Geochronology of the Mesoproterozoic State Farm gneiss and associated Neoproterozoic granitoids, Goochland terrane, Virginia

Research Article| November 01, 1996 Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia John N. Aleinikoff; John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar J. Wright Horton, Jr.; J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Search for other works by this author on: GSW Google Scholar Marianne Walter Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1996) 108 (11): 1481–1491. https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John N. Aleinikoff, J. Wright Horton, Marianne Walter; Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia. GSA Bulletin 1996;; 108 (11): 1481–1491. doi: https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast majority of zircons are more equant, subangular to anhedral, contain 38–52 ppm uranium, and are interpreted to be metamorphic in origin. One fraction of elongate zircon, and four fragments of a very large zircon (occurring in a nelsonite segregation) yield an upper intercept age of 1045 ± 10 Ma, interpreted as the time of anorthosite crystallization. Irregularly shaped metamorphic zircons are dated at 1011 ± 2 Ma (weighted average of the 207Pb/206Pb ages). The U-Pb isotopic systematics of metamorphic titanite were reset during the Alleghanian orogeny at 297 ± 5 Ma. These data provide a minimum age for gneisses of the Goochland terrane that are intruded by the anorthosite. Middle Proterozoic basement rocks of the Goochland terrane may be correlative with those in the Shenandoah massif of the Blue Ridge tectonic province, as suggested by similarities between the Montpelier Anorthosite and the Roseland anorthosite. Although the areal extent of Middle Proterozoic basement and basement-cover relations in the eastern Piedmont remain unresolved, results of this investigation indicate that the Goochland terrane is an internal massif of Laurentian crust rather than an exotic accreted terrane. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

ABSTRACTThe Goochland Terrane is an enigmatic crustal block in the Appalachian Piedmont Province of central Virginia, USA. Sparse exposures of terminal Mesoproterozoic and late Neoproterozoic igneous rocks in the central Goochland Terrane offer the opportunity to investigate both the continental affinity of the terrane during the Proterozoic Eon and the timing and mechanisms of crustal growth. We apply multiple geochemical tools to these rocks: tectonic discrimination using whole-rock major and trace element abundances; whole-rock Sm-Nd isotopes; O, U-Pb, and Lu-Hf isotope analyses of spots in zircon; and measurement of O isotopes in multi-grain quartz separates. Eruption of the Sabot Amphibolite protolith is difficult to date, but we tentatively assign an age of 552 ± 11 Ma. Goochland Terrane continental crust first separated from the mantle prior to ca. 1050–1010 Ma intrusion of the Montpelier Anorthosite and the State Farm Gneiss protolith. The granitic magma that became the State Farm Gneiss protolith could have been derived entirely from partial melting of this initial Goochland Terrane crust. In contrast, the magmas that became the Montpelier Anorthosite, Neoproterozoic granitoid, and the Sabot Amphibolite were mixtures of mantle melt and preexisting Goochland Terrane crust. This production of juvenile continental crust occurred during continental extension and, eventually, rifting. The timing and compositions of terminal Mesoproterozoic magmatism in the Goochland Terrane closely match those in the nearby Blue Ridge Province. Although the compositions of the Neoproterozoic magmas in the two regions are similar, intrusion and possibly eruption occurred about 10 M.y. later in the Goochland Terrane.

The Goochland terrane in the central Piedmont Province of Virginia contains two documented units of Mesoproterozoic age, the State Farm Gneiss (ca. 1023–1046 Ma) and the Montpelier Anorthosite (ca. 1045 Ma). The heterogeneous Maidens gneiss, the most extensive unit in the terrane, has previously been assumed to be Mesoproterozoic. This inferred age was based primarily on the presence of locally preserved granulite-facies assemblages (particularly in metapelites), with granulite conditions assumed to reflect metamorphism accompanying the Grenville orogeny. However, we report new U-Pb zircon results for meta-igneous varieties of Maidens gneiss that indicate Paleozoic (Devonian) crystallization ages. Whole-rock major- and trace-element compositions of these and additional samples suggest intermediate igneous protoliths of high-K, calc-alkaline affinity. Our age determinations clearly demonstrate that the protoliths for these samples were not Mesoproterozoic, and could not have been affected by Grenvillian metamorphism. As an alternative, we suggest that the protoliths were plutonic igneous rocks, reflecting deep-seated emplacement of magmas approximately coincident with high-grade metamorphism in associated rocks during the Acadian orogeny. Whether our age results can be applied to the entirety of the Maidens gneiss is uncertain, but if so, a large portion of the Goochland terrane as currently defined is not Mesoproterozoic.

Research Article| January 01, 1977 U-Pb zircon dates from the central Appalachian Piedmont: A possible case of inherited radiogenic lead MICHAEL W. HIGGINS; MICHAEL W. HIGGINS 1U.S. Geological Survey, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar AKHAURY K. SINHA; AKHAURY K. SINHA 2Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24016 Search for other works by this author on: GSW Google Scholar ROBERT E. ZARTMAN; ROBERT E. ZARTMAN 3U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar WILLIAM S. KIRK WILLIAM S. KIRK 1U.S. Geological Survey, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Author and Article Information MICHAEL W. HIGGINS 1U.S. Geological Survey, Reston, Virginia 22092 AKHAURY K. SINHA 2Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24016 ROBERT E. ZARTMAN 3U.S. Geological Survey, Denver, Colorado 80225 WILLIAM S. KIRK 1U.S. Geological Survey, Reston, Virginia 22092 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1977) 88 (1): 125–132. https://doi.org/10.1130/0016-7606(1977)88<125:UZDFTC>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation MICHAEL W. HIGGINS, AKHAURY K. SINHA, ROBERT E. ZARTMAN, WILLIAM S. KIRK; U-Pb zircon dates from the central Appalachian Piedmont: A possible case of inherited radiogenic lead. GSA Bulletin 1977;; 88 (1): 125–132. doi: https://doi.org/10.1130/0016-7606(1977)88<125:UZDFTC>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Zircon dates from metavolcanic and metaplutonic rocks of the central Appalachian Piedmont in Maryland and Virginia are important for interpreting the age of the Glenarm Series. Compilation and evaluation of available data from this area suggest that Piedmont zircons may have inherited a component of older radiogenic lead in seed crystals, which were derived from the Pre-cambrian basement complex. The zircons were also affected by lead and uranium loss during subsequent Paleozoic metamorphism recorded in the Piedmont terrain and (or) recent dilation of the rock at surface conditions. Thus, the apparent dates might not represent precise rock ages, but may still give valuable information about the evolution and history of the rocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The Goochland terrane is a structurally isolated crustal block in the eastern Piedmont of Virginia. It is composed of the previously named State Farm Gneiss, Montpelier Anorthosite, Sabot Amphibolite, and Maidens Gneiss, but also includes the Scotchtown Gneiss, Teman Gneiss, and Old Bandana Gneiss which are formally named and defined herein. The eastern part of the Goochland terrane is antiformal and cored by Mesoproterozoic rocks (the State Farm Gneiss and the Montpelier Anorthosite). These basement units are overlain by a late Neoproterozoic to early Paleozoic (Ediacaran to Early Cambrian) saprolitic, metavolcanic, and metasedimentary sequence that sequentially includes the Scotchtown Gneiss, Sabot Amphibolite and Maidens Gneiss. The western part of the terrane is synformal and includes in its core two additional units that overlie the Maidens Gneiss: the Teman Gneiss and the Old Bandana Gneiss. Based on mineralogy and zircon grain morphology, the protoliths of the Maidens, Teman, and Old Bandana gneisses were predominantly sedimentary rocks. The protoliths of the Teman Gneiss and Old Bandana Gneiss were deposited unconformably upon the protolith of the Maidens Gneiss. The eastern and western parts of the Goochland terrane are separated by the Dabneys fault, which has considerable east-side-up vertical offset and possibly also significant transverse displacement. Correlation of the upper part of the Goochland terrane (Teman and Old Bandana gneisses) with the Setters and Cockeysville gneisses in the Baltimore region suggests that the Goochland terrane was left about 135 miles (ca. 220 km) southwest of its original North American location, which was to the east of Baltimore, Maryland. This displacement was caused by the oblique collision of the eastern North American continent with the western edge of the Gondwanan craton during the later Carboniferous (Pennsylvanian) Period.

U–Pb single zircon geochronology of granitoids in the Vumba granite–greenstone terrain (NE Botswana):: Implications for the evolution of the Archaean Zimbabwe craton

Other| December 01, 1977 Tectonic evolution of the Cocos-Nazca spreading center RICHARD HEY RICHARD HEY 1Department of Geological and Geophysical Sciences, Princeton University, Princeton, New Jersey 08540 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1977) 88 (12): i–vi. https://doi.org/10.1130/0016-7606(1977)88<i:TEOTCS>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation RICHARD HEY; Tectonic evolution of the Cocos-Nazca spreading center. GSA Bulletin 1977;; 88 (12): i–vi. doi: https://doi.org/10.1130/0016-7606(1977)88<i:TEOTCS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract GSA Bulletin, Volume 88, page 1404.GSA Bulletin, Volume 87, page 1678.GSA Bulletin, Volume 88, page 247.GSA Bulletin, Volume 88, page 364.GSA Bulletin, Volume 88, page 299.GSA Bulletin, Volume 88, page 1479.Magnetic and bathymetric data from the eastern Pacific have been analyzed and a model for the evolution of the Galapagos region developed. The Farallon plate appears to have broken apart along a pre-existing Pacific-Farallon fracture zone, possibly the Marquesas fracture zone, at about 25 m.y. B.P. to form the Cocos and Nazca plates. This break is marked on the Nazca plate topographically by the Grijalva scarp and magnetically by a rough-smooth boundary coincident with the scarp. The oldest Cocos-Nazca magnetic anomalies parallel this boundary, implying that the early Cocos-Nazca spreading center trended east-northeast. This system soon reorganized into an approximately east-west rise–north-south transform configuration, which has persisted until the present, and the Pacific-Cocos-Nazca triple junction has since migrated north from its original location near lat 5°S. If correct, the combination of these simple geometric constraints produced the “enigmatic” east-trending anomalies south of the Carnegie Ridge.The axes of the Cocos-Nazca spreading center and the Carnegie Ridge are essentially parallel; this can lead to paradoxical conclusions about interpretation of the Cocos and Carnegie Ridges as hotspot tracks. Hey and others (1977) have shown that recent accretion on the Cocos-Nazca spreading center has been asymmetric, resulting at least in part from small discrete jumps of the rise axis. I show here that the geometric objections to both the “hot-spot” and “ancestral-ridge” hypotheses on the origin of the Cocos and Carnegie Ridges can be resolved with an asymmetric-accretion model. However, all forms of the ancestral-ridge hypothesis encounter more severe geometric difficulties, and these results support the hotspot hypothesis. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Geochemical characteristics and genesis of Neoproterozoic granitoids in the northwestern margin of the Yangtze Block

Research Article| August 01, 1999 U/Pb dating of detrital zircons: Implications for the provenance record of Gondwana margin terranes Peter A. Cawood; Peter A. Cawood 1Tectonics Special Research Centre, School of Applied Geology, Curtin University, G.P.O. Box U1987, Perth 6001, Western Australia, Australia Search for other works by this author on: GSW Google Scholar Alexander A. Nemchin; Alexander A. Nemchin 1Tectonics Special Research Centre, School of Applied Geology, Curtin University, G.P.O. Box U1987, Perth 6001, Western Australia, Australia Search for other works by this author on: GSW Google Scholar Axel Leverenz; Axel Leverenz 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar Ayesha Saeed; Ayesha Saeed 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar Peter F. Balance Peter F. Balance 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar Author and Article Information Peter A. Cawood 1Tectonics Special Research Centre, School of Applied Geology, Curtin University, G.P.O. Box U1987, Perth 6001, Western Australia, Australia Alexander A. Nemchin 1Tectonics Special Research Centre, School of Applied Geology, Curtin University, G.P.O. Box U1987, Perth 6001, Western Australia, Australia Axel Leverenz 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Ayesha Saeed 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Peter F. Balance 2Department of Geology, University of Auckland, Private Bag 92019, Auckland, New Zealand Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1999) 111 (8): 1107–1119. https://doi.org/10.1130/0016-7606(1999)111<1107:UPDODZ>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Peter A. Cawood, Alexander A. Nemchin, Axel Leverenz, Ayesha Saeed, Peter F. Balance; U/Pb dating of detrital zircons: Implications for the provenance record of Gondwana margin terranes. GSA Bulletin 1999;; 111 (8): 1107–1119. doi: https://doi.org/10.1130/0016-7606(1999)111<1107:UPDODZ>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract SHRIMP U/Pb age data for more than 300 detrital zircons from late Mesozoic samples of the Torlesse and Waipapa arc-trench terranes in New Zealand range from ca. 100 Ma (Early Cretaceous) to 3140 Ma (Archean). More than 65% of the analyzed zircon grains are Permian or Mesozoic age. The remaining detritus is largely of Paleozoic age with progressively smaller amounts of Proterozoic and Archean debris. Cathodoluminescence imaging indicates that the younger grains are exclusively of igneous origin, whereas the older grains show evidence for a more complex history including metamorphic overprints and inherited cores. The youngest zircon grains in most of the samples approximate the age of deposition of the rock units, suggesting input into the depositional basins from contemporaneous igneous activity. The overall age profile of the detrital zircons is consistent with sediment accumulation adjacent to the Gondwana margin rather than in exotic blocks accreted to the margin. The bulk of the detritus is derived from a late Paleozoic to Mesozoic Gondwana margin, Andean-style magmatic arc. Elements of this arc extend from Marie Byrd Land in Antarctica, through New Zealand (Median tectonic zone) to New England in eastern Australia. Paleozoic and older grains form a minor but significant component of all samples and have an age signature indicative of derivation from the Paleozoic and Neoproterozoic fold belts of East Australia and Antarctica (Gondwana). A characteristic feature of the older grains is ages in the range 500–650 and 1000–1200 Ma, which is also a feature of the zircon age spectrum for early Paleozoic graywackes from the Lachlan-Tuhua fold belt, suggesting derivation from these sedimentary rocks or from the same original source rocks. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| July 01, 2004 Geologic evolution of the Xolapa Complex, southern Mexico: Evidence from U-Pb zircon geochronology Mihai N. Ducea; Mihai N. Ducea 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar George E. Gehrels; George E. Gehrels 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Sarah Shoemaker; Sarah Shoemaker 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Joaquin Ruiz; Joaquin Ruiz 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Victor A. Valencia Victor A. Valencia 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Mihai N. Ducea 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA George E. Gehrels 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Sarah Shoemaker 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Joaquin Ruiz 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Victor A. Valencia 1University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA Publisher: Geological Society of America Received: 06 Aug 2003 Revision Received: 06 Dec 2003 Accepted: 12 Jan 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (7-8): 1016–1025. https://doi.org/10.1130/B25467.1 Article history Received: 06 Aug 2003 Revision Received: 06 Dec 2003 Accepted: 12 Jan 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mihai N. Ducea, George E. Gehrels, Sarah Shoemaker, Joaquin Ruiz, Victor A. Valencia; Geologic evolution of the Xolapa Complex, southern Mexico: Evidence from U-Pb zircon geochronology. GSA Bulletin 2004;; 116 (7-8): 1016–1025. doi: https://doi.org/10.1130/B25467.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Xolapa Complex of southern Mexico is composed of mid-crustal arc-related gneisses of poorly resolved ages, intruded by undeformed Cenozoic calc-alkaline plutons. Twelve undeformed and deformed tonalitic/granodioritic samples from three transects across the Sierra Madre del Sur (Acapulco, Puerto Escondido, and Puerto Angel) were chosen for U-Pb zircon analysis. The measurements were performed on single crystals of zircons, using a multiple-collector laser-ablation inductively coupled plasma–mass spectrometer (MC-LA-ICP-MS). About 20–30 crystals were measured from each sample. Three gneisses and migmatites from the eastern transect (Puerto Angel), located 30–42 km from the coast, yielded Grenville-aged zircons (970–1280 Ma), suggesting that the samples represent Oaxacan basement, not deformed Xolapa Complex. The central transect (Puerto Escondido) yielded Oligocene ages (25–32 Ma) on undeformed plutons as well as mid-Mesozoic and Permian ages on gneisses. Most samples along the Puerto Escondido transect contain inherited ca. 1.1 Ga xenocrystals of zircons. The western transect (Acapulco) yielded Late Jurassic–Early Cretaceous ages (160–136 Ma) on gneisses, and Paleocene (55 Ma) and Oligocene (34 Ma) ages on undeformed plutons, with no inherited Grenville ages. The older ages and xenocrystic zircons in arc-related Xolapa Complex mirror the crustal ages found in neighboring terranes (Mixteca and Oaxaca) to the north of the Xolapa Complex, suggesting an autochthonous origin of Xolapa with respect to its neighboring north-bounding terranes. The new data and previously published ages for Xolapa suggest that metamorphism and migmatization of the deformed arc rocks took place prior to the Cenozoic. Eocene and Oligocene plutons representing renewed arc-related magmatism in the area are common throughout Xolapa, and probably represent the more deeply exposed continuation of the Sierra Madre Occidental arc to the northwest. The available U-Pb data argue against the previously proposed eastward migration of magmatism between Acapulco and Puerto Angel during the Oligocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli–Erguna area of Inner Mongolia, China: Geochronological, geochemical and Hf isotopic evidence

Steep tilting of metavolcanic rocks by multiple mechanisms, central Sierra Nevada, California

Research Article| February 01, 1985 Late Proterozoic and Devonian plutonic terrane within the Avalon zone of Rhode Island O. DON HERMES; O. DON HERMES 1Department of Geology, University of Rhode Island, Kingston, Rhode Island 02881 Search for other works by this author on: GSW Google Scholar ROBERT E. ZARTMAN ROBERT E. ZARTMAN 2U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information O. DON HERMES 1Department of Geology, University of Rhode Island, Kingston, Rhode Island 02881 ROBERT E. ZARTMAN 2U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1985) 96 (2): 272–282. https://doi.org/10.1130/0016-7606(1985)96<272:LPADPT>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation O. DON HERMES, ROBERT E. ZARTMAN; Late Proterozoic and Devonian plutonic terrane within the Avalon zone of Rhode Island. GSA Bulletin 1985;; 96 (2): 272–282. doi: https://doi.org/10.1130/0016-7606(1985)96<272:LPADPT>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The U-Th-Pb radiometric age of zircons demonstrates that much of Rhode Island consists of a late Proterozoic plutonic complex that subsequently was intruded by a large Devonian alkalic to subalkalic igneous complex.Two groups of late Proterozoic rocks can be recognized: (1) the Esmond Granite and related plutonic rocks in northern Rhode Island, ranging in composition from gabbro to granite and yielding an upper concordia intercept of 621 ± 8 m.y., and (2) quartz-rich, recrystallized gneissic rocks (Ten Rod Granite Gneiss and Hope Valley Alaskite Gneiss) in southern Rhode Island, giving an upper concordia intercept age of 601 ± 5 m.y. The lower intercept of the zircon discordia for the gneissic rocks indicates the isotopic systems were disturbed during the late Paleozoic Alleghanian Orogeny, whereas zircons from the Esmond Granite and related plutonic rocks have been subjected mainly to loss of lead attributable to recent dilatancy.Rocks determined to be of Devonian age include the Scituate Granite and plutonic rocks of the East Greenwich Plutonic Suite. The Quincy Granite of Quinn (1971) in northeastern Rhode Island may be of a similar Devonian age, or it may be slightly younger. Zircon data from these rocks fall upon a chord that gives an upper concordia intercept of 370 ± 7 m.y. and a lower intercept close to the origin. Collectively, these rocks form a composite pluton with an area >700 km2. The Devonian rocks exhibit petrologic characteristics distinct from slightly older Acadian orogenic rocks that occur in lithostratigraphic zones to the west and are more comparable to anorogenic Ordovician to Devonian alkalic granitoids that trend north-northeast across Massachusetts and the Gulf of Maine.The new age determinations confirm that much of Rhode Island contains plutonic rocks intruded during the Avalonian Orogeny but that a hertofore unrecognized major Devonian plutonic episode also occurred. The distinctly different ages probably had gone unrecognized because of generally similar lithologic and textural features exhibited by the late Proterozoic and Devonian rocks. We present new petrologic and geochemical criteria that should assist in distinguishing the rocks of different ages as additional mapping and geologic study proceeds. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| May 01, 1986 Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska JOHN N. ALEINIKOFF; JOHN N. ALEINIKOFF 1U.S. Geological Survey, Box 25046, M.S. 963, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar CYNTHIA DUSEL-BACON; CYNTHIA DUSEL-BACON 2U.S. Geological Survey, 345 Middlefield Road, M.S. 904, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar HELEN L. FOSTER HELEN L. FOSTER 2U.S. Geological Survey, 345 Middlefield Road, M.S. 904, Menlo Park, California 94025 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN N. ALEINIKOFF 1U.S. Geological Survey, Box 25046, M.S. 963, Denver Federal Center, Denver, Colorado 80225 CYNTHIA DUSEL-BACON 2U.S. Geological Survey, 345 Middlefield Road, M.S. 904, Menlo Park, California 94025 HELEN L. FOSTER 2U.S. Geological Survey, 345 Middlefield Road, M.S. 904, Menlo Park, California 94025 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1986) 97 (5): 626–637. https://doi.org/10.1130/0016-7606(1986)97<626:GOAGAR>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN N. ALEINIKOFF, CYNTHIA DUSEL-BACON, HELEN L. FOSTER; Geochronology of augen gneiss and related rocks, Yukon-Tanana terrane, east-central Alaska. GSA Bulletin 1986;; 97 (5): 626–637. doi: https://doi.org/10.1130/0016-7606(1986)97<626:GOAGAR>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Using several isotopic techniques, we have determined the ages of selected metamorphic rocks in the Yukon-Tanana terrane (YTT) of east-central Alaska. U-Pb zircon data from an augen gneiss body in the Big Delta quadrangle indicate that the granitoid protolith of the gneiss was intruded 341 ± 3 m.y. ago (lower intercept age). An upper intercept age of 2,136 ± 31 m.y. indicates an inherited early Proterozoic component in these zircons. This inheritance age is substantiated by a Sm-Nd whole-rock model age of 2.09 ± 0.08 b.y. from the Big Delta augen gneiss body. Detrital zircons from quartzitic wall rocks to this body were also derived from an early Proterozoic (∼2.1 to 2.3 b.y. old) crustal source(s). Zircons from three other augen gneisses occurring in an east-west belt which extends into the southern Yukon Territory, Canada, have similar Mississippian and early Proterozoic intercept ages. A Rb-Sr whole-rock isochron from widely separated bodies of augen gneiss has an age of 333 ± 26 m.y. and an initial 87Sr/86Sr ratio of 0.728 ± 0.002, confirming the Mississippian intrusive age for the protolith. The high initial 87Sr/86Sr ratio further indicates an old crustal component in these rocks. A Rb-Sr mineral isochron (115 ± 4 m.y.), K-Ar data from hornblende and micas (128 to 107 m.y.), and U-Pb data from sphene (134. m.y.) from augen gneiss and related rocks are similar to many K-Ar ages in this region and confirm the occurrence of an early Cretaceous thermal event. U-Pb ages of zircons from three metavolcanic units in the YTT suggest that extrusion of the protoliths of these rocks occurred 360–380 m.y. ago. Scatter in the data is caused by ubiquitous inheritance and multiple lead-loss events.Significant Devonian-Mississippian igneous activity (380-340 m.y.) took place in the YTT, followed by one, or possibly two, metamorphic episodes (Mississippian? and Cretaceous). As yet, no early Proterozoic source rocks for the Paleozoic magmas have been identified in the YTT, but rocks of similar early Proterozoic ages occur to the east and south in the Northwest Territories and British Columbia, Canada. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Research Article| January 01, 2006 Plutonism in three orogenic pulses, Eastern Blue Ridge Province, southern Appalachians Brent V. Miller; Brent V. Miller 1Department of Geological Sciences, University of North Carolina at Chapel Hill, CB#3315, Mitchell Hall, Chapel Hill, North Carolina 27599-3315, USA Search for other works by this author on: GSW Google Scholar Allen H. Fetter; Allen H. Fetter 2Departamento de Petrologia e Metalogenia, Universidade Estadual Paulista (UNESP), Avenida 24A, no. 1515, CEP 13506-900, Rio Claro, São Paulo, Brazil Search for other works by this author on: GSW Google Scholar Kevin G. Stewart Kevin G. Stewart 3Department of Geological Sciences, University of North Carolina at Chapel Hill, CB#3315, Mitchell Hall, Chapel Hill, North Carolina 27599-3315, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Brent V. Miller 1Department of Geological Sciences, University of North Carolina at Chapel Hill, CB#3315, Mitchell Hall, Chapel Hill, North Carolina 27599-3315, USA Allen H. Fetter 2Departamento de Petrologia e Metalogenia, Universidade Estadual Paulista (UNESP), Avenida 24A, no. 1515, CEP 13506-900, Rio Claro, São Paulo, Brazil Kevin G. Stewart 3Department of Geological Sciences, University of North Carolina at Chapel Hill, CB#3315, Mitchell Hall, Chapel Hill, North Carolina 27599-3315, USA Publisher: Geological Society of America Received: 02 Feb 2004 Revision Received: 16 May 2005 Accepted: 11 Jun 2005 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2006) 118 (1-2): 171–184. https://doi.org/10.1130/B25580.1 Article history Received: 02 Feb 2004 Revision Received: 16 May 2005 Accepted: 11 Jun 2005 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Brent V. Miller, Allen H. Fetter, Kevin G. Stewart; Plutonism in three orogenic pulses, Eastern Blue Ridge Province, southern Appalachians. GSA Bulletin 2006;; 118 (1-2): 171–184. doi: https://doi.org/10.1130/B25580.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Eastern Blue Ridge Province of the southern Appalachians contains, in part, remnants of an Ordovician accretionary wedge complex formed during subduction of an oceanic tract before mid-Ordovician accretion with Laurentia. The Eastern Blue Ridge Province consists of metapelite and amphibolite intruded by low-K plutons, high-temperature (T >750 °C) Ordovician eclogite, and other high-pressure metamafic and meta-ultramafic rocks. Felsic plutons in the Eastern Blue Ridge Province are important time markers for regional-scale tectonics, deformation, and metamorphism. Plutons were thought to be related to either Taconian (Ordovician) or Acadian (Devonian-Silurian) tectonothermal events.We dated five plutonic or metaplutonic rocks to constrain pluton crystallization ages better and thus the timing of tectonism. The Persimmon Creek gneiss yielded a protolith crystallization age of 455.7 ± 2.1 Ma, Chalk Mountain 377.7 ± 2.5 Ma, Mt. Airy 334 ± 3 Ma, Stone Mountain 335.6 ± 1.0 Ma, and Rabun 335.1 ± 2.8 Ma. The latter four plutons were thought to be part of the Acadian “Spruce Pine Suite,” but instead our new ages indicate that Alleghanian (Carboniferous-Permian) plutonism is widespread and voluminous in the Eastern Blue Ridge Province. The Chattahoochee fault, which was considered an Acadian structure, cuts the Rabun pluton and thus must have been active during the Alleghanian orogeny. The new ages indicate that Persimmon Creek crystallized less than 3 m.y. after zircon crystallization in Eastern Blue Ridge eclogite and is nearly synchronous with nearby high-grade metamorphism and migmatization. The three phases of plutonism in the Eastern Blue Ridge Province correspond with established metamorphic ages for each of the three major orogenic pulses along the western flank of the southern Appalachians. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.