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s The Bedrock Geology of Massachusetts itigraph) ol the \lill<n<l Dedham Z< .IStCl 11 Massachusetts: \n \\.il<>iu.ni ferrane I Stratigraph) <>i the Nashoba Zon rn Massachi Itii.in i< ( . Sn iir'i ii)li\ ol the \1 I \1, ,n 1111srlI I SiI IK Iin ,|l ,IIKI \h I.IIIH>l I>lll( IIIsli SS.K IIIIS(IIS IIIII 11si l\.n!i<n I .S. (. 1 () I ( )(. I( \ ! SI K \ I \ i'KOI I SSIONAI PAPEK The Bedrock Geology of Massachusetts NORMAN L. HATCH,JR., Editor E. Stratigraphy of the Milford-Dedham Zone, Eastern Massachusetts: An Avalonian Terrane By RICHARD GOLDSMITH F. Stratigraphy of the Nashoba Zone, Eastern Massachusetts: An Enigmatic Terrane By RICHARD GOLDSMITH G. Stratigraphy of the Merrimack Belt, Central Massachusetts By PETER ROBINSON and RICHARD GOLDSMITH H. Structural and Metamorphic History of Eastern Massachusetts By RICHARD GOLDSMITH I. Intrusive Rocks of Eastern Massachusetts By DAVID R. WONES and RICHARD GOLDSMITH Radiometric Ages of Rocks in Massachusetts J. By ROBERT E. ZARTMAN and RICHARD F. MARVIN U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1366-E-J Chapters E-J are issued as a single volume and are not available separately FftAiu OOCUMENTS Exi-F')iTWC Wttiw? 80V«NMENTDOCUMENTSDEHARTMENI FEQ92 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1991 U.S. DEPARTMENT OF THE INTERIOR MANUEL LUJAN,Jr., Secretary U.S. GEOLOGICALSURVEY Dallas L. Peck, Director Anyuseoftrade,product,orfirmnamesinthispublicationisfor descriptivepurposesonlyanddoesnotimplyendorsementbythe U.S.Government LibraryofCongressCataloginginPublicationData ThebedrockgeologyofMassachusetts. (U.S.GeologicalSurveyprofessionalpaper;1366-E-J) Bibliography:p. Supt.ofDocs,no.:I19.16:1366E^I Q1.E1G2e3o.lBo4g4y—Massa1c9h8u8sbetts. 5I.57H.a4t4ch,Nor8m7-a6n00L4.7,2Jr. II. Series:GeologicalSurveyprofessionalpaper;1366-E-J. Forsalebythe Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box25425, Denver, CO80225 Editor's Preface to Chapters E through J ThisProfessionalPaperwasplannedasacompanionto grouping ofthe 343 individual lithic units on the State the bedrock geologic map of Massachusetts (Zen and bedrockmapintothe 8lithotectonicpackages discussed others, 1983; hereafterreferred to asthe State bedrock by Hatch and others (1984). The temporal and geo- map). It is being published as lettered chapters of graphic distributions of these eight packages are indi- ProfessionalPaper1366, sixofwhichareincludedinthis catedonfigures1and2.Alsoindicatedonthefiguresare volume, and four of which were published in a single the geographic and geologic coverages ofthe chapters volume as chapters A-D (Hatch, 1988). Compilation of included in this volume. In this packaging scheme, the thegeologyfortheStatebedrockmapwascompletedin older, primarily pre-Silurian, rocks of the State are 1980. Some of the chapters in this Professional Paper grouped into five "zones" whose exposed and buried reflectfieldorlaboratorydatathatweregleanedasmuch parts completely cover the State. From west to east, as 6 years later. Each chapter was prepared, however, these zones are the Taconic-Berkshire, the Rowe- with the objective ofexplaining and further describing Hawley,theBronsonHill,theNashoba,andtheMilford- the geology as portrayed on the State bedrockmap. In Dedham. Theirmutualboundaries are, orcould reason- some instances, information and interpretations devel- ably be interpreted to be, faults. Overlying and oped since 1980have caused chapterauthors to suggest overlappingthezonesinthecentralpartoftheStateare revisionsthattheywouldmaketothe mapiftheywere the ConnecticutValleyandMerrimack"belts"ofprima- able to redraw it, but in each case these suggested rilySilurianandDevonianstrata.Theirmutualboundary revisionsarediscussedinthecontextofthemapasitwas is somewhat arbitrarily taken to be the east contact of published. the easternmost exposed Silurian Clough Quartzite. The previous State bedrock map (which also showed Finally,theMesozoic"basins"unconformablyoverliethe the geology ofRhode Island) was published in 1917 by Connecticut Valleybelt. Benjamin K. Emersonas U.S. Geological Survey Bulle- For some packages, all aspects of the geology are tin 597. (The publication date of Bulletin 597 is 1917. treatedinthesamechapter. Forothers, aspectssuchas Someconfusionarisesfromthefactthatthebedrockmap the structure, metamorphism, and tectonics are dis- ofthetwo States, whichisincludedinthepocketofthe cussedseparatelyfromstratigraphyandlithology.These Bulletin, bearsthedate of1916.)Allwhowereinvolved differences in treatment resulted from peculiarities of inthepreparationofthe newbedrockmap, particularly the geology and the preferences of the individual those responsible for the parts of the State in which authors. Many of the plutonic rocks of the State are Emersonhimselfhaddonetheoriginalfieldwork, feela describedand discussedin chapter I. great deal of respect for Professor Emerson and his Many ofthe lithologic subdivisions offormal units on remarkablyperceptiveandthoroughunderstandingand the State bedrock map have not been given formal portrayalofthegeology. Althoughthenewmapis very names. Inordertoavoidpotentiallycumbersomediscus- different from Emerson's in many aspects, particularly sions of such things as "the thick-bedded micaceous withregardtotheinterpretationofthegeologichistory, quartzite and mica schist unit ofthe XYZ Formation," thebasicdistributionofmapunitsisremarkablysimilar. manychapterauthorshavechosentorefertosuchunits The State bedrock map and this report are direct simplybytheirmapsymbols.Thusthemicaceousquartz- outgrowths ofa cooperative geologic mapping program ite, quartz-mica-garnet schist, and calc-silicate unit of between the U.S. Geological Survey and the Common- the Devonian Goshen Formation may be referred to wealthofMassachusetts,whichwasbegunin1938. They simplybyitsmapsymbol"Dgq,"butinacontextwhere alsoincludetheresultsofmorethan25yearsofmapping thereaderwill be easilyguidedtothe correctunit. and topical studies by faculty and students at the Uni- Theterms"granulite"and"granofels"havebeenused versityofMassachusettsatAmherstandatmanyother rather arbitrarily and interchangeably throughout this collegesanduniversities. Professional Paper, although onthe State bedrock map The subdivision of the material in this Professional the term "granofels" was used exclusively. Both terms Paper into the constituent chapters is based on the are used to describe a metamorphic rock composed PREFACE predominantlyofeven-sized, interlockinggranularmin- faultonthewest. ChapterGdescribesthe stratigraphy erals;noimplicationastothegradeofmetamorphismis oftheSilurianandDevonianrocksoftheMerrimackbelt, intended by either term. The choice of words merely whichadjoinsandoverliestheNashobazoneonthewest. reflects individual author preference, and we hope that ChapterHdiscussesthestructureandmetamorphismof no confusion to the reader will result from the unre- therocksoftheMilford-DedhamandNashobazonesand straineduse oftwowordsforthe samekind ofrock. oftheeasternmostpartofthe Merrimackbelt. Chapter This volume contains six chaptersthat deal primarily I describes and discussesthecriticallydistinctiveintru- with terranes of eastern Massachusetts, terranes that sive rocks of the eastern part of the State. Finally, were amalgamatedand accreted to NorthAmericadur- ChapterJtabulates all oftheisotopicages ontherocks ingthePaleozoic. ChapterE, onthestratigraphyofthe ofthewholeStateavailableasof1986.Mostoftheseages Milford-Dedham zone, deals withthe stratified rocks of arefromtheabundantplutonicrocksoftheeasternpart the easternmostpartofthe State, aterrane considered ofthe State. torepresentpartofAvalonia. ChapterF dealswiththe We would herein like to acknowledge the invaluable stratifiedrocksoftheNashobazone, a"suspectterrane" contributions to this Professional Paper of two key westoftheMilford-Dedhamzone,thatisboundedbythe people. Jewel Dickson didthecartographicworkonthe BloodyBlufffaultontheeastandthe Clinton-Newbury majority of the illustrations, the principal exceptions MIDDLE PROTEROZOIC Figure 1.—Diagram simplified from the "Correlation ofMap Units" on the State bedrock map showing the eight lithotectonic packages into which the rock units have been divided. Also indicatedaretheletterdesignation(s)ofthechapter(s)inthisvolumecoveringvariousaspectsof thegeology.ChapterJdealswithrocksfromtheentireStateandthusisnotshownonthefigure. ModifiedfromHatchandothers(1984,fig. 1). PREFACE ChapterG MERRIMACK BELT TACONIC- BERKSHIRE ZONE Nantucket Figure2.—MapofMassachusettsshowingthegeographicdistributionoftheeightlithotectonicpackagesintowhichtherockunitsoftheState havebeengroupedandtheletterdesignation(s)ofthechapter(s)inthisvolumeinwhichaspectsofthegeologyarediscussed.ChapterJdeals withrocksfromtheentireStateandthusisnotshownonthefigure.ModifiedfromHatchandandothers(1984,fig.2). being those prepared by author Peter Robinson. Kath- Hatch,N.L.,Jr.,editor,1988,ThebedrockgeologyofMassachusetts: leen Krafft Gohn suffered bravely over the years with U.S. Geological SurveyProfessionalPaper 1366-A-D, variously the editor and authors ofthis Professional Paper as its Hatch, N.L., Jr., Zen, E-an, Goldsmith, Richard, Ratcliffe, N.M., technicaleditor. Robinson, Peter, and Wones, D.R., 1984, Lithotectonic assem- blagesasportrayedonthenewbedrockgeologicmapofMassa- chusetts:AmericanJournalofScience,v.284,p. 1026-1034. REFERENCESCITED Zen, E-an, editor, Goldsmith, Richard, Ratcliffe, N.M., Robinson, Peter,andStanley, R.S.,compilers, 1983, Bedrockgeologicmap Emerson, B.K., 1917, Geology ofMassachusetts and Rhode Island: ofMassachusetts:Reston,Va.,U.S. GeologicalSurvey,3sheets, U.S.GeologicalSurveyBulletin597,289p. scale1:250,000. VOLUME CONTENTS [Lettersdesignatechapte: Editor'sPrefacetoChaptersEthroughJ,byNormanL. Hatch,Jr. (E) StratigraphyoftheMilford-Dedhamzone,easternMassachusetts:AnAvalonianterrane,by RichardGoldsmith (F) StratigraphyoftheNashobazone,easternMassachusetts:Anenigmaticterrane,byRichard Goldsmith (G) StratigraphyoftheMerrimackbelt,centralMassachusetts,byPeterRobinsonandRichard Goldsmith (H) StructuralandmetamorphichistoryofeasternMassachusetts,byRichardGoldsmith (I) IntrusiverocksofeasternMassachusetts,byDavidR.WonesandRichardGoldsmith (J) RadiometricagesofrocksinMassachusetts,byRobertE.ZartmanandRichardF.Marvin ThefollowingchaptersofProfessionalPaper1366werepublishedinasinglevolumein1988: (A) Thepre-SiluriangeologyoftheRowe-Hawleyzone,byRolfeS.StanleyandNormanL. Hatch,Jr. (B) StratigraphyoftheConnecticutValleybelt,byNormanL.Hatch,Jr.,PeterRobinson,and RolfeS. Stanley (C) Post-TaconianstructuralgeologyoftheRowe-HawleyzoneandtheConnecticutValleybelt westoftheMesozoicbasins,byNormanL. Hatch,Jr.,andRolfeS. Stanley (D) TheWhatelythrust:AstructuralsolutiontothestratigraphicdilemmaoftheErvingForma- tion,byPeterRobinson,NormanL. Hatch,Jr.,andRolfeS. Stanley Digitized by the Internet Archive in 2010 with funding from Boston Public Library http://www.archive.org/details/bedrockgeologyofOOhatc