The southwestern margin of the Late Cretaceous Sonora Pass Intrusive Suite, northern Sierra Nevada, California (USA), preserves a densely populated zone of magmatic structures that record dynamic magmatic layer formation and deformation (faulting and folding) within a solidifying upper-crustal magma mush. This zone consists largely of coupled melanocratic (or schlieren) and leucocratic bands hosted within the 95.6 ± 1.5 Ma Kinney Lakes granodiorite (Leopold, 2016), with orientations approximately parallel to the intrusive margin and with inward younging directions. Schlieren consist of a high modal abundance of medium-grained ferromagnesian minerals (hornblende + biotite), zircon, sphene, apatite, opaque minerals, and minor plagioclase and interstitial quartz. Leucocratic bands are dominated by coarse-grained feldspar + quartz with minor ferromagnesian and accessory minerals. Whole-rock geochemical and Sr and Nd isotopic data indicate that the schlieren are derived from the Kinney Lakes granodiorite by effective mechanical separation of mafic minerals and accessory phases. We interpret that the schlieren zone at the margin of the Kinney Lakes granodiorite formed by large-scale collapse of crystal mush by “magma avalanching,” facilitated by gravity, local convection, and possibly by host-rock stoping at the margin. This process eroded a significant portion of the solidifying margin of the chamber and resulted in the formation of magmatically deformed layered structures, which experienced further mingling, re-intrusion, magmatic erosion, and recycling processes. We envisage that magma avalanching of magma mushes in plutons can be achieved by any unstable process (e.g., tectonic, fluid-assisted, stoping, or gravity-driven) in large, long-lived magma-mush chambers.

The >1000 km 2 , ~95-88 Ma Sonora Pass intrusive suite is the oldest and most northern of the four voluminous, normally-zoned Late Cretaceous suites of the Sierra Nevada batholith. It consists of the older, marginal, equigranular Kinney Lakes hornblende-biotite granodiorite and the inner, porphyritic to megacrystic Topaz Lake biotite granodiorite. The suite intruded the ~109 Ma Bummers Flat biotite granodiorite, Jurassic diorites, and Pre-Cambrian to Cambrian metasedimentary rocks of the Snow Lake pendant. The Topaz Lake granodiorite records evidence of the development of a sizable magma chamber. The Bummers Flat and Kinney Lakes granodiorites were likely constructed by many increments, were capable of flow and disaggregation of host and co-magmatic mafic rocks, are marked by widespread schlieren, and may have not formed a single magma chamber. Accommodation of magmas was facilitated by multiple material transfer processes; stoping was the best documented process, followed by minor ductile flow and magmatic wedging of the Kinney Lakes granodiorite. There is no direct evidence for transfer processes during emplacement of the Topaz Lake granodiorite. Magmatic foliation within the study area records regional tectonic strain and complex internal magmatic processes. Solid-state structures including steep ductile shear zones, foliations, and lineations occur within the Bummers Flat granodiorite. One of these structures, the Toe Jam Lake shear zone, may extend for 10s of km, likely formed during ENE-WSW shortening, and probably predated the Sonora Pass intrusive suite. ACKNOWLEDGMENTS Completion of this thesis would not have been possible without the support, love, mentoring, and understanding from so many individuals in my life. I would like to thank Katie Bryant, your unwavering friendship and positivity undoubtly helped make the completion of this thesis possible. Callie Sendek, you were the best field assistant a geologist could ask for. You carried heavy rocks on your back ridiculous distances, while eating sub-par backpacking food for 6 weeks. Thank you for all your hard work, hearty laughs, and friendship. To my family, my dream to complete my graduate degree meant moving far from Texas, and you all were nothing but supportive. Thank you for believing I could succeed. Nick Valoff, you've never been able to understand my motives behind this huge endeavor, however, were nothing but understanding and loving through the whole writing process. Thank you for showing me a life so special outside of academics. I would also like to extend a huge thanks to the United States Geological Survey (USGS) for funding my project through an EDMAP grant that ultimately made my research possible. Aaron Yoshinobu, you encouraged me from the beginning at Texas Tech and initially are the reason I pursued a graduate degree. Thank you so much for introducing me to a life full of geology. I would also like to extend a sincere thank you to my committee, Jonathan Miller and Joe Petsche. Also, thank you Jonathan Miller for spending time in my...