9-5 Provenance of Bisbee Basin Sediments using Detrital Zircon U-Pb and Fission Track Double Dating

Session: Sedimentary Systems and Provenance in the Western Cordillera (Posters)

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Abstract:

The Bisbee Basin extends across southern Arizona, USA, and northern Sonora, Mexico, and preserves sedimentary records from the Late Jurassic-Early Cretaceous period. The geodynamic context responsible for the subsidence associated with the formation of the Bisbee Basin continues to be debated, with models including intracontinental rifting linked to the opening of the Gulf of Mexico, back-arc extension associated with the Jurassic Cordilleran Arc, and pull-apart subsidence related to the Mojave–Sonora megashear. This study focuses on sandstones from the Morita and Cintura formations, outcropping at El Ocuca, Sonora. The rocks were described petrographically along the stratigraphic column, and double U–Pb and fission track (FT) dating were obtained on detrital zircons to study the provenance, exhumation and erosion processes of the source rocks of the Bisbee Group sediments. The Maximum Depositional Ages indicate that the Morita and Cintura formations were deposited during the Aptian to Lower Cenomanian, which is consistent with the ages published at the regional level. In the Morita Formation, detrital zircon U-Pb age distribution shows a dominance of Triassic-Jurassic crystallization ages, which is interpreted as originating from the subduction-associated Cordilleran Arc. In the Cintura Formation, we observe a greater contribution from Paleozoic and Proterozoic detrital zircons, suggesting that the basement of the arc was already exposed at the time of deposition. In all analyzed samples, zircon FT ages younger than the Maximum Depositional Ages obtained by U-Pb are observed, indicating a post-depositional partial reset of the FT thermochronometer. FT in zircons begin to anneal at 180°C and disappear completely above 260°C. Therefore, the partial annealing observed indicates that the sediments of the Bisbee Basin were buried between ~5 and 8 km. This is consistent with the estimated thickness of the units overlying the studied sediments, coupled with the structural thickening caused by the Laramide orogeny. In some samples, the youngest zircon FT peak age is close to ~30 Ma, suggesting that zircons with these FT ages were completely reset and likely recorded the cooling associated with the Oligocene-Miocene Basin and Range extension. In addition, one sample exhibits a FT peak age of ~9 Ma, which is considered to be the result of more recent local hydrothermal activity, similar to that existing today in the Aconchi region.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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