72-6 Hinterland to foreland regional transition from basement-involved to thin-skinned Laramide deformation in the southern U.S. Cordillera: Sierra Rica, NM

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains (Posters)

Presenting Author:

Authors:

Abstract:

Contractional deformation associated with the Laramide Orogeny in the southern Basin and Range province is obscured by widespread, Cenozoic extensional faulting and volcanism.  As a result, debate continues about the structural style and tectonic evolution of the region.  There are two end-member structural models that have been proposed for deformation: 1) high-angle reverse faulting and basement uplift, and 2) thin-skinned faulting and development of a thrust belt.  We undertook new geologic mapping, cross-section construction and restoration, and structural analysis in Sierra Rica, in the Bootheel region of southern New Mexico, to help evaluate these hypotheses.  A major thrust system, the Sierra Rica Fault, is present in the study area and forms a low-angle (< 20° dip) thrust ramp that places Cambrian through Mississippian carbonate strata structurally above mid-Cretaceous clastic rocks and a sub-horizontal thrust flat that places Pennsylvanian carbonate rocks structurally above mid-Cretaceous clastic rocks.  Erosional remnants of the thrust sheet are locally exposed as klippe.  Sedimentary structures, including trough cross-bedding, indicate that the units are upright and not overturned.  Regional restoration of Cenozoic extension suggests that the Sierra Rica Fault is equivalent with the Granite Pass Fault in the Little Hatchet Mountains, a basement-involved reverse fault located ~15 km to the east.  Sierra Rica is interpreted to record a transition from predominantly basement-involved deformation to the west (hinterland) to thin-skinned deformation to the east (foreland), consistent with predictions for deformation within an orogenic thrust wedge. Small granitic intrusions and dikes locally cross-cut the Sierra Rica Fault, and the intrusions cross-cut by normal faults. New zircon U-Pb LA-ICPMS geochronology indicates these intrusive rocks have crystallization ages of 32-36 Ma, which constrains the timing of deformation.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6564

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