12 Tectonics, Volcanism, and Sediment Dispersal Within and Proximal to the Rio Grande Rift and Southern Rocky Mountains

This session integrates research on coupled tectonics, volcanism, and sediment dispersal in the Rio Grande Rift and southern Rockies. We examine how extensional faulting controls volcanic processes and reshapes sediment routing from Colorado through Texas.

Monday, 18 May 2026
1:30 PM - 4:30 PM
Alvarado A

Insights into Lithospheric Extension in a Rio Grande Rift Basin from Bayesian modeling of Tectonic Subsidence and High-Precision Geochronology

Paper number: 12-6
Program: Technical Sessions
Time: 3:15 PM – 3:35 PM

Authors

Abstract

Lithospheric thinning is the primary driver of rift basin subsidence. We explore the resolution of the record of Rio Grande rifting and La Jencia Basin development by investigating the Miocene Popotosa Formation. New U-Pb zircon ages from detrital and ash deposits were used to build a high-resolution chronostratigraphic framework that was integrated with field observations and Bayesian accommodation modeling to more accurately document Miocene rift basin development. Laser ablation-inductively coupled mass spectrometry (LA-ICPMS) was used to identify young populations of zircon and characterize U-Pb distributions in samples. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) was subsequently used to generate high-precision, accurate ages for the studied horizons from the same zircon crystals. This high-fidelity basin chronology, along with field observations and existing high-resolution geologic maps provide an apt dataset from which to investigate and model rift basin development.

Rifting in the area of the La Jencia Basin evolved from a system of closely spaced faults with minimal displacement into a system of fewer faults with greater displacement, driving similar behavior in associated basin development. Ages and accommodation model results support rapid development (<1-3 Myr) of the nascent La Jencia Basin from a series of small depocenters to a larger basin by ca. 16 Ma, the extent of which was likely similar to the area of the modern basin (~10 km2). Accommodation models indicate that following this <1-3 Myr period of fault organization, ~95% of Miocene sedimentary accumulation occurred during a period of major normal faulting defined by pulses of increased basin subsidence. This work is a case study of rapid rift basin development and the possible insights gleaned from high-resolution chronostratigraphy and high accuracy age data combined with Bayesian accommodation modeling.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410516

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