7 Tectonic History of the Trans-Pecos Region

Thursday, 8 March 2012
1:30 PM - 5:00 PM
Espino A & B

TECTONIC RECONSTRUCTION OF LARAMIDE THRUST AND CRETACEOUS EXTENSION IN THE INDIO MOUNTAINS, TRANS PECOS TEXAS

Paper number: 7-4
Program: Theme Sessions
Time: 2:15 PM – 2:30 PM

Authors

Abstract

In the Indio Mountains of Trans-Pecos, Texas, Laramide thrusting inverted the fill of the Jurassic/Cretaceous Chihuahua Trough, providing a three-dimensional exposure of the rift fill. These exposures provide insights both into the structure of the trough and to the influence of the Jura-Cretaceous structure on subsequent Laramide thrust systems. The Indio Mountains extend from the Rio Grande to the Eagle Mountains, Southwest of Van Horn Texas. The range is a North-Northwest trending Basin and Range extensional uplift that was on the eastern margin of the Chihuahua trough, and during the Early Tertiary was just inside the frontal thrust of the Chihuahua tectonic belt.

The Chihuahua trough initiated in the Late Jurassic either as a pull-apart basin formed along with the Gulf of Mexico, or a back-arc spreading system. The trough contains almost 5 km of sediments, largely of middle Cretaceous age (Aptian through Cenomanian). During the Laramide Orogeny (84-43 Ma) the Basin was inverted, producing the Chihuahua tectonic belt.

Reconstruction of the structure and stratigraphy in the Indio Mountains indicates that the range exposes a duplex riding on a an unexposed decollement that extends to the basin margin, 12 km east of the present range. Within the range, a duplex exposes strata shortened 8.5 km along two thrusts. The strata are twice as thick in the upper thrust plate, derived from deeper in the basin, indicating a major Cretaceous extensional fault that lies somewhere under the modern course of the Rio Grande, approximately 25 km from the basin margin.

The Chihuahua Trough was a complex extensional basin with major internal structures as is evident in the basin stratigraphy that show dramatic along-strike facies changes and thickening both into the basin and along strike, to the northwest and southeast. Although not diagnostic as to tectonic regime, this complex internal fill and structure are similar in scale to those of modern rifts.