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The Great Valley Forearc basin of California preserves >15 km of strata deposited during latest Jurassic-earliest Cretaceous to Eocene sedimentation. Along the western margin of the central-northern Great Valley forearc, the oldest basin strata are preserved as an eastward dipping homoclinal belt. Previous work on the thermal history of the western outcrop belt has constrained sub-normal geothermal gradients (<20C/km) during middle Cretaceous to Eocene time related to subduction refrigeration. However, the timing of maximum burial and subsequent exhumation is restricted to a few local studies. This study applies apatite and zircon (U-Th)/He and apatite fission track thermochronology to quantify maximum burial temperatures and the timing and rate of cooling of latest Jurassic-middle Cretaceous strata of the western homocline and neighboring subsurface along 350 km of the basin margin. Zircon (U-Th)/He dates range from ~167 to 85 Ma, which are either older or bracket corresponding depositional ages. Apatite fission track dates range from ~162 to 90 Ma, with the majority of grains between ~110-90 Ma. All apatite (U-Th)/He dates are less than 50 Ma, with most grains yielding dates between ~40-20 Ma. Preliminary integration of these data into thermal history models indicate that maximum burial temperatures did not exceed 120-180 C. The timing of basin cooling ranges based on locality, with the western outcrop yielding rapid exhumation starting between ~100-65 Ma and subsurface cooling at ~50 Ma. Final cooling to modern temperatures, as constrained by apatite (U-Th)/He dates, generally coincides with the transition to a transform margin after ~30 Ma.
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YOUNGER THAN ANTICIPATED MAXIMUM DEPOSITIONAL AGES OF SANDSTONES FOUND IN THE GREAT VALLEY FOREARC BASIN REVEAL LENGTHENED UNCONFORMITY BETWEEN THE COAST RANGE OPHIOLITE AND BASAL GREAT VALLEY GROUP, DEL PUERTO CANYON, CALIFORNIA, USA
- Award ID(s):
- 1942460
- PAR ID:
- 10495833
- Publisher / Repository:
- Geological Society of America
- Date Published:
- Journal Name:
- Abstracts Geological Society of America
- ISSN:
- 0435-3986
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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