New Mexico Geological Society Annual Spring Meeting — Abstracts

Active rift systems accommodate deformation through the development of normal fault systems. The Rio Grande rift (RGR) in central New Mexico consists of a north-south-trending zone of intracontinental extension and is characterized by a series of normal fault zones bounding half-graben basins. Extension in the RGR is thought to have started during the late Oligocene-Miocene. Fault scarps offsetting recent deposits indicate that deformation has been ongoing through the Quaternary. Rupture along these structures poses a potential danger to local communities and infrastructure; however, the slip histories of many of the fault systems in the RGR are understudied. The Socorro Canyon Fault Zone (SCFZ) is one of several normal faults that demarcate the western boundary of the Socorro basin, a Miocene half-graben basin associated with the development of the RGR. Although the SCFZ is one of the best-studied fault systems within the RGR, the role of surrounding structures in accommodating deformation of bedrock and Quaternary deposits is not as well-constrained. In conjunction with a companion geophysical study, we show that an unnamed series of normal and oblique faults, ~5 km west of the SCFZ, play an important role in accommodating RGR deformation. Our study area is composed of a series of north-northwest normal faults and secondary east-west strike-slip faults offsetting the Oligocene-Miocene volcanic successions of the Hells Mesa tuff, the Miocene Popotosa Formation, and Quaternary deposits. A primary bedrock fault consists of a ~11m damage zone that incorporates lenses of volcanic rocks surrounded by fault gouge, breccia, and cataclasite. Our neotectonic map and soil profile analysis demonstrate how the fault system deforms Quaternary deposits, as evidenced by scarps and tilted Quaternary strata. The development of pedogenic carbonate horizons above deformed Quaternary alluvial fans helps to constrain the timing of deformation along this system. Our study sheds light on the complexity of faulting and strain partitioning in rift systems and how deformation occurs in intracontinental extensional settings. Future work will integrate microstructural observations to constrain how deformation is accommodated at the microscopic level.