Tectonic Evolution of the Southern Portion of the Indio Mountains, West Texas: From Laramide Shortening and Arc Volcanism to Basin and Range Extension


This study investigates the contractional deformation of Laramide, the transition to associated arc volcanism, and the extensional deformation of Basin and Range in the southern part of the UTEP Indio Mountains Research Station, southern Indio Mountains, Texas. This involved detailed mapping at a scale of 1:20,000 of structural and stratigraphic elements such as fault and bed attitudes, unit contacts, and fault kinematic indicators, as well as the use of aerial photography and satellite imagery. Where possible, kinematics and geometry of faults were determined and series of structural cross-sections across the region were constructed. Results indicate that the Cretaceous rocks show several types of contractional structures that are cut by extensional normal faults, likely associated with the Basin and Range extensional faulting. The Cenozoic volcanic rocks are cut by extensional structures (some normal and listric normal faults), but they were not affected by thrusting and folding related to the contractional deformation. This contrast is manifested by an angular unconformity between folded and thrusted Cretaceous rocks and younger Cenozoic volcanic rocks. This suggests that the Laramide shortening in the area must have ceased before the occurrence of the oldest volcanic rock in the area. The Hogeye Tuff, the oldest volcanic rock above the angular unconformity, is dated at 38.02±0.99 Ma by U/Pb dating of zircons (Davidson, 2014), and the dominant Laramide’s contractional deformation observed in Cretaceous rocks must have ceased before the age of Hogeye Tuff in the mapping area. Applying an extensional fault-bend fold model to the Indio Fault with current and previous measurements and observations, it is possible that the Indio Fault initiated as a high-angle oblique normal fault, but evolved to become a listric normal fault, which may be linked to a pre-existing detachment or a major unconformity at depth. Extensional deformation is as young as the age of youngest deformed gravel deposition, which is the undivided group of terrace gravels. No fossils were found that would allow age determination of the undivided group of terrace gravels; however, the age of the Bolson Fill is interpreted to be as young as the Kansan-age by Underwood (1962); so the recent extensional period could be younger than 1.65 Ma – 0.7 Ma B.P. in the mapping area.



Laramide orogeny, Recent basin and range extension, Remote sensing, West Texas, Trans-Pecos, Cenozoic volcanism