CAN SMALL-SCALE FRACTURES ACCOMMODATE INCREMENTAL PLUTON EMPLACEMENT? CASE STUDY IN THE TUOLUMNE INTRUSIVE SUITE, CALIFORNIA

Recent geochronology studies have demonstrated that the Tuolumne Intrusive Suite, Sierra Nevada batholith may have been incrementally assembled, rather than the temporally segregated plutonism previously thought. In the Tuolumne Intrusive Suite, a consequence of these data is that: 1) Older rock must accommodate the numerous incremental intrusions; and 2) The rock surrounding the incremental intrusions does not necessarily need to accommodate large-scale displacements. This study focuses on the development of mineralized fractures in the Cathedral Peak granodiorite, Sierra Nevada batholith that may have accommodated ‘small-scale’ intrusions. The observed fractures exhibit epidote and chlorite mineralization, and are associated with a cm-scale bleached zone. Chattermarks, lineations, and microstructures suggest they are dominantly left-lateral features. Similarities with other, known Cretaceous-age Sierra Nevada batholith fractures suggest the observed fractures are also Cretaceous in age. The fractures, however, are difficult to interpret as tectonic, given the dextral transpression during the Cretaceous. Instead, we interpret the fractures to be non-tectonic in origin. We suggest that these faults formed as a result of directional, incremental emplacement of the Johnson granite Porphyry into the older Cathedral Peak granodiorite. Specifically, this model posits the development of the sinistral faults to accommodate vertical and northerly translation of Cathedral Peak granodiorite blocks due to the forceful intrusion of the Johnson granite porphyry.