Petrology and Trace Element Thermometry of Rutile in Garnet-Quartzite from the Catalina Schist

Science Center, Bent Corridor

The Catalina Schist has long served as a laboratory for studying fluid flow in subduction zones. Garnets in quartzite blocks from the amphibolite unit of the Catalina mélange preserve extreme oxygen isotope zoning recording evidence of high metasomatism. within the region: here we present the first temperature estimates and petrologic descriptions of these unusual rocks. Garnet quartzite from Catalina occurs primarily as meter-scale blocks in the amphibolite facies mélange, but also as 10-100m scale slabs in lower-grade levels of the subduction complex. The rocks consist of quartz (65-80%), fine-grained (40-200µm) garnet (~10-20%) and variable and minor chlorite, biotite, muscovite, hornblende, sphene, rutile, allanite and monazite. Rutile and zircon are commonly found as inclusions within garnet grains. Trace element analyses by LA-ICPMS were performed on rutile grains (100-300µm) from five samples of quartzite. This allowed for application of Zr-in rutile thermometer (estimated P of 15 kbar) which yielded temperatures in tectonic blocks of 650-730˚C. These temperatures are consistent with thermometry from the more common mafic and migmatitic blocks in the same mélange. Samples from coherent slabs at lower structural levels in the subduction complex preserve lower temperatures (610-643˚C), consistent with their later formation in a cooler trench.