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%XOOHWLQ %HGURFN *HRORJ\RI WKH %DWK ÿ 0DS 6KHHW &RDVWDO 0DLQH $UWK X U 0 +XVVH\,, +HQU\1 %HUU\,9 0DLQH*HRORJLFDO6XUYH\ '(3$570(17 2 ) &216(59$7,21 5RE HUW* 0D UYLQQH\ 6WDWH*HRORJLVW 0$,1( %XOOHWLQ %HGURFN*HRORJ\RIWKH%DWKÿ 0DS6KHHW&RDVWDO 0 DLQH $UWKXU0 +XVVH\,, +HQU\1%HUU\,9 0DLQH *HR ORJLFDO6 XUYH\ $XJ XVWD 0DLQH %RZGRLQ&ROOHJH %UXQVZLFN0DLQH 0DLQH*HRORJLFDO 6XUYH\ '(3$570(172)&216(59$7,21 5REHUW* 0DUYLQQH\6WDWH*HRORJLVW 7KLVEXOOHWLQLVDFRPSDQLRQWR0DLQH*HRORJLFDO6XUYH\*HRORJLF0DS %HGURFN*HRORJ\RIWKH%DWK ÿ 4XDGUDQJOH0DLQH Copyright © 2002 by the Maine Geological Survey, Department of Con- servation. All rights reserved. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, pho- tocopying, recording or otherwise, without the prior written permission of the publisher. Cover photograph: Upright folds in metamorphic rocks of the Bucksport Formation at Pemaquid Point Lighthouse. The spectacular exposures here reveal many such structural features to the careful observer. This photograph looks directly along the crest of a fold, with layering on the left tilting to the left and layering on the right tilting to the right. In the middle distance the form of the fold is clearly visible. On the skyline to the right is a large ridge underlain with white pegmatite, a very coarse-grained, igneous rock that intrudes the metamorphic rock. The laws and policies of Maine and the United States prohibit discrimination in Department of Conservation programs and/or employment because of race, religion, national origin, sex, age, or handicap. Any person who believes discrimina- tion has occurred should contact the Commissioner, Maine Department of Conservation, Station #22, Augusta, ME 04333; Telephone (207)287-2211. Contents Abstract....................................................1 Introduction..................................................1 CentralMainesequence............................................3 Torrey Hill Formation (SOth)....................................3 Richmond Corner Formation (SOrc)................................3 Hutchins Corner Formation (SOhc).................................3 Falmouth-Brunswicksequence........................................3 Nehumkeag Pond Formation (Onp, Onpr).............................5 Mount Ararat Formation (Oma) ..................................5 CascoBayGroup...............................................6 Cushing Formation (Ocp, Oca, Ocm, Ocw)............................6 Peaks Island Member (Ocp).................................6 Merepoint Member (Ocm)..................................6 Wilson Cove Member (Ocw) ................................7 Cape Elizabeth Formation (Oce, Ocer, Ocep, Ocea, Ocec)....................7 TheCapeElizabeth-Cushingcontact...............................10 Spring Point Formation (Ospb, Ospf)...............................10 Diamond Island Formation (Odi).................................10 Scarboro Formation (Osc).....................................10 Spurwink Metalimestone (Osk) and Jewell Formation (Oj) ...................11 EastHarpswellGroup............................................11 Yarmouth Island Formation (SOy, SOya).............................11 Bethel Point Formation (SObp)..................................12 Sebascodegan Formation (SOs, SOsa, SOsr, SOspi).......................12 Frederictonsequence............................................13 Bucksport Formation (SOb)....................................13 Megunticooksequence...........................................14 Penobscot Formation (OCp)....................................14 BennerHillsequence............................................14 Mosquito Harbor Formation (Omh)................................14 Hart Neck Formation (Ohn)....................................15 Benner Hill Formation (Obh)...................................15 RocksexposedontheGeorgesIslands,St.George........................15 Sequenceuncertain.............................................16 Cross River Formation (OCcr, OCcrg)..............................16 Unnamed amphibolite unit (Ouv).................................16 Unnamed sulfidic schist (Ouss)..................................16 Correlationsandagesofthestratifiedrocks.................................17 CentralMainesequence......................................17 Falmouth-Brunswicksequence..................................17 CascoBayGroup.........................................18 EastHarpswellGroup.......................................18 Frederictonsequence........................................19 BennerHillsequence.......................................19 Megunticooksequence.......................................19 Sequenceuncertain.........................................19 A. M. Hussey II and H. N. Berry IV Intrusiverocks................................................20 Raccoon pluton (Srgb, Srgbh) ..................................20 Spruce Head pluton (Ssg, Ssgb, Ssgd)...............................20 Monhegan pluton and other gabbro and diorite bodies (Sgb)...................21 Miscellaneous metamorphosed mafic to intermediate plutons (DSmdg).............21 Oak Island Gneiss (DSoi).....................................21 Edgecomb Gneiss (DSeg).....................................21 Two-mica granite (DSg)plutons,Woolwich-Phippsburgbelt..................22 Lincoln Sill (DSls).........................................22 Quartz diorite at Georgetown (Dqd)................................23 Waldoboro pluton (Dwga, Dwgp, Dwgn, Dwgl).........................23 Granitic pegmatites . 24 ChristmasCovedike........................................25 Structuralgeology..............................................25 Folds ..............................................26 Folds in the Falmouth-Brunswick sequence and the Central Maine sequence . 26 Merepointanticline.....................................27 HarpswellSoundsynclineandHenCoveanticline....................27 PhippsburgandCapeSmallsynforms...........................29 Robinhood Cove synform, Georgetown antiform, and Bay Point synform . 30 Boothbayanticline.....................................30 EastBoothbayrecumbentfolds...............................31 FoldsintheLinekinNeck-SouthBristolarea.......................32 PemaquidHarboranticline.................................33 PortClyderefoldedanticline................................33 Faultsandshearzones.......................................33 Thrustfaults.........................................34 Boothbaythrust...................................34 Possibleblindthrust.................................34 Norumbegafaultsystem..................................34 FlyingPointfault..................................34 SouthHarpswellfault................................34 Brittle faults. 35 CapeElizabethfault.................................35 BackRiverfault...................................35 TheBasinfault....................................35 Phippsburgfault...................................35 St.GeorgeEstuaryfault...............................35 Miscellaneousminorfaults.............................36 Lineation..............................................36 Metamorphismandmigmatization.....................................39 Timing of volcanism, sedimentation, deformation, metamorphism, and plutonism . 40 Mineralresourcesandpastminingactivity.................................43 Acknowledgments..............................................48 Referencescited...............................................48 Maine Geological Survey Bulletin 42 Bedrock Geology of the Bath 1:100,000 Map Sheet, Coastal Maine Arthur M. Hussey II 1,2 Henry N. Berry IV 1 1 Maine Geological Survey Augusta, Maine 04333 2 Bowdoin College Brunswick, Maine 04011 ABSTRACT Bedrock that underlies the area of the Bath 1:100,000 map sheet includes metamorphosed sedimentary and vol- canic rocks of Late Cambrian to Silurian age, gabbroic and granitoid intrusive rocks ranging from Late Silurian to Permian age, and basaltic or diabasic dikes of Mesozoic age. The metamorphic rocks have been assigned to seven tectono-stratigraphic sequences: Central Maine, Falmouth-Brunswick, Casco Bay, East Harpswell, Fredericton, Benner Hill, and Megunticook. These sequences are separated by inferred early tectonic thrust faults and late tec- tonic or post tectonic strike-slip faults of the Norumbega fault zone, so have uncertain relationships to each other. For a few structurally isolated units, the sequence assignment is not clear. Several stages of folding characterize each sequence and are believed to be mostly the result of Late Silurian to Early Devonian phases of the Acadian orogeny. Prograde metamorphism of the volcanic and sedimentary rocks ranges from staurolite grade to sillimanite + K- feldspar grade in a Buchan-type low-pressure metamorphic facies series. Multiple stages of Buchan series metamor- phism are clearly indicated by large muscovite pseudomorphs at Small Point. At the highest grade (sillimanite + K- feldspar), pelitic rocks are extensively migmatized. 40Ar/39Ar cooling ages on hornblende from sequences east of the Flying Point fault suggest that major regional high-grade metamorphism occurred during the Silurian-Devonian Acadian orogeny. Younger hornblende cooling ages from the Falmouth-Brunswick sequence in the Brunswick area suggest a more limited region of high-grade metamorphism of Late Paleozoic age possibly related to the intrusion of Permian