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Title: A gravity model for the Coso geothermal area, California

Two- and three-dimensional gravity modeling was done using gridded Bouguer gravity data covering a 45 {times} 45 km region over the Coso geothermal area in an effort to identify features related to the heat source and to seek possible evidence for an underlying magma chamber. Isostatic and terrain corrected Bouguer gravity data for about 1300 gravity stations were obtained from the US Geological Survey. After the data were checked, the gravity values were gridded at 1 km centers for the area of interest centered on the Coso volcanic field. Most of the gravity variations can be explained by two lithologic units: (1) low density wedges of Quarternary alluvium with interbedded thin basalts (2.4 g/cm{sup 3}) filling the Rose Valley and Coso Basin/Indian Wells Valley, and (2) low density cover of Tertiary volcanic rocks and intercalated Coso Formation (2.49 g/cm{sup 3}). A 3-D iterative approach was used to find the thicknesses of both units. The gravity anomaly remaining after effects from Units 1 and 2 are removed is a broad north-south-trending low whose major peak lies 5 km north of Sugarloaf Mountain, the largest of the less than 0.3 m.y. old rhyolite domes in the Coso Range. Most of this residualmore » anomaly can be accounted for by a deep, low-density (2.47 g/cm{sup 3}) prismatic body extending from 8 to about 30 km below the surface. While some of this anomaly might be associated with fractured Sierran granitic rocks, its close correlation to a low-velocity zone with comparable geometry suggests that the residual anomaly is probably caused a large zone of partial melt underlying the rhyolite domes of the Coso Range. 12 refs., 9 figs.« less
Authors:
;
Publication Date:
OSTI Identifier:
5684468
Report Number(s):
LBL-28878; CONF-900823--13
ON: DE91011874
DOE Contract Number:
AC03-76SF00098
Resource Type:
Conference
Resource Relation:
Conference: Annual meeting of the Geothermal Resources Council and international symposium on geothermal energy, Kailua Kona, HI (USA), 20-24 Aug 1990
Research Org:
Lawrence Berkeley Lab., CA (USA)
Sponsoring Org:
DOE; USDOE, Washington, DC (USA)
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; GEOTHERMAL FIELDS; GEOLOGIC MODELS; COSO HOT SPRINGS; GRAVITY SURVEYS; HEAT SOURCES; MAPS; RHYOLITES; THREE-DIMENSIONAL CALCULATIONS; TWO-DIMENSIONAL CALCULATIONS; CALIFORNIA; FEDERAL REGION IX; GEOPHYSICAL SURVEYS; IGNEOUS ROCKS; NORTH AMERICA; ROCKS; SURVEYS; USA; VOLCANIC ROCKS Geothermal Legacy 150301* -- Geothermal Exploration & Exploration Technology-- Geophysical Techniques & Surveys