Upper-crustal structure beneath the Columbia River Basalt Group, Washington: Gravity interpretation controlled by borehole and seismic studies
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Abstract
A three-dimensional gravity model based on deep-borehole stratigraphy, densities from borehole gravimetry, and crustal structure from deep seismic and electrical surveys puts limits on sub-basalt crustal structure in the northwest quadrant of the Columbia Plateau, Washington. The gravity model indicates that the Miocene Columbia River Basalt Group (CRBG) overlies a broad basin filled with sedimentary rocks that reach thicknesses in excess of 5 km; thickest sub-basalt sedimentary rocks are beneath the late Cenozoic Yakima basin. Analysis of residual gravity shows that the Eocene Chiwaukum graben does not continue beneath the CRBG and that sub-basalt sedimentary rocks are not thrust into the cores of the basalt anticlines in the Yakima fold belt. A gravity high that trends north-south in the center of the CRBG is probably caused by a broad basement ridge marked by thinner sedimentary rocks beneath the Columbia River basalts; the western edge of the north-south basement high is traced at the surface by the Hog Ranch-Naneum Ridge. A major crustal feature, the Olympic- Wallowa lineament, is expressed in the gravity field; the lineament crosses the north-south basement high but does not offset it, suggesting that any strike- slip motion on the lineament preceded development of the north-south basement high. An alternative interpretation of the north-south gravity high, based on a previous seismic study, relates it to a high-density structure in the crystalline basement, perhaps associated with a failed continental rift.
Study Area
Publication type | Article |
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Publication Subtype | Journal Article |
Title | Upper-crustal structure beneath the Columbia River Basalt Group, Washington: Gravity interpretation controlled by borehole and seismic studies |
Series title | Geological Society of America Bulletin |
DOI | 10.1130/0016-7606(1993)105<1247:UCSBTC>2.3.CO;2 |
Volume | 105 |
Issue | 9 |
Year Published | 1993 |
Language | English |
Publisher | Geological Society of America |
Description | 13 p. |
First page | 1247 |
Last page | 1259 |
Country | United States |
State | Idaho, Oregon, Washington |
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