Title page for ETD etd-10302008-120444


Type of Document Master's Thesis
Author Keller, Mary Ruth
URN etd-10302008-120444
Title Geologic framework of gravity anomaly sources in the central Piedmont of Virginia
Degree Master of Science
Department Geophysics
Advisory Committee
Advisor Name Title
Robinson, Edwin S. Committee Chair
Costain, John K. Committee Member
Glover, Lynn III Committee Member
Keywords
  • Geology
Date of Defense 1983-06-15
Availability unrestricted
Abstract

Bouguer gravity anomalies at 1870 locations on the central Piedmont of Virginia from 37° 3TN to 37° 52'N and 77° 44' W to 78° 23'W display patterns of variation produced by upper crustal density contrasts and thickening of the crust in a WNW direction. No other deep sources are evident. Upper crustal density contrasts are associated with rock units known from geologic mapping. The subsurface distribution of these rock units interpreted from seismic reflection data was confirmed by measured variations in gravity. A two-dimensional model analysis indicates the following average in situ density values for the principal formations: Arvonia Formation-2.77 gm/cc, Columbia Granitoid-2.75 gm/cc (tonalite) and 2.73 gm/cc (pegmatite), Chopawamsic Volcanics- 2.77 gm/cc (felsic units), and 2.79 gm/cc (mafic units), Catoctin/ Lynchburg-2.815 gm/cc, Maidens Gneiss-2.775 gm/cc, Grenville Basement- 2.71 gm/cc. Gravity and seismic data are consistent with the existence of a major thrust fault at depths between 9 km and 16 km that separates Grenville Basement rocks from younger Catoctin/Lynchburg rocks. The slight eastward dip of this thrust fault beneath the western part of the area increases significantly east of 78° 05' W. Gravity anomalies suggest the existence of several mafic inclusions within the Columbia Granitoid that were not identified by geologic mapping.

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