheirng biotite 321 BtGran/Calc W69 56.618 granofels and calc-silciate gneiss

N44 06.761 Road cut, biotite granofels and 322 285,71 005,50 BtGran/Calc W69 55.239 calc-silicate gneiss

Slightly rusty weathering biotite N44 06.727 323 017,66 BtGran/Calc granofels and calc-silicate - W69 55.447 abundance of pegmatite boudins

Slightly to moderately rusty N44 06.397 weathering biotite schist and 324 029,32 BtGran/Calc W69 56.275 granofels. Abundant tourmaline bearing pegmatite

Nearly all tourmaline bearing N44 06.539 325 Peg pegmatite, very minor (<10%) W69 56.271 biotite gneiss

Big outcrops of biotite granofels N44 06.497 326 BtGran/Calc and calc-silicate gneiss - - W69 56.097 abundant pegmatite

N44 06.086 Slightly rusty weathering, slabby, 327 058,26 BtGran/Calc W69 56.757 biotite granofels

N44 06.025 Slightly rusty weathering biotite 328 BtGran/Calc W69 56.442 granofels and pegmatite

N44 05.986 "Swirly", biotite granofels and 329 BtGran/Calc W69 56.235 sharply discordant pegmatite dikes

N44 06.008 Lichen covered pavement outcrop 330 Peg W69 56.339 of pegmatite

130

Abundant large outcrops of foliated N44 06.208 granitic rock - - some with coarse 331 PltGn W69 54.510 aligned feldspars (like 181), some mafic gneiss

Mixture of poikilitic garnet-biotite N44 06.178 granitoid gneiss with coarse (181 332 PtlGn W69 54.562 type) feldspar granite gneiss - in contact, but not cross-cutting

Slightly rusty weathering biotite N44 07.506 333 010,34 BtGran/Calc granofels and gniess - minor calc- W69 58.787 silicate (south side of turnpike)

N44 07.504 Slightly rusty weathering biotite 334 119,90 BtGran/Calc W69 58.723 granofels and calc-silicate gneiss

New subdivision, lots of float and N44 06.156 blasted blocks but nothing in place 335 RustSch W69 59.417 for sure - - rusty weathering schist - possible Al-silicate

New subdivision, lots of float, but N44 06.134 coarse grained granite to 336 Peg W69 59.535 pegmatite - large euhedral black tourmaline

N44 05.886 Small pavement outcrop of 337 Peg W69 59.535 pegmatite

N44 05.946 Tourmaline-bearing muscovite 338 Peg W69 59.595 pegmatite

Pavement but looks to be in place, N44 05.799 339 BtGran/Calc nonrusty weathering biotite W69 59.557 granofels and calc-silicate

N44 05.773 340 Peg Granitic pegmatite W69 59.750

Small pavment outcrop of N44 07.254 341 Peg pegmatite with small bit of biotite W69 59.108 granofels on the edge

N44 06.189 Tourmaline-bearing muscovite 342 Peg W69 58.357 pegmatite

N44 06.636 Large mass of pegmatite and 343 Peg, Btgran W69 58.497 woods outcrop of biotite granofels

131

N44 06.660 344 240,29 BtGran Biotite granofels, no pegmatite W69 58.646

N44 06.664 Biotite granofels and calc-silicate 345 137,81 352,32 BtGran/Calc W69 58.773 gneiss (huge stream exposure)

N44 06.601 Slabby biotite granofels and calc- 346 240,30 BtGran/Calc W69 58.353 silicate

N44 06.056 Slabby biotite granofels and calc- 347 249,21 BtGran/Calc W69 58.231 silicate

N44 06.013 Pavement outcrop, biotite 348 BtGran/Calc W69 58.261 granofels and calc-silicate

N44 05.928 Biotite granofels and calc-silicate 349 129,78 BtGran/Calc W69 58.345 gneiss

N44 05.787 Nonrusty weathering, biotite 350 235,47 BtGran/Calc W69 58.434 granofels and calc-silicate gneiss

N44 05.702 Vassalboro biotite granofels, calc- 351 BtGran/Calc W69 57.888 silicate +/- discordant pegmatite

N44 05.726 Vassalboro biotite granofels, calc- 352 BtGran/Calc W69 58.174 silicate +/- discordant pegmatite

N44 05.737 Vassalboro biotite granofels, calc- 353 BtGran/Calc W69 58.281 silicate +/- discordant pegmatite

N44 05.523 354 Peg Woods outcrop of pegmatite W69 58.379

N44 05.698 Biotite granofels and calc-silicate 355 BtGran/Calc W69 58.536 Gneiss

N44 05.426 356 Peg Muscovite bearing pegmatite W69 58.666

N44 04.918 Biotite granofels and calc-silicate 357 145,77 BtGran/Calc W69 58.798 with some discordant granitic dikes

Slabby weathering biotite N44 04.841 358 312,31 BtGran/Calc granofels with discordant W69 58.609 pegmatite

N44 04.829 75% pegmatite - the rest is biotite 359 303,34 BtGran/Calc W69 58.548 granofels

N44 04.803 slabby biotite granofels and calc- 360 292,60 BtGran/Calc W69 58.510 silicate with some pegmatite

N44 04.793 Biotite granofels and lots of calc- 361 228,46 BtGran/Calc W69 58.444 silicate

132

N44 04.503 Slabby Vassalboro and sharply 362 341,23 BtGran/Calc W69 57.946 cross-cutting pegmatite

N44 04.999 363 BtGran/Calc Biotite granofels and calc-silicate W69 59.075

Gas line piles - 90% is pegmatite N44 04.248 some very tourmaline rich, other 364 Peg W69 58.367 containing biotite - little bit of granofels

Gas line, but nice small outcrop of N44 04.260 365 284,26 BtGran, Peg slabby biotite granofels and lots of W69 58.305 tourmaline pegmatite boulders

N44 04.242 Hill is covered with large boulders 366 Peg W69 58.183 of tourmaline pegmatite

N44 04.327 367 Peg More huge boulders of pegmatite W69 58.160

Slightly rusty weathering biotite N44 03.480 368 357,23 BtGran/Calc granofels and calc-silicate - - some W69 57.524 pegmatite sills

N44 03.589 369 BtGran/Calc Biotite granofels and calc-silicate W69 57.506

N44 05.971 370 BtGran/Calc Biotite granofels and calc-silicate W69 56.162

N44 05.929 371 358,34 BtGran/Calc Biotite granofels and calc-silicate W69 56.119

Very big outcrops of tourmaline N44 05.816 pegmatite - a few "rafts" of 372 Peg W69 56.358 Vassalboro rocks, but nearly all peg

House sized boulders of N44 05.824 tourmaline pegmatite - lots of 373 Peg W69 56.447 Vassalboro float, but nothing in place (no crop on steep slope)

N44 05.951 Nice outcrop of biotite granofels 374 006,29 BtGran/Calc W69 56.053 and calc-silicate gneiss

N44 06.143 May not be in place, but huge 375 Peg W69 57.209 boulders of tourmaline pegmatite

Big blasted outcrop of tourmaline N44 05.543 376 Peg pegmatite - - some Vassalboro W69 57.496 rafts

133

N44 05.414 Small pavement of biotite 377 Peg, BtGran W69 57.617 granofels but lots of pegmatite

Pegmatite with a bit of granofels - - N44 05.398 378 Peg little to no biotite or tourmaline in W69 57.553 the pegmatite

N44 04.648 Slabby biotite granofels and calc- 379 BtGran/Calc W69 59.261 silicate

N44 04.561 380 BtGran/Calc Biotite granofels W69 59.319

N44 04.470 Biotite granofels and calc-silicate, 381 319,19 BtGran/Calc W69 59.386 minor peg

N44 04.381 382 BtGran/Calc Biotite granofels and calc-silicate W69 59.450

N44 04.346 Biotite granofels and calc-silicate, 383 296,19 BtGran/Calc W69 59.514 and tourmaline pegmatite

N44 04.394 384 BtGran/Calc Biotite granofels and calc-silicate W69 59.643

N44 04.222 Gas line boulders, 95% pegmatite 385 Peg W69 59.717 and rest biotite granofels

N44 04.068 386 323,19 BtGran/Calc Biotite granofels and calc-silicate W69 59.896

N44 04.073 387 BtGran/Calc Biotite granofels and calc-silicate W69 59.817

N44 04.084 60 to 70% is pegmatite, rest is 388 BtGran, Peg W69 59.774 biotite granofels

N44 03.895 389 Peg Small pegmatite outcrop W69 59.351

Large pavement outcrop, 90% N44 03.841 390 Peg, BtGran pegmatite and the rest biotite W69 59.251 granofels

Gas Line boulders, about 50% N44 04.220 391 Peg,BtGran/Calc pegmatite and 50% calc-silicate W69 59.534 gneiss and biotite granofels

Basically a drumlin walk - but lots N44 06.669 of float, some quite large that 392 BtGran W69 57.227 could be in place - - biotite granofels

N44 07.107 80% pegmatite, rest biotite 393 Peg, BtGran W69 57.127 granofels

134

Biotite granofels and calc-silicate N44 07.156 gneiss - slightly rusty weathering 394 022,43 BtGran/Calc W69 57.044 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.223 gneiss - slightly rusty weathering 395 027,70 BtGran/Calc W69 56.976 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.282 gneiss - slightly rusty weathering 396 116,81 034,48 BtGran/Calc W69 56.908 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.302 gneiss - slightly rusty weathering 397 324,31 BtGran/Calc W69 56.797 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.383 gneiss - slightly rusty weathering 398 BtGran/Calc W69 56.710 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.423 gneiss - slightly rusty weathering 399 192,72 BtGran/Calc W69 56.675 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.218 gneiss - slightly rusty weathering 400 283,81 030,46 BtGran/Calc W69 56.802 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.149 gneiss - slightly rusty weathering 401 112,77 017,36 BtGran/Calc W69 56.776 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 07.094 gneiss - slightly rusty weathering 402 BtGran/Calc W69 56.764 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.975 gneiss - slightly rusty weathering 403 123,72 019,38 BtGran/Calc W69 56.733 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.831 gneiss - slightly rusty weathering 404 091,74 008,29 BtGran/Calc W69 56.590 on foliation surfaces +/- pegmatite dikes

135

Biotite granofels and calc-silicate N44 06.821 gneiss - slightly rusty weathering 405 349,24 BtGran/Calc W69 56.537 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.812 gneiss - slightly rusty weathering 406 094,90 BtGran/Calc W69 56.400 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.769 gneiss - slightly rusty weathering 407 122,75 023,21 BtGran/Calc W69 56.316 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.757 gneiss - slightly rusty weathering 408 BtGran/Calc W69 56.238 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.446 gneiss - slightly rusty weathering 409 BtGran/Calc W69 56.468 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.307 gneiss - slightly rusty weathering 410 BtGran/Calc W69 56.776 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.833 gneiss - slightly rusty weathering 411 BtGran/Calc W70 00.049 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 06.816 gneiss - slightly rusty weathering 412 BtGran/Calc W70 00.005 on foliation surfaces +/- pegmatite dikes

Biotite granofels and calc-silicate N44 04.703 gneiss - slightly rusty weathering 413 106,71 BtGran/Calc W69 59.060 on foliation surfaces +/- pegmatite dikes

N44 03.885 414 Peg Granitic Pegmatite W69 55.375

N44 04.001 415 Peg Pegmatite W69 55.224

N44 04.047 Foliated leucogranite - large 416 PtlGn W69 55.884 aligned feldspars similar to 181

136

Foliated biotite granite - N44 04.061 intermediate between porphyritic 417 PtlGn W69 55.946 granite (181) and garnet gneiss -- but contains no garnet

Mesozoic Dike - at least 10 meters N44 04.024 418 MzD thick - runs up the east side of the W69 56.060 hill

Mixed bag - - sheared granite and N44 04.108 419 PtlGn pegmatite along with migmatized W69 56.094 garnet rich gneiss

N44 04.241 Foliated biotite granitic gneiss - no 420 PtlGn W69 56.131 garnet observed

Slabby biotite granofels and calc- N44 03.976 421 351,32 BtGran, MzD silicate gneiss, Mesozoic dike cuts W69 56.150 part of the outcrop

N44 03.902 422 BtGran/Calc Slabby biotite granofels W69 56.135

Mix of very rusty weathering N44 03.721 423 RustSch sulfidic schist and some rusty W69 56.168 weathering granitic rocks

Not 100% sure the rocks are in N44 03.898 place, but several bus sized 424 PtlGn W69 56.082 boulders of granitoid gneiss - some garnet bearing

Bizarre outrop - lots of Mesozoic dike material, but also some N44 03.964 425 MzD carbonate, greenschist facies W69 56.099 broken up rock - ? Intrusive breccia ?

Nice outcrop of well foliated N44 04.072 metagranitoid rock with some 426 016,26 PtlGn W69 55.856 migmatite. Garnet bearing granitoid in places

N44 04.166 427 014,36 PtlGn Garnet bearing granitoid gneiss W69 56.365

N44 04.200 428 PtlGn Granitic gneiss W69 56.359

Nice outcrops on west side of hill - N44 04.194 -sheared granitic rocks - some 429 014,22 PtlGn W69 56.528 garnet bearing but not big poikilitic garnets

137

East side of hill - more granitoid N44 04.150 430 PtlGn gneiss - garnet bearing and some W69 56.471 big poikilitic garnets

N44 04.232 Large outcrops and boulders of 431 PtlGn W69 56.443 felsic granitic gneiss

Granitoid gneiss - some is N44 05.612 intermediate in composition 432 PtlGn W69 54.456 (dioritic) - other is felsic and highly foliated

All the way up are big slabs of N44 05.628 granitic gneiss - some pegmatite 433 PtlGn W69 54.496 on top but mostly gneiss some poikilitic garnets

Mix of sheared granite and very N44 05.664 434 PtlGn, Peg coarse grained poikolitic garnet W69 54.532 granitoid gneiss

N44 05.802 435 Peg Pegmatite W69 54.871

N44 05.766 Greenish gray calc-silicate and 436 358,24 BtGran/Calc W69 54.983 some biotite-plagioclase gneiss

N44 07.449 Pegmatite and migmatic biotite 437 Peg W69 54.293 gneiss

Small pavement, garnet (small) N44 07.431 438 BtGn gneiss cut by pegmatite (doesn't W69 54.360 look metaplutonic)

N44 06.875 Rusty weathering schist and 439 334,38 RustSch W69 54.511 granofels - slabby in places

Small outcrop of biotite gneiss and N44 05.938 granofels cut by pegmatite - 440 344,30 BtGran/Calc W69 54.753 closely spaced joints (looks metasedimentary)

Slightly rusty on foliation surfaces, N44 05.786 441 011,46 BtGn biotite gneiss and migmatite - W69 54.113 doesn't look metaplutonic

Biotite gneiss with quartz pods - N44 07.607 442 006,50 BtGn some green calc-silicate - - not W69 54.156 metaplutonic!

138

Appendix II

Samples Collected at Field Stations

Field Station Location (NAD83) Field Unit Why Collected Description Garnet-bearing felsic gneiss (popcorn in places), also a massive B4 N44º06.064’ W69º53.612’ Oug Thin Section Mesozoic mafic dike on west side of road, slight rust-weathering. Very rusty weathering B6 N44º06.230’ W69º53.668’ Ougm Thin Section sulfidic schist. Very rusty weathering B7 N44º06.249’ W69º53.627’ Ougm Thin Section sulfidic schist. Moderately rusty weathering biotite "popcorn" gneiss with B41 N44º05.655’ W69º53.894’ Oug Thin Section, ICP, REE some nice black biotite- bearing amphibolite: no calc-silicates. Variety of lithologies: rusty sulfidic schist, B64 N44º06.572’ W69º53.307’ Ougm Thin Section garnet-hbl-qtz gneiss (similar to 59), ribbed weathering amphibolite. Unusual, foliated hornblende bearing B86 N44º03.766’ W69º55.160’ Ougm Thin Section gabbro-diorite. Hornblende is both porphyritic and in matrix. Garnet-biotite- plagioclase-quartz B104 N44º06.535’ W69º55.117’ Dhh Thin Section, ICP, REE gneiss - - looks metaplutonic with large poikilitic garnets. Poikilitic garnet biotite granitoid gneiss - - B113 N44º05.535’ W69º54.824’ Dhh Thin Section, ICP, REE possible hornblende; pegmatite boudins. Biotite granofels and calc-silicate gneiss - - also some darker biotite B125 N44º05.577’ W69º54.866’ Sv Thin Section, ICP gneiss; coarse pegmatite sills; possible amphibolite. Granitic gneiss with B130 N44º04.222’ W69º55.545’ Dhh Thin Section large aligned feldspars; very minor garnet. Foliated garnet bearing granitic gneiss along B184 N44º04.303’ W69º56.153’ Dhh Thin Section, ICP with some slightly rusty weathering biotite schist.

Mostly coarse garnet granitoid gneiss but N44º04.317’ W69º56.237’ Dhh Thin Section, ICP, REE B185 some slabby biotite schist (< 10%) Rounded exposure of meta-granitoid gneiss - - B207 N44º04.111’ W69º56.315’ Svr Thin Section some large garnets observed. Gas line exposure of very garnetiferous biotite B209 N44º04.253’ W69º56.556’ Svr Thin Section sillmanite schist/gneiss. Coticule garnets.

139

Mafic gneiss - weathers salt & pepper but dark B259 N44º05.425’ W69º54.624’ Dhh Thin Section, ICP, REE on fresh surfaces, some granitic gneiss too. Huge outcrops of metaplutonic biotite gneiss - B274 N44º03.553’ W69º56.786’ Dhh Thin Section, ICP felsic to intermediate in composition - no garnet. Foliated dioritic gneiss-- B276 N44º03.555’ W69º56.698’ Dhh Thin Section lower strain (fewer strung-out feldspars). Blasted from house foundation, fairly uniform B296 N44º04.875’ W69º55.238’ Dhh Thin Section, ICP, REE bioite gneiss - - looks dioritic. Relatively felsic granite B299 N44º04.830’ W69º55.172’ Dhh Thin Section, ICP, REE gneiss - no garnets observed. Very mafic biotite/hornblende schist, some small felsic N44.096388º W- FT-73 Mt. Ararat Thin Section, ICP, REE bands. Collected in the 69.872055º Richmond 7.5’ Quadrangle, at the I-295 interchange. Diopside-rich light- colored amphibolites Falmouth- N44.027888º W- with minor titanite; GC5 Brunswick ICP 69.943333º metasedimentary Undivided appearance (very layered/foliated). Diopside-rich light- colored amphibolites Falmouth- N44.027888º W- with minor titanite; GC6 Brunswick Thin Section, ICP 69.943333º metasedimentary Undivided appearance (very layered/foliated). Poikilitic garnet biotite GC-11 (B132) N44º04.104’ W69º55.461’ Dhh Thin Section, ICP, REE granitoid gneiss - possible hornblende.

Garnet-biotite granitoid GC-12 (B179) N44º03.914’ W69º55.904’ Dhh Thin Section, ICP gneiss, coarse-grained popcorn feldspars. Clean black amphibolite surrounded by migmatic GC-13 N44.061555º W-69.918º Ougm Thin Section, ICP, REE felsic biotite gneiss (10m south of 82) Massive amphibolite granofels 50% hornblende 50% plagioclase, relatively N44.096111º W- R1 Mt. Ararat Thin Section, ICP homogeneous. 69.872833º Collected in the Richmond 7.5’ Quadrangle, at the I-295 interchange. Massive amphibolite granofels 60% hornblende 40% plagioclase, relatively N44.094583º W- R2 Mt. Ararat Thin Section, ICP homogeneous. 69.873416º Collected in the Richmond 7.5’ Quadrangle, at the I-295 interchange.

140

Massive amphibolite granofels 60% hornblende 40% plagioclase, relatively R3 N44.095º W-69.872694º Mt. Ararat Thin Section, ICP, REE homogeneous. Collected in the Richmond 7.5’ Quadrangle, at the I-295 interchange. Massive granofelsic hornblende amphibolite, ~70% hornblende/biotite. R4 N44.095º W-69.872694º Mt. Ararat ICP Collected in the Richmond 7.5’ Quadrangle, at the I-295 interchange. Amphibolite gneiss with definite foliation, quartz/feldspar N44.094888º W- R5 Mt. Ararat ICP stringers. Collected in 69.872805º the Richmond 7.5’ Quadrangle, at the I-295 interchange.

141

Appendix III

ICP-AES Analysis Results for MRG-1 and AGV-2 Standards MRG=Mount Royal (QC) Gabbro; AGV=Guano Valley (OR) Andesite

MRG-1 MRG-1 MRG-1 AGV-2 AGV-2 (1) (2) (Certified) (Certified)

SiO2 38.45 38.50 39.86 58.02 60.15 TiO 3.76 3.81 3.74 1.09 1.07 2 Al2O3 8.35 8.51 8.62 17.69 17.15 Fe2O3(t) 18.21 18.15 17.99 7.29 6.79 MnO 0.17 0.17 0.17 0.11 0.10 MgO 14.91 14.96 13.68 2.14 1.82 CaO 14.58 16.78 14.97 5.78 5.27 Na2O 0.68 0.66 0.72 4.48 4.25 K2O 0.16 0.15 0.18 2.96 2.92 P2O5 0.06 0.06 0.06 0.46 0.49 Total 99.34 101.74 99.99 100.01 100.00

Sc 53 52 54 12 13 V 553 526 520 68 120 Cr 476 472 475 32 17 Co 90 96 90 18 16 Ni 220 218 195 58 19 Cu 151 151 135 59 53

Zn 243 241 190 249 86 Sr 278 267 260 638 658 Y 14 14 16 18 20 Zr 102 99 105 218 230 Ba 54 53 50 1080 1140

142

Appendix IV

ICP-AES Geochemistry Results for Falmouth-Brunswick Amphibolite Samples Starred Samples Analyzed By ICP-MS at Activation Laboratories

143

Appendix V

ICP-AES Geochemistry Results for Hornbeam Hill Pluton Samples Starred Samples Analyzed By ICP-MS at Activation Laboratories

144

Appendix VI

Mineralogy of Thin Sections

Amphibolite Sample Mineralogical Description B41 80% hornblende, minor elongate biotite, small euhedral apatite, opaques and titanite. Plagioclase feldspar, minor quartz. B64 75% hornblende, 20% plagioclase, 4% opaques, 1% garnet. Minor quartz. Small interlocking crystals. B86 60% hornblende, 35% plagioclase, 3% titanite, 2% chlorite. Trace opaques, apatite. Range of sizes in hornblende crystals, both matrix and clasts, and large, euhedral-subhedral titanite crystals. B125 70% quartz/plagioclase feldspar, hornblende and clinopyroxene. More hornblende than pyroxene, which is generally colorless and nonpleochroic. Elongate biotite, all aligned in one direction. Trace titanite, illmenite, apatite, calcite, zircon. Plagioclase feldspar, quartz. GC6 Very banded with thin hornblende bands and then thicker pyroxene bands (75% pyroxene and 25% hornblende). Two types of pyroxene, 1) a colorless nonpleochroic pyroxene and 2) a light green, slightly pleochroic pyroxene. Considerable amounts of lenticular titanite, also trace amounts of calcite and apatite. Plagioclase feldspar and quartz. GC13 Very hornblende-rich (75%), small euhedral, non-poikilitic garnets. Considerable titanite (10%) and opaques (2-5%). Trace apatite. Plagioclase feldspar. R1 75% hornblende, plagioclase feldspar, elongate biotite needles, trace apatite and titanite, very few opaques. R2 70% hornblende, 25% plagioclase feldspar, 5% clinopyroxene. Trace apatite, titanite. R3 65% hornblende, plagioclase feldspar, biotite, trace muscovite, titanite, apatite, and opaques.

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FT-73 70% hornblende, plagioclase feldspar, trace prismatic biotite, titanite, apatite.

Pluton Sample Mineralogical Description B104 75% quartz/plagioclase feldspar, 20% biotite, considerable allanite. Large poikilitic garnets, trace apatite, zircon, illmenite. Relatively fine-grained matrix with larger crystals. B113 50% quartz/plagioclase feldspar, 25% biotite, 2% hornblende, 15% large poikilitic garnets. These garnets are extremely pervaded by quartz, feldspar, and biotite. Large crystals of quartz and feldspar, minor allanite, hornblende, titanite, opaques. Quartz and feldspar seem to be in equal ratio. B130 95% quartz/feldspar, 3% garnet, 2% biotite. Most feldspar is microcline, but there is also orthoclase and plagioclase. Garnets are small and euhedral-subhedral. Trace illmenite, apatite, muscovite, and chlorite. B184 60% quartz/plagioclase feldspar, 30% biotite, 5% big poikilitic garnets. Titanite intergrown with illmenite, also coarse titanite. Euhedral apatite, chlorite, very trace allanite. B185 55% quartz/plagioclase feldspar, 25% biotite, 15% large poikilitic garnets, considerable titanite (large crystals). Trace chlorite, apatite, zircon, allanite (large crystals).

B259 50% hornblende, 35% quartz/ dirty plagioclase feldspar, 10% biotite, 2% apatite, trace titanite, opaques. B274 65% quartz/plagioclase feldspar, 30% biotite, 2-5% large poikilitic garnets. Trace zircon, apatite, allanite, illmenite. Trace hornblende. B276 50% quartz/plagioclase feldspar, 23% biotite, 23% hornblende, 4% apatite. Large euhedral apatites, no garnet. Trace sphene, illmenite, zircon.

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B296 35% biotite, 30% hornblende, 30% quartz/plagioclase feldspar, 5-10% apatite. Plentiful apatite is large and euhedral, both in end sections and tabular grains. Lots of titanite that is relatively coarse and is punctuated by small apatites. Illmenite provides cores to many of these titanite grains. Trace amounts of allanite. Coarse feldspar crystals. B299 90-95% quartz/feldspar, both plagioclase and K-feldspar. Very little biotite, small euhedral garnets. Trace chlorite, apatite, titanite, illmenite muscovite, zircon, and allanite. GC11 (B132) 60% quartz/plagioclase feldspar, 20% biotite. 15% Large poikilitic garnets, considerable allanite. Trace apatite, titanite, retrograde chlorite, zircon, calcite, and relic hornblende in process of being replaced by chlorite and biotite. GC12 (B179) 55% quartz/plagioclase, 30% biotite, 10% large poikilitic garnets, 1% allanite. Trace zircon, muscovite, and chlorite.

F-B Gneiss Sample Mineralogical Description B4 Mesozoic mafic dike, volcanic textures preserved with little deformation. Dominated by elongate, euhedral plagioclase crystals, also with magnetite, pyroxene, and biotite. Pyroxene crystals are poorly developed, biotite is seen replacing older large phenocrysts. B6 65% quartz/plagioclase, 25% biotite, 15% opaques (sulfides). Trace apatite and muscovite. B7 45% quartz/plagioclase, 30% biotite, 25% opaques (sulfides). Trace apatite.

Vassalboro Gneiss/Granofels Sample Mineralogical Description B207 40% quartz/plagioclase, 30% biotite,20% sillmanite, 10% garnet. Garnets are euhedral to subhedral, and non- poikilitic.Trace apatite, zircon, opaques. B209 75% garnet coticule, 15% quartz/plagioclase, 8% biotite, 2% opaques. Trace sillmanite, titanite, apatite.

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Appendix VII

Fold Axis Measurements

Field Station Location Fold Axis Orientation 73 N44º04.214’ W69º53.891’ 035, 27 104 N44º05.897’ W69º54.610’ 013, 22 275 N44º03.541’ W69º56.719’ 035, 14

Mineral Foliation Lineation Measurements

Field Station Location Foliation Rake

34 N44º05.902’ W69º53.772’ 347, 35 80º NW 66 N44º06.890’ W69º54.558’ 340, 36 85º SE 71 N44º04.263’ W69º54.265’ 329, 29 65º NW 81 N44º03.777’ W69º55.064’ 341, 34 75º NW 187 N44º04.288’ W69º56.364’ 345, 24 77º NW 274 N44º03.553’ W69º56.786’ 325, 21 75º NW

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