Structure, Construction, and Emplacement of the Late Cretaceous Sonora Pass Intrusive Suite [thesis]

Monika B. Leopold
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
more » ... ke 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.
doi:10.31979/etd.pq8y-gb84 fatcat:zj4p26ntaneynkqsypzs3bz2by