22 Evolution of Cordilleran-type orogenic systems (Posters)

This session seeks contributions that connect surface, crustal, and mantle processes associated with Cordilleran systems, specifically addressing geodynamics, kinematics, magmatism, uplift, erosion, basin subsidence, and sediment dispersal in ancient and modern settings.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

Thermokinematic Evaluation of the San Bernardino Mountains

Paper number: 22-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

  • Erick Inostros Presenting Author
    California State University San Bernardino, San Bernardino, California
  • Shantel Alban
    California State University San Bernardino, San Bernardino, California
  • Susana Henriquez
    California State University San Bernardino, San Bernardino, California

Abstract

The San Bernardino Mountains (SBM) have been uplifted due to transpression across a restraining bend of the San Andreas Fault System (SAFS). Constraining when, how, and how fast relief is created in restraining beds is essential for understanding transform plate boundaries. The SBM are bounded by the SAFS to the southwest and the North Frontal Thrust (NFT) system  to the northeast. Geomorphologically, the SBM comprises a plateau approximately 3.5 km elevation and a deeply incised slope along the SAFS. Published apatite (U-Th)/He (AHe) ages along southwestern slope suggest the SBM were uplifted in the last 3.3 Ma. In the plateau, published thermochronologic data show an inherited cooling signature (ca. 55-90 Ma, apatite fission-track (AFT) ages and ca. 50-65 Ma AHe ages). This research integrates structural (Move, Petex) and thermokinematic (Fetkin) modeling to test the extent to which slip along the NFT, combined with enhanced and steady erosion along the SAFS, can explain the uplift and exhumation (cooling record) of the SBM. Preliminary results include a simplified structural cross-section, a palinspastic restoration, and a series of cooling patterns that test different thermokinematic scenarios. Each scenario was evaluated by comparing the predicted cooling patterns to available thermochronologic data. Because the cooling record on the plateau is largely inherited, thermokinematic models that focus on recent SBM uplift cannot reproduce plateau ages. However, these models can evaluate how recent exhumation modifies inherited cooling patterns and help identify areas where additional data are needed to indirectly constrain fault geometries and their slip history. Preliminary results indicate that, assuming an inherited cooling age of 65 Ma (approximately the oldest inlier among plateau cooling ages): (1) a constant slip rate under modern geothermal conditions (ca. 34 °C/km) predicts older plateau ages and a broad slope age range (AHe: 0–40 Ma); (2) a higher geothermal gradient (ca. 43 °C/km) narrows the slope age range (AHe: 0–35 Ma); and (3) varying slip rate under modern conditions has little effect on cooling patterns. Results indicate that constraining cooling histories including the partial retention and annealing zones along the southwestern slope and near the NFT has the greatest potential for constraining the SBM thermokinematic history. Future modeling will test sample variability and an older deformation onset.

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

doi: 10.1130/abs/2026CD-410834

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