The Origin and Tectonic Significance of the Basin and Range–Rio Grande Rift Boundary in Southern New Mexico, USA

Jason W. Ricketts

Dept. of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, 500 West University Ave., El Paso, Texas 79968, USA, jricketts@utep.edu

Jeffrey M. Amato

Dept. of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA

Michelle M. Gavel

Dept. of Geological Sciences, New Mexico State University, Las Cruces, New Mexico 88003, USA

Abstract

Cenozoic extension in the western United States occurred within two iconic domains: the Basin and Range and Rio Grande rift. These provinces merge in southern New Mexico to form an interconnected zone of extension, although the existence, location, and nature of the boundary between the two provinces are uncertain. In southern New Mexico, existing thermochronologic, geologic, and geophysical data sets, combined with thermal modeling of zircon (U-Th)/He (ZHe) data, define a subvertical, 30–40-km-wide boundary that extends through the lithosphere to depths of at least 100 km. Thermal modeling indicates Proterozoic basement in the upper crust of the southeastern Basin and Range exceeded 225 °C during Oligocene magmatism, resetting ZHe dates and creating a thermal boundary that coincides with independent geologic and geophysical data sets. Although many aspects of this boundary are transient, others may become permanent features to define a lithospheric-scale boundary prone to reactivation during future tectonism. This assessment of the boundary supports models in which the southern Rio Grande rift is a separate structural entity from the adjacent Basin and Range, and this region provides an exceptional case study for understanding how extensional lithospheric-scale boundaries evolve to become stable features of continents.

Manuscript received 20 Mar. 2021. Revised manuscript received 1 June 2021. Manuscript accepted 11 June 2021. Posted 8 July 2021.

© The Geological Society of America, 2021. CC-BY-NC.

https://doi.org/10.1130/GSATG509A.1