Abstract
Abstract Heat flow data and thermochronologic derived paleotemperature gradient data are examined to calculate heat flow ~25 Ma and, at present, for a southern Basin and Range location north of Tucson, Arizona. An increase in the surface heat flow is estimated from ~25 Ma to the present; changing from ~47 to ~83 mW m-2. Steady-state conduction temperature vs. depth profiles provide estimates of lithosphere thicknesses both for the present and for ~25 Ma. Different heat transfer models for present heat flow predict present LAB depth that agrees with seismic studies. From these temperature profiles, lithosphere thinning from ~184 km to ~70 km is suggested during the Neogene. Mantle lithosphere thinning caused by thermal phenomena is likely a fundamental driving force for southern Basin and Range extension. Because the mantle lithosphere has likely thinned much more than the crust, it is shown that additional vertical advection, such as an asthenosphere plume, delaminating part of the mantle lithosphere, convection cells, and rising magmas along conduits, add to the vertical advection component of upper mantle lithosphere extension. Interestingly, values of heat flow 25 Ma, lithosphere thicknesses 25 Ma, and Neogene lithosphere thinning are somewhat similar for the Four Corners area of the Colorado Plateau and the southern Basin and Range, even though Neogene tectonic development was quite different, i.e., no Neogene extension in the Colorado Plateau vs. ~57% in the southern Basin and Range. Neogene lithosphere thinning phenomena are likely different in the two regions.
Highlights
Obtaining data-driven estimates of lithosphere thickness ~25 Ma and Neogene lithosphere thinning in different geological provinces of the western United States may provide valuable boundary conditions for geologic models of Neogene tectonics
Geothermal information providing subsurface temperature estimates relevant to a past geologic time can be considered with present heat flow data to estimate the related past lithosphere thickness as well as lithosphere thinning over the corresponding geologic interval
Heat flow analyses provided estimates of present lithosphere thickness from the present heat flow data for the Colorado Plateau, which was consistent with seismic studies [1]
Summary
Obtaining data-driven estimates of lithosphere thickness ~25 Ma and Neogene lithosphere thinning in different geological provinces of the western United States may provide valuable boundary conditions for geologic models of Neogene tectonics. Mineralogy and heat flow studies were used to estimate heat flow ~25 Ma for the Four Corners Area of the Colorado Plateau [1, 2] and to suggest Neogene lithosphere thinning of ~100 km for the area. A heat flow-temperature-depth expression, the same as in this study, was used to match upper mantle depth-temperature estimates at ~25 Ma consistent with the mineralogy data relevant at ~70 and~140 km depth [1, 2] From this analysis, a heat flow estimate of ~47 mW m-2 for 25 Ma was possible, and an estimate of lithosphere thickness could be made [1]. Heat flow analyses provided estimates of present lithosphere thickness from the present heat flow data for the Colorado Plateau, which was consistent with seismic studies [1].
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