Regional crustal structures of Pacific Northwest
Long-wavelength gravity anomalies combined with regional seismic refraction data, obtained during the last two decades, allow a regional mapping of crustal thickness variations in the Pacific Northwest and the adjacent continental margin. When the effects of these variations in crustal thickness are removed from the gravity data, the residual gravity anomalies outline major upper crustal structures in the Pacific Northwest. Residual gravity anomalies show that the Cascade Range in Oregon fills a major north-south-trending graben. The graben is approximately 60 km wide and 160 km long, and is oriented approximately N10/sup 0/E. Its well-developed western wall exhibits a throw of 2-3 km. The Cascade Range and its associated graben overlie a prominent northeast-southwest structural trend that demarks a Mesozoic orocline. The oroclinal structure extends from the continental margin northwest of the Klamath Mountains in southwestern Oregon through the Blue Mountains in northeastern Oregon, and separates the late Mesozoic to early Tertiary basins of central Oregon and central Washington. A large regional gravity high observed over the Columbia basin in central Washington is attributed to both the thick surface layer of flood basalts and an anomalous lower crust. Gravity data integrated with seismic refraction and geologic data yield a computed model of the crustal structure of the Columbia Plateau. Removing the basalt layer of the model reveals a rift topography or complex graben structure that connects with or adjoins the Cascade graben on the southwest side of the basin and the Chiwaukun, Methow, and Republic grabens on the north side of the basin. These structures in the Pacific Northwest reflect generally east-west extension and wrench tectonics.
- Research Organization:
- Northwest Geophysical, Corvallis, OR
- OSTI ID:
- 6931523
- Report Number(s):
- CONF-8604187-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:4; Conference: American Association of Petroleum Geologist Pacific Section convention, Bakersfield, CA, USA, 16 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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