U.S. DEPARTMENT OF THE INTERIOR Prepared in cooperation with the SCIENTIFIC INVESTIGATIONS MAP 3052 U.S. GEOLOGICAL SURVEY STATE OF CONNECTICUT, DEPARTMENT OF ENVIRONMENTAL PROTECTION, SHEET 1 OF 2 GEOLOGICAL AND NATURAL HISTORY SURVEY Explanatory pamphlet accompanies map

SEA LEVEL 52 53 Zos 52 OL292 49 45

FEET 23 54 38 55 30 82 CORRELATION OF MAP UNITS amphibolite layers or xenoliths occur east of Mink Island and southwest EXPLANATION OF MAP SYMBOLS 4000 3000 2000 1000 1000 2000 3000 4000 5000 Zog 44 47 44 53 37 43 47 34 30 72 58 43 54 81 37 of Uncas Pond and are shown on the map as Zgdla; their size is greatly 34 55 50 Pa 24 30 IGNEOUS ROCKS 46 26 45 exaggerated on the map to show the locations. The massive nature and A 57 40 56 17 Surficial deposits not shown 1000 feet = 305 meters 34 40 Westerly Granite Contact—Dotted where concealed by water 67 Zoa 79 53 presence of amphibolite xenoliths suggests that the rock is intrusive. A T 45 49 42 52 Zoq CONNECTICUT RIVER UL Pp SHRIMP U-Pb zircon age of 582±9 Ma (sample OL316, table 3) FA Zo K 47 38 Granite pegmatite E DSoh 50 Zo Zoq 27 Pp PERMIAN indicates that the rock is Neoproterozoic. Informally named for Outcrops—Areas of exposed bedrock or closely spaced contiguous A RE 49 43 28 33 C 60 51 53 26 17 bedrock exposures examined in this study P Sh 55 52 54 Zog 29 30 exposures on Lord Hill and on the northeastern slopes of Bills Hill. EE 53 45 Pg Pa D 45 Pp Zwr OL31651 Zgdla 48 49 61 51 34 44 38 34 Zoa Similar to the hornblende-bearing gneiss at Johnnycake Hill (Zgdh), but

Zwr 60 6 70 17 26 DSohrs 45 Zo Pa 48 70 42 28 Pp PZmig Zgdl does not contain the shear band boudin texture or calc-silicate Zgb 53 53 41 SELDEN NECK BLOCK 60 DSos 42 45 49 58 19 81 METASEDIMENTARY ROCKS FAULTS 73 57 50 36 78 pods of , and it is more strongly foliated because of its proximity to 48 34 Zgdh 32 18 Pp 32 75 39 86 Thrust fault parallel to regional S1 foliation—Sawteeth on upper plate; 24 44 34 the Ferry Point fault. Zgdl also contains more pink K-feldspar and Sil–Mus 58 51 66 52 55 dotted where concealed by water 35 Sil–Kfs 50 14 magnetite than Zgdh. The map unit forms a belt that extends from the 59 SURFACE Zog 41 51 66 31 20 45 60 Hamburg quadrangle in the north to the Essex quadrangle in the west 66 Zos 88 31 71 DSoh Left-lateral strike-slip fault—Arrows show relative movement 9 62 Zo Merrimack DSos and marks the structurally highest unit in the Lyme dome 45 53 Zgb 21 DSohrs Zwra 52 59 51 70 43 58 13 Terrane Sh 42 45 50 DEVONIAN AND 9 35 51 51 50 55 88 SILURIAN Zgdl 65 32 78 METASEDIMENTARY AND METAVOLCANIC ROCKS FOLDS 43 53 64 50 10 50 50 43 78 67 11 79 18 Old Lyme Gneiss (Neoproterozoic) 53 Zo 53 39 Axial trace of the Lyme dome (Alleghanian)—Upright F2 anticline

DSohrs 49 48 53 13 2 48 10 Zo Biotite gneiss—Dark- to light-gray, locally rusty-weathering, well- showing generalized plunge direction 52 53 44 65 17 24 METAIGNEOUS ROCKS METAIGNEOUS ROCKS layered, migmatitic K-feldspar-biotite-plagioclase-quartz gneiss. Deep Creek 28 18 45 Pa Avalon Zwr Contains accessory garnet and sillimanite. Modal analyses indicate Strike and dip of axial surface of minor fold D 64 36 56 Pp Zgb E 38 31 12 E Zo that the gneiss contains 22 to 71 percent quartz, 3 to 40 percent P 50 74 Terrane Zwra C 44 32 DSoh R 37 21 Zgd F1 fold parallel to S1 schistosity (Alleghanian) E 44 8432 14 E 48 64 Pp alkali feldspar, 1.5 to 44 percent plagioclase, 5 to 24 percent biotite, K 55 60 84 Zgdh F 58 37 20 A Pa 76 38 85 80 0 to 8 percent garnet, 0 to 13 percent sillimanite, trace to 1 percent U 65 38 Inclined LT 48 46 Pp 31 55 Zo 50 35 Pa Zgdl opaque Fe-Ti oxides, 0 to 1.5 percent muscovite, and trace amounts Sh S 61 50 5B 74 P 67 52 26 78 R 54 43 30 68 40 36 Zgdla of zircon and apatite. The rock is characteristically well layered and Vertical IN 62 55 29 75 41 28 88 65 Gander G 67 46 NEOPROTEROZOIC D 43 44 35 18 consists of alternating bands, generally 5 to 30 cm thick, of quartzo- DSos A 44 40 58 76 Terrane O L 40 L E 55 Pp METASEDIMENTARY AND METAVOLCANIC ROCKS F2 fold parallel to S2 cleavage or schistosity (Alleghanian) IV P 71 81 feldspathic biotite gneiss, with varying percentages of quartz, feldspar, ER O 47 72 64 S N 49 68 43 86 38 51 D 45 47 15 H 40 82 Zoa Zog and biotite. Quartz-feldspar leucosomes generally occur parallel to the FE O FA Zgdla 63 33 51 44 Inclined R LE U 43 46 31 R L Pp 78 Y FA T 8C 23 88 41 86 61 Zo gneissic layering. Locally the unit contains thin, less than 20 cm, P U 37 42 43 30 54 O L IN T Zgdla 73 70 15 42 Pa Zos Zos layers of dark-gray to black biotite-rich schist. Near the northeastern Vertical T Pa 45 74 85 FA 82 19 U corner of the quadrangle, well-formed muscovite crystals are 77 L 38 Zolq Zgdl T 73 42 24 Zoq F fold parallel to S cleavage (Alleghanian) 65 36 Zoa interlayered with biotite and form inclusions in plagioclase; these may 3 3 67 30 Zoq 48 70 51 56 Lord Hill 59 43 30 Pa 81 be examples of retrograde muscovite. Unit is interpreted as a 70 34 48 39 78 metamorphosed psammite. Typical exposures occur on ridges east of PLANAR FEATURES

Zo 47 65 85 39 the Duck River, at roadcuts on I-95 west of Exit 71, and at Saltworks 78 25 39 [Symbols may be combined; point of intersection shows location of measurement] 48 42 44 74 Pp 48 Pa 45 15 Point near Old Lyme Shores 65 62 68 58 82 82 74 54 79 36 50 49 Strike and dip of Westerly Granite dike Zgb 74 8D,E Zos Sillimanite schist—Dark-gray to black and white, rusty-weathering, 69 69 29 49 42 DESCRIPTION OF MAP UNITS Zos 81 29 36 18 DSohrs Rusty-weathering, biotite-, garnet-, and sillimanite-rich schist and schistose 6 24 23 [Major minerals listed in order of increasing abundance] coarse-grained garnet-sillimanite-K-feldspar-biotite-plagioclase-quartz 52 66 29 81 58 6C 6A,8B 77 46 gneiss. Moderately to well-layered, well-foliated schist and schistose Strike and dip of granite pegmatite (Pp) 73 42 81 52 81 Pa schist characterized by distinct bundles of sillimanite, fibrolitic 87 56 59 Pa 50 18 48 Pp 32 Zoq gneiss with 28 percent quartz, 24 percent alkali feldspar (orthoclase), sillimanite, or quartz and sillimanite. Sillimanite bundles are more 42 49 32 Pa 51 81 66 Inclined Zo 68 85 59 69 82 Zoq 51 15 percent plagioclase, 15 percent biotite, 9 percent sillimanite, 10 21 28 IGNEOUS ROCKS resistant than the rock matrix and occur in clusters, 1 to 5 cm long. 84 Zo 41 81 76 5E 64 67 70 64 67 30 56 77 percent garnet, and 1 percent Fe-Ti oxides. This belt of rocks was Zoa 53 35 30 34 Westerly Granite (Permian)—Pink to light-grayish-pink, fine- to The long axes of the sillimanite bundles locally create distinct mineral Vertical 71 Zgd 75 6D 54 previously mapped as Tatnic Hill Formation (Lundgren, 1967). Our 62 64 44 Zoa 40 81 67 lineations that are parallel to both F and F fold axes. The rock O 51 65 medium-grained, equigranular, non-foliated biotite-quartz-K-feldspar- 1 2 53 44 22 47 L Pa Zoq mapping does not find this rock unit (DSohrs) to be as extensive as 6B 74 70 contains 44 to 72 percent quartz, 5 to 51 percent alkali feldspar, 1 to I 67 77 Zoa 51 oligoclase granite dikes with accessory muscovite, chlorite, and opaque Strike and dip of deformed S or S gneissosity parallel to composi- V 48 36 32 48 Zog Lundgren indicated; it is restricted to a 50- to 75-m-wide and 0 1 E 68 82 56 77 71 19 73 10 percent plagioclase, 1 to 19 percent biotite, trace to 8 percent tional layering R 75 55 78 minerals. Locally contains K-feldspar megacrysts up to 10 cm long 47 84 Pp 78 S 68 80 1.2-km-long belt south of, and structurally below, the Rope Ferry 78 71 54 Pa sillimanite, 0 to 11 percent poorly formed clinozoisite or epidote, 64 24 55 along the borders of the dikes where they are in gradational contact H 50 74 56 62 78 64 57 Zo 71 1C Pa 24 Gneiss (Zwr) in the northwestern part of the map. Similar to rocks O 5C Pp trace to 2.5 percent opaque Fe-Ti oxides, 0 to 0.5 percent Strike and dip of S gneissosity (Alleghanian) 76 80 Zoa 55 56 Zoq Pa with granite pegmatite. Dikes range in thickness from 10 cm to 2 m. 1 L 63 58 Pp 30 64 Pa mapped as “DSos” E 55 52 35 51 OL290 67 35 71 82 43 56 Dikes are straight walled, tabular, undeformed intrusions shown on the muscovite, and trace amounts of apatite and zircon. Well-formed 20

F 78 64 Inclined A 26 74 DSos F 81 42 42 72 78 26 26 Old Saybrook schist (Devonian to Silurian)—Well-foliated, moderately retrograde muscovite is interlayered with biotite north of Game

Pa map by strike and dip symbols. A SHRIMP U-Pb zircon age from a dike U E 74 83 49 72 26 R 31 Zoa Pa 63 L 86 72 Zo 72 Pp 35 layered, medium- to coarse-grained (0.5–11 mm long), very pale orange Ledge, but in other areas it is poorly formed or absent. Included in R 60 34 at Point O’Woods is 275±4 Ma (sample OL294A, table 3; Walsh and T 38 36 80 43 62 12 Vertical Y 13 Zgd 64 to light-gray, sillimanite-bearing, rusty-weathering metasedimentary this map unit is undifferentiated biotite gneiss and schist that is similar 53 S 77 78 58 Pp 68 others, 2007) indicating a Permian age 74 P 77 77

P O 52 79 schist. The rock is commonly migmatitic and typically contains a higher to the Zo unit. Unit is gradational by intercalation with the biotite R I 41 59 N 24 Granite pegmatite (Permian)—Pink, pinkish-orange, and white, very Strike and dip of S cleavage or schistosity (Alleghanian) I 82 Pp N 42 36 2 T 71 49 Pp concentration of pegmatite bodies than do other units. The rock gneiss and schist unit (Zo) and locally contains layers up to 20 cm 46 G Zoa 35 F 59 Pa Zoq 27 45 57 36 coarse grained, non-foliated to weakly foliated biotite-quartz-K-feldspar- 35 D A 50 82 contains about 35 to 53 percent quartz, 6 to 31 percent alkali feldspar thick of biotite gneiss similar to Zo. The map unit is best exposed in 48 83 82 82 42 25 Inclined U 82 A oligoclase granitic pegmatite with accessory muscovite, chlorite, 48 71 69 82 26 L 62 65 83 L 57 Zoq 54 73 24 84 (orthoclase), 9 to 18 percent plagioclase, 20 to 23 percent biotite, trace the eastern part of the quadrangle and is poorly exposed in low areas T 57 75 Lieutenant River E 53 62 79 79 71 Zoa 49 magnetite, and opaque minerals. Biotite, K-feldspar, and oligoclase OL96 48 Zoq to 3 percent sillimanite, and trace amounts of garnet, opaque Fe-Ti Vertical P 38 15 71 2 Zos between ridges of alaskite gneiss (Pa) in the western part of the O OL291 54 Zo 41 crystals range in size up to 15 cm. Occurs as straight-walled, tabular, 65 42 5D 50 Zoa Pp oxides, apatite, and zircon (two modes). The amount of sillimanite is N Pp 72 65 4A,B 88 56 17 quadrangle. Unit is interpreted as a metamorphosed pelite. Typical 47 Pp 66 Zoa undeformed dikes shown on the map by strike and dip symbols; larger DSoh D 77 58 Zoq 52 52 19 62 probably underestimated because the more sillimanite- and biotite-rich exposures occur at Point O’Woods and along State Route 51 at the Strike and dip of S cleavage (Alleghanian) 2 3

66 F 63 Pa 61 Pp 80 55 irregular masses mapped separately. Dikes range in thickness from 15 A Zo 58 9 69 52 74 66 79 71 parts of the map unit are more readily weathered and eroded, and East Lyme-Old Lyme town boundary 88 U 56 60 66 Zoa cm to 30 m. Dikes locally contain a boxwork pattern of coarse biotite Inclined L 69 77 56 17 therefore, are difficult to sample for petrography. The map unit forms a T 66 Pa 72 Zoa 2113 77 phenocrysts. Locally, the margins of the pegmatite are gradational with Zog Garnetiferous biotite gneiss and schist—Poorly foliated, poorly layered, 69 63 68 22 16 belt that extends from north of Uncas Pond southwestward across the 4 Pp finer grained granite that resembles the Westerly Granite dikes. Smaller medium- to coarse-grained, medium-gray garnet-quartz-plagioclase- Vertical 46 54 10 53 75 83 86 61 42 56 Connecticut River to south of the Penn Central railroad in Old 52 Zos 32 62 68 bodies of unmapped pegmatite occur throughout the map area, but biotite-K-feldspar gneiss and schist containing 10 percent quartz, 40 65 68 Pa Zoa 75 20 20 18 48 Saybrook. Informally named here for rocks exposed just south of the

Pa percent alkali feldspar, 20 percent plagioclase, 20 percent biotite, 10 57 68 44 11B only larger bodies are shown on the map in places where the pegmatite Strike and dip of outcrop-scale brittle fault (shown on sheet 2) 77 86 34 Penn Central railroad in Old Saybrook. Similar to rocks mapped as 82 64 occupies 90 percent or more of the exposed bedrock. Described by percent garnet, and trace amounts of apatite and zircon with 81 58 78 Zoa 45 “DSohrs.” Unit mapped previously as Brimfield Formation (Lundgren, 81 22 65 Pp conspicuous red garnets, 0.5 to 1.5 cm in diameter. Locally abundant Inclined Zo 81 58 Lundgren (1967) as “Black Hall type” granite for exposures near Black 78 5A 86 24 82 86 1967) or Brimfield Schist (Rodgers, 1985) 65 46 Zoq 10 54 84 Hall and at the abandoned MacCurdy quarry (Dale and Gregory, 1911) garnet porphyroblasts give the rock a knobby appearance. Occurs as Pa Lower Millpond 85 81 80 76 25 Vertical 55 52 49 16 Pa 66 Pp Zo Zo Pp 7 84 east of the Duck River and north of Lyme Station. A SHRIMP U-Pb Sh Hebron Formation (Silurian)—Interlayered, medium-dark-gray biotite- small map units interlayered with both Zo and Zos, and as xenoliths in Zoa 71 69 16 82 Pp Pa 59 Pg 87 42 66 16 61 78 zircon age from a pegmatite at Point O’Woods is 288±4 Ma (sample plagioclase-quartz gneiss to schistose gneiss and dark-greenish-gray Zgb. Typical exposures occur on the western side of Becket Hill north Zgb 9 Zos Strike and dip of joint (shown on sheet 2) 81 57 72 81 calc-silicate metasedimentary gneiss and granofels. Has a characteristic of Rogers Lake 82 82 OL294B, table 3; Walsh and others, 2007) indicating a Permian age NO VERTICAL EXAGGERATION 53 82 Zoa 26 82 84 32 64 49 74 20 “salt and pepper” texture that can be distinctly unlayered. Where 54 Zoq 56 Pp Pp Pa Zoq Quartzite—Gray to light-gray, bedded, vitreous quartzite and poorly to Inclined 54 Pa Pa Pp Alaskite and granite gneiss (Permian)—Gray to pink to orange-pink, 35 74 77 81 83 79 layered, the layers are 0.5 to 2 cm thick. The well-foliated biotite- 71 16 74 68 46 locally rusty-weathering, medium- to coarse-grained, poorly to well-foliated, massive to well-layered, medium-grained, white quartzite 58 Pp Pp 70 68 79 plagioclase-quartz layers have coarser grains (~1–2 mm in diameter) Vertical Sh 51 70 11A 71 64 49 well-foliated quartz-plagioclase-K-feldspar alaskite gneiss to granofels and very light gray to medium-dark-gray feldspathic and biotitic 75 Zoa compared to the equigranular calc-silicate layers (~0.5 mm in diameter). Zoa 81 quartzite. Quartz grains are locally highly recrystallized and annealed 51 44 66 Pa and lesser biotite-K-feldspar-quartz-plagioclase granite gneiss. Occurs as

Zo 26 The rock contains about 29 to 46 percent quartz, 12 to 45 percent Pp Zo orthogneiss within the Old Lyme Gneiss. Layering is formed by to such a degree that the rock resembles vein quartz. The rock 66 plagioclase, 7 to 35 percent biotite, 0 to 26 percent alkali feldspar, 2 to LINEAR FEATURES 14 49 79 Zoa 68 51 83 74 62 86 segregation of quartz, K-feldspar, plagioclase, and locally biotite. contains approximately 64 to 91 percent quartz, 0 to 11 percent [Symbols may be combined; point of intersection shows location of measurement] 59 77 69 30 35 12 percent diopside, trace to 3 percent clinozoisite, 0 to 4 percent 73 62 66 Locally, rod-shaped mineral segregations form lineations. The foliation alkali feldspar, 0 to 10 percent plagioclase, 1 to 16 percent biotite, 0 Zo 10 26 71 Pp 21 62 calcite, and trace amounts of zircon, apatite, opaque Fe-Ti oxides, 45 Zoa 10 Zo is defined both by the planes of biotite flakes and elongated quartz and to 3 percent clinozoisite, 0 to 3 percent chlorite, 0 to 1 percent Bearing and plunge of fold axes and lineations Zoq Pa 26 81 21 Pp hornblende, chlorite, and muscovite (six modes). The chlorite and 71 44 30 80 49 73 51 feldspar crystals and is largely concordant with layering. The rock muscovite, 0 to trace sphene, and trace amounts of opaque Fe-Ti 42 Pg 79 68 35 muscovite are considered to be retrograde phases. The calc-silicate F1 fold axis 65 79 contains about 25 to 47 percent quartz, 25 to 48 percent alkali feldspar oxides and zircon. Muscovite is present in trace amounts as a 52 50 81 layers contain plagioclase, quartz, biotite, and hornblende or diopside. 59 86 56 retrograde alteration product of K-feldspar. Biotite is partly 13 Zo 54 (K-feldspar), 22 to 30 percent plagioclase, trace to 8 percent biotite F2 fold axis 50 84 64 Locally, minor garnet-bearing plagioclase-quartz-biotite gneiss is 50 25 67 Zoa Pp 11C (typically less than 3 percent), and trace amounts of zircon, apatite, and retrograded to chlorite. Occurs as thin (up to 3 m thick) layers that Pa 55 7 58 67 85 78 present. The distinctive layered character becomes obscure where the 50 F fold axis 13 71 opaque Fe-Ti oxides. Locally, some parts of the map unit contain as may be continuous for several hundred meters and as large map units 3 DSos Pp 75 Zgdh 84 80 71 map unit has been migmatized by granite and pegmatite. Exposures are 60 Zoa 84 consisting of well-bedded quartzite with subordinate biotite gneiss and 46 46 Zoa 9 70 much as 4 percent garnet. The plagioclase has well-developed 34 S /S intersection lineation 58 66 68 25 48 discontinuous, and the unit is locally migmatitic near Mack Creek; sillimanite schist. The largest exposures of the quartzite are found 1 2 Zo 80 myrmekitic textures, particularly near the contacts with K-feldspar. The 64 82 however, the unit is well exposed in Nehantic State Forest in the 75 73 north of Game Ledge and on the northern side of Hart Hill in the 30 S -S /S intersection lineation 75 32 Zo Pp 48 68 alkali feldspar commonly contains microperthite texture of sodic 1 2 3 45 52 62 northern part of the quadrangle and near Springdale Pond in the 23 northern part of the quadrangle. SHRIMP U-Pb data on detrital 33 84 feldspar inclusions and displays K-feldspar polysynthetic grid twining. 61 Zgdl 46 59 69 58 western part 68 24 82 48 Separation of alaskite from granite phases is not possible in the field so zircon cores from a 2-m-thick quartzite bed (sample OL96, table 3) Zgdh70 67 46 51 Mineral lineations 20 Pa yields ages ranging from about 2,127 to 925 Ma OL293 16 77 84 Pp the units are mapped as composite intrusive bodies. In the northern 68 82 83 67 60 Zgb 84 37 79 METAIGNEOUS ROCKS 22 L consisting of one or more minerals including quartz, plagioclase, 80 76 part of the quadrangle, two major northeast-trending belts of the gneiss, Zolq Layered quartzite and schist—Gray to light-gray, thinly bedded, vitreous 1 30 71 54 50 28 52 68 55 Zolq K-feldspar, sillimanite, and (or) hornblende 4C 65 which form distinct, sharp, discontinuous ridges, extend from the Zwr Rope Ferry Gneiss of the Waterford Group (Neoproterozoic)— Zo 59 34 quartzite and dark-gray to black and white, rusty-weathering, LYME DOME 74 Pa 87 85 74 49 72 48 54 49 72 62 adjacent Hamburg quadrangle (Lundgren, 1966a) at Game Ledge and Uniform, moderately to well-foliated and layered, medium-grained coarse-grained garnet-sillimanite-K-feldspar-biotite-plagioclase-quartz

Zgd 61 83 Zo 24 Black Hall River 81 83 60 PZmig Zwra L2 consisting of one or more minerals including quartz, sillimanite, 84 77 from the ridge south of Game Ledge. These belts wrap around the (0.5–2 mm long), light- to medium-gray and pinkish-gray biotite-quartz- schist. Bedding is generally 10 to 20 cm thick. Two horizons are 44 Pp 63 42 biotite, and (or) K-feldspar 34 57 71 northwestern and western flanks of the Lyme dome to exposures south plagioclase gneiss and granofels that commonly displays a pinstripe 66 82 61 mapped near Point O’Woods. Schist within the map unit is similar to 56 82 42 Zos 84 35 Pp of Exit 70 on I-95. On the eastern side of the dome, north-northwest- layering created by segregation of biotite-rich layers. The rock is 57 68 89 68 50 Zoa Zos, and quartzite is similar to Zoq 45 Zgd A' Pp 73 82 28 10 trending ridges are underlain by the map unit including Smith Ledges granodioritic and contains about 20 to 36 percent quartz, 42 to 61 OTHER FEATURES 66 73 65 79 Zoa Amphibolite—Dark-green to black, medium- to coarse-grained, well- COVER 70 53 44 and several unnamed ridges west of the lake of Plants Dam. A SHRIMP percent plagioclase, 5 to 10 percent biotite, trace to 3 percent alkali 57 74 67 Zoa 43 foliated quartz-biotite-plagioclase-hornblende amphibolite. The rock Abandoned rock quarry—Quarries shown on base map are gravel pits 46 6F 48 71 67 U-Pb zircon age of the alaskite and granite gneiss is 290±4 Ma (sample feldspar (interstitial orthoclase), 0 to 5 percent hornblende, trace to 1 62 43 72 52 Zo 72 42 73 contains 4 to 9 percent quartz, 27 to 45 percent plagioclase, trace to 69 57 OL291, table 3; Walsh and others, 2007) indicating a Permian age. All percent opaque Fe-Ti oxides, and trace amounts of apatite and zircon. 88 68 70 12 percent biotite, 34 to 62 percent hornblende, 0 to 6 percent OL293 67 75 76 U-Pb zircon sample locality—See table 3 (in explanatory text file) for 67 80 45 59 40 the alaskite and granite gneiss is limited to the Gander terrane and The map unit is well exposed in the northwestern part of the Zo 67 47 42 62 chlorite, trace to 1 percent opaque Fe-Ti oxides, and trace amounts age 12 73 86 intrudes the Old Lyme Gneiss. Locally, unmapped, discordant, coarse quadrangle in the Selden Neck block. A thin (20-cm-thick) lens of 55 20 of apatite and zircon. Coarse-grained retrograde chlorite veins locally 56 Zoa 47 53 OL294 amphibolite occurs within the gneiss along Ely Ferry Road. The Sil–Mus Zo pegmatitic dikes cut the map unit. It is unclear whether the map unit Pp 45 63 62 47 1A,B 6E A and B cut the amphibolite. Occurs as disarticulated boudinaged layers or Metamorphic isograd (from Lundgren, 1967)—Sil, sillimanite; Mus, Zo 78 80 Sil–Kfs 67 82 Pp Zolq 82 extends west of the Connecticut River or into the Essex quadrangle to amphibolite is shown on the map as Zwra; its size is greatly exaggerated 33 52 lenses ranging from tens of centimeters to several meters thick. muscovite; Kfs, K-feldspar 43 Zoq 58 the west (R.B. Scott, written commun., 2003; Lundgren, 1964). The on the map to show the location 73 44 Zos 73 57 Contacts with the enclosing units are sharp. Size of the amphibolite 78 77 Pp 6E 27 48 southwesternmost outcrop of the alaskite and granite gneiss occurs on 63 Zgb Granite gneiss at Becket Hill (Neoproterozoic)—Coarse-grained (2–6 bodies is exaggerated in order to show their locations. Typical Site of photograph—Tip of arrow at point of observation; number keyed 25 87 the northern side of Great Island along the Back River 57 Pp Pp mm in diameter), moderately to well-foliated, pinkish-gray to light-gray exposures occur at Saltworks Point and Point O’Woods to figure in explanatory text file

Pp OL295 67 15 Zoq 77 62 67 Pg granite orthogneiss. Locally, lenses of Old Lyme Gneiss are enclosed 86 57 Granite gneiss (Permian)—Very light gray to black and white, medium- 38 Zo 40 38 within the map unit, and the map unit contact is locally discordant INTERSTATE ROUTE 95 52 to coarse-grained, well-foliated biotite-K-feldspar-quartz-plagioclase 28 Zos Zoa Zoa granite orthogneiss. Biotite defines a distinct foliation and makes up 10 relative to Old Lyme Gneiss layering and foliation attitudes. Layering, Zo 40 67 68 to 15 percent of the rock. Quartz and K-feldspar are equally abundant typically 5 to 10 mm thick, is formed by segregations of biotite, quartz, 67 55 8A Zoa 30 70 (20–25 percent each). K-feldspar is very light pink to white. The rock K-feldspar, and plagioclase. Locally where the map unit is attenuated, Zgb 29 contains 40 to 45 percent plagioclase. Occurs in two places on the layering is thinner (3–4 mm thick). Folia are defined by biotite and by 53 Zgd western border of the map near Obed Heights Reservoir where it is elongate crystals of quartz and feldspar. Locally, pegmatite dikes cut 30 18 compositionally homogenous without distinct layering. Foliation-parallel across the layering and contain muscovite north of Rogers Lake. The 72°45’ 72°30’ 72°15’ 72°00’ 71°45’ 66 42 sill-like bodies intrude the schist and gneiss at Obed Heights (DSoh). rock contains approximately 24 to 41 percent quartz, 26 to 48 percent

Zo 52 Rock resembles the unmapped granitic phases of the alaskite and alkali feldspar (K-feldspar), 17 to 43 percent plagioclase, 0 to 6 percent granite gneiss (Pa) but contains more biotite and less K-feldspar than the biotite, 0 to 1 percent hornblende, 0 to 2 percent garnet, trace to 3.5 Avalon terrane 42°00’ alaskite phases of Pa percent opaque Fe-Ti oxides, trace to 1 percent zircon, and trace Gander terrane Armstrong Brook PZmig Migmatite gneiss (Permian and Neoproterozoic)—Light-gray to pink, amounts of apatite, epidote, and allanite. Locally as much as 1 percent coarse-grained, well-foliated, migmatitic K-feldspar-quartz-plagioclase muscovite is present. K-feldspar displays typical polysynthetic grid EXPLANATION alaskite gneiss and biotite-K-feldspar-quartz-plagioclase granite gneiss twining. Plagioclase commonly has myrmekitic intergrowths near Hartford basin Zos with thin septa of dark- to light-gray sillimanite-biotite-quartz-plagioclase contacts with K-feldspar. At some localities large (4–9 mm in diameter) gneiss and schist of the Old Lyme Gneiss. The rock consists of greater opaque Fe-Ti oxides clusters are present. One minor belt of the gneiss Central Maine terrane T pinches out southwest of Uncas Pond, but the major belt of the map L than 75 percent leucocratic migmatite in which the leucosomes U

A T Merrimack terrane unit, which forms low rounded discontinuous ridges, extends from the F resemble rocks of the alaskite and granite gneiss unit (Pa). Exposed L

U C Y

R

A adjacent Hamburg quadrangle (Lundgren, 1966a) at Becket Hill to o

U F

between South Lyme and Point O’Woods n Putnam-Nashoba terrane

SURFACE B

R

Quarry Hill, where it wraps around the northwestern and western flank n

W A

e E H

c

N C Zo of the Lyme dome. West of the Connecticut River only two small - Bronson Hill terrane t

i N E 41°45’ c Willimantic K outcrops are exposed just southwest of the confluence of Rock Creek u O METASEDIMENTARY ROCKS t D dome T A Avalon terrane L

R N

U I with the Connecticut River. A SHRIMP U-Pb zircon age is 611±8 Ma L i v DSoh C Westerly Granite Schist and gneiss at Obed Heights (Devonian to Silurian)—Schist, (sample OL290, table 3) confirming its Neoproterozoic age. It is unclear e r gneiss, amphibolite, and calc-silicate gneiss. This largely if or how far the map unit extends westward into the Essex quadrangle. Joshua Rock Granite Gneiss Zo metasedimentary unit consists of highly variable lithologies that include Informally named for exposures on Becket Hill. Other type localities Voluntown Threemile River (1) quartz- and feldspar-dominated gneiss and biotite-rich schist, (2) local Granite, granitic and granodioritic gneiss include exposures along Blood Street north of Rogers Lake, on cliffs dome amphibolite and other mafic metaigneous rocks, and (3) minor east of Lord Cove, and at Quarry Hill Paragneiss and granitic gneiss calc-silicate gneiss. Informally named here for rocks exposed at Obed Zgd Heights Reservoir along the boundary between the Old Lyme and Essex Granodiorite gneiss at Johnnycake Hill (Neoproterozoic)—Light-gray, Gander terrane moderately foliated, massive, medium- to coarse-grained biotite- quadrangles and at Obed Heights in the adjacent Essex quadrangle. (1) Zgdh Granite, granitic and granodioritic gneiss K-feldspar-quartz-plagioclase granodiorite orthogneiss. The distribution Hopyard ONE The quartz- and feldspar-dominated rocks are moderately to H Y H basin ILL FA Paragneiss of biotite defines a characteristic pseudo-flaser or “shear band boudin” UL 41°30’ Pp T PZmig well-foliated and layered, medium- to coarse-grained (1–10 mm long), texture (Passchier and Trouw, 2005) in the gneiss. Typical outcrops are Mus Montville dome medium-light-gray to grayish-orange-pink gneiss and schist. These rocks Fault—U, upthrown side; D, downthrown side contain about 22 to 40 percent quartz, 0 to 40 percent alkali feldspar homogeneous and show very little compositional segregation. Two Kfs Joshua Mus observed outcrops contain accessory amounts of uniformly distributed Rock (orthoclase), 26 to 51 percent plagioclase, 3 to 17 percent biotite Potter Hill Isograd—Muscovite (Mus) and K-feldspar (Kfs) along the dome Kfs Zo hornblende and rare, small (<10 cm) pods or xenoliths of garnet- (locally in coarse layers), 0 to 1 percent garnet (locally garnet-rich), and Seldenblock Neck Mystic second sillimanite (or sillimanite-orthoclase) isograd sphene-diopside-hornblende-biotite-quartz-plagioclase calc-silicate rock basin Zolq trace amounts of opaque Fe-Ti oxides, hornblende, zircon, and apatite. Killingworth dome mapped as Zgdh. The Zgdh unit typically contains anastomosing dome Chlorite and white mica are retrograde products of biotite and Stonington Pa Zos ? Mystic fold leucosomes of quartz and feldspar that are generally absent from Zgd. Lyme antiform LONG ISLAND SOUND plagioclase, respectively. (2) The amphibolite is well foliated and Hunts Brook ? A layered, medium grained (0.5–3 mm), and medium dark gray; the rock The massive nature, the presence of amphibolite and calc-silicate slice ' xenoliths, and the crosscutting nature of the contact with the Old Lyme 3000 1000 2000 3000 40000 1000 2000 4000 5000

SEA LEVEL ? contains about 5 to 14 percent quartz, 15 to 40 percent plagioclase, 0 Stony Gneiss indicates that the rock is intrusive. A SHRIMP U-Pb zircon age Clinton Old Lyme FEET d Sound to 10 percent biotite, 45 to 75 percent hornblende, trace to 1 percent Creek dome dome quadrangle Long Islan opaque Fe-Ti oxides, and trace amounts of zircon, apatite, of 619±7 Ma (sample OL293, table 3) indicates that the rock is 41°15’ clinopyroxene, and sphene. One example of mafic gneiss contains 8.5 Neoproterozoic. Informally named for exposures on the eastern side of 0 6 12 MILES percent quartz, 47.5 percent plagioclase, 1 percent biotite, 35 percent Johnnycake Hill in the core of the Lyme dome clinopyroxene, 4.5 percent opaque Fe-Ti oxides, 2.5 percent zircon, Zgdl Granodiorite gneiss at Lord Hill (Neoproterozoic)—Light-gray to 0 9 18 KILOMETERS Base from U.S. Geological Survey, 1958 (photorevised 1970) 14° SCALE 1:24 000 Geology mapped by Armstrong in 2001 and by and 1 percent apatite. Amphibolite layers are 0.3 to 2 m thick, light-pink, well-foliated, massive, medium-grained, slabby weathering Hydrography compiled from U.S. Coast and Geodetic Survey 1 1/ 2 0 1 MILE Walsh and Scott in 2002 Zgdla MAGNETIC NORTH CONNECTICUT Scott hornblende-biotite-K-feldspar-quartz-plagioclase granodiorite orthogneiss. TRUE NORTH TRUE commonly have pinstripe layering, and are discontinuous. (3) West of Figure 1.—Generalized tectonic map of eastern Connecticut showing the location of the Old Lyme quadrangle Charts 214 and 215 (1957) Digital compilation by Walsh, Typical outcrops are homogeneous and show very little compositional 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET the Connecticut River, poorly to well-layered, moderately foliated, and distribution of terranes and major Alleghanian domes and basins (modified from Goldsmith, 1985; Rodgers, Polyconic projection. 1927 North American Datum assisted by Aaron Satkoski segregation but are well foliated. Contains approximately 20 to 30 medium-grained, dark-greenish-gray calc-silicate gneiss consists of 1985; Walsh and others, 2007). Upper left inset map shows the distribution of the Gander and Avalon terranes. 10,000-foot grid ticks based on Connecticut coordinate system 1 .5 0 1 KILOMETER Walsh and Geochronology by Aleinikoff equigranular hornblende and diopside, plagioclase, quartz, and percent quartz, 5 to 30 percent alkali feldspar (orthoclase and Armstrong 1,000-meter Universal Transverse Mercator grid ticks, MAP LOCATION occasional pyrite interlayered with more felsic gneiss. One mode has microcline), 30 to 50 percent plagioclase, 4 to 9 percent biotite, and APPROXIMATE MEAN CONTOUR INTERVAL 10 FEET zone 18, shown in blue DECLINATION, 2009 approximately 37 percent quartz, 44 percent plagioclase, 8 percent trace to 3 percent hornblende, and trace amounts of garnet, opaque NATIONAL GEODETIC VERTICAL DATUM OF 1929 DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOW WATER biotite, 5 percent diopside, 5 percent hornblende, and trace amounts of Fe-Ti oxides, apatite, and zircon. Locally, where the alkali feldspar THE RELATIONSHIP BETWEEN THE TWO DATUMS IS VARIABLE opaque Fe-Ti oxides, calcite, and apatite. Unit mapped previously by forms close to one-third of the rock, the plagioclase is myrmekitic and SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER INDEX TO MAPPING THE MEAN RANGE OF TIDE IS APPROXIMATELY 3.5 FEET Lundgren (1967) and Rodgers (1985) as Tatnic Hill Formation the alkali feldspar is K-feldspar. Thin (15–20 cm thick), discontinuous

BEDROCK GEOLOGIC MAP OF THE OLD LYME QUADRANGLE, NEW LONDON AND MIDDLESEX COUNTIES, CONNECTICUT By 1 2 2 3 This map is available for sale by U.S. Geological Survey, Information Services, Gregory J. Walsh, Robert B. Scott, John N. Aleinikoff, and Thomas R. Armstrong Box 25286, Denver Federal Center, Denver, CO 80225 For product and ordering information: 1 2 3 U.S. Geological Survey, Montpelier, VT 05601. U.S. Geological Survey, Denver, CO 80225. U.S. Geological Survey, Reston, VA 20192. World Wide Web: http://www.usgs.gov; Telephone: 1-888-ASK-USGS Any use of trade, product, or firm names is for descriptive purposes only and 2009 does not imply endorsement by the U.S. Government