Northern ancestry for the Goochland terrane as a displaced fragment of Laurentia

Research Article| August 01, 1962 Isotopic Age Study of the Metamorphic History of the Manhattan and Reading Prongs LEON E LONG; LEON E LONG Lamont Geological Observatory (Columbia University), Palisades, New York 1 Present address: Department of Geology, University Museum, Oxford University, Oxford, England. Search for other works by this author on: GSW Google Scholar J. LAURENCE KULP J. LAURENCE KULP Lamont Geological Observatory (Columbia University), Palisades, New York Search for other works by this author on: GSW Google Scholar GSA Bulletin (1962) 73 (8): 969–996. https://doi.org/10.1130/0016-7606(1962)73[969:IASOTM]2.0.CO;2 Article history received: 24 Sep 1959 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 LEON E LONG, J. LAURENCE KULP; Isotopic Age Study of the Metamorphic History of the Manhattan and Reading Prongs. GSA Bulletin 1962;; 73 (8): 969–996. doi: https://doi.org/10.1130/0016-7606(1962)73[969:IASOTM]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 Potassium-argon and rubidium-strontium age measurements have been made on mica separated from many rock types of the Manhattan Prong and New Jersey-New York Highlands (Reading Prong). Most of the rocks from the Manhattan Prong were dated within experimental error at 360 m.y. (million years). Since this age is identical with those obtained by the U-Pb method by other workers on intrusive pegmatites, it probably represents the last major metamorphic event in the area. The isotopic age of mica in the Highlands at least 10 miles from the zone where complete re-crystallization took place 360 m.y. ago is about 840 m.y. Apparent ages of mica in a transition zone range between these two. The ages in the transition zone are determined by the extent of re-crystallization which in turn is strongly dependent on the local structure. If the 1150-m.y. zircon age obtained by Tilton and others (1960) in the Highlands is the primary age of the basement in this region, major metamorphic events took place at 1150, 840, and 360 m.y. Relict ages as old as 480 m.y. in the Manhattan Prong suggest a fourth event if the rocks of the Prong were deposited in the Cambrian or later. This study illustrates both the difficulties and the effectiveness of isotopic geochronometry in areas of complex metamorphic history. 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.

A detrital zircon (DZ) provenance study of the Cretaceous Potomac Group (Kp) was used to determine the paleogeographic setting of structurally juxtaposed terranes and intrusive units that occur to the west of and beneath the Coastal Plain as well as the source of clasts of volcanic rocks that occur in the unit. The Kp is an immature siliciclastic unit that forms the base of the Coastal Plain and crops out along the Fall Line of VA and MD. In central VA, The Kp overlies ~300 Ma Petersburg Granite (PG). To the W-NW are sedimentary and intrusive rocks of the Triassic Richmond-Taylorsville basin that are separated by the Hylas fault zone from Mesoproterozoic to Devonian medium to high-grade rocks of the Goochland terrane (GT). To the W-SW are low-grade metasedimentary and metaigneous rocks of the Roanoke Rapids terrane (RRT). West of the RRT and the Gaston Dam-Hollister faults are low to medium grade gneisses and schists of the Raleigh, Spring Hope and Triplet terranes. The Vulcan Materials Puddledock Quarry near Hopewell, VA exposes the Kp beneath the Paleocene Aquia Formation. Kp in the quarry consists mostly of feldspathic sand and gravel. Pebble to boulder-size clasts within the gravel include relatively undeformed volcanic rocks, along with more common vein quartz and quartzite. DZ analyses of Kp matrix sand indicate, in descending abundance, populations at ~1065 Ma, 328 Ma, 455-409 Ma, and 574-540 Ma. Meso- and Neoproterozoic DZ ages compare well to published ages from the GT and RRT, respectively, but outcrops of undeformed volcanic rocks are sparse in the RRT and absent in the GT. Grenvillian DZ may have been sourced from the Blue Ridge, or recycled from other Piedmont terranes. Carboniferous DZs are ~30 My older than published ages for late Paleozoic plutons that crop out in the eastern Piedmont. Mid-Paleozoic plutons are only known from the western Piedmont in VA, but include the Concord-Salisbury plutonic suite and potentially rocks of the central Piedmont shear zone in NC. Exposures of undeformed volcanic rocks similar to those in the quarry are unknown from any of these terranes in VA. DZ analyses suggest that either (1) the provenance of the Kp, including volcanic clasts, is more distant than expected based on immaturity of the sediment; or (2) the DZs and clasts may represent sources that were completely eroded during the Cretaceous.

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.

Research Article| August 01, 2003 Geochronology of the Mesoproterozoic State Farm gneiss and associated Neoproterozoic granitoids, Goochland terrane, Virginia Brent E. Owens; Brent E. Owens 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Search for other works by this author on: GSW Google Scholar Robert D. Tucker Robert D. Tucker 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Brent E. Owens 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Robert D. Tucker 1Department of Geology, College of William and Mary, Williamsburg, Virginia 23187, USA Publisher: Geological Society of America Received: 14 Sep 2002 Revision Received: 15 Jan 2003 Accepted: 07 Feb 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2003) 115 (8): 972–982. https://doi.org/10.1130/B25258.1 Article history Received: 14 Sep 2002 Revision Received: 15 Jan 2003 Accepted: 07 Feb 2003 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 Brent E. Owens, Robert D. Tucker; Geochronology of the Mesoproterozoic State Farm gneiss and associated Neoproterozoic granitoids, Goochland terrane, Virginia. GSA Bulletin 2003;; 115 (8): 972–982. doi: https://doi.org/10.1130/B25258.1 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 Goochland terrane is an isolated block of Mesoproterozoic crust in the Piedmont Province of central Virginia. We report U-Pb zircon dates and whole-rock major and trace element data for the State Farm gneiss, one of the main units in the terrane, and additional results for a newly recognized suite of Neoproterozoic granitoids that intrude the gneiss. The State Farm gneiss ranges in bulk composition from quartz monzodiorite to granite, and three samples yield U-Pb zircon dates of 1046 +7/–6 Ma, 1039 +18/–11 Ma, and 1023 ± 10 Ma. We interpret these dates as igneous crystallization ages, which indicate a maximum emplacement interval of ca. 1057–1013 Ma for these samples. Neoproterozoic granitoids (including the Fine Creek Mills and Flat Rock granites) are more alkaline than the State Farm gneiss and display all compositional characteristics of A-type granites (e.g., high Fe/Mg, Ga, Ga/Al, Nb, Zn, Y, Zr). U-Pb zircon analyses from five separate bodies indicate crystallization ages from ca. 654 to 588 Ma, but all results are complicated by Mesoproterozoic (ca. 1 Ga) inheritance, coupled, in some cases, with secondary Pb loss. We interpret the ages and compositions of the younger rocks to reflect Neoproterozoic rifting of the Goochland terrane, but its location during rifting is uncertain. The terrane may have been separated from Laurentia during the Neoproterozoic breakup of Rodinia and later reattached. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

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.

The area of wetlands in the U.S. is being estimated as part of the National Wetlands Inventory (NWI). Minimal information is available to verify the effectiveness of NWI maps to inventory wetlands or delineate jurisdictional wetlands. We evaluated the use of NWI maps (1∶24,000 scale) to inventory and delineate jurisdictional wetlands in the Virginia Blue Ridge. Each wetland identified in the Woolwine and Meadows of Dan NWI maps was field-checked to determine if the areas met the criteria as a jurisdictional wetland. Of the 171 palustrine wetlands identified, 91% met the criteria. Jurisdictional wetlands were delineated in four 2.5-minute study areas. Two study areas, located in the Blue Ridge Highlands region, contain 91.8 and 109.3 hectares of jurisdictional wetlands. The NWI maps indicated 2.5 and 17.4 hectares of wetlands in these two study areas. A similar but smaller discrepancy occurred in the areas mapped in the Blue Ridge Escarpment region. We concluded, because of the small scale that photo interpreters must work with and the number of wetlands located in dense woodlands, that NWI maps may not adequately inventory wetlands in the Blue Ridge. This conclusion was based on a detailed study of 22% (6888 ha) of the area covered on the NWI maps. Predominant plant species in the forested, scrub-shrub, and emergent wetlands were red maple (Acer rubrum), speckled alder (Alnus rugosa), and yellow nutsedge (Cyperus esculentus), respectively, Wetland soils were classified as Typic Humaquents and Humaqueptic Fluvaquents.

In the 1930s, Shenandoah National Park was established in the Virginia Blue Ridge through the displacement of nearly 500 white families. In recent decades, my scholarship and that of others focused upon the manner in which hackneyed stereotypes about backward mountaineers were mobilized to garner public support for the condemnation of family farms and, in some cases, the institutionalization, sterilization, and incarceration of some of the most impoverished. But, in focusing solely upon the 20th century and the impacts on the white displaced, this research has perpetrated structural violence by obscuring the role of race and racism in the wider Blue Ridge. Archaeological and documentary evidence from the 1990s National Park Service–funded “Survey of Rural Mountain Settlement” is reexamined and reconsidered to begin the process of redressing the silencing of African American histories in the Blue Ridge and surrounding valley and piedmont regions.

Breece came from and his letters to his mother that fill the second half of the book are full of homesickness as well as the estrangement he felt at the changes that had taken place there. Douglass hints at placing Pancake's work in the context of other Appalachian writers, but could have done more with this. We know he read and lent out his copy of Chuck Kinder's Snakehunter, and we know he was friends with Mary Lee Settle and presumably knew her work-but we get no sense oftheir influence (if any) or that of Davis Grubb or of the book of Tom Kromer's stories he was editing. Pancake in turn has influenced such younger writers as Chris Offutt, Chris Holbrook, and Pinckney Benedict. At times Douglass is off-base (as are many others) who use the word "Appalachian" loosely and list such writers as Bobbie Ann Mason and Marsha Norman under this rubric. The second half ofthe book is a collection of Pancake's unpublished writing, mostly the letters to his mother-which add to our knowledge of the author. The letters are a bit of a chore to wade through, but ifone is interested in Pancake they have their rewards. And occasionally, like the unsent letter to his girlfriend Emily Miller or the late letter to his friend and teacher John Casey, they are loaded with intimations ofthings his suicide sheds light on in a new way. There are also the beginnings of a few stories and two sketches for a novel. A few newspaper portraits he had published are mentioned, but not included (one wonders if they might not have been more interesting than so many letters to his mother which have a tedious sameness to them). Pancake's suicide was not from lack of publication, for his work had been published in the Atlantic and editors in New York were soliciting stories as well as a novel. Ironically, two artists' colonies sent him letters unknowingly offering fellowships within days ofhis death. His small output has also been published in England and has been translated into German and Portuguese. Unfortunately, A Room Forever has its quota of typos. For example on page 112 there are two separate quotes from "Trilobites," each with its own annoying, easily found typos. But anyone interested in Pancake's work, which would mean anyone interested in contemporary Appalachian fiction, needs to read this book-both for what light it sheds on Pancake's work and for the peripheral issues his life and work have provoked. -Jonathan Greene Branch, Michael P., and Daniel J. Philippon. The Height ofOur Mountains : Nature Writing from Virginia's Blue Ridge Mountains and Shenandoah Valley. Baltimore: Johns Hopkins Press, 1998. 448 pages. Hardcover $39.95. Paperback $18.95. 68 The attention given to nature writing in the past two decades has intensified dramatically, so much so that it now forms an increasingly distinct discipline ofliterary study. What once was the topic ofan occasional "special offerings" course is now the center of graduate concentrations and even programs. With this progression comes the creation of such works as Michael P. Branch and Daniel J. Philippon's The Height of Our Mountains. This anthology focuses on Virginia's Blue Ridge and Shenandoah Valley, drawing selections from seventy writers ranging from the colonial period to the present. That the work seeks an academic audience is immediately evident. Following a foreword by distinguished environmentalist John Elder, the editors present an extensive scholarly introduction putting forth a clear ideological statement of their approach to nature writing as a discipline. It succinctly sketches the academic considerations that customarily define the field and, in distinction, arranges the broadened boundaries for the editors' own choices. Most notably, they extend beyond that form most closely associated with nature writing, the personal essay, to include not only the more intuitive additions such as journals, discovery narratives, and travel writing, but even fictional works grounded in the region. In fact, the only exclusion based on genre is that all the works included are prose-and that with the admission that "regional nature poetry . . . could easily fill another volume." Given the fine geographical focus ofthe book, to...

Precambrian massifs and terranes of the eastern U.S.A. are in the present day separated by three major tectonic boundaries. The westernmost external massifs lie along the east side of the “Paleozoic Basement Tectonic Front” and originated inboard of the late Proterozoic (post-Grenvillian) margin of the Ancestral North American Craton (ANAC). The second major boundary (equivalent to the late Proterozoic ANAC) is presently approximated by the Hayesville-Gossan Lead Fault, Martic Line, Huntingdon Valley Fault, and Brompton Line. Restoration of the “Paleozoic Basement Tectonic Front” eastward to coincide with the prominent gravity gradient (which marks the Paleozoic margin of the ANAC) allows examination of the ANAC during the late and middle Proterozoic. During the late Proterozoic, the Adirondacks, most of the northern Appalachian massifs and the Blue Ridge massifs were all inboard of the ANAC. Only the Goochland terrane and Chain Lakes massif clearly originated outboard of the late Proterozoic ANAC margin. Along that margin are other terranes, massifs and “domes”, some of which (e.g. Baltimore “domes”) have affinities to the inboard group, and some of which (e.g. Mars Hill) have only questionable affinities to the ANAC.During the middle Proterozoic, inboard massifs of the southern Appalachian Blue Ridge appear to be part of a Grenvillian volcanic belt that formed the ANAC margin northeastward of the parautochthonous Pine Mountain window. During Paleozoic orogenesis, westward transposition of the volcanic belt occurred. The Mars Hill terrane along the late Proterozoic ANAC tectonic boundary lies structurally above, and adjacent to, Blue Ridge massifs in northwestern North Carolina and may have been accreted to the ANAC during the Grenville event, then thrust to its present position during Paleozoic deformation. The Goochland terrane shows greater affinity with the northern Appalachians than with nearby Blue Ridge massifs, and probably experienced considerable dextral translation. The Avondale-West Chester Prong and Baltimore “domes” may also have experienced some post-Grenvillian dextral translation.

A regional seismic reflection line (I‐64) across the Virginia Piedmont has provided a stacked section suitable for an integrated interpretation of geophysical data in the region. A highly reflective upper crust, an allochthonous Blue Ridge Province, underlying thrust sheets including the Blue Ridge master decollement, and a basal decollement at a depth of about 9 km (3 s) are confirmed on the seismic data. Immediately east of the Blue Ridge Province, Appalachian structures plunge to as much as 12 km (4 s) depth. The Evington Group, Hardware terrane, and Chopawamsic metavolcanic rocks (Carolina terrane) crop out in the Piedmont Province, and numerous eastward dipping reflections originate from these rocks in the subsurface. These eastward dipping reflectors overlie a gently west dipping (10°–15°), highly reflective zone that varies in depth from 1.5 s (4.5 km) beneath the Goochland terrane to 4 s (12 km) beneath the rocks of the Evington Group. Some of the overlying eastward dipping reflections apparently root in this zone. The zone may include decollement surfaces along which the overlying rocks were transported. Relatively few reflections originate from within autochthonous Grenville basement at the western end of the profile. The Goochland granulite terrane is interpreted to be a westward thrust nappe structure that has overridden a portion of the Chopawamsic metavolcanic rocks. A broad zone of east dipping (20°–45°) reflections bounds the Goochland terrane on the east. These reflections may originate from deformation zones and continue to Moho depths. They appear to be correlative with similar events seen on other Appalachian lines. The pervasiveness of the zone of east dipping events on other seismic reflection lines and the continuity of the adjacent Piedmont gravity high suggest continuity of crustal features along the length of the Appalachians. A major conclusion of this study is that crustal thinning is responsible for the main components of the gravity field in Virginia, that is, the Appalachian gravity gradient and the Piedmont gravity high. The crust thins from about 52 km beneath the Appalachian mountains to about 35 km beneath Richmond, Virginia, and then rethickens by up to 10 km beneath the zone of east dipping reflections (mylonites?) east of Richmond. The I‐64 seismic data also contain a sequence of reflections at about 9–12 s, indicative of lower crustal layering; the base of this zone of reflections coincides almost exactly with the Mohorovicic discontinuity interpreted from earlier refraction work. The layering extends about 70 km west from Richmond, Virginia, and is interpreted as a lower crustal transition zone that is believed to persist across most of Virginia.

Pennsylvania has a diverse geology. A small portion of the northeastern corner of the state is covered by Atlantic Coastal Plains sediments. To the northwest metamorphic rocks in the Piedment, Blue Ridge and Reading Prong areas are exposed. Triassic basine cut across portions of the Piedmont. The western portion of the state is underlain by Paleozoic sediments of the folded Appalachians and the Appalachian or Allegheny Basin. Crystalline rocks are limited to the metamorphic and igneous rocks of the Piedmont, Blue Ridge, and Reading Prong and to Triassic diabase intrusives. Potential for geothermal resources in Pennsylvania appear to be limited to small hydrothermal systems associated with deep convection in the folded Appalachians or deep sources in the Appalachian Basin. Heat flow measurements and temperature gradients from oil and gas wells suggest normal continental heat flow in Pennsylvania. Under such conditions temperatures of about 200{sup 0}C (392{sup 0}F) are possible near the base of the sedimentary section (about 9 km, 30,000 feet). Warm springs are not as common in Pennsylvania as they are to the south in West Virginia and Virginia. Apparently the structure does not facilitate convective circulation. Geothermal resources in Pennsylvania appear to be restricted to those available inmore » an area of normal temperature gradients.« less

The Mesoproterozoic southeastern margin of Laurentia, which consisted primarily of the ca. 1.5–1.35 Ga Granite-Rhyolite Province, was extensively reworked during ca. 1.3–0.9 Ga phases of the Grenville orogenic cycle. Questions remain for much of southeastern Laurentia regarding the transition from the Granite-Rhyolite Province to Grenville orogenic cycle, and for potential collisional interaction with Amazonia, due to Paleozoic sedimentary cover or tectonic reworking. Basement rocks sampled by drill core in the east-central United States include 1.5–1.35 Ga magmatic rocks, some overprinted by late Geon 10 (Ottawan) orogenesis, which are the most outboard evidence of Granite-Rhyolite Province crust. Newly recognized 1.35–1.30 Ga (pre-Elzevirian) granitic orthogneisses within the Mars Hill terrane of southeastern Laurentia (1) expand the along-strike distribution of the earliest crustal age components of the Grenville orogenic cycle in Appalachian basement inliers; (2) contain Geon 19–16 inherited zircons; and (3) were metamorphosed during late Ottawan to Rigolet tectonism. Paragneisses enveloping the Geon 13 orthogneisses are dominated by Geon 19–16 and Geon 13–12 detrital zircons overgrown by Geon 10–9 metamorphic zircon. The zircon age systematics require the paragneiss protoliths to be younger than orthogneiss protoliths and be partly sourced from the latter. Orthogneisses and paragneisses have Pb isotope compositions that overlap those of south-central Appalachian and southwest Amazonia basement, both of which are distinct from Laurentian Pb isotope compositions. The boundary between Amazonian (southern Appalachian) and Laurentian (northern Appalachian) Pb isotope compositions is thus a terrane boundary, with Geon 13 magmatic rocks being the youngest common crustal component. In comparison, the Paraguá block of the southwestern margin of Amazonia consists of a Geon 19–16 basement complex intruded by the batholithic-scale Geon 13 San Ignacio granite suite. The latter also contains inherited Geon 19–16 zircon and has Pb isotope compositions that help define the Amazonian trend. The correspondence of magmatic, inherited, and detrital ages and similarity in Pb isotope compositions are consistent with an origin for the exotic/orphaned Mars Hill terrane as an outboard sliver of the Paraguá block that developed before Grenvillian orogenesis (Geons 12–9). Manifestations of the latter are concentrated around the margins of the Paraguá block in the Sunsás (southwest), Nova Brasilândia (north), and Aguapeí belts (east). The Sunsás belt is a mostly low-grade metasedimentary belt with only minor Geon 10–9 magmatism and no Geon 12 or 11 magmatism, thus distinguishing it from the Mars Hill terrane. The Arequipa-Antofalla terrane, exposed in Andes basement inliers, lies outboard of the Sunsás belt and has Pb isotope and geochronologic characteristics that permit a correlation with the Mars Hill terrane and a paleogeographic position between the Mars Hill terrane and the Sunsás belt. The histories of the Mars Hill terrane, Arequipa-Antofalla terrane, and Paraguá block merge during Geons 10–9 and final collisional orogenesis between southeast Laurentia and southwestern Amazonia.

A Place in the South Michael Branch and Daniel Philippon One ofthe things that we are told is a key attribute of southern literature is the devotion to place.... We constantiy hear this advanced as an essential characteristic of southern writing. And I agree. But what exactly does it mean? What has it meant to various southern writers? Has anyone ever really tried to see what place is made to signify in southern writing? -Louis D. Rubin Southern Literature and Southern Society: Notes on a Clouded Relationship. Place, it must be said, is inherently particular, there is no such thing as a general place. The same must also be said about nature writing: it, too, is particular; it must necessarily "take place." In Virginia's Blue Ridge Mountains and Shenandoah Valley, American nature writing has been taking place for nearly four centuries, ever since the first setders in Jamestown recorded their thoughts about the unknown landscapes to the west. But what exactly has the idea of "place" meant to the hundreds ofwriters who followed these initial attempts to understand this place? What does "place" signify in their texts? In keeping with the notion ofparticularity, we have tried to answer this question by offering a few selected examples of how the idea of"place" has been used by some ofthe many nature writers who have taken this place in the South as their subject. What follows, therefore , is not a traditional literary history, but rather a series of illustrative moments, moments we feel may help illuminate some of the things theoften contradictory idea of "place" has meant for these writers. Michael P. Branch and DanielJ. Philippon are the editors of'The Height of Our Mountains: Nature Writing from Virginia's Blue Ridge Mountains and Shenandoah Valley, to bepublished byJohnsHopkins UniversityPress in the spring of1998. Branch is associate professor ofenvironmental literature at the University ofNevada, Reno, and Philippon is completing his Ph.D. in English at the University of Virginia. 18 What, then, is "place," or, more properly, what are "places"? First and foremost, places are both distinctive and continuous. On the one hand, we can define the Blue Ridge Mountains and Shenandoah Valley ofVirginia in contrast to the places that surround it: it is not the tidewater or the piedmont; it is not in Maryland, North Carolina, or West Virginia; it is not that portion of northern Virginia that surrounds Washington, D.C, nor that portion ofsouthwestern Virginia that borders Kentucky and Tennessee. On the other hand, it is clearly continuous with all of these regions, sharing aspects of their natural and cultural histories, separable only in name, but never in fact. The simultaneous existence of distinctive and continuous elements in this particular place may best be revealed by the separation ofthis region from West Virginia, an event that quite literally "took place" in 1861 during the Civil War, forever changing people's perceptions of what had previously seemed a united landscape. The confusion and uncertainty created by this division is a central theme in the work of such wartime writers as Cornelia Peake McDonald, Lucy Rebecca Buck, Walt Whitman, and George Stevens, who watched the land to die north and west of die Blue Ridge region become "free soil" while the Shenandoah Valley was transformed into the "breadbasket ofthe Confederacy." This place also contains many smaller units of place-such as local watersheds; counties, cities, and towns; and parks and wildlife preservesand participates in many larger units of place that contain it or overlap with it-such as the South, Appalachia, the Middle Atlantic region, the United States, and the North American continent. Thus while the cities ofWinchester and Roanoke are both part ofthe continuous landscape of the Valley ofVirginia, the residents of Roanoke to die southwest may be more likely to consider themselves part ofAppalachia than may the residents of Winchester, which lies further northeast. Such differences of placeconsciousness are perhaps most present in narratives written by the many travelers and itinerant naturalists who journeyed through this region in the eighteenth century, but they also are the subject for such modern travelers as Jonathan Yardley, who chronicled his journey from Washington , D.C, to Chatham, Virginia, in States of...

Two aeromagnetic anomalies of regional extent outline two previously unknown buried masses of highly magnetic, probably Precambrian, rocks in southeastern New York and adjacent Vermont, Massachusetts, and Connecticut. The northern mass extends northeastward from Albany, New York, to Bennington, Vermont, where it appears to be buried beneath weakly magnetic Precambrian rocks of the Green Mountains. The southern mass extends north-northeastward from Beacon, New York, through Stissing Mountain, to Copake, New York, and appears to be the buried northeast extension of the Reading Prong. The shape of the Beacon-Copake magnetic anomaly indicates that the source is near the surface and has a sharp boundary, probably a fault, on its northwestern side; the shape also indicates that the source becomes deeply buried to the southeast and thus supports a parautochthonous interpretation for the northern part of the Reading Prong. In southwestern Massachusetts, the highly magnetic Beacon-Copake mass appears to be overstepped on the east by a buried slice of weakly magnetic Precambrian rocks which, in turn, is overstepped on the east by imbricate slices of weakly magnetic Precambrian rocks exposed along the western front of the Berkshire Highlands. Precambrian rocks exposed in the Green Mountains, the Berkshire and Housatonic Highlands, the eastern part of the Hudson Highlands, and the Manhattan Prong have a remarkably lower amplitude magnetic pattern than those in the Adirondack Mountains and the Reading Prong. This difference in magnetic character appears to represent more than different thicknesses of Precambrian rocks and may reflect a different sequence of Precambrian rocks to the east, a lower grade of Precambrian metamorphism to the east, or possibly a reduction in magnetite content in the eastern Precambrian rocks because of Paleozoic metamorphism.

Anthropogenic emissions have dominated marine Pb sources during the past century. Here we present Pb concentrations and isotope compositions for ocean depth profiles collected in the eastern Tropical Atlantic Ocean (GEOTRACES section GA06), to trace the transfer of anthropogenic Pb into the ocean interior. Variations in Pb concentration and isotope composition were associated with changes in hydrography. Water masses ventilated in the southern hemisphere generally featured lower 206Pb/207Pb and 208Pb/207Pb ratios than those ventilated in the northern hemisphere, in accordance with Pb isotope data of historic anthropogenic Pb emissions. The distributions of Pb concentrations and isotope compositions in northern sourced waters were consistent with differences in their ventilation timescales. For example, a Pb concentration maximum at intermediate depth (600–900 m, 35 pmol kg−1) in waters sourced from the Irminger/Labrador Seas, is associated with Pb isotope compositions (206Pb/207Pb = 1.1818–1.1824, 208Pb/207Pb = 2.4472–2.4483) indicative of northern hemispheric emissions during the 1950s and 1960s close to peak leaded petrol usage, and a transit time of ∼50–60 years. In contrast, North Atlantic Deep Water (2000–4000 m water depth) featured lower Pb concentrations and isotope compositions (206Pb/207Pb = 1.1762–1.184, 208Pb/207Pb = 2.4482–2.4545) indicative of northern hemispheric emissions during the 1910s and 1930s and a transit time of ∼80–100 years. This supports the notion that transient anthropogenic Pb inputs are predominantly transferred into the ocean interior by water mass transport. However, the interpretation of Pb concentration and isotope composition distributions in terms of ventilation timescales and pathways is complicated by (1) the chemical reactivity of Pb in the ocean, and (2) mixing of waters ventilated during different time periods. The complex effects of water mass mixing on Pb distributions is particularly apparent in seawater in the Tropical Atlantic Ocean which is ventilated from the southern hemisphere. In particular, South Atlantic Central Water and Antarctic Intermediate Water were dominated by anthropogenic Pb emitted during the last 50–100 years, despite estimates of much older average ventilation ages in this region.