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.