Structural, emplacement, and tectonic history of spatially and temporally linked volcanic, hypabyssal, and plutonic units in the Beartrap Lake area: eastern Sierra Nevada, CA

2018-07-30The Sierra Nevada arc in California provides exposures of Cretaceous magmatism which can be studied to greater understand the relationship between emplacement, tectonism, and regional deformation of magmatic systems. Areas that contain volcanic, hypabyssal, and plutonic units in close proximity and age are called “triads” and allow for the study of the potential relationships between the different levels of a magmatic feeder system, and are found throughout the Sierra Nevada. Combined with the tectonics of emplacement-related and regional deformation, they provide excellent areas to study the effects of magmatism and tectonics while providing windows into different levels of the magmatic column. The Beartrap Lake area, which is located in the eastern Sierra Nevada, is a “triad” that contains metavolcanic host strata intruded by a small, shallow hypabyssal porphyry, as well as two large intrusive bodies: the Long Canyon granodiorite and the Cathedral Peak granodiorite. The area has been previously mapped by the USGS (Huber 1989, Wahrhaftig 2000), as well as later researchers (Cao 2015), but has never been studied in great detail. New mapping (1:10,000 scale) as well as isotope, geochemical, geochronological, structural, and petrographical analysis of newly collected samples provide a more detailed look at the Beartrap Lake area, and serve as a foundation for further research. This study finds that the interbedded volcanics appear to be have been tilted and subsequently intruded by the hypabyssal porphyry, evidenced by discordant intrusive contacts. Ages for this package were dated to be ~100 Ma, and there exists shear zone deformation evidenced by solid-state fabrics and σ porphyroclasts. The package was brought down to emplacement level of the granodiorite units (Long Canyon and Cathedral Peak), with evidence for emplacement related strain. A combination of Material Transfer Processes (MTP’s; Paterson 1992) appear to accommodate the intruding bodies, with evidence of wall downward flow present. Further study needs to be done in order to determine if the package is genetically related, but the area does provide a look into a potential magmatic feeder system during Cretaceous magmatism in the eastern Sierra Nevada. Areas like Beartrap Lake can be tied into regional patterns and processes, and provide excellent opportunities to study the relationship between volcanic, hypabyssal, and plutonic systems in an area that contains a structural history of regional deformation and emplacement-related strain