Many models of continental extension and rifting call upon crustal heating from magmatism or other processes to trigger and localize rifting (active rift models).
However, it is often difficult to measure the thermal structure of the crust directly for ancient rift zones, so such models have been difficult to evaluate.
M.S. Wong and colleagues present new (U-Th)/He apatite thermochronology from the Grayback tilted normal fault block in the North American Basin and Range extensional province confirming that a very low geothermal gradient (14 to 17 degrees Celsius per kilometer) existed just prior to major Tertiary extension.
This result challenges the notion that reheating of the crust was a significant driving force of crustal extension in the Basin and Range.
Confirmation of a low pre-extensional geothermal gradient in the Grayback normal fault block, Arizona: Structural and AHe thermochronologic evidence M.S. Wong et al., Dept. of Geology, Colgate University, Hamilton, New York 13346, USA. Published online 7 Aug. 2014; http://dx.doi.org/10.1130/B31033.1.