300-3 Characterizing Sediment Sources of Jurassic Strata in the Western Sierra Nevada Foothills, CA:  Petrographic Analysis of Mesozoic units in the Central California Transect and Dike Classification

Session: Reconstructing Earth Surface Processes in Orogenic Systems (Posters)

Poster Booth No.: 136

Presenting Author:

Nathan Quigley

Authors:

Quigley, Nathan¹, Botha, Brandon², Orme, Devon A.³, Craig, Lucas⁴, Shaffer, Cate⁵, Sikes, William⁶, Surpless, Kathleen DeGraaff⁷

(1) Department of Earth Sciences, Montana State University, Bozeman, MT, USA, (2) Department of Earth Sciences, Montana State University, Bozeman, MT, USA, (3) Department of Earth Sciences, Montana State University, Bozeman, MT, USA, (4) Earth and Environmental Geosciences, Trinity University, San Antonio, TX, USA, (5) Earth and Environmental Geosciences, Trinity University, San Antonio, TX, USA, (6) Earth and Environmental Geosciences, Trinity University, San Antonio, TX, USA, (7) Earth and Environmental Geosciences, Trinity University, San Antonio, TX, USA,

Abstract:

The characterization of sediment sources in the Western Sierra Nevada Foothills (WSNF) can provide insight to the sedimentary provenance and history of subduction polarity in the region. Constraining subduction polarity along the North American Cordillera is essential to reconstructing the tectonic history along the North America Cordilleran margin. Three models of subduction have been proposed in the region: west-facing, east-facing, and double-subduction models. In the east-facing model, subduction occurred during the Jurassic at intraoceanic trenches as North America migrated westward, resulting in terrane accretion. Alternatively, the west-facing model suggests an Andean style of subduction, where the Farallon plate subducted along the continental margin in an east-dipping subduction zone. The double-subduction model includes subduction beneath North America and an outboard archipelago. Each of these models predicts different transport pathways and depositional environments for the sedimentary units in the region.  

We are characterizing four units in the WSNF: the Clipper Gap, Colfax, and Calaveras Formations, along with the Don Pedro terrane. These units consist of primarily Mesozoic clastic, meta-clastic, schist, slate, and igneous lithologies. Samples of igneous intrusions that cross-cut the Clipper Gap and the Calaveras Complex were collected to determine their relation to the Sonoran Dike Swarm (SDS), an important feature in the region linked to magmatic activity during the Jurassic. To characterize the petrology of these units, fifteen samples are being analyzed under a petrographic microscope to determine their mineral composition. Hand sample analysis of a cross-cutting dike along the South Fork of the Yuba River indicates a gabbroic composition, composed primarily of plagioclase feldspars and pyroxenes. This composition is consistent with that of dikes in the SDS. Metasedimentary samples from the Colfax formation are highly micaceous and contain abundant plagioclase and quartz in hand sample, suggesting derivation from a magmatic arc. This work will present a comparison of all aforementioned lithologies and, in turn, be integrated with ongoing geochronologic and geochemical work to test models for subduction zone polarity.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8998

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