Density, topography, and regional, tensile stresses: Gravity-driven extension of the northern Basin and range
- Lettis and Associates, Inc., Oakland, CA (United States)
It has long been recognized that regional topographic gradients may give rise to tectonic (non-lithostatic) stresses in the lithosphere (Artyushkov, 1973). The elevation of a buoyantly-uplifted region represents a balance between these stresses and the strength of the lithosphere. This study uses existing data on crustal and lithospheric structure in the western United States to test the hypothesis that the topographically high (1.5--2.2 km) northern Basin and Range is spreading under it own weight. Following England and Jackson (1989), the total deviatoric tensile force (Fl) in the northern Basin and Range (NBR) due to the regional high topography is the difference between the vertically-integrated lithostatic stress in the NBR and in western California. Using available velocity models for the crust and upper mantle, and empirically-derived velocity-density relationships, calculated values of Fl range between 1--3 [times] 10[sup 12] N/m. Assuming a visco-elastic rheology for the lithosphere, an average heat flow of 90 m W/m[sup 2], and a crustal thickness of 35 km, values of Fl ranging from 1--3 [times] 10[sup 12] N/m may result in horizontal extension rates of approximately 10[sup [minus]15]/s to 10[sup [minus]15]/s to 10[sup [minus]16]/s. This is comparable to the rate of seismically-released strain in the NBR, and to extension rates of 8--9 mm/yr across the region determined from geologic and geodetic data. These results imply that shear tractions on the base of the lithosphere from mantle convection are not necessary to explain NBR extension. In addition to driving active extension, the weight of the topographically high NBR may exert a compressive force on surrounding lowlands. If so, this may account for some of the active shortening in western California, and the state of horizontal compressive stress in the western Great Plains.
- OSTI ID:
- 5023122
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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