Presentation Title

Timing of Deformation Along the Borrego Springs Shear Zone

Faculty Mentor

Sinan Akciz

Start Date

23-11-2019 8:45 AM

End Date

23-11-2019 9:30 AM

Location

256

Session

poster 2

Type of Presentation

Poster

Subject Area

physical_mathematical_sciences

Abstract

Shear zones play a significant role in the deformation of the crust at a variety of scales. Information about structures found within the shear zone and determining an accurate age for the duration of strain is critical in characterizing the properties of shear zones and determining their tectonic significance. Exhumed shear zones provide unique exposures of materials that can be studied in detail to answer such questions. Eastern Peninsular Ranges Mylonitic Zone (EPRMZ), located between Western and Eastern Peninsular Ranges batholiths, is one such exhumed structure. This east-dipping, mylonitic thrust shear zone, extending from the border of Mexico to Palm Springs, California, is broken into three sections by currently active faults including the San Jacinto Fault and the Elsinore Fault: Santa Rosa Shear Zone, Borrego Springs Shear Zone (BSSZ), and Cuyamaca-Laguna Mountains Shear Zone. The focus of this research project is to date an undeformed dike that cross-cuts the mylonites to constrain the minimum age of deformation in the BSSZ. New 206Pb/238U zircon analyses indicate that shearing along the BSSZ must have terminated by 89.66 ± 0.41 Ma (95% confidence). This data is compatible with the age of a deformed dike, 90.90 ± 0.48 Ma (95% confidence), which was determined in another study. These preliminary results indicate that the juxtaposition of EPRB and WPRB was likely contemporaneous with the formation of the Peninsular Ranges batholiths.

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Nov 23rd, 8:45 AM Nov 23rd, 9:30 AM

Timing of Deformation Along the Borrego Springs Shear Zone

256

Shear zones play a significant role in the deformation of the crust at a variety of scales. Information about structures found within the shear zone and determining an accurate age for the duration of strain is critical in characterizing the properties of shear zones and determining their tectonic significance. Exhumed shear zones provide unique exposures of materials that can be studied in detail to answer such questions. Eastern Peninsular Ranges Mylonitic Zone (EPRMZ), located between Western and Eastern Peninsular Ranges batholiths, is one such exhumed structure. This east-dipping, mylonitic thrust shear zone, extending from the border of Mexico to Palm Springs, California, is broken into three sections by currently active faults including the San Jacinto Fault and the Elsinore Fault: Santa Rosa Shear Zone, Borrego Springs Shear Zone (BSSZ), and Cuyamaca-Laguna Mountains Shear Zone. The focus of this research project is to date an undeformed dike that cross-cuts the mylonites to constrain the minimum age of deformation in the BSSZ. New 206Pb/238U zircon analyses indicate that shearing along the BSSZ must have terminated by 89.66 ± 0.41 Ma (95% confidence). This data is compatible with the age of a deformed dike, 90.90 ± 0.48 Ma (95% confidence), which was determined in another study. These preliminary results indicate that the juxtaposition of EPRB and WPRB was likely contemporaneous with the formation of the Peninsular Ranges batholiths.