Volume 31 Issue 10
Article, pp. 4-10 | Full
The Origin and Tectonic Significance of the Basin and Range–Rio Grande Rift Boundary in Southern New Mexico, USA
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.
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