Bedrock Geology of North Haven and Vinalhaven Islands
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DE PART MENT OF CON SER 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. re port 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 in cluded 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 match ing 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 geo logic rela ti on ships. 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 in cluded 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 - stan tive com ments for which we thank them. plana ti on of units, and a narra ti ve descri p tion of the geologi c his - On the final map, Geologi c Map 01-352, we have taken tory with lit era 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 pub lish 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 on ships 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 in form 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 scrip tions. 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 scrip tions 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 Un fortu nate ly, Olli e passed away in July of 1999 before re- com plete text, from which the map expla na ti on was de rived. vi sions were completed. His wife, Jane, gave ma teri als re lated to The brief Intro duc ti on is ours. At certai n places we have ed ited 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 Ol lie'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 chang ing 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 na ture of the con tact be tween the Seal and mylar with sketches of possi ble con tacts and cross- section 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 in fer his meaning, and have in serted 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 ex plana 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 ap parent to us. nati on of sym bols, and geologi c his tory. The geo logic 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 fun dam ental soundness of the map. This is aside in a set of plain white en velopes . an excel lent piece of geologi c mapping that has sig nifi cantly im - Al though these ma te ri als col lec tively in cluded all the types proved our under sta nd ing 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 fi nal in stall ment in 1998, it soon becam e clear to us that Ol lie had not quite fin ished 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 Ha ven 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.), Tour naisian (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- cutting 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 tologi c find ings.