Constraining Times of Extension in the Southern Rio Grande Rift and Basin and Range Using Apatite and Zircon (U-Th)/He Thermochronology
The Rio Grande rift and the Basin and Range are adjacent extensional domains that have evolved contemporaneously in western North America. Although the rift is often considered to be the easternmost boundary of Basin and Range extension, there is geologic and geophysical evidence that suggests the two are discrete provinces. Existing low-temperature thermochronologic data indicate that a period of synchronous extension occurred across the entire length of the rift from ~25–10 Ma. However, these studies were more focused on the northern and central sections of the rift, and thermochronologic data remains sparse in southern New Mexico. We collected rock samples from the footwalls of normal faults in seven mountain ranges across southern New Mexico and southeastern Arizona, and from these samples a total of 42 zircon (U-Th)/He and 23 apatite (U-Th)/He ages were obtained. A change in thermochronologic age vs. eU relationships is observed to the west of the Cookes Range and Florida Mountains and suggests different extensional styles in the region. The change coincides with a previously proposed boundary between the Basin and Range and Rio Grande rift. We propose a master detachment fault controlling low-angle faulting in the Basin and Range in southern New Mexico. The hypothesized detachment, along with the crustal and mantle structure beneath the southern Rio Grande rift, are consistent with the simple shear model of lithospheric stretching.
Biddle, Julian, "Constraining Times of Extension in the Southern Rio Grande Rift and Basin and Range Using Apatite and Zircon (U-Th)/He Thermochronology" (2017). ETD Collection for University of Texas, El Paso. AAI10688885.