Between August 2015 and June 2016, Trey Klopfenstein participated in a Research Experience for Undergraduates funded by the National Science Foundation. He was advised by Prof. Craig Grimes. This project involved field investigations in the Chemehuevi Mountains, Mohave Desert, SE California, as well as lab based studies (optical microscopy and X-ray fluorescence geochemical analysis) at Ohio University. His work culminated in the successful completion of a senior thesis, and he presented the findings from his project at the 2016 Geological Sciences of America Annual Meeting in Denver CO, USA.
At the request of the topical session convener, Trey gave an oral presentation titled “An assessment of synextensional dikes emplaced during early slip on the Mohave Wash low angle normal fault, Chemehuevi Mountains, SE California”. His co-authors were Craig B. Grimes, Barbara E. John, Justin LaForge, and Evan Cox.
Abstract: Dikes near the Mohave Wash low-angle normal fault (LANF) in the Chemehuevi Mountains, Colorado River Extensional Corridor (California, USA), were documented to better understand the relationship between dike emplacement and early slip on the Miocene Chemehuevi LANF system. Dike composition, geometry, orientation, distribution, and structural relations with the Mohave Wash Fault (MWF) were characterized. Field work concentrated on two areas with contrasting paleodepths of ~5 km (Range Front area of the SW Chemehuevi Mountains) and >10 km (Bat Cave Wash area, NE Chemehuevi Mountains). Collectively, dikes comprising the swarm define a subalkaline trend of dominantly magnesian, meta-peraluminous intrusions. Dikes make up ~2% of the footwall in the Range Front area, and are dominantly mafic to intermediate compositions (52-63% wt. % SiO2) with lesser dacite-rhyolite dikes (68-73 wt. % SiO2). Clear cutting relations indicate mafic-intermediate dikes postdate felsic varieties. Dikes in the Range Front area exhibit sharp contacts, commonly with chilled margins. They vary in thickness from 0.5 to >12 meters and intrude all structural levels of the MWF. Individual dikes cannot be traced across the MWF and appear to be truncated or rarely to have intruded into a network of brittle fractures defining the damage zone. Dike emplacement appears to have been episodic. In contrast, dikes in the Bat Cave Wash comprise ~10% of the footwall, are dominantly felsic (typically >67 wt. % SiO2), notably thinner (typically <2 m), and have well developed deformation fabrics (S>L). In the Range Front area, dikes occur with two general orientations striking nominally E-W and N-S with moderate to steep dips. Orientations are not consistent with emplacement via mode 1 cracks formed during regional extension oriented at ~050°, and instead may have been controlled by some preexisting fracture system. Based on structural analysis, hangingwall dikes have been rotated up to 24° CCW (axis at 285°) relative to footwall dikes in the Range Front area. Dikes in the Bat Cave Wash area exhibit contacts striking dominantly E-W to NW-SE, shallow dips, and uniform lineations trending ~240°. These observations indicate that extension at greater paleodepths was partitioned, at least in part, on the synextensional dikes and resulted in rotation and thinning.
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