301-11 Coupled Hematite and Apatite (U-Th)/He Geo-thermochronology Records Miocene to Pleistocene Deformation in the Eastern Precordillera, Argentina

Session: Geochronology (Posters)

Poster Booth No.: 152

Presenting Author:

Joseph Brooks-Kahn

Authors:

Brooks-Kahn, Joseph¹, Weeks, Chloe², Odlum, Margaret³, Mackaman-Lofland, Chelsea A.⁴, Ortiz, Gustavo⁵, Capaldi, Tomas N.⁶

(1) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA, (2) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA, (3) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA, (4) University of Tennessee, Knoxville, TN, USA, (5) Universidad Nacional de San Juan, San Juan, Argentina, (6) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA,

Abstract:

Reconstructions of Andean thrust front propagation within the flat-slab subduction segment of Chile and Argentina have large uncertainties in the kinematic links among thin-skinned and basement-involved structures. The seismically active Eastern Precordillera is an enigmatic, west-directed frontal thrust system that is either linked to the thin-skinned style Central Precordillera to the west, or to the thick-skinned-style basement block uplifts of the Sierras Pampeanas to the east. We seek to determine the timing and style of fault slip and associated fluid flow processes along strike of the Eastern Precordillera to constrain the kinematic link among these Andean structures. We integrated multiscale structural and thermochronological characterization of the Sierra de Villicum and Sierra Mogna thrust fault systems. We established a structural framework via new and existing geologic mapping and field observations of exposed fault zones and collected hematite coated or cemented fault rocks. Hematite (U-Th)/He thermochronology serves as a powerful tool to constrain slip-related processes in the shallow crust. Hematite coated fault rocks were analyzed with a scanning electron microscope to characterize hematite microstructures, and a subset of samples were targeted for hematite (U-Th)/He geo/thermochronometry. The hematite from the Sierra Mogna fault yielded preliminary (U-Th)/He dates between 43-31 ka with primarily botryoidal structures, which we interpret as recording late Pleistocene fault-related fluid flow in the shallow crust. Sierra de Villicum fault rock hematite dates range from 6.3-3.7 Ma and exhibit cataclastic hematite microstructures. These dates overlap with existing apatite (U-Th)/He dates sampled from the hanging wall, which suggests the hematite (U-Th)/He dates record late Miocene-mid Pliocene fault-related exhumation in the upper ~4.4 km of the crust. Structural and thermochronological characterization integrated with hematite (U-Th)/He dates reveals late Miocene to recent thrust-related exhumation and fluid flow within the Eastern Precordillera. These multiscale data resolve spatiotemporal gaps in Andean thrust-front evolution critical to determining kinematic links among these seismically active Andean structures, while clarifying the recent tectonic history of the Eastern Precordillera.

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

doi: 10.1130/abs/2025AM-8912

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