T271 Coupling of Deformation and Chemical Processes in Earth (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

FLUID (?) CONTROLLED SLIP SYSTEMS AND RECRYSTALLIZATION IN A HIGH STRAIN AUREOLE, EJB PLUTON, CALIFORNIA

Paper number: T271-3
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Within the highly strained eastern aureole of the Eureka Valley-Joshua Flat-Beer Creek (EJB) pluton, in the White Mountains of eastern California, over 30 quartzite samples have been analyzed for their crystallographic preferred orientation (CPO), oxygen isotopes, fluid inclusions, and microstructure. Quartzites in the aureole are subvertical wrapping around the pluton. Samples were collected between 10 and 1800 m from the pluton contact. Slip systems switch from <a> slip within the first 300 m from the pluton contact to [c] slip and combined [c] & <a> slip between 300 m and 1800 m. Quartzites within the first 300 m are interbedded with marble and calc-silicate layers while the remaining quartzites are dominantly pure quartzite. Preliminary Zr in rutile thermometry from three quartzites indicates temperatures of ~730°C at 300 m, ~670°C at 500 m, and ~710°C at 1700 m from the contact. To the north of the traverse, a small segment of the pluton wraps around so that the end of the sampling traverse is once again approaching the pluton contact.

The correlation between type of slip system, degree of recrystallization, oxygen isotope ratios, and surrounding rock type suggests that either the interbedding of weak marbles affected the rheology of the quartzites in the inner aureole or CO2-rich fluid generated by calc-silicate reactions in the inner aureole resulted in water-poor conditions which prevented recrystallization of quartz and resulted in “lower” temperature slip systems.

Within 300 m from the pluton, δ18O of quartz is between 13.4 and 16.5‰ and quartz grains are incompletely recrystallized and CL images indicate that ellipsoidal-shaped relict sedimentary grains are deforming plastically and cataclastically. Beyond 300 m, δ18O varies between 13.8 and 12.13‰ and quartzites are completely recrystallized. In three samples from the same quartzites collected >10 km away from the pluton, δ18O is between 15.2 and 15.5‰

The composition of aqueous fluid inclusions (FI) is essentially the same throughout the aureole, in spite of the higher total homogenization temperatures of FI’s in recrystallized quartz. The small isotopic shift combined with the FI data suggest that fluids were derived in situ from intergranular and inclusion fluid and that there were no large fluxes of H2O-rich fluid moving through the aureole system.