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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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This content will become publicly available on December 16, 2026
Preliminary insights into faulting and fluid-rock interactions on the Iberia-Newfoundland margin using low-temperature thermochronology
Hyper-extended, magma-poor rifted margins are characterized by thinned continental crust, exhumed subcontinental mantle, and limited volcanism. The timing of exhumation, particularly mantle exhumation, during the formation of hyper-extended margins has key implications for our geodynamic understanding of the transition from continental breakup to seafloor spreading and the relationship between magmatism, lithospheric extension, and mid-ocean ridge development. We use zircon and apatite from rifted igneous intrusions and lower continental crustal blocks within the exhumed mantle section of the Iberia-Newfoundland margin to track the cooling of these rocks below ~200°C, with implications for fault timing and fluid-rock interactions. Zircon (U-Th)/He data from 8 core samples (from 4 drill holes) exhibit a general younging trend from east to west during the Late Cretaceous, consistent with exhumation driven by a lithosphere-scale, westward-dipping detachment fault. Of 10 apatite (U-Th)/He samples (from 7 drill holes), 5 record Cretaceous cooling, while the remaining 5 indicate Oligo-Miocene cooling, with no clear geographic pattern distinguishing the two populations. Inverse thermal history modeling will be applied to constrain the thermal evolution of the lithosphere during hyperextension. These models can indirectly constrain the timing at which the lithosphere entered the thermal window conducive to serpentinization and ophicalcite formation with implications for lithospheric rheology, thermal structure, and the potential habitability of subsurface environments for ancient microbial life.
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- Award ID(s):
- 2049848
- PAR ID:
- 10646547
- Publisher / Repository:
- AGU Annual Meeting
- Date Published:
- Format(s):
- Medium: X
- Location:
- New Orleans, United States
- Sponsoring Org:
- National Science Foundation
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