Fabric Study on Solider Lake Pluton, Sierra Nevada, California

The 97 Ma Soldier Lake Pluton (SLP), located adjacent to the Tuolumne Batholith in the central Sierra Nevada, California and, intruded into a package of metavolcanic and metasedimentary rocks of Paleozoic to Mesozoic age during the high-flux Cretaceous magmatic event. Field mapping established that the magmatic foliation in the SLP is not influenced by contact orientations, overprints internal contacts, is of NW strike and deep dip, and is subparallel to the metamorphic foliation in the host rocks. These fabrics are interpreted to record syn- emplacement regional deformation.

The examination on the microstructures in the SLP shows both magmatic and solid-state strain occurred. The magmatic strain in the SLP is mainly shown by the magmatic crystal growth and alignment; high-temperature solid-state strain is mainly shown by the intracrystalline deformation of feldspars and recrystallization in quartz; low-temperature ,solid-state strain is recorded by the development of the s-c structures. Both magmatic and solid-state strain are the reflection of the regional deformation during and after the SLP emplacement.

Timing relationships based on field observations and new geochronology reveal that the magmatic fabric formed at 97 Ma, the high-temperature solid-state fabric at sometime between 97 and 85 Ma, and the low-temperature s-c fabric after 86 Ma. The metamorphic foliation in host is also considered to be the result of the regional deformation with a thermal overprint during emplacement of ~86 Ma Cathedral Peak Granodiorite.

The fabric pattern and the characteristics of fabrics in both pluton and its surround host rocks are coupled to reflect regional strain during the high-flux Cretaceous magmatic event in the Sierran arc.