Collaborative Research: Testing models for the Late Jurassic Nevadan Orogeny: Age, provenance, and structural evolution of the Galice and Mariposa basins, OR and CA

The proposed research will improve the understanding of the development of the North American continental margin in southern Oregon and northern California just prior to and during a critical and poorly understood period of contractional deformation. During this time (the Latest Jurrassic), mountain building closed the Galice and Mariposa sedimentary basins in the western Klamath and Sierra mountains, respectively.

Details of the basins’ sediment sources, depositional ages, and extent of metamorphism and deformation may provide the best geologic record just prior to and during the mountain-building event. The project provides key educational benefits for students at the undergraduate and graduate level, requiring integration of a range of disciplinary knowledge and skills that cannot be duplicated in a classroom.

The project will recruit women and underrepresented minority students at graduate and undergraduate levels, and these students will be full participants in the research, not observers. The experiential learning through this research will provide skill development and training that will translate directly to the STEM workforce. In addition, field guides highlighting this research and key areas of interest will be broadly disseminated through Forest Service districts and the NSF Flyover Country® app, improving public scientific literacy.

The ongoing interest in gold mining and the mining history of the rocks that form the focus of this research increase the likelihood of public engagement.

The Upper Jurassic Galice and Mariposa Formations in the Klamath Mountains and western Sierran provinces have long been considered fundamental to understanding the mid-Mesozoic history of the U.S. Cordilleran continental margin. Two opposing tectonic models for the Late Jurassic Nevadan orogeny variously interpret the tectonic setting and age of Galice and Mariposa deposition.

The first model invokes the genesis of the Mariposa Formation in an intra-oceanic basin that progressively closed along oppositely dipping subduction zones, while the age-equivalent Galice Formation represents an inter-arc basin native to the western margin of North America. In the second model, both formations occur within transtensional basins above an east-dipping, long-lived subduction zone along the western North American margin.

Because these strata constitute the youngest rocks deformed during the Late Jurassic Nevadan deformation, details of depositional age, sediment provenance, and the kinematics and style of deformation are critical to informing the proposed tectonic models and assessing their viability. This comprehensive and integrated analysis of each of these basins that includes petrofacies characterization, detrital zircon U-Pb age and Hf analysis, heavy mineral analysis, interpretation of sedimentary structures, assessment of the degree of metamorphism, and analysis of the timing and kinematics of deformation, will provide a robust framework for modification and refinement of the understanding of the Late Jurassic continental margin.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.