Refining the footwall cooling history of a rift flank uplift, Rio Grande rift, New Mexico

Abstract

Apatite fission track (AFT) and (U‐Th)/He data from the Sandia Mountains and Hagan embayment provide new insights into the thermal and tectonic evolution of the eastern flank of the Rio Grande rift in northern New Mexico. AFT and (U‐Th)/He data reveal rapid cooling in the Sandia Mountains between 22 and 17 Ma, followed by a decrease in cooling rate at 16 to 14 Ma that temporally corresponds to a hiatus in deposition in the Albuquerque basin. A second increase in cooling rate at approximately 14 Ma was followed by continued slow cooling until present. Cooling ages from Jurassic to Permian sandstones in the Hagan embayment northeast of the Sandia Mountains are used to constrain the thermal conditions in Oligocene time that are necessary to map cooling histories into exhumation histories, thereby providing a limit on the amount of section removed during rift flank development. Thermal modeling, geologic constraints, and low‐temperature thermochronology are used to demonstrate that the heat flow in the Sandia Mountain region was at least 25 mW/m2 higher during Oligocene time compared to today. Furthermore, at least 3.1 km of material has been exhumed from the Sandia Mountains and 2.4 km of rock uplift occurred during flexural tilting of the block since middle Miocene time.