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Arthur Merschat

Arthur Merschat is a Research Geologist at the USGS Florence Bascom Geoscience Center.

"I have worked for the USGS from 2006 until present, a period that includes a SCEP appointment during my Ph.D., and as a Research Geologist (2009–present).  My research is focused on (1) the structure and tectonics of the Appalachian orogen; (2) the provenance of the different crystalline terranes of the Blue Ridge and Piedmont; and (3) the thermochronologic evolution of the orogen.  I have integrated geologic mapping, structural analysis, SHRIMP U-Pb geochronology, petrology, and geochemistry into my research.  Currently, I am involved with bedrock geologic mapping projects in the Blue Ridge — Mount Rogers area, VA–NC–TN, and Roan Mountain, NC–TN — and in New England — southwest NH and parts of VT."
 

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Image of the Blue Ridge taken from the top of Stone Mountain

Piedmont and Blue Ridge Project

The Piedmont and Blue Ridge Project is a geologic mapping project supported by the USGS National Cooperative Geologic Mapping Program. The Piedmont Blue Ridge Project aims to understand the geologic framework and tectonic evolution of terranes and basins in the Appalachian Piedmont and Blue Ridge, and their significance for water, mineral and energy resources, natural hazards, and engineering...
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Florence Bascom Geoscience Center
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Piedmont and Blue Ridge Project

The Piedmont and Blue Ridge Project is a geologic mapping project supported by the USGS National Cooperative Geologic Mapping Program. The Piedmont Blue Ridge Project aims to understand the geologic framework and tectonic evolution of terranes and basins in the Appalachian Piedmont and Blue Ridge, and their significance for water, mineral and energy resources, natural hazards, and engineering...
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Xenoliths of metagraywacke/biotite gneiss in the Toluca Granite contain an early foliation. A hammer lies on top for reference.

Blue Ridge and Inner Piedmont Geologic Mapping

The Blue Ridge and Inner Piedmont Geologic Mapping Task (BRIP) is the western focus of geologic mapping and framework studies of the Piedmont and Blue Ridge Project. BRIP will conduct modern geologic mapping and geologic framework studies in the Wytheville, Hickory and Boone 30x60-min. sheets. Collectively, the objectives of BRIP are to (1) characterize the geologic framework of the Blue Ridge and...
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Florence Bascom Geoscience Center
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Blue Ridge and Inner Piedmont Geologic Mapping

The Blue Ridge and Inner Piedmont Geologic Mapping Task (BRIP) is the western focus of geologic mapping and framework studies of the Piedmont and Blue Ridge Project. BRIP will conduct modern geologic mapping and geologic framework studies in the Wytheville, Hickory and Boone 30x60-min. sheets. Collectively, the objectives of BRIP are to (1) characterize the geologic framework of the Blue Ridge and...
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Photoluminescence Imaging of Whole Zircon Grains on a Petrographic Microscope - An Underused Aide for Geochronologic Studies

The refractory nature of zircon to temperature and pressure allows even a single zircon grain to preserve a rich history of magmatic, metamorphic, and hydrothermal processes. Isotopic dating of micro-domains exposed in cross-sections of zircon grains allows us to interrogate this history. Unfortunately, our ability to select the zircon grains in a heavy mineral concentrate that records the most ge
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Florence Bascom Geoscience Center

GIS and Data Tables for Focus Areas for Potential Domestic Nonfuel Sources of Rare Earth Elements

In response to Executive Order 13817 of December 20, 2017, the U.S. Geological Survey (USGS) coordinated with the Bureau of Land Management (BLM) to identify 35 nonfuel minerals or mineral materials considered critical to the economic and national security of the United States (U.S.). Acquiring information on possible domestic sources of these critical minerals is the basis of the USGS Earth Mappi
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Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Bedrock geologic map of the Springfield 7.5- x 15-minute quadrangle, Windsor County, Vermont, and Sullivan County, New Hampshire

The bedrock geology of the 7.5- by 15-minute Springfield quadrangle consists of highly deformed and metamorphosed Mesoproterozoic through Devonian metasedimentary and meta-igneous rocks. In the west, Mesoproterozoic gneisses of the Mount Holly Complex are the oldest rocks and form the eastern side of the Chester dome. The Moretown slice structurally overlies the Chester dome along the Keyes Mounta
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Florence Bascom Geoscience Center

Bedrock geologic map of the Worcester South quadrangle, Worcester County, Massachusetts

The bedrock geology of the 7.5-minute Worcester South quadrangle, Massachusetts, consists of deformed Neoproterozoic to Paleozoic crystalline metamorphic and intrusive igneous rocks in three fault-bounded terranes (zones), including the Avalon, Nashoba, and Merrimack zones (Zen and others, 1983). This quadrangle spans the easternmost occurrence of Ganderian margin arc-related rocks (Nashoba zone)
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Florence Bascom Geoscience Center

Geologic map of the Great Smoky Mountains National Park region, Tennessee and North Carolina

The geology of the Great Smoky Mountains National Park region of Tennessee and North Carolina was studied from 1993 to 2003 as part of a cooperative investigation by the U.S. Geological Survey with the National Park Service (NPS). This work resulted in a 1:100,000-scale geologic map derived from mapping that was conducted at scales of 1:24,000 and 1:62,500. The geologic data are intended to suppor

Temporal and spatial distribution of Paleozoic metamorphism in the southern Appalachian Blue Ridge and Inner Piedmont delimited by ion microprobe U-Pb ages of metamorphic zircon

Ion microprobe U-Pb zircon rim ages from 39 samples from across the accreted terranes of the central Blue Ridge, eastward across the Inner Piedmont, delimit the timing and spatial extent of superposed metamorphism in the southern Appalachian orogen. Metamorphic zircon rims are 10–40 µm wide, mostly unzoned, and dark gray to black or bright white in cathodoluminescence, and truncate and/or embay in
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Florence Bascom Geoscience Center

Linkages and feedbacks in orogenic systems: An introduction

Orogenic processes operate at scales ranging from the lithosphere to grain-scale, and are inexorably linked. For example, in many orogens, fault and shear zone architecture controls distribution of heat advection along faults and also acts as the primary mechanism for redistribution of heat-producing material. This sets up the thermal structure of the orogen, which in turn controls lithospheric rh
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Florence Bascom Geoscience Center

Confirmation of the southwest continuation of the Cat Square terrane, southern Appalachian Inner Piedmont, with implications for middle Paleozoic collisional orogenesis

Detailed geologic mapping, U-Pb zircon geochronology and whole-rock geochemical analyses were conducted to test the hypothesis that the southwestern extent of the Cat Square terrane continues from the northern Inner Piedmont (western Carolinas) into central Georgia. Geologic mapping revealed the Jackson Lake fault, a ∼15 m-thick, steeply dipping sillimanite-grade fault zone that truncates litholog
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Florence Bascom Geoscience Center

Geology along the Blue Ridge Parkway in Virginia

Detailed geologic mapping and new SHRIMP (sensitive high-resolution ion microprobe) U-Pb zircon, Ar/Ar, Lu-Hf, 14C, luminescence (optically stimulated), thermochronology (fission-track), and palynology reveal the complex Mesoproterozoic to Quaternary geology along the ~350 km length of the Blue Ridge Parkway in Virginia. Traversing the boundary of the central and southern Appalachians, rocks along
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Florence Bascom Geoscience Center

Metaultramafic schists and dismembered ophiolites of the Ashe Metamorphic Suite of northwestern North Carolina, USA

Metaultramafic rocks (MUR) in the Ashe Metamorphic Suite (AMS) of northwestern North Carolina include quartz ± feldspar-bearing QF-amphibolites and quartz-deficient, locally talc-, chlorite-, and/or Mg-amphibole-bearing TC-amphibolites. Some workers divide TC-amphibolites into Todd and Edmonds types, based on mineral and geochemical differences, and we provisionally add a third type – olivine ± py
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Florence Bascom Geoscience Center

Geology of the Mount Rogers area, revisited: Evidence of Neoproterozoic continental rifting, glaciation, and the opening and closing of the Iapetus ocean, Blue Ridge, VA–NC–TN

Recent field and geochronological studies in eight 7.5-minute quadrangles near Mount Rogers in Virginia, North Carolina and Tennessee recognize important stratigraphic and structural relationships for the Neoproterozoic Mount Rogers and Konnarock formations, the northeast end of the Mountain City window, the separation of Mesoproterozoic rocks of the Blue Ridge into three age groups, and timing an
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Florence Bascom Geoscience Center

Stratigraphy, structure and regional correlation of eastern Blue Ridge sequences in southern Virginia and northwestern North Carolina: an interim report from new USGS mapping

Examination of key outcrops in the eastern Blue Ridge in southern Virginia and northwestern North Carolina is used to evaluate existing stratigraphic and structural models. Recent detailed mapping along the Blue Ridge Parkway and the eastern flank of the Mount Rogers massif provides the opportunity to (1) evaluate legacy data and interpretations and (2) formulate new ideas for regional correlation
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Florence Bascom Geoscience Center

Implications for late Grenvillian (Rigolet phase) construction of Rodinia using new U-Pb data from the Mars Hill terrane, Tennessee and North Carolina, United States

New data for zircon (external morphology, cathodoluminescence zoning, and sensitive high resolution ion microprobe [SHRIMP] U-Pb ages) from the Carvers Gap granulite gneiss of the Mars Hill terrane (Tennessee and North Carolina, United States) require reevaluation of interpretations of the age and origin of this rock. The new results indicate that the zircon is detrital and that the sedimentary pr
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Geology, Geophysics, and Geochemistry Science Center

The Neoacadian orogenic core of the souther Appalachians: A geo-traverse through the migmatitic inner Piedmont from the Brushy Mountains to Lincolnton, North Carolina

The Inner Piedmont extends from North Carolina to Alabama and comprises the Neoacadian (360–345 Ma) orogenic core of the southern Appalachian orogen. Bordered to west by the Blue Ridge and the exotic Carolina superterrane to the east, the Inner Piedmont is cored by an extensive region of migmatitic, sillimanite-grade rocks. It is a composite of the peri-Laurentian Tugaloo terrane and mixed Laurent
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Florence Bascom Geoscience Center

Linking the Central and Southern Appalachian Blue Ridge: What We Know and Don’t Know about Stratigraphy, Structure, Tectonism, and Regional Correlation in the Eastern Blue Ridge of Virginia

The transition from Neoproterozoic Lynchburg Group rocks on the eastern limb of the para-autochthonous Blue Ridge anticlinorium in central Virginia to the fault-bounded Ashe Formation and Alligator Back Formation in southern Virginia has been a source of intense debate and speculation for decades. There are fundamental differences in the tectonogenetic interpretation for these rock packages, desp
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Florence Bascom Geoscience Center

Photoluminescence imaging of whole zircon grains on a petrographic microscope—An underused aide for geochronologic studies

The refractory nature of zircon to temperature and pressure allows even a single zircon grain to preserve a rich history of magmatic, metamorphic, and hydrothermal processes. Isotopic dating of micro-domains exposed in cross-sections of zircon grains allows us to interrogate this history. Unfortunately, our ability to select the zircon grains in a heavy mineral concentrate that records the most ge
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Energy Resources Program, Volcano Hazards, Volcano Science Center, Florence Bascom Geoscience Center

Geochronology of the Oliverian Plutonic Suite and the Ammonoosuc Volcanics in the Bronson Hill arc: Western New Hampshire, USA

U-Pb zircon geochronology by sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) on 11 plutonic rocks and two volcanic rocks from the Bronson Hill arc in western New Hampshire yielded Early to Late Ordovician ages ranging from 475 to 445 Ma. Ages from Oliverian Plutonic Suite rocks that intrude a largely mafic lower section of the Ammonoosuc Volcanics ranged from 474.8 ± 5.2 to 4
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Florence Bascom Geoscience Center

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