38 Plate Boundary Evolution and Lithospheric Dynamics of Western North America (Posters)

We invite presentations on Cenozoic tectonics, volcanism, sedimentation, and geohazards offshore and along the margin of western North America. Example topics include crustal structure, mantle processes, triple-junction migration, paleomagnetism, active faulting, marine stratigraphy, and seismicity.

Friday, 24 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Preliminary Mapping and Age Constraints of the Ibex Pass Basin, Southern Death Valley, CA

Paper number: 38-3
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Ibex Pass basin sits within the region of southern Death Valley, CA, which has accommodated extension since the Neogene. Broadly speaking, the basin contains a suite of volcanic rocks overlain by a sequence of younger alluvial and landslide deposits. However, despite some previous mapping throughout Ibex Pass, the details of the stratigraphy, both volcanic and sedimentary, are poorly understood. This study presents ongoing geologic mapping in the Ibex Pass basin with a focus on developing a cohesive stratigraphy across the basin. Previous mapping in the area revealed that the volcanic package sits atop the Neoproterozoic bedrock in the southern part of Ibex Pass, however, along the northern flank of the Ibex Hills the overlying sedimentary rocks of the basin lie directly atop bedrock, suggesting a structural control on the basin geometry. The eastern portion of the study area displays a more coherent stratigraphy, less interrupted by faulting, and was sampled throughout the exposed section. In the more deformed western section, targeted sampling focused on appropriate marker units to facilitate stratigraphic correlations east, across the Ibex Pass basin. Analyses of the collected samples revealed predominantly intermediate compositions, with notable textural variations, particularly variations in phenocryst percentage, that serve as potential markers for correlation. 40Ar/39Ar ages for this study, taken throughout the section, range from 13.03 ± 0.1 Ma to 12.6 ± 0.03 Ma, and previous work in the area revealed an age as young as ~11.7 Ma for one of the tuffaceous units interpreted to be near the top of the section. This suggests that the Ibex Pass basin is a long-lived feature, relative to the history of regional extension. The development of the basin itself, in terms of accommodating structures, is an open question. Work to the east highlights the importance of the Sheephead fault in the opening of the China Ranch basin. However, a likely age of ~12.4 Ma for volcanics in the northern Ibex Hills, loosely correlated to rocks in Sheephead Pass, potentially limits movement along the Sheephead Fault after that time. Therefore, another major goal of this project is to provide further details on the structures throughout Ibex Pass, allowing for a better understanding of how the basin developed.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-411019

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