Significance of past and recent heat-flow and radioactivity studies in the Southern Rocky Mountains region

Heat flow and thermal modeling of the Appalachian Basin, West Virginia

“…The Q o was originally identified as the heat that originates from below the radiogenically enriched upper crustal layer and includes the mantle and deep crustal contribution to heat flow (Roy et al, 1988). The combined data of New England and the central stable region of the United States, which included West Virginia, yield a slope b of 7.5 ± 0.2 km and an intercept (Q o ) of 33 ± 1 mW/m 2 ; subsequent studies (Costain et al, 1986;Decker et al, 1988) resulted in the same average. Roy et al (1968Roy et al ( , 1972 suggested that the linear relationship may have broad applicability for continental heat flow and to the stable portion of the continents (Thakur, 2011).…”

“…Heat flow provides insight into the thermal regime of the lithosphere on a million year time scale. Stable continental igneous terrains have been shown to have an approximately linear relationship between measured surface heat flow and crustal heat production Lachenbruch, 1968;Roy et al, 1968;Costain et al, 1986;Decker et al, 1988). This relationship implies that changes in surface heat flow within a stable crustal block are related primarily to lateral variation in average crustal heat production.…”

Lithospheric Signature of Late Cenozoic Extension in Electrical Resistivity Structure of the Rio Grande Rift, New Mexico, USA

“…However, within the Rio Grande rift, the close proximity of a hot upper mantle to the base of an attenuated lithosphere could produce these same observations without the need for melt. Modeling heat flow data in the rift with the assumption of a conductive geotherm produces temperatures above the solidus at depths above the Moho (Decker et al, ), suggesting extremely high volumes of partial melt are present in the crust or more likely, there has been advective heat transfer into the crust from the mantle. Seismic attenuation in the crust beneath the rift is high (Phillips et al, ), which would support the presence of melt if we assume intrinsic attenuation rather than scattering attenuation (e.g., heavily fractured rock dispersing seismic energy).…”

“…In Feucht et al (), high electrical conductivity beneath central Colorado is explained by, alternatively, 7–15% basaltic partial melt distributed from the top of the conductor to the crust‐mantle boundary (higher concentrations if partial melt is hybridized or nonuniformly distributed), free saline brine in volumes as low as 0.7 vol %, or some combination of the two conductive phases, with free saline fluid more likely to be stable near the middle crust. We favor the two‐phase conductor model, with saline fluid concentrated in the midcrust, given that crustal temperatures at depths corresponding to the top of the LCC are insufficient to support melting (Decker et al, ).…”

Geophysical Constraints on the Flexural Subsidence of the Denver Basin

“…Normal faulting related to the Rio Grande Rift can be mapped out along the ridge of the Rocky Mountains into northern Colorado with diminishing effect as it reaches the Wyoming border (Chapin and Cather, 1994;Naeser et al, 2002;Buffler, 2003). Further evidence of lithospheric thinning consists of delay times for P-wave arrivals (Cleary and Hales, 1966;Olsen et al, 1979;Allenby and Schnetzler, 1983;Schmandt and Humphreys, 2010) and upper mantle electrical conductivities (Porath, 1971) over the basin area, and high heat flow in Northern Colorado (Lachenbruch and Sass, 1977;Decker et al, 1980Decker et al, , 1988.…”