Bedrock Geology of North Haven and Vinalhaven Islands

DEPART MENT OF CONSER VA TION Maine Geo logi cal Sur vey Rob ert G. Marv in ney, State Ge olo gist

OPEN- FILE NO. 01-373

Ti tle: Bedrock Geol ogy of North Haven and Vinalhaven Islands

Author: Ol cott Gates

Date: 2001

Fi nan cial Sup port: Maine Geo logi cal Survey

As so ci ated Maps: Bedroc k Geol ogy of North Haven and Vinalhaven Islands, Ge olo gic Map 01-352

Con tents: 28 p. report Editors' Preface

In 1992, Olcott Gates brought to the Maine Geologi cal Sur- of units in his com puter file did not include a key to the letter vey a preli minary draft of the Geologi c Map of North Ha ven and sym bols shown on the map. None of the mate ri als after the 1992 Vinal haven Is lands. The 1992 draft include d unit outli nes and version were dated, so we could not be sure in all cases which struc tural sym bols, a brief expla na ti on of major rock units, three changes were the most re cent. For tu nately, Ol lie had been dis - cross sections, and a sche matic diagram. At that time, the Maine cussing his ideas with other geolo gist s, through let ters and on Survey could not produce color maps in-house. Due to the large field visit s to the is lands. These other geolo gist s suppli ed infor - expense of color press runs, it was im portant that each map be in mati on that proved crucia l to us in matching map units with the its final form before going to pub li cati on. With this in mind, Ol - ex pla na tion, and in de cid ing which of the in ter pre ta tions was the lie re turned to the is lands to clar ify parts of the map with com- most re cent. Some of the infor m ati on they provided is repro - plex geologi c rela ti onships . In the spring of 1998 he brought to duced in appen di ces to this re port. In the fall of 2000, a mockup the Maine Survey an update d version of the map with much more of the map was reviewe d by D. B. Stewart, R. A. Wobus, and detai l, espe cia lly around the Thorofare. The 1998 draft include d R. A. Wiebe who pointed out several of our errors and made sub - unit outli nes and struc tural sym bols, a com plete and de tailed ex - stanti ve com ments for which we thank them. plana ti on of units, and a narra ti ve descri pti on of the geologi c his - On the final map, Geologi c Map 01-352, we have taken tory with litera ture ref er ences. By this time, the Maine Sur vey cross sec tions C-D and E-F from Olli e's origi nal drawings. had devel oped the capa bil ity to publi sh color maps in-house, al- Cross sec tion A-B and the Sche matic Diagram were taken from lowing the publi cati on proces s to be more flexible and inex pen - his 1992 draft and modifie d slightly to conform with the map sive, and al lowing photo graphs to be include d direct ly on the changes. As much as possi ble, rela ti onships descri bed in his text map sheet. He discusse d with MGS staff the lay out of the map were taken to be authori tative, since the text pres ents an in ter - sheet, and the sorts of infor m ati on he wanted to show on it. He nally con sis tent in ter pre ta tion. Con se quently, we modi fied the did not bring cross secti ons with him at that time, becaus e there map and cross secti ons to conform with his written de scripti ons. were still some problem s that he had not re solved to his sat isfac - In edit ing the map and com pil ing the other infor m ati on dis- tion. In addi ti on, there was a possi bil ity that labora tory analyses played on the map sheet, we were forced to ab bre vi ate the de - then in progress might be able to de ter mine the age of certai n scripti ons of rock units and omit some dis cussion be cause of rocks, clari fy ing their re la tion ships. space limita ti ons. The purpose of this re port is to present Olli e's Unfor tu nate ly, Olli e passed away in July of 1999 before recom plete text, from which the map expla na ti on was de rived. vi sions were completed. His wife, Jane, gave mate ri als re lated to The brief Intro duc ti on is ours. At certai n places we have edit ed the map to the Maine Geo logi cal Sur vey. These mate ri als in - the text to make it con sis tent with what we think is Ollie's most cluded a hand-draft ed map (lit tle changed since 1998), two recent inter preta ti on. Most changes are sim ple, such as changing drafted cross sec tions, seven field notebooks, dozens of field the name of a fault, but in some insta nces the origi nal meaning is maps of various sizes and qual ity, and various scraps of pa per not en tirely clear, as in the nature of the con tact be tween the Seal and mylar with sketches of possi ble contac ts and cross-sec tion Cove and Perry Creek form ati ons. In such cases, we have done con figu ra tions, re plete with era sures, mul ti ple lines, and even our best to infer his meaning, and have insert ed num bers in some white- out. Most im portant ly, a text file was saved on his brackets [ ] that refer to appended Notes which explai n our un- com puter with a lengthy detai led expla na ti on of units, descri p - cer tainty. This may allow other ge olo gists to glean sub tle ties tion of struc tural ge ol ogy, ac knowl edg ments, ref er ences, ex pla - from his own words that were not appar ent to us. nati on of sym bols, and geologi c his tory. The geologi c his tory In the end, the points of uncer tai nty turn out to be minor in include d num bered refer ence s to photo graphs which were set com pari son with the funda m ental soundness of the map. This is aside in a set of plain white enve lopes . an excel lent piece of geologi c mapping that has signifi cantly im - Al though these ma te ri als col lec tively in cluded all the types proved our under sta nding of an im portant and com plex part of of infor m ati on we had discusse d putti ng on the map sheet in the Maine coast. It stands as an impr es sive final in stall ment in 1998, it soon becam e clear to us that Ol lie had not quite finishe d Ol lie's se ries of con tri bu tions to Maine ge ol ogy. iron ing out all the de tails. In par ticu lar, there were sev eral places where the text made refer ence to things that were not on the draft Henry N. Berry IV and Rob ert G. Marvinney of the map we thought to be the most re cent. The cross secti ons Maine Geo logi cal Sur vey did not quite match the map in a few places. And the expla na ti on Janu ary 2001

1 2 Maine Geo logi cal Sur vey Open- File 01- 373

Bedrock Ge ology of North Haven and Vinalhaven Is lands

by Ol cott Gates

ed ited by Henry N. Berry IV and Rob ert G. Marvin ney

IN TRO DUC TION

This re port ac com pa nies Geo logic Map 01- 352, Bed rock whole rock age for Dcg of 353 ± 7 Ma (correct ed using the new Geol ogy of North Haven and Vinal haven Is lands. The bulk of Rb decay consta nt of 1.42 x 10-11 yr.), Tournais ian (Early the report de scribes rock units in more detai l than could be Carbon if er ous) by the Geo logi cal So ci ety of Amer ica Time shown on the map it self. In addi ti on, it of fers jus ti fica ti on for Scale (Palm er, 1983)[*1]. The uncer tai nty of 7 Ma allows for a some of the rela ti on ships il lustra ted on the map, such as the ages Devo nian age as well. However , other granit ic and gabbroic plu- of units and their cross-cutt ing re lati on ships. A table of geo- tons in the coastal Maine belt have iso topic ages in the Si lu - chemical analyses rep re sentative of the major vol canic rock rian-Dev onian time inter val (Hogan and Sinha, 1989; Hill and units is present ed, as well as new pale on to logi c findings. Abbott , 1989; Stewart and others, 1988; West and others, 1992) and in some cases, zircon and 40Ar/39Ar ages are older than Rb- Sr AC KNOW LEDG MENTS ages. The Deer Isle gran ite, which bears a litho logic re sem- blance to the Vin alhaven coarse- grained gran ite, has a zir con I am indebte d to Arthur J. Boucot, Oregon State Uni versit y, date of 371 Ma (Stewart, 1998) which is Devo nian. Unti l a reli - and J. M. Berdan, U.S. Geologi cal Survey , for identi fica ti on of able zir con date is available, a De vo nian age is as sumed, to sim- my fos sil col lec tions from Cal der wood Point, Cal der wood Is- plify the map sym bol (D). land, and Greens Island (Appen dix IV). Philip H. Os berg of the Univer sity of Maine at Orono helped me in the field with the Cal - ap Aplite dike. derwood Form ati on. At my re quest, David B. Stewart of the U.S. Geo logi cal Sur vey, Wash ing ton D.C. made a critical and Dcg Coarse-grai ned biotite-hornble nde granit e and quartz- very helpful re view of an earli er version of the map. monzonite with a few man tled feld spars. En claves and I am also indebte d to Walter A. Ander son, former State Ge- cog nate in clu sions are rare. On the ba sis of chemical ologist , and to the other mem bers of the Maine Geologi cal Sur- analyses Mitchell and Rhodes (1989) clas sifie d Dcg as vey for their un end ing pa tience and gen er ous co op era tion. The I- type crus tal, mini mum melt with some chemical char - Maine Geologi cal Survey finance d the field work during sum - ac ter is tics of ano ro genic A- type. In te rior of plu ton has mers part time from 1988 to 1992, and the cost of geochem ical not been mapped. analy ses. Fi nally, my wife Jane, also a ge olo gist, has given me field, logis ti c, edi toria l, and moral support for half a century . Dfg Fine-grai ned bioti te granit e. Roof phase of Dcg.

EX PLANA TION OF UNITS Dqd Grano di orit e, quartz-di orite. Bioti te, hornble nde, rem - nant py rox ene. In cludes a dike near Mul len Head. PLUTONIC ROCKS Dg Gabbro and diabase . Mi nor diorit e. Olivine and pyrox - Mis sis sip pian? De vo nian? ene va rie ties. Chemical analyses (Mitchell and Rho - des, 1989) indi cat e a range of com posi ti ons. High The assign m ent of this age to the plutoni c rocks is based on MgO (8.9-11.8 wt %) gabbros are thought to have accu - a single Rb-Sr age. Brookins (1976, p. 137) reporte d a Rb- Sr mu lated oli vine and pla gio clase crys tals; me dium to

3 O. Gates

low MgO (4.1-7.5 wt %) gabbros show evidence of METAMOR PHOSE D PLUTONIC ROCKS frac tiona tion and con tami na tion by the neigh bor ing gran ite. Or do vi cian? Cam brian?

~ ~ Granit ic and gabbroic magma mingli ng zone. Stoped OCg Hornblende gabbro. Hornblende laths form strong blocks of gabbro, Si luria n sedi mentar y rocks, and pre- linea tion. In tru sive into Ccs [*3]. Silurian schists are intrude d by granit ic and diaba sic dikes and bounded by dikes consis ting of diabase pil - lows with chilled mar gins in a ma trix of gran itic rock. STRATIFIE D AND VOLCANIC ROCKS These pil low dikes re sult from the mingli ng of basal tic and granit ic magma whose dif ference s in viscos it y and De vo nian tem pera ture pre vented mix ing and the con se quent chemi cal and physi cal ho mog eni za tion (Mitchell and Vinal haven Rhyo lite Rhodes, 1989, give a brief lit erature review) . The min- gling zones in di cate in tru sion by Dqd, Dfg, and Dcg Brookins (1976, p. 138) reporte d a Rb- Sr whole rock age into an overly ing gabbro pluton [*2] which contai ned for the Vinal haven Rhyoli te of 381 ± 6 Ma (correct ed), Middle stoped blocks of schist (re sem bling rocks of the Ells- Devo nian by the GSA Time Scale (Pal mer, 1983). In the absenc e worth For ma tion) and of un fo li ated, con tact meta mor- of a more ac cu rate zir con age, the Vinal haven Rhyo lite is thus as - phosed Si luria n rocks includ ing one with Silu ria n signed to the Devo nian. Based on the uncor rect ed Rb- Sr age and brachiopods (A. J. Boucot letter , 1/31/1990), Su(f), on some poorly pre served ostra codes from Fish Head (Seal Cove Greens Island southwest of Vinal haven. The gabbro Form ati on of this paper) [*4], Brookins and others (1973) as- blocks cut by granit ic and diaba sic dikes repre sent signed an Early Devo nian age to the Vinal haven Rhyoli te, a crystal lized parts of the gabbro pluton. The pil low ba - more likely age as Dvr overli es DSp along a tran siti onal con tact salt - gran itic dikes in clude those with nested pillow s [*5]. sepa rated by thin gran itic mate rial, the re sult of sink ing The Vinal haven Rhyoli te con sists of several lithologi c of the pil lows which squeezed out the host granit ic units all derive d from a si li ceous magma that cooled rapidl y to magma, and those consis ting of broken pil lows and an- glass, subse que ntly devit ri fi ed and hydro t herm ally alt ered to gu lar ba salt frag ments in a gran itic matrix . In these the green schist grade. Fel sic or mafic phe no crysts are sparse. Its basal t pillows cooled, becam e brittl e, and were broken rhyo lite clas si fi ca tion awaits com ple tion of chemi cal analy ses apart by dif feren ti al movem ent of the increa singl y vis- [*6]. Spheruli tes in the flow-banded units oc cur com monly near cous host granit ic magma. The mingli ng of the two contac ts with under ly ing bedded rocks from which water vapor magm as indi cat es that parts of the gabbro pluton were was proba bly derive d. The for mati on probably repre sent s the still liquid or conti nued to be fed when intrude d by the rem nants of a small volcani c erupti on center . gran itic magma. The cir cu lar out line of Dcg and as so- ciated rocks and the steep to ver tical, sharp con tacts Dvr2 Flow- banded rhyo lite with autobrec cia. Crys tal lite suggest that the Dcg and Dfg pluton was em placed by concen tra tions mark flow bands. This unit rests on sev- caul dron subsi dence of which intru sion of the gabbro eral of the older units, local ly along erosiona l uncon for - pluton was the ini tial phase [*2]. Mitchell and Rhodes mities, and is in ter preted as a remnant of a late dome or (1989) report on a detai led geochem ical study of the flow. It over lies the Perry Creek fault and may have min gling zone. been erupted along it. (See Sche matic Diagram on the map sheet for presum ed rela ti onships .) [*7] Dpg Quartz- perthite gran ite of Ot ter Is land. De vo nian age un cer tain. Dvb Coarse, hy dro ther mally al tered rhyo lite brec cia. Much perli te, possi bly due to erupti on into a lake in which d Diabase dike. Predom inantl y with northerl y trends. Dvt was de posit ed. Older than Dcg, Dfg, Dqd. Dvtb Coarse, crudely bed ded to mas sive crys tal, lithic tuff- qp Quartz porphyry northwest of Vinal haven on Dogfish breccia. A va ri ety of rhyo litic frag ments. Re worked Is land, and dikes elsewher e. Of un cer tain age. Some coarse tephra. are com posit e with diabase dikes. Dvt Thinly bed ded fine-grai ned tuff. Water laid, possi bly in r Rhyoli te dike, of uncer tai n age. a lake.

4 Bedrock Geology of North Haven and Vinalhaven Islands

Dvw Welded vitric, crys tal lithic tuff de vit ri fied and al tered. Along the shore from Browns Head to Crockett Cove, Base not welded. A massive unit without inter nal the bedded rocks consis t largely of rhyoli tic tuff- variati ons both in outcrop and thin-sec tion. At Fox breccias and bedded tuffs, and tuf faceous mudstone s Rocks it is perhaps 200 meter s thick, but thins abruptly and silt stones. Thick coarse massive tuff-breccias, along Perry Creek and then pinches out below a unit of cross- bedding, cut- and- fill, and lens ing of dif fer ent Dvr [*8]. The ini tial erupti on, which depos it ed the thin rock types suggest that the Perry Creek Form ati on por- layer now exposed along Perry Creek overly ing DSp, trays in creas ingly vio lent ap proach ing vol can ism, was fol lowed by subsi dence during which Dvw conti n- largely rhyo litic, ac com pa nied by steep en ing stream ued erupt ing along or was em placed against the con- gra di ents and in creas ingly fre quent de bris flows. tem pora ne ous Fox Rocks fault that offset s the un der ly ing rocks [*9]. Vinal haven Dia base Dvr Rhyoli te. A com plex unit of flow-banded rhyoli te, several va rie ties of autobrec cia and mixed brec cia. Base is The Vinal haven Dia base is a sill within the Perry Creek and a coarse autobrec cia that over lies a once soft maroo n Seal Cove Form ati ons [*12]. It was intrude d largely into still tuff- breccia de formed by the basal autobreccia. soft maroon mudstone s and silt stones that, local ly on the east Spheruli tes, indi cat ed by black cir cles on the map, are side of Browns Head and south of Perry Creek, result ed in inclu - com mon above bedded (once wet?) DSp rocks. Local sions of maroon muds and a vesic ular top east of Browns Head per lite. In ter preted to be mul tiple flows but lo cally is in - and a hydro clastite of ba salt frag ments in a red matrix (DSvdb) trusive into soft DSp rocks. south of Perry Creek, and hence probably intrude d at shallow depth soon after deposi ti on of enclos ing DSp rocks. How ever, At its base, the Vinal haven Rhyo lite is tran si tional with the since the siltstone s and mudstone s of the Perry Creek Form ati on Perry Creek Form ati on. Red and tan mudstone s and silt stones were still soft when the basal tuff- breccia of the Vinal haven like those of the Perry Creek Form ati on are mapped within it. It Rhyoli te was depos it ed, the Vinal haven Diabase may be is marked by the first appear ance of flow-banded rhyoli te in an- younger than the former. Inter nal contac ts and small faults sug - gular to subrounded fragm ents up to 0.5 meter s in size in a gest that parts of the sill are a complex of multi ple in tru sions. At coarse-bedded tuff-brecc ia along with varying amounts of clasts Fish Head and Crockett Cove it appears to have changed its in- of once glassy feldspat hic rocks, tuf faceous siltstone s, and a few tru sion ho ri zon [*13]. of basal t. Ac com pany ing rocks in the transi ti on zone are de- scribed below as part of the Perry Creek Form ati on. DSvd Dia base and ba salt. Pri mary min er al ogy con sists of lab ra dor ite, cli no py rox ene, and mag net ite in a fine- grained in ter granu lar tex ture. The domi nant dia base Devonian- Silurian has xe nocry sts of quartz bordered by pyrox ene or hornblende and of uni denti fied feldspar with a once melted Perry Creek For mation (new name) in te rior within a thin rim of clear pla gio clase. Other fa - cies include strongly porphy rit ic, vesic ular , and felty This form ati on under li es the Vinal haven Rhyoli te along a tex tures. Most of the dia base is hy dro ther mally altered transi ti onal contac t per haps with some local erosion. The Perry to chlo rite, epi dote, and saus suri tized pla gio clase with Creek and Seal Cove form ati ons appar entl y overli e the Thoro- some rem nant cli no py rox ene. fare Andes it e, but the na ture of the contac t is hidden beneat h the Thoro fare. Be cause the stra tigraphic in ter val be tween DStrt DSvdb Brec cia of amygdu lar (chlo rite and cal cite filled) ba salt and DSvd is ap proximately con stant, it may be that the con tact is lo cally with ma roon in ter sti tial hema tite. It over lies and de po si tional. The map, al ter na tively, pos tu lates a fault, the was intrude d by DSvd. In ter preted as a remnant of a hy - Thorofare fault, betwee n the Vinal haven Diabase and the Thoro- dro clas tite (pep er ite) re sult ing from in tru sion of DSvd fare An des ite be cause a sig nifi cant part of the Seal Cove For ma - into very wet muds. tion appears to be miss ing [*10]. Seal Cove Form ati on (new name) DSp Near the mouth of Perry Creek above the Vinal haven Diabase , the Perry Creek Form ati on is overlai n by the DSsc Along the Thorofare be neath the Vinal haven Diabase , basal tuff-brecc ia of the Vinal haven Rhyoli te along an the Seal Cove Form ati on [*14] is largely maroon tuf fa- irregu lar contac t and grades downward through fluvi - ceous mudstone , feldspat hic sandstone , and thinly bed - ally depos it ed feldspat hic tuffs, tuff-brecc ias, and peb- ded tan argil lite. Be neath the DSvd sill, to Smith Point ble conglom erate s to laminate d and thinly bedded and southwest along the shore, the Seal Cove Form a- mudstone s and ar gil lite like those at Smith Point [*11]. tion consis ts of laminate d and thinly bedded mudstone s

5 O. Gates

and silt stone with fine-sca le cross-bedding, flame tuff- breccia and fine- grained tuffs as well as sev eral blocks of struc tures, and soft sedim ent de form ati on. Southwest fossi li fer ous Ames Knob For mati on. The fol lowing units are not along the shore towards the contac t with Dcg, these listed in stra tigraphic or der. fine- scale struc tures be come in creas ingly ob scured by con tact meta mor phism to horn fels, pro duc ing granu lar DSta Green, purple, gray, and maroon andes it e with con- epi dote, quartz, cal cite, tremo lite, and fine- grained bio - spicu ous pla gio clase phe no crysts and lo cally flow- tite. Near Smith Point sev eral less metamor phosed banded. Some are clearly intru sive into the vol canic beds have uni den ti fi able small fos sils, proba bly os tra - pile. Others with chlorit e and quartz amygdules are in - codes. A shoal exposed at low tide in Seal Cove has ter preted as flows. beds like those at Smith Point [*15]. As yet unnam ed os tra codes at Fish Head resem ble those in the Her sey DStab Pur ple to ma roon an des ite brec cias and ag glom er ates and Eastport Form ati ons of probable Gedinnian age in parti cular ly prominent on Stimpsons Island and to a the East port area (Brookins and others, 1973). My lesser extent on Cal derwood Point. Include s unm apped hand lens ex ami na tion sug gests that os tra codes found DSta. Angu lar to subrounded blocks up to a meter in di - in a low-ti de expo sure of varie gated siltstone and ar gil - ameter in a highly oxi dized si liceou s matrix lo cally of lite be neath the DSvd near Browns Head are proba bly mudstone . Some brec cias are oligomict of andes it e the same [*16]. blocks only. Oth ers are po lymict in cor po rat ing large blocks of andes it e, bedded round-pebble poly mict an- DSsct Bedded tuffs [*17]. desitic con glom er ate, tuf fa ceous cross- bedded sandstone, bedded tephra, and fossi li fer ous Sak rocks. DSsctb Tuff-brecc ias. Local ly contai ns small, pink feldspars Some lenses of DStt and DStrt are in sedim en tary con - or coarse chlo rite clots with white rims. Some coarse tact with DStab and are overlai n and cut out by DStab conglom erate s and tuff-brecc ias similar to rocks inter - or DSta. The oligomict breccia s are probably autobrec- bedded with and intrude d by DSta [*17]. ciated flows. The po lymict brec cias and ag glomer ate with he matitic mud in ter sti ces are de bris flows or la - hars mix ing vari ous sur face rocks in clud ing ag glom er- Thoro fare An des ite ate blocks violent ly erupted from a vent.

The Thorofare Andes it e under li es the Seal Cove Form a- DStrt A rhyoli te vitric tuff of shards, col lapsed pum ice, and tion with its probable Gedinnian os tra codes. In the Cox Cove scattered bro ken quartz and pla gio clase crys tals. It is area the Thoro fare An des ite over lies a section of Ames Knob overlai n by andes it e at Tele graph Point and on the Form ati on ranging in age through most of the Si luria n, and in - Dumpli ng Islands , and is not the top of the form ati on. cludes blocks of fossi li fer ous Ames Knob rocks within it [*18]. The various flows, brec cias, agglom erate s, and shallow in - DStt Tuff, ar gil lite, maroon siltstone , and mudstone . Lapil li trusions have a com mon miner al ogy . The least al tered sam ples tuffs with occa siona l larger blocks up to a meter across. have blocky pla gio clase phe no crysts with com plex os cil la tory Bed ded tuffs, mas sive tuffs, amyg da loi dal la vas with zoning in the oligoclase-labr adorite range, euhedral pheno cry sts mud inclu sions [*19]. The DStt on the Sugar Loaves is of cli no py rox ene, and mag net ite in a pilo taxi tic ground mass of very coarsely bed ded po lymict ag glom er ate of an des ite pla gio clase mi cro lites, com monly show ing felty tex ture, and boulders, cobbles , and pebbles of andes it e. small euhe dral phe no crysts of cli no py rox ene, com monly al tered to chlorit e and hemati te. There are a few pseudo m orphs of oli - DSl Intru sive latite on Babbidge Island. Oli gocla se phe no - vine. Lo cally, par ticu larly near the base, the an des ite con tains ir - crysts in a quartzo-fel dspathic de vit rifie d matri x [*20]. regular amygdules of chlorit e and quartz. Most of the andesi tic rocks are very hydro ther mally al tered to saussuri ti zed plagio - The Thorofare Andes it e is a rem nant of an andesi tic vol- clase, cal cite, epi dote, chlo rite, leu cox ene, clay, and hematite. cano, but most of the criti cal contac ts with other units are con- Pyrox ene is al tered to chlo rite and hematite. Hematite colors cealed be neath the Fox Islands Thorofare and Carver Cove. The much of the andes it e maroon. It re places groundm ass miner als only exposed contac t of any length is in the Ames Knob and Cox and the origi nal pyroxenes, forms veins and the matri x of brec- Cove area. There from west to east suc ces sively the Thoro fare cias, pene trates the mar gins of andes it e blocks, and colors inter - Andes it e rests on gray fossi li fer ous li mey shale along a sheared stitial muds in some brec cias. Hot oxidiz ing hy drother mal contac t dipping to the south; a lens of shale oc curs within andes - solu ti ons must have pervaded much of the andesi tic pile. ite brec cia; andes it e appar entl y intrude s highly folded dark gray The Thorofare Andes it e is a com plex vol canic pile in siltstone with distort ed brachiopods; and andes it e overli es vitric which indi vid ual lithologi c units are discon ti nuous, are both in - tuff along a sheared contac t dipping south. On the west shore of trusive and extru sive , and include isolat ed lenses of bedded Wa ter man Cove, an des ite over lies and also ap par ently in trudes

6 Bedrock Geology of North Haven and Vinalhaven Islands highly folded shale. Faulting as soci ate d with the Cox Cove fault Si lu rian fur ther compli cates the con tact. Em place ment of the Thoro fare Andes it e was accom panied by folding and fault ing of the under - Ames Knob For mati on ly ing Ames Knob For mati on and intru sion along the contac t. The Thorofare Andes it e on the islands of the Lit tle Thoro- The abun dantly fos si lif er ous Ames Knob For ma tion fare consis ts largely of vari ous block agglom erate s and breccia s ranges in age from late Llandovery through Pri doli (Brookins that en close, in trude between, and have sheared con tacts with and others, 1973), which for al most a century has served as a blocks of distort ed Ames Knob For mati on on Burnt, Stimpsons, bench mark date in the Pe nobscot Bay area. Smith (1896) and and Cal der wood Is lands. On Cal der wood Is land si li ceous lime- Smith and others (1907) de scribed the marked dif ference in stone with a probably Llandovery to Wenlock (Silu ria n) age meta morphism and structure betwee n the highly deform ed fauna (A. J. Boucot letter s 2/6/91; 3/7/91; see Appen dix IV) of North Ha ven Greenstone and the much less deform ed and very brachio pods, cor als, bryo zoa, and Ten tacu lites is faulted against fos si lif er ous Ames Knob For ma tion, and not ing the con glom er- quartz ite and quartz peb ble con glom er ate, ma roon silt stone, ate be tween them (Scg), con cluded that the two were sepa rated bedded tuff, rhyoli tic tuff like that on Burnt Island (identi cal to by a peri od of regional meta morphism and erosion. The Si luria n the vitric tuff beneat h andes it e at Ames Knob) and folded ar gil - fossil s (Niagaran ac cording to Smith) served to di vide the rocks lite all as sumed to be Silu rian. Con tacts are highly sheared and of the Penob scot Bay area into meta morphosed Ordo vi cia n or many are cut off by intru sive DSta. Similarly along the north older rocks on one hand and Silu ria n Ames Knob and younger shore of Burnt Island a shear zone bounds Sakt, but does not rocks on the other. Today the epi sode of meta morphism and de- conti nue into andes it e. The Sak(f) block on Stimpsons Island is form ati on would be identi fied as the Taconian orogeny . of Prido li an age (Brookins and others, 1973) and thus younger than that on Calder wood Island although it appears to be struc - Sak Gray, maroon, tan shale, silt stone, limestone , pebble turall y lower. On the northwest shore of Calder wood Neck a con glom er ate, bed ded tuf fa ceous sand stones, and a much dis torted and broken block of Ames Knob shale, Sak(f), thin rhyoli te shardy tuff. The exposed secti on suggest s en closed by DStab has a scrappy fauna of undi ag nos ti c brachio- deposi ti on in shallow wa ter. The type sec tion along the pods and Ten tacu lites which is Silu rian (A. J. Bou cot let ter shore northwest of Ames Knob is folded and faulted. 3/1/91) and perhaps re sem bling the fauna on Stimpsons Island Map units in which fossil s have been discov ered are in - (J. M. Berdan letter 9/1/89). (See Appen dix IV for excerpt s of di cated by an (f). Although the fauna spans the Si luria n Boucot and Ber dan letter s.) from late Llandovery through Pri doli, much secti on has The Thorofare Andes it e built a partly subaer ial , partly ma- probably been lost. The occur rence s as blocks in the rine volcanic pile in the Late Si lu rian to Early De vo nian Ames Thoro fare An des ite are de scribed above. Knob shal low sea. The Lower Silu ria n block on Calder wood Is- land and its conglom erate and bedded tuffs may com prise a rem - Sakt Vitric tuff. Shards, col lapsed pum ice fragm ents, and nant of the Ames Knob For mati on through which the Thorofare perli te fragm ents exposed east of Cox Cove and on An des ite ini tially erupted. Erup tion into wa ter ex plains the ex - Burnt and Calder wood Islands [*22]. ten sive breccia tion as the la vas chilled. Debris flows were partly subaer ial and partly subm arine , lubri cat ed by silts, muds, and Scg Ba sal con glom er ate of Sak? Angu lar to subround sea water . Blocks of bedded tephra, stream gravels , sandstone s, clasts of the under ly ing Cnh and of bull quartz in a he- siltstone s, and mudstone s are rem nants of ash falls, stream sedi - matitic matrix . It is a col lu vium depo sit that along its ments depos it ed on subaer ial flanks of the pile, and perhaps base con tains blocks of the im me di ate ly un der ly ing mudfla t silts and muds that were isolat ed and engulfe d by blocky North Ha ven Greenstone . It is in fault contac t with the flows, debris flows, and intru sive sills and dikes as the volcani c rest of the Ames Knob For mati on. It shares the strong pile grew ac com pa nied by fluc tu at ing shal low ma rine and sub- fo lia tion of Cnh includ ing flatten ing of clasts. Its prox- aerial condi ti ons on its flanks. Circu la ti on of sea water heated by imity is the only eviden ce that it may be the ba sal con - the erupt ing an des ite pro duced the very ex ten sive hy dro ther mal glom erate of the Ames Knob For mati on [*23]. al tera tion and strong oxi da tion. The mas sive ag glom er ates and breccia s, the abundant intru sive andesi te, and the blocks of Sak, the youngest of which is on Stimpsons Island and struc turall y be - Polly Cove Form ati on (new name) low the older one on Calder wood Island, suggest that the Thoro- fare An des ite of the Lit tle Thoro fare area is a par tially collapsed The Polly Cove Form ati on occu pies the same strati graphic vent. Cross section E-F specu la tively il lus trates this idea. The and structura l posi ti on as the Ames Knob For mati on, but it is maroon sands, silts, and muds of the Seal Cove Form ati on [*21] given a dif fer ent for mation name be cause of dif fer ences in li - conti nue the shal low wa ter and mudfla t deposi ti on after the an - thol ogy, a lack of fos sils, and problem atic facie s rela ti onship to desitic vol can ism ceased in the Early Devo nian. the Ames Knob For mati on.

7 O. Gates

Spct Gray ar gil lite, shale, silt stone, peb ble con glom er ate, the miner al ogy and texture s of the origi nal rocks have been oblit- feldspat hic bedded tuff, and massive tuff-brecc ia. er ated. In thin sec tion many of the rocks re semble re crys tallized Folded and faulted. Hornfel sed near Dcg. The bedded mylo nit es, perhaps part of a broad shear zone. Alm ost all of the tuffs west of Vinal haven on Green Island and Green Cal der wood For ma tion is ex posed on Cal der wood Neck, but Ledge are also assigne d to the Polly Cove Form ati on. Cal derwood schists also crop out on a small island northwest of Big White Island, west of Vinal haven. The pre-Silu ria n age is Spcr White- weathering, vit re ous, black rhyo lite [*24]. based on strong foli ati on and uncon form able contac t with Spca. Rocks lithologi cally like the Cal derwood Form ati on have not Spca Horn fel sed si li ceous ar gil lite and calc- silicate. A ba sal been found else where in coastal Maine, and its re lati on to the bedded quartz grit lens rests uncon form ably on the Cal- North Ha ven Greenstone is unknown. der wood For ma tion. Cca Quartz am phi bo lite. In cludes a fo li ated gab bro.

Un dif fer en ti ated Si lu rian Rocks Ccs Quartz-biot ite-act inolite schist. Augen of granular quartz and acti noli te in a granular quartz matri x. Origi - These lithologi c units are assigne d to the Si luria n becaus e nally chert, ar gil lite, and si liceou s volcanic rocks. Lo - they are un fo liated and of green schist fa cies where not con tact cally py ritic. meta mor phosed. Ccl Meta latite sill with sheared mar gins. Pla gio clase phe - Su Stoped blocks of con tact meta mor phosed un fo li ated nocry sts in matri x of fine-grai ned granular quartz, K- bed ded ar gil lite and silt stone in Dcg and Dg. Block la - feldspar, bio tite. beled Su(f) on Greens Island has Si luria n brachiopods (A. J. Boucot letter 1/31/1990; see Appen dix IV). Ccb Sheared pil low ba salt on Ash Tree Point. Nest ing and vesic ular tops suggest younging to the northwest . Sut Tuf faceous and ar gil laceous rocks on Robert s and Hay is lands. Ccp Foli ated plagio cla se porphyry on Widow Island. As- signed to the Calder wood Form ati on based only on its Sur Rhyo lite in trud ing Sut ar gil lite on Rob erts and Hay is - fo lia tion and geo graphi cal po si tion. lands.

Sub Basalt, dia base, and ba saltic brec cias on Brimstone Is - North Ha ven Greenstone land. Cnh Pil low ba salts, ba sal tic tuffs, car bo na ceous schist, con - Sup Flow-banded plagio cla se porphyry on the Brim stone glomer ate. Highly altered to clays, chlo rite, cal cite, ac- Is lands. ti noli te, tremoli te, leucox ene, iron ores. Only ghosts of origi nal texture s rem ain. Strongly sheared with flat- tened pil lows and mineral streaking and pillow elonga - Pre- Silurian (Cam brian?) tion which plunge steeply southwest . Tops indi ca tors such as pil low nesting indi cat e most dips are to the These for ma tions are fo li ated, re gion ally meta mor phosed south and southeas t. Struc ture is a monocli ne repeat ed rocks and hence presum ed to be older than the Ames Knob For - by northeast-tre nding faults of uncer tai n age, but as- mati on. The for mati ons below are not listed in strati graphic or- sumed to be pre- Silurian because they are par allel to the der as their stra tigraphic rela ti ons to each other are not known trends of shearing foli ati on in the greenstone . To the [*25]. northeas t, the North Haven Greenstone under li es Oak Island and Grass Ledge, and conti nues on strike to Ea - gle Island (Pinette and Os berg 1989). Similar rocks are Cal der wood For ma tion reporte d by Stewart (1998) as part of the Ellsworth For- mati on in Deer Isle, im ply ing a probable Cam brian age Fo li ated blas to my lo nitic rocks meta mor phosed to epi dote for the North Ha ven Greenstone . Pinette and Os berg am phi bo lite grade. Brown and oxi dized bio tite as so ci ated with (1989) con clude that their geo chem is try in di cates an late cracks. Ex cept for some pos si ble lap illi in the schist units, in-plat e ori gin. The fol lowing rock types of inland out - pil lows in the ba salt units, and remnan t tex tures in the latite sill, crops too sparse to map with conti nuit y and shoreli ne

8 Bedrock Geology of North Haven and Vinalhaven Islands

ex po sures too small to dif fer en ti ate are des ig nated by Fish Point Form ati on (new name) let ter sym bols: (g) green stone, un dif fer en ti ated; (p) pil - low lava; (q) granular quartz veins com mon in fault Cfp Slightly fo li ated re crys tal lized gray wacke, de vit ri fied zones; (qc) quartz-carbona te- pyrite veins; (rp) “rot ten” rhyo lite, con glom er ate of rhyo lite peb bles, and sheared pyrit ic rock, most com monly asso ci ate d with sheared limestone on Fish Point and ledges, and highly sheared rocks. In addi ti on, the follow ing units are mapped. pyrit ic feldspar porphyry on the west shore of Water - man Cove. In fault contac t with Cnh along the Water - a Ar gil lite. man Cove fault and probably with Cal derwood cg Po lymict rhyo lite, latite, ba salt peb ble con glom- Form ati on along the presum ed Cox Cove fault [*26]. er ate lenses. gb Gabbro, some unshea red. Pre- Silurian sc Black, my lo nitic schist. sd Sheared dia base and gabbro. Un dif fer en ti ated Pre- Silurian Rocks

Cnhl Latite and rhyo lite tuff- breccias, chlo ritic tuffs, and pil - pSs Crinkly mica schists with quartz lenses and veins, fo li - low lavas at Pul pit Harbor and Bartlett Har bor and as ated am phi bo lite, and mi nor quartz ite re sem bling rocks lenses in Cnh elsewher e. of the Ellsworth Form ati on. Occurs in stoped blocks in the granite-gabbro mingli ng zone and as a roof pendant in the gabbro of the Bar ley Hill area.

AN NO TATED BIB LI OG RAPHY AND REF ER ENCES

(in or der of pub li ca tion date)

Smith, G. O., 1896, The Geol ogy of the Fox Islands, Maine: Ph.D. disser ta tion, Palm er, A. R. (com piler), 1983, The Decade of North American Ge ol ogy 1983 The Johns Hopkins Uni versity , pri vately publishe d. The origi nal map- Geologic Time Scale: Geol ogy, v. 11, no. 9, p. 503- 504. ping estab lish ing the main lithologic units. It includes a very com plete Stewart, D. B., Arth, J. G., and Flohr, M. J. K., 1988, Pet ro gene sis of the South fauna list for the Ames Knob Form ation based on Beecher, C.E., 1892, Penob scot in trusive suite, Maine: Ameri can Jour nal of Science, v. On the occur rence of up per Si lu rian strata near Pe nob scot Bay, Maine: 288-A, p. 75-114. Ameri can Jour nal of Science, 3rd serie s, v. 43, p. 416- 418. Pinette, S. R., and Osberg, P. H., 1989, Geochem ical aspects of volcanic rocks on Smith, G. O., Bastin, E. S., and Brown, C. W., 1907, Penob scot Bay Folio: U.S. islands in east Penob scot Bay, in Tucker, R. D., and Marv in ney, R. G. Geologi cal Survey, Atlas of the United States, Fo lio 149, 14 p., 3 maps, (edi tors), Stud ies in Maine geol ogy, Volume 3 – Igne ous and metam or- scale 1:125,000. Incor po rat es the mapping of Smith (1896) whose litho- phic geol ogy: Maine Geologi cal Survey, p. 91-110. logic units were given form al form ation names: North Haven Green- Hogan, J. P., and Sinha, A. K., 1989, Com po sitional variation of pluton ism in the stone, Ames Knob For ma tion, Cal der wood For ma tion, Thoro fare coastal Maine magm atic province: mode of origin and tectonic setting, An des ite, Vinal haven Rhyo lite. in Tucker, R. D., and Marv in ney, R. G. (edi tors), Stud ies in Maine ge ol - Dow, G. M., 1965, Petrol ogy and struc ture of North Haven Island and vi cinity , ogy, Volume 4 – Igne ous and metam orphic geol ogy: Maine Geologi cal Maine: Ph.D. disser ta tion, Univer sity of Illi nois, Urbana, 165 p. Fol lows Survey, p. 1-33. Smith and others (1907) with minor changes. Named the Vinalhaven Hill, M. D., and Abbott, R. N., Jr., 1989, Com mingled gabbroic and gran itic mag- Dia base. mas in the northern Bays- of-Mai ne Igne ous Com plex, Calais area, in Brookins, D. G., Ber dan, J. M., and Stewart, D. B., 1973, Isotopic and pale on to - Tucker, R. D., and Marvin ney, R. G. (edi tors), Stud ies in Maine geol ogy, logi cal evi dence for cor relat ing three vol canic se quences in the Maine Volume 4 – Igne ous and metam orphic geol ogy: Maine Geologi cal Sur- coastal vol canic belt: Geo logi cal So ci ety of Amer ica, Bul le tin, v. 84, p. vey, p. 35-43. 1619-1628. Contains previous and new fossil infor m ation com bined Mitchell, C. B., and Rhodes J. M., 1989, Geochem istry of the granite- gabbro with Rb-Sr whole rock ages to re fine ages of the Ames Knob Form ation, com plex on Vinalhaven Island, Maine, in Tucker, R. D., and Marv in ney, Vinal haven Rhyo lite, and coarse-grai ned gran ite (Dcg). Uses the old de- R. G. (edi tors), Stud ies in Maine geol ogy, Volume 4 – Igne ous and meta- cay con stant. morphic geol ogy: Maine Geologi cal Survey, p. 45-62. Brook ins, D. G., 1976, Geo chrono logic con tri bu tions to stra tigraphic in ter pre ta- West, D. P., Jr., Lud man, A., and Lux, D. R., 1992, Si lu rian age for the Po co - tion and cor rela tion in the Pe nob scot Bay area, east ern Maine, in Page, L. moon shine gabbro-diori te, southeast ern Maine, and its regional tectonic R. (editor) , Contri butions to the stratigr aphy of New England: Geologi - im plica tions: Ameri can Jour nal of Science, v. 292, p. 253-273. cal So ciety of America, Mem oir 148, p. 129-145. Uses the old decay con- Stewart, D. B., 1998, Ge ology of north ern Penob scot Bay, Maine: U.S. Geologi - stant. cal Sur vey, Mis cel la ne ous In ves ti ga tions Se ries, Map I- 2551, 2 sheets, scale 1:62,500. [*28]

9 O. Gates

WHOLE ROCK GEO CHEM IS TRY

Bi mo dal vol can ism in clud ing abun dant rhyo lites as so ci- where within the belt. The petro ge neti c and struc tural place of ated with fos si lif er ous Si lu rian sedi men tary and vol canic rocks the Thorofare Andes it e and its asso ci ate d struc tural blocks in the has been de scribed in the coastal volcanic belt east ward as far as coastal vol canic belt re mains to be solved. the East port area and New Brunswick. However , no andesi tic Chemical analyses for the major rock units are pre sented in volcan ism like that of the Thorofare Andes it e nor rocks like Table 1 [*27]. Sam ple loca ti ons are indi cat ed on maps in Appen - those of the Cal derwood Form ati on have been descri bed else- dix V.

TABLE 1. Chemical analy ses of rocks from North Haven and Vinalhaven Islands. Major elem ents reporte d in weight per cent. Fe2O3= to tal iron, as sum ing all 3+ Fe is convert ed to Fe during igni tion. L.O.I. = Loss on igni tion to 1050 °C. Trace ele ments in parts per million, except TiO2 in weight %. De tection limits for trace elem ents as fol lows: TiO2 0.01%; Th and Pb 10 ppm; all others 5 ppm. n.d.=not deter mined. Analy ses per formed by X-ray fluores cence spectros copy at the Re gional Geo chemi cal Cen ter, Depart ment of Ge ol ogy, St. Mary's Uni ver sity, Halifax, Nova Sco tia, ex cept FeO and CO2 de term ined by the Tech ni cal Uni - versity of Nova Scotia.

North Haven Greenstone and Fish Point For mation Thorofare Andes ite Sam ple G85 G117 G179 G183 G346 G121 N30 N40B N42 N118 N99 VH67A N270G

SiO2 51.06 45.49 46.50 47.26 73.89 69.77 60.20 57.15 57.50 58.56 49.98 66.06 76.88 Al2O3 13.42 16.06 14.80 14.73 13.39 9.03 16.52 17.77 16.84 16.52 18.33 15.50 11.99 Fe2O3 12.20 12.32 12.08 13.56 2.36 8.82 6.96 7.75 8.52 7.79 9.24 6.77 1.26 MgO 3.12 6.43 6.91 6.77 0.70 0.67 3.09 3.99 3.56 3.25 2.78 0.54 0.24 CaO 6.86 7.63 8.90 8.02 0.06 0.65 6.18 3.21 7.01 6.65 6.27 2.92 0.65 Na2O 5.60 3.20 3.58 3.75 4.43 2.89 2.60 3.36 2.52 2.57 4.62 4.15 3.38 K2O 0.54 1.44 0.69 0.07 3.37 2.81 2.01 2.32 2.11 2.11 1.19 3.18 3.53 TiO2 3.13 2.97 2.80 2.78 0.42 0.21 0.81 0.76 0.80 0.82 1.00 0.52 0.14 MnO 0.22 0.17 0.20 0.21 0.03 0.17 0.14 0.15 0.15 0.12 0.23 0.07 0.02 P2O5 1.55 0.32 0.60 0.32 0.05 0.03 0.14 0.10 0.11 0.14 0.16 0.15 0.02 L.O.I. 2.70 4.60 2.70 2.90 0.70 4.80 1.80 4.10 1.40 1.60 7.40 0.50 1.50 ______To tal 100.39 100.63 99.76 100.38 99.42 99.83 100.45 100.67 100.53 100.12 101.19 100.35 99.61

FeO 9.16 9.02 8.96 9.89 n.d. 6.96 3.90 4.50 4.83 4.23 1.97 2.33 n.d. CO2 0.60 0.98 0.07 0.28 n.d. 4.71 0.30 0.90 0.16 0.24 3.94 0.21 n.d.

Ba 44 424 179 11 376 164 331 372 344 381 260 531 465 Rb 10 14 <5 <5 17 34 50 89 63 56 40 95 139 Sr 181 480 480 331 50 11 222 294 205 219 248 205 55 Y 91 27 42 30 151 626 31 24 26 31 30 50 29 Zr 354 156 244 169 1094 5312 167 123 133 165 147 223 96 Nb 19 15 18 13 51 440 8 6 8 8 9 11 12 Th <10 <10 <10 <10 10 40 <10 <10 <10 <10 <10 <10 20 Pb <10 <10 <10 <10 <10 10 10 <10 10 16 <10 18 11 Ga 19 17 20 16 28 49 17 14 15 18 19 17 7 Zn 125 86 95 94 57 151 80 75 81 76 59 46 38 Cu 8 36 53 45 5 8 16 5 23 22 8 7 <5 Ni 5 59 52 60 <5 <5 16 22 10 17 14 <5 5 TiO2 2.92 2.79 2.40 2.70 0.44 0.20 0.74 0.84 0.78 0.75 0.97 0.50 0.15 V 167 374 280 379 <5 <5 140 211 195 154 155 29 7 Cr <5 68 147 146 5 <5 44 35 8 50 9 6 11 North Haven Greenston e: G85 - Pil low lava, Mackerel Point, North Ha ven (N.H.); G117 - Pil low lava, east shore of Wa ter man Cove, N.H.; G179 - Dia base, head of Southern Har bor, N.H.; G183 - Pil low lava, head of South ern Har bor, N.H.; G346 - Rhyolite tuff, north shore of Pulpit Har bor, N.H. Fish Point Forma tion: G121 - Rhyolite, Fish Point, N.H. Thoro fare An des ite: N30 - Andes ite, north side of golf course, N.H.; N40B - Andes ite, close to con tact, north side of Ames Knob, N.H.; N42 - An- des ite, Ames Knob, N.H.; N118 - Andes ite, golf course hill; N99 - Andes ite, oxi dized, north side of the Thoro fare, N.H.; VH67A - Andes ite, south of Swimming Pool, Vinal haven (V.H.); N270G - Rhyolite vitric tuff, Tele graph Point, N.H.

10 Bedrock Geology of North Haven and Vinalhaven Islands

TABLE 1. Chemi cal analy ses of rocks from North Haven and Vinal haven Is lands (con tin ued).

Vinalhaven Diabase Vinalhaven Rhy o lite Calderwood For mation Widow Island porphyry Sam ple V90 V104 N51 VH119 VH121 VH124 VH145 VH377 VH3 VH9 VH12 WI1

SiO2 55.97 55.05 50.53 76.79 74.17 75.47 74.17 73.65 60.98 64.71 60.24 59.50 Al2O3 14.74 15.62 16.29 12.75 13.65 13.60 13.59 13.32 13.83 12.30 14.30 18.32 Fe2O3 7.97 7.50 9.52 0.94 1.51 1.64 1.88 2.87 8.50 10.47 7.86 5.00 MgO 5.11 3.58 7.39 0.07 0.11 0.10 0.27 0.42 1.98 3.53 2.37 0.47 CaO 8.71 7.48 8.38 0.24 0.37 0.58 0.71 0.65 5.64 1.93 4.67 1.87 Na2O 2.63 2.92 3.09 6.01 4.12 4.05 4.03 3.58 1.58 1.14 6.26 6.23 K2O 1.81 1.77 0.97 1.51 5.00 3.46 3.93 4.06 5.11 3.92 1.58 5.70 TiO2 1.06 1.20 1.30 0.10 0.11 0.10 0.17 0.21 0.92 0.58 1.22 0.51 MnO 0.14 0.13 0.17 0.02 0.03 0.10 0.04 0.11 0.12 0.10 0.20 0.14 P2O5 0.17 0.21 0.10 0.01 0.04 0.00 0.02 0.03 0.17 0.04 0.20 0.14 L.O.I. 2.20 4.80 2.10 0.60 0.10 0.40 0.80 0.70 1.20 1.60 1.50 1.80 ______To tal 100.53 100.25 99.85 99.05 99.21 99.50 99.62 99.60 100.04 100.33 100.40 99.68

FeO 5.23 4.90 6.83 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. CO2 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d.

Ba 205 213 130 199 382 312 364 308 310 191 113 197 Rb 50 59 40 40 158 187 148 159 101 75 12 42 Sr 423 332 250 29 21 18 48 29 269 233 87 174 Y 35 37 35 75 65 71 67 58 337 371 149 51 Zr 139 141 129 165 174 176 197 182 3378 2295 1148 757 Nb 5 8 <5 12 14 12 14 13 224 122 56 78 Th <10 <10 <10 14 14 16 14 15 21 18 12 <10 Pb <10 14 <10 <10 <10 <10 14 <10 14 <10 <10 10 Ga 16 18 14 14 17 16 15 15 66 66 33 33 Zn 68 65 72 7 7 18 23 28 75 81 109 51 Cu 34 18 53 <5 <5 <5 6 <5 13 5 5 9 Ni 35 28 85 <5 6 <5 <5 5 <5 6 <5 <5 TiO2 0.98 1.17 1.31 0.10 0.10 0.10 0.17 0.23 0.75 0.62 1.10 0.48 V 173 177 193 5 <5 <5 12 17 <5 <5 75 <5 Cr 134 103 191 7 10 12 9 18 <5 <5 6 <5 Vinalhaven Diabase : V90 - Dia base sill, south shore of the Thoro fare, V.H.; V104 - Dia base in trud ing mud, west of Browns Head, V.H.; N51 - Dia - base dike, east shore of Browns Cove, N.H. Vinal haven Rhyo lite: VH119 - Breccia fragment in breccia along base of rhyo lite, V.H.; VH121 - Flow-banded rhyolite along road near ra dio tower, V.H.; VH124 - Brec cia on hill north west of end of Long Cove, V.H.; VH145 - Welded tuff near base, east shore of Crock ett Cove, V.H.; VH377 - Welded tuff, near top of Mid dle Moun tain, V.H. Cal der wood For ma tion: VH3 - Quartz am phi bo lite, on shore east of Polly Cove, V.H.; VH9 - Schist, east shore of Carver Cove, V.H.; VH12 - Latite, on shore north west of Salt Works Cove, V.H.; WI1 - Porphy ry, Widow Island.

11 O. Gates

Editor s' Notes

[*1] The abso lut e ages assigne d to the Geologi c Time Scale had been having ongo ing discus sions with Olli e, sug- are con tinu ally re vised as new in for ma tion be comes gest that their obser va ti ons had im pressed upon him available . In the text, Gates has used the 1983 G.S.A. that there was more com mingli ng of magm as than he time scale of Pal mer. On the map, we show a porti on of had origi nally thought. At the same time, it is not clear the geologi c time scale using re visions recom mended to the edi tors whether he had abandoned the idea that by R. D. Tucker and W. S. McKerrow (Ca nadian Jour- the east ern side of the pluton was near the roof of the nal of Earth Sci ences, 1995, v. 32, no. 4, p. 368-379). magma cham ber. As Weibe points out, Olli e had not drawn any cross sec tions through the pluton that might [*2] In 1996, Olli e Gates intro duced the geol ogy of Vinal - have il lus trated his in ter pre ta tion. Fur ther more, we are haven to Robert A. Wiebe of Frankli n and Marshal l not sure just when Olli e wrote the present manuscri pt. Col lege. Wiebe was par ticu larly in ter ested in the re la - So we have decide d to re tain Olli e's text, even though it tionships betwee n granit e and gabbro, espe cia lly in the may not re flect his most re cent thinking. mingli ng zones that Olli e had mapped. Based on his prior ex pe ri ence in simi lar ig ne ous com plexes at Pleas- [*3] Gates had listed this unit under the Calder wood Form a- ant Bay and on Mt. Desert Island, Maine, Wiebe form u - tion in his expla na ti on. lated a model of the Vinal haven pluton in which the granit e magma cham ber was intrude d by gabbro, and [*4] Gates's manu script as signed the Fish Head lo cality to rocks near the south and east mar gins of the granit e the Perry Creek Form ati on, but his map clearly shows it were near the base of the magma cham ber. Wiebe to be in the Seal Cove Form ati on. In fact, his manu- brought a group of students to Vinal haven in the sum - script does not separat e the Seal Cove Form ati on from mer of 1998 to study igne ous fea tures in several small the Perry Creek Form ati on at all; rocks of both for ma- ar eas to test and refine this model. tions are include d in the Perry Creek. The editors be - It is not clear to the editor s to what ex tent Ollie lieve this to in di cate that the map was re vised to divid e had adopted these new inter preta ti ons. The model de - the Seal Cove Form ati on from the Perry Creek Form a- scribed in the manuscri pt, that the granit e intrude d an tion after the manuscri pt had been written. There fore, overly ing gabbro, had been devel oped by Olli e before gen eral ref er ences in the manu script to the “Perry 1996, mainly to account for the angu lar blocks of gab- Creek For mation,” we have replaced with “Perry Creek bro in the granit e concen tra ted toward the east mar gin and Seal Cove for mations”; and spe cific ref er ences to of the pluton, and the large area of meta morphic rock the lower part of the “Perry Creek For mation,” as in the near Bar ley Hill which he in ter preted as a roof pen dant. case of the Fish Head lo cality , we have re placed with He thought these had sunk into the granit e magma, and “Seal Cove For mation” to agree with the map and with therefore must have come from higher levels . He obvi - Olli e's 1998 writ ten com muni ca ti on to Bud Wobus (see ously did agree that the texture s descri bed by Mitchell Ap pen dix I). and Rhodes (1989) indi cat ed com mingli ng of mafic and granit ic magm as, and his statem ent that gabbro [*5] The ar gum ent present ed here is that the Vinal haven “conti nued to be fed” after the granit e magma had in - Rhyoli te is not substa nti ally younger than the Gedin - truded is en tirely con sis tent with Wiebe's model of ma- nian? (Early Devo nian) fossil s at Fish Head, and there- fic replen ish m ents. Com ments to the edi tors in 2000 by fore is more likely Early Devo nian than Middle Wiebe and R. A. Wobus (Appen di ces II and III), who Devo nian as the Brookins (1976) Rb-Sr age would in -

12 Bedrock Geology of North Haven and Vinalhaven Islands

di cate. This ar gu ment re lies on the fact that the con tact The map expla na ti on, however , lists two units of rhyo - betwee n the top of the Perry Creek Form ati on and the lite flows. Unfor tu nate ly, no unit labels were given, but base of the Vinal haven Rhyo lite is tran si tional, imply - the younger unit is descri bed as a “late dome or flow,” ing no time gap. Also implicit in the argu ment is the in - while the older unit is de scribed as being transi ti onal ter pre ta tion that the fos sils are in the Perry Creek with the Perry Creek For mation at its base. Fur ther - Form ati on. But sepa rat ing the Seal Cove Form ati on more, one is listed above the welded tuff unit Dvw and from the Perry Creek For mation af ter the manu script the other is listed below it in the expla na ti on. Togethe r, was written (see note 4), means that the Fish Head fos sil we take these indi ca ti ons to mean that the unit north- local ity is now as signed to the Seal Cove Form ati on. In west of the fault, which rests on the Perry Creek Form a- the Geologi c His tory (see map), Gates suggest s that up- tion, is the older unit, and the unit southeas t of the fault, lift and erosion may have occurred after deposi ti on of which rests above the welded tuff unit, is the younger the Seal Cove For mation. In that case, the argu ment unit. On a sepa rate pa per copy of the map, Ol lie has la - that the fos sils and the Vinal haven Rhyo lite are close in beled some of the units Dvr2 and others Dvr1 in a way age may be less com pel ling. that is con sis tent with this in ter pre ta tion and con sis tent with the cross secti ons. While we don't know for cer- [*6] The geo chemical analyses pre sented in Table 1 in clude tain when he labele d that paper copy, we have followe d samples from the Vinal haven Rhyo lite, which are clas - it here in label ing the younger unit Dvr2. We decide d si fied as rhyo lite on stan dard geo chemi cal clas si fi ca - not to label the older units Dvr1 becaus e not all of them tion diagram s (see note 27). This sentenc e in the text were la beled on the pa per copy, and they may well be of sug gests it was writ ten bef ore Ol lie had in ter preted the dif ferent ages. Therefore the older units, most of which geo chemi cal analy ses. rest be low Dvw, are la beled simply as Dvr, al low ing that several flow units and intru sive units of vari ous [*7] One of the uncer tai nti es on the map is whether a defi- ages are proba bly include d. nite age se quence can be deter mined among the flow units in the Vinal haven Rhyoli te. On Gates's 1992 draft [*8] The manuscri pt at this place says “pinches out below map, all flow units were labele d “Dvr” even though it Dvr1,” but the map unit to which it appar entl y re fers is was ap par ent that they were not all the same age. His labele d only Dvr. Since we have decide d not to use sche matic diagram clearly shows a younger dome of Dvr1 on the map (see note 7), we have substi tuted “be - Dvr cut ting through an older unit of Dvr; and the expla - neath a unit of Dvr.” nati on on the 1992 draft says about the Vinal haven Rhyoli te “The above units not in order of age. Dvw un- [*9] The Fox Rocks fault was not labele d on the draft map. derlai n and overlai n by Dvr.” On that draft, the Perry It is clear from con text to which fault it re fers. Creek fault is drawn through the length of Perry Creek and through the length of Crockett Cove, but it does not [*10] This is an other place where Ollie had con sid ered two conti nue across the inter vening land. Inste ad, a con - in ter pre ta tions to ac count for the ap par ent change in tinuous unit of Dvr spans the region where the fault breadth of the Seal Cove Form ati on from Seal Cove to would be project ed. This rela ti onship im plies that the Fish Head. By one inter preta ti on, the thinning to the Perry Creek fault was buried be neath the rhyoli te flow, northwest was caused by upli ft and erosion of the Seal as stated in the text. At some time af ter 1992, Gates had Cove Form ati on before deposi ti on of the Perry Creek re labeled this area be tween Perry Creek and Crock ett For ma tion pro duc ing an an gu lar un con for mity. This Cove Dvr2, appar entl y to indi cat e that it was younger inter preta ti on is de scribed in the Geologi c His tory. The than other units of Dvr. However , on the 1998 draft, the other inter preta ti on, il lustra ted on the map and cross Perry Creek fault was drawn conti nuously through the sec tions, calls for the Thorofare fault to cut out the rhyo lite to con nect with the fault in Crock ett Cove (as lower part of the Seal Cove Form ati on under the Thoro- shown on the final map). Inter est ingly, the fault was fare. The Thorofare fault was not shown on the 1992 drawn through the old Dvr2 letter ing that had been only draft map, and it was not descri bed in the map expla na - partly erased. By this new in ter pre ta tion, the unit that tion, so it ap pears to the edi tors that it was a re cent in ter - had been Dvr2 was now di vided by the fault into north- pre tation. The edi tors have in serted the last sen tence in west ern and southeas tern parts, with all units labele d this para graph to refle ct the map inter preta ti on. We Dvr. think, however , that Ol lie would still favor an uncon -

13 O. Gates

form ity beneat h the Perry Creek Form ati on, in addi ti on [*22] Units of Sakt were not deli neate d on the mylar draft to trunca ti on of the lower Seal Cove Form ati on along map. They were shown, how ever, on a paper copy of the Thorofare fault. the map that Ol lie had modifie d with a pen and white- out. The loca ti ons of units la beled Sakt on that modi- [*11] The rocks at Smith Point are now assigne d to the Seal fied copy corre spond to the loca ti ons descri bed in the Cove Form ati on. This sentenc e may be descri bing the text. On previous drafts these units of tuff were as- stra tigraphic secti on from the Vinal haven Rhyoli te signed to the Thorofare Andes it e as unit DSttb. down through the Perry Creek Form ati on into the Seal Cove Form ati on (see note 4). [*23] On Olli e's 1992 draft map, this unit is descri bed as “Ba - sal conglom erate of Sak,” yet the 1998 draft manuscri pt [*12] The original manu script read “... a sill within the Perry is much more equivocal . We think that he came to doubt Creek Form ati on,” but the diabase intrude s near the the longsta nding view of Smith and others (1907) that con tact be tween the Perry Creek and Seal Cove For ma - the conglom erate was part of the Ames Knob For mations as indi cat ed on the map and cross secti ons (see tion. The feature s he de scribes show that the conglom - note 4). er ate has lit tle in common with the Ames Knob Form ati on. Perhaps be cause Smith and others had in- [*13] On the southeas t side of Crockett Cove, the diabase in- cluded it with the Ames Knob, he still al lows for that trudes be low the Perry Creek- Seal Cove con tact, within pos si bil ity. Even though it is listed in the ex pla na tion the Seal Cove Form ati on (see note 4). under the heading of Ames Knob For mati on, Olli e did not as sign it a sym bol such as Sakc, which would be the [*14] In the origi nal manuscri pt, this paragraph was include d conven ti onal way to indi cat e a unit within a form ati on. under the Perry Creek Form ati on. The editors have substi tuted Seal Cove Form ati on in this paragraph for [*24] The unit Spcr appears on both the 1992 and 1998 draft Perry Creek For mation (see note 4). maps, yet is omit ted from the expla na ti on. The unit de- scripti on is taken from Olli e's field notes, which sug- [*15] The loca ti on of this shoal is not known to the edi tors. gest the “r” stands for rhyoli te.

[*16] The loca ti on of this low-ti de expo sure is not known to [*25] Ol lie had des ig nated the age of these units as “Pre- the editor s. It may be be low the Fish Head lo cal ity. The Silurian” since the begin ning of the mapping project , map does not indi cat e a mappa ble unit of Seal Cove an age range which is re quired by the fact that the meta- For ma tion be neath the Vinal haven Dia base south west morphism which af fects them does not af fect the Silu - of Fish Head on Browns Head. rian and younger rocks. We have added the slightly more re stric tive “Cam brian?” des ig na tion be cause of [*17] Units DSsct and DSsctb were indi cat ed on the map, but Ol lie's stated be lief that some of these units proba bly no descri pti on was given. Their de scripti ons have been corre lat e with the Ellsworth Form ati on east of Pe nob - taken from Ollie's field notes. scot Bay, for which a Cambrian age has re cently been de ter mined (Stewart, 1998). [*18] The im pli ca tion is that Seal Cove fos sils above and Ames Knob fos sils below bracket the Thorofare An- [*26] The fault referred to in the manuscri pt as the Cox Cove des ite to Late Silurian- Early De vo nian in age. fault was labele d as the Fish Point Ledge fault on the 1998 mylar . It is not clear to us why one name should [*19] Unit DStt was indi cat ed on the map, but the only de- be preferred over the other, so we have chosen to use scripti on was for rocks on the Sugar Loaves. The rest Cox Cove fault. By this we do not mean to im ply any of the descri pti on was taken from Olli e's field notes. par ticu lar age re la tion ship be tween the Wa ter man Cove fault and the Cox Cove fault. Indeed, in his text [*20] De scrip tion taken from 11/1/97 let ter from Ollie to Pe - con cern ing Struc tural Ge ol ogy (see map), Ol lie in ter- ter Gar rett, Wa ter ville, Maine. prets the two faults to have been ac tive at the same time.

[*21] Seal Cove Form ati on has been substi tuted here where [*27] While Ollie col lected the samples and ob tained the the manuscri pt has Perry Creek Form ati on. (See note chemical analyses, the editors do not know the extent to 4) which he had analyzed the re sults. We have taken the

14 Bedrock Geology of North Haven and Vinalhaven Islands

Fig ure 1. Geo chemi cal clas si fi ca tion of ana lyzed sam ples ac cord ing to the SiO2 vs. Na2O+K2O plot of Le Bas and oth ers (1986). Plot ted by for mation: A. North Ha ven Green stone, in clud ing a rhyolite (G346) from the latite mem ber (Chnl), and a dac ite (G121) from the Fish Point Forma tion. B. Thoro fare An des ite, includ ing a rhyolite vitric tuff (N270G). C. Vinal haven Dia base. D. Vinal - haven Ryolite.

libert y of plotti ng the geochem ical data on standard (VH67A) as dacit e, and a vitric tuff at Tele graph Point diagram s as a way to present the data. Figure 1 shows (N270G) is rhyoli te. Sam ple N99, plots in the field of an SiO2 vs. al ka lis (Na2O+K2O) clas si fi ca tion plot af ter tra chy ba salt, but the sample is de scribed as “oxi dized,” Le Bas and others (1986)1. For the North Haven Green- so it might not repre sent a magm atic com posi ti on. The stone (Figure 1A) the mafic lavas plot gener all y as ba- Vinal haven Diabase sam ples (Figure 1C) plot as ba salt salt, the sample from the latite mem ber at Pulpit Har bor to basal tic andes it e, and the Vinal haven Rhyoli te sam - (G346) is rhyoli te, and the sam ple from the Fish Point ples (Fig ure 1D) plot clearly in the rhyo lite field (see Form ati on (G121) is dacit e. For the Thorofare Andes - note 6). ite (Figure 1B), four sam ples plot as andes it e, one Two discri minant diagram s, shown in Figures 2 and 3, com pare the ana lyzed rocks with rocks formed in 1Le Bas, M. J., LeMai tre, R. W., Streckeisen, A., and Zannet - mod ern tec tonic en vi ron ments based on cer tain trace tin, B., 1986, A chemi cal clas sifi ca tion of vol canic rocks ele ment com posi ti ons. Figure 2 shows the manga nese , based on the to tal alkali- silica dia gram: Journal of Pe trol ogy, ti ta nium, and phos pho rous pro por tions of the ma fic v. 27, p. 745- 750. rocks in com pari son with rocks in vari ous modern oce -

15 O. Gates

anic en vi ron ments ac cord ing to Mul len (1983)2. The North Ha ven Greenstone sam ples (Figure 2A) plot in the fields of ocean is land vol canics , consis tent with the inter preta ti on of Pinette and Os berg (1989), and sup- porting Ol lie's view of erupti on on the Cam brian ocean floor (see Geologi c His tory on the map sheet). The North Ha ven sam ples are are disti nct from the Thoro- fare Andes it e (Figure 2B) and Vinal haven Diabase (Figure 2C), which plot in the field of island arc rocks, suggest ing they formed along a conver gent plate boundary relat ed to a subduc ti on zone. Figure 3 shows Y+Nb vs. Rb com posi ti ons for the fel sic rocks in com pari son with fields of granit e in various mod ern tec tonic en vi ron ments ac cord ing to Pearce and others (1984)3. The North Haven Greenstone (G346) and Fish Point (G121) sam ples plot in the field of ocean ridge granit es. The rhyoli te from the Thoro-

2 Mullen, E. D., 1983, MnO/TiO2/P2O5: a minor element dis - crimi nant for ba sal tic rocks of oce anic en vi ron ments and its im pli ca tions for pet ro gene sis: Earth and Plane tary Sci ence Let ters, v. 62, p. 53- 62.

3 Pearce, J. A., Harris, N. B. W., and Tindle, A. G., 1984, Trace ele ment dis crimi na tion dia grams for the tec tonic in ter pre tation of gran itic rocks: Journal of Pe trol ogy, v. 25, p. 956- 983.

Figure 2. Tec tonic set ting of ana lyzed sam ples ac cord ing to the Figure 3. Tec tonic dis crimi na tion dia gram for the rhyolites and dac ites MnO(x10)-TiO2 -P2O5(x10) plot of Mul len (1983). Fields show typi cal based on Y+Nb vs. Rb af ter Pearce and oth ers (1984). Rhyolite (G346) val ues for ocean is land tho lei ites (OIT), ocean is land an des ites (OIA), from the North Ha ven Green stone, dacite (G121) from the Fish Point mid- ocean ridge basalts (MORB), is land arc tholei ites (IAT), and calc- Forma tion, latite (VH12) and dac ite (VH9) from the Cal der wood For- alkaline ba salts (CAB). Samples are plot ted by for mation: A. North mation plot in the field of ocean ridge gran ites. Rhyolite tuff (270G) of Ha ven Green stone, in cluding a rhyolite (G346) from the latite mem ber, the Thoro fare An des ite plots in the field of vol canic arc gran ites. All and a dac ite (G121) from the Fish Point For mation; B. Thoro fare An - five rhyo lites (circles) of the Vinalhaven Rhyo lite plot in the field of des ite; and C. Vinal haven Dia base. within- plate gran ites.

16 Bedrock Geology of North Haven and Vinalhaven Islands

fare An des ite (sample N270G) plots as a vol canic arc show that rocks from within a unit are similar , and gran ite. Rhyo lites from the Vinal haven Rhyo lite plot in rocks from dif fer ent units are chemically dis tinct from the field of within- plate gran ites. Thus, the fel sic rocks each other. from the three form ati ons are disti nct from one another The sam ples from the Calder wood Form ati on, in- and consis tent with the setti ng indi cat ed for the mafic cluding one sam ple (WI1) from Widow Island, are rocks in Figure 2. plot ted on chemical diagram s in Figure 5. The four An ar ray of trace ele ments is dis played in “spider sam ples scat ter across the dac ite, trachy an des ite, and diagram s” in Figure 4. Spi der diagram s show the trace tra chyte fields of the SiO2 vs. al ka lis (Na2O+K2O) clas- ele ment abundance s of the analy zed rocks in com pari - sifi ca ti on plot (Figure 5A). The plot of Mullin (1983) son with the abundance s of the same elem ents in typi cal suggest s a vol canic arc set ting (figure 5B), whereas the mid-ocea n ridge basal t (MORB), here using the val ues fel sic rocks (VH9, VH12) suggest an oce anic set ting of Pearce (1983)4. As does Figure 3, these diagram s (Figure 3). The spi der diagram (Figure 5C) shows a consis tent patter n among the four sam ples, with simi-

4 lariti es to the felsic rocks (G346 and G121) of the North Pearce, J. A., 1983, Role of sub-continent al litho sphere in magma gene sis at ac tive con ti nen tal mar gins, in Hawkes- Haven Greenstone (Figure 4A), parti cular ly with re- worth, C.J., and Norry, M. J. (edi tors), Con ti nen tal ba salts spect to the rela tively high val ues of niobium (Nb) and and man tle xe no liths: Shiva Pub lish ing Co., Chesh ire, U.K., zir conium (Zr). Some of the scatter display ed in the p. 230- 250. major ele ment diagram (Figure 5A), and the appar ent

Figure 4. Spi der dia grams of ana lyzed sam ples nor mal ized to MORB us ing val ues of Pearce (1983). Plot ted by for mation: A. North Ha ven Green stone, in clud ing a rhyo lite (G346) from the latite mem ber, and a dac ite (G121) from the Fish Point For mation; B. Thoro - fare An des ite, in clud ing a vitric rhyo lite (N270G); C. Vinal haven Dia base; and D. Vinal haven Rhyo lite.

17 O. Gates

Figure 5. Geo chem istry of three sam ples from the Cal der - wood Forma tion and one from Widow Island (WI1). A. Clas - si fi ca tion ac cord ing to the Na2O+K2O vs. SiO2 plot of Le Bas and oth ers (1986). B. Tec tonic set ting for the less sili cic rocks (SiO2<63%) ac cord ing to the MnO(x10)-TiO2- -P2O5(x10) plot of Mullin (1983). C. Spider dia gram normal - ized to MORB using val ues of Pearce (1983).

incon sis tency in tec tonic setti ng betwee n Figures 3 and [*28] The manu script re fers to “David B. Stewart (per sonal 5B may re flect chemical changes dur ing metam or - com mu ni ca tion).” The edi tors have sub sti tuted the ref- phism. er ence to Stewart's map, which con tains the in for ma - tion, but was publi shed only a short time before Gates's death.

18 Bedrock Geology of North Haven and Vinalhaven Islands

AP PEN DIX I AP PEN DIX II

Par tial stra tigraphic col umn, hand- written by Ollie Gates Letter Ex cerpt from Re in hard A. Wobus to Henry Berry, for Bud Wobus, 7/27/1998 10/12/2000

Silurian- Devonian ... You have done an excel lent job of portra ying Ol lie's map and of rep re sent ing what I be lieve were his ideas about the area. I Perry Creek Form ation know you want to keep this Ol lie's map in spite of some of the SDp Bed ded maro on, pur ple, white vitric, crys tal, lithic new ideas that have de veloped since he put it togethe r. I'm sorry tuffs, tuff- breccia and in ter bed ded tuf fa ceous silt stone, we were unable to convince him about several things relat ed to pebble conglom erate . Coarse breccia s of flow-banded the Vinal haven gran ite—e.g., ba sal tic/gab broic magma in truded rhyo lite sig nal be gin ning of rhyo litic vol can ism. a granit ic mush more than the other way around. And the age questi on of what are likely co-m agmatic hy brid plutoni c and vol - Seal Cove For mation canic rocks rem ains unan swere d, al though we ought to have SDsc Red, maroon, green, purple shales, silt stones, and sand- some good zircon dates at some point. [Olli e's] caveat in the stones - Along shore south of Smith Point hornfel sed [text] about the likely un re liabil ity of Brook ins' Rb- Sr ages is to wards gran ite con tact. good. Our work in the volcan ics veri fies Olli e's mapping and Thoro fare An des ite gen er ally sup ports his stra tigra phy and in ter pre ta tions, though SDta Green, purple, tan por phyrit ic andes it e sills, dikes and the por trayal of the welded tuff unit of the Vinal haven rhyoli te in flows. the sche matic cross sec tion seems im plau sible; a welded tuff (a subaer ial unit) wouldn't drape around a subside d caul dron block SDtab Pur ple to ma roon an des ite brec cias. An gu lar to as shown. rounded blocks up to a meter in highly oxidize d sili - ceous matrix lo cally of mudstone. Breccia lo cally en- gulfs inclu sions of round-pebble andesi tic con glom er ate, sand stones and fos si lif er ous Si lu rian (Ames Knob) sedim ents. Inter preted as rubbly andes - ite flows, debris flows, ava lanche depos it s. AP PEN DIX III SDttb Mixed andesitic- rhyolitic po lymictic tuff brec cias. Letter Ex cerpt from Rob ert A. Wiebe to Henry Berry, SDl Intru sive latite on Babbidge Island. 10/26/2000

Si lu rian ... The only thing that I found troubli ng was the reten ti on of his [Gates's] early plutoni c inter preta ti ons. I thought, though I Ames Knob For mati on could be wrong, that he real ize d that the de posi ti onal feature s Sak Gray, maroon, tan shale, silt stone, limestone , pebble (parti cular ly, the pipes, I thought, im pressed him) asso ci ate d conglom erate , and bedded lithic tuffs. Llandovery to with the gabbroic rocks re quired that the east ern and southern Prido li an fauna. Include s blocks in SDta. sides of the pluton must really be the floor of the cham ber, not the roof as he origi nally pre ferred. The oc currence of the volcan ics Scg Basal conglom erate of Sak? An gular to subround on the NW mar gin of the intru sion certai nly lends strong support clasts of un der lying pSnh in he matitic matrix . Col lu - to this noti on. It seems appar ent, then, that [the large area of vium deposit ? meta morphic rocks at] Barley Hill is not a “roof pendant” but sim ply more large stoped blocks, just like those seen along the Polly Cove For mation coast. It also seems likely, look ing at his atti tud es on the meta - Spct Gray ar gil lite, shale, peb ble con glom er ate, feld spathic morphic rocks, that that area of meta morphic rocks is likely to be tuff, much folded and faulted. many separat e blocks sitti ng within the gabbro/di orit e.

Spca Sili ceous ar gil lite. Bedded quartz grit lens uncon form - able on Cal derwood Fm.

19 O. Gates

AP PEN DIX IV

Letter ex cerpts from J. M. Berdan and A. J. Boucot to Ol cott Gates, 1989-1991

Excer pt 1: J. M. Berdan to Jane and Ol lie Gates, Septem ber 1, Excer pt 3: Ol lie Gates to A. J. Boucot, Octo ber 4, 1990 1989 “I found another new fossil occur rence , this time on Cal- “Well, I have taken a prelim inary look at the col lection derwood Island east of North Ha ven. It appears to be from a from Cal derwood Point, Vinal haven Is land, and al though they large block of well-bedded limestone and ar gil lite in the Thor- look good in the hand, under the micro scope they are not so hot. oughfare [sic] Andes it e, per haps a slump block within a caldera. The slabs have molds and casts of choneti d, rhynchonel lid and It is a very scrappy col lection be cause the limestone beds are spirif erid brachio pods, some pe le cy pods, bryo zo ans, bey ri chiid thin, have weath ered into small val leys be tween the argil lite ostra codes, cri noid colum nals, etc., but nothing that is identi fi- beds, and the whole block is somewhat hornfel sed. It is of able even gen eri cally. How ever, the gen eral as so ciation is like mostly small horn corals , bryozoa, and a few brachs, not typical that reporte d from Stimpsons Island by Brookins, Berdan and of many Silu rian col lections I have made over these many years. Stewart (GSA Bull., v. 84, p. 1619-1628, May, 1973), and I have It would take a real expert to get the age even in the ball park, so a hunch that this may be the same stuff. I think that you proba bly I'm asking if you would mind taking a look at it. I don't really ex- have a copy of the GSA paper , but am enclos ing a copy of the pect any re sults but it is worth a try.” origi nal report to Dave Stewart, which you may not have. As you will see from the enclos ed report, the col lec tions from Excer pt 4: A. J. Bou cot to Olli e Gates, Febru ary 6, 1991 Stimpsons Island were not very good, ei ther.” “Figured I'd better write you to “confirm ” what we just said [Note writ ten on bot tom in Ol lie's hand: “Inclu sion in Thorofare over the phone! NF-178, Calder wood Island, certai nly looks An des ite on Cal der wood Point.”] Upper Llandovery to early Wenlock to me (and more likely Llandovery ) because of the smooth pentam erini d. It's the kind of Excer pt 2: A. J. Bou cot to Olli e Gates, January 31, 1990 thing we used to al ways call Pen tamerus ob lon gus, but since with your somewhat scrappy collec tion I couldn't make out “Your littl e box arrive d safely, and has been unduly un - whether or not there is any tri loba ti on I'd probably call it “Pen - wrapped! The mate ria l is, as you know, kind of scrappy. BUT, tamerus” today to indi cat e a smooth pentam erini d with discrete when eve rythi ng is taken into consid era ti on I would have to con - bra chial lam ellae (no median sep tum as in Pen tam er oi des). I'll clude that it's probably of Silu ria n age, and probably Upper Si lu- call Bill Ol iver on Friday and see if I can con him into looking at rian. The “logic” is as follow s: 1) in the Coastal Belt the your corals (which are not all that bad, al though maybe com ing youngest marine , pre-Acadi an fossil s known are earli est Devo - from me that does n't mean too much). nian (Gedin nian stuff from the East port Fm. and equivalent s); 2) “NF 60 will need some acid work—all I could see on the your hornfel s yielded fragm ents of a rhynchonen nid [sic*] (the weath ered sur faces are non de script rhyn chonel lid brachs. kind of thing I com monly refer to as “Ca ma ro toechia”), and a Wouldn't dare say much about age based on them.” finely cos tel late cho netid that is similar to mate ri als I've called Pro to cho ne tes in the past (such as your Leighton Shale Coll. No. [Note writ ten on bot tom in Ol lie's hand: “Calder wood Island 17086). Choneti ds don't come in worldwide unti l the latest Or- Sak”] dovi cia n (Anti costi only), and don't becom e com mon unti l the later Llandovery (later Lower Silu ria n). So...sounds like you Excer pt 5: A. J. Bou cot to Olli e Gates, Febru ary 13, 1991 have somethi ng that would proba bly be pre-Pem broke Fm. type fauna (some of that fauna is known on North Haven, a local ity of “The Stimpson 's Point [sic*] ma te rial is CER TAINLY Dave Stewart's that I col lected some time ago). I sus pect that you much younger than your Calder wood Point collec tion. Quad ri - might be able to match your stuff up if you got back to North Ha- far ius is still a Pridoli-Geddi nian age item (and abundant Salop- ven and worked in the pre-Pem broke Form ati on type faunas.” ina are known from coastal Acadia mostly in the Pridoli (includ ing Arisaig, Nova Scota). So...guess you still have a real [* rhyn chonel lid] head ache.”

[Note writ ten on bot tom in Ol lie's hand: “Inclu sion in mingli ng [*Stimp sons Is land] zone on Greens Is land”]

20 Bedrock Geology of North Haven and Vinalhaven Islands

Excer pt 6: A. J. Bou cot to Olli e Gates, March 1, 1991 Excer pt 7: A. J. Bou cot to Olli e Gates, March 7, 1991

“As far as I can see your #56, Calder wood Point collec tion “Bill Oliver called me yester day about the cor als from NF has lots of a choneti d, probably a proto cho neti d, a How el lella, a 178. All he could see were overall of “Si luria n” type, with Try - “Car mar to toechia” [sic] type rhyn chonel lid, a dal man el lid (rare, plasma be ing the only gen eri cally iden tifi able item. So...the best and I'm not sure of its identi tiy), a tri lobit e scrap or two, and lots that can be said is that the cor als are per missively con sis tent with of Ten tacu lites. The small How el lella suggest s a C3 (Llan - the brac story (i.e., the Pen tamerus from NF 178? indi cat es an dovery) - Prido li an or even earli er Gedinnian age span—that's Upper Llandovery or maybe even earli er Wenlock age). NF 60 about all I could say. Ecol ogical ly I would guess for pretty shal- only has a sphaerirhy nchid brac, as I said earli er, which doesn't low wa ter, near shore, subti dal condi ti ons (lots of cri noidal de - help in the relative age business very much. bris), in about the B.A. 2 posi ti on in view of the overall “If it's prac ti cal next sum mer I would suggest that you re- abun dance of Ten tacu lites, rhynchonel lids and the choneti d. col lec t NF 178 in a big way—blocks rather than small ham mer Sorry that I can't be more helpful. type sam ples (get out the old sledge, crowbar and cold chisels ). . With a hunderd pounds or so of blocks I can try to get a more ex- . ten sive brac collec tion, and also get bet ter cor als (Bill would like . to have them for refer ence purposes— this is really the first Silu - “P.S. Got NF 60 out of the acid—only re covered an rian coral lo cal ity in the Coastal Si lu rian from St. John to Bos - uncinuloi d rhynconel lid that could be anywhere from C3 into the ton—could be even tu ally im por tant for bio ge og raphic pur poses Devo nian— not much help. Com ing from where it does I guess when we know more abouth the corals ).” its most likely to be Si luria n, and pre-Pem broke in age, i.e., pre- Pridolian, but that's a guess based on local bios tra t.” [Note writ ten on bot tom in Ol lie's hand: “Calder wood Island Sak”] [Note writ ten on bot tom in Ol lie's hand: “Calder wood Point. Sak in clu sion in an des ite”]

21 O. Gates

AP PEN DIX V Lo ca tion maps for sam ples whose geo chem istry is re ported in Ta ble 1.

Map A-1. An enlarged por tion of the North Ha ven West 1:24,000 quad ran gle. North Haven Green stone: G85 - Pillow lava, Mack- erel Point, North Ha ven; G346 - Rhyolite tuff, north shore of Pul pit Har bor, North Ha ven.

22 Bedrock Geology of North Haven and Vinalhaven Islands

Map A-2. An enlarged por tion of the North Ha ven West 1:24,000 quad ran gle. North Haven Green stone: G179 - Diabase, head of Southern Har bor, North Haven; G183 - Pil low lava, head of South ern Har bor, North Haven. Thoro fare An des ite: N40B - Andes ite, Close to con tact, north side of Ames Knob, North Haven; N42 - Andes ite, Ames Knob, North Haven; N51 - Diabase dike, east shore of Browns Cove, North Ha ven; N270G - Rhyo lite vitric tuff, Tele graph Point, North Haven.

23 O. Gates

Map A-3. An enlarged por tion of the North Ha ven East 1:24,000 quad ran gle. North Haven Green stone: G117 - Pillow lava, east shore of Water man Cove, North Ha ven. Fish Point Forma tion: G121 - Rhyolite, Fish Point, North Ha ven. Thoro fare An des ite: N30 - Andes ite, north side of golf course, North Haven; N99 - Andes ite, oxi dized, north side of the Thoro fare, North Ha ven; N118 - Andes ite, golf course hill, North Ha ven.

24 Bedrock Geology of North Haven and Vinalhaven Islands

Map A-4. An enlarged por tion of the North Ha ven East 1:24,000 quad ran gle. Cal der wood For ma tion: WI1 - Porphy ry, Widow Is- land.

25 O. Gates

Map A-5. An enlarged por tion of the Lead bet ter Is land 1:24,000 quad ran gle. Vinal haven Dia base: V104 - Dia base in trud ing mud, near Browns Head, Vinal haven. Vinal haven Rhyo lite: VH119 - Breccia fragment in breccia along base of rhyo lite, Vinalhaven; VH145 - Welded tuff near base, east shore of Crock ett Cove, Vinal haven.

26 Bedrock Geology of North Haven and Vinalhaven Islands

Map A-6. An enlarged por tion of the Lead bet ter Is land 1:24,000 quad ran gle. Vinal haven Dia base: V90 - Dia base sill, south shore of the Thoro fare, Vinal haven; Vinal haven Rhyo lite: VH121 - Flow-banded rhyolite along road west of ra dio tower, Vinalhaven; VH124 - Brec cia on hill north west of end of Long Cove, Vinalhaven; VH377 - Welded tuff, near top of Mid dle Moun tain, Vinalhaven.

27 O. Gates

Map A-7. An enlarged por tion of the Vinalhaven 1:24,000 quad ran gle. Cal der wood For ma tion: VH3 - Quartz am phi bo lite, on shore east of Polly Cove, Vinalhaven; VH9 - Schist, east shore of Carver Cove, Vinalhaven; VH12 - Latite, on shore north west of Salt Works Cove, Vinal haven. Thoro fare An des ite: VH67A - Andes ite, south of Swim ming Pool, Vinal haven.