Affiliation:
1. 1Department of Earth, Environmental and Resource Sciences, The University of Texas at El Paso, El Paso, Texas 79902, USA
2. 2New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
Abstract
AbstractRocks exposed in the southern Indio Mountains provide an important geologic record of the transition from Laramide contraction to Rio Grande rift extension. These rocks include (1) a package of folded and faulted Mesozoic rocks deformed during Laramide compression, (2) Eocene volcanic and sedimentary rocks that are tilted (but not folded) and fill a paleovalley, and (3) Miocene conglomerate deposited within a Rio Grande rift halfgraben. We present a combination of geologic mapping, sedimentological and structural analysis, and geothermochronology to document the timing and nature of this transition in western Texas as an important comparison with the more thoroughly studied tectonic and erosional history of New Mexico and Colorado. Detailed geologic mapping and cross-section reconstruction reveal a highly irregular angular unconformity overlying Mesozoic rocks and that post-Laramide topography funneled local Eocene deposition through an EW-trending paleovalley. New and existing 40Ar/39Ar geochronology constrains the timing of paleovalley deposition to 38.1–36.6 Ma. The presence of megabreccia units, coupled with paleoflow analysis, argue that major Laramide topographic relief in western Texas persisted into the Middle Eocene and that detritus was shed toward the Tornillo basin to the east. These data, when viewed within the context of regional tectonic patterns, suggest that Laramide deformation in western Texas had ceased by 38.1 Ma, although they do not preclude translation along an underlying buried thrust. Eocene paleovalley cutting and filling are reminiscent of widespread Eocene erosion and fluvial deposition that occurred in Colorado and northern New Mexico and suggest that this event may have been more widespread than previously thought, extending into Chihuahua and western Texas.Subsequent Rio Grande rift extension occurred primarily along several NW-striking normal faults that dissected the older structures and the paleovalley and led to deposition of conglomerate within a half-graben. Apatite (U-Th)/He thermochronology applied to normal fault footwall rocks indicates exhumational cooling was occurring by 27 Ma, and detrital sanidine 40Ar/39Ar geochronology of basin fill indicates a maximum depositional age of 11.9 Ma. Clast count data from the conglomerate show a prominent unroofing trend, wherein clasts include locally derived Mesozoic units and Eocene volcanic rocks.
Publisher
Geological Society of America
Reference131 articles.
1. Low-temperature thermochronometric constraints on fault initiation and growth in the northern Rio Grande rift, upper Arkansas River valley, Colorado, USA;Abbey;Geology,2018
2. Perspectives on continental rifting processes from spatiotemporal patterns of faulting and magmatism in the Rio Grande rift, USA;Abbey;Tectonics,2020
3. Structural geology algorithms: Vectors and tensors;Allmendinger,2012
4. Anderson, A. , 2017, Depositional controls and sequence stratigraphy of lacustrine to marine transgressive deposits in a rift basin, Lower Cretaceous Bluff Mesa, Indio Mountains, west Texas [M.S. thesis]: El Paso, Texas, The University of Texas at El Paso, 195 p.
5. Sevier Orogenic Belt in Nevada and Utah;Armstrong;Geological Society of America Bulletin,1968