EARLY PALEOGENE ANATEXIS IN THE SOUTHERN U.S. CORDILLERA AND NEW CONSTRAINTS ON PEAK METAMORPHISM IN THE DEEP CRUST: COYOTE MOUNTAINS, ARIZONA

New geochemical, isotopic, and zircon petrochronologic data from an anatectic leucogranite suite, the Pan Tak Granite, in the Coyote Mtns., AZ provide insight into tectonic and metamorphic processes associated with the Laramide/Mexican orogeny. Increasing Ti-in-zircon temperatures, from 650-850 °C and a concomitant increase in zircon HREE are interpreted to record prograde metamorphism, melting, garnet breakdown, and initial melt crystallization from 62-53 Ma. A period of zircon dissolution from 53-51 Ma is interpreted to reflect peak metamorphic conditions, peak melt generation, and the timing of emplacement. Crystallization and cooling dominated afterwards, from 51-42 Ma, supported by temporal increases in zircon U/Th and zircon Hf, decreases in Ti-in-zircon temperature and zircon HREE, and textural evidence for coupled dissolution-reprecipitation processes. Whole rock geochemical data suggest that the leucogranite suite experienced advanced fractional crystallization during this time. The most evolved, residual melts are represented by high silica, muscovite ± garnet leucogranite dikes and pegmatite dikes that cross-cut an earlier two-mica granite. The majority of zircon in the two-mica granite are interpreted to be xenocrysts or antecrysts that were mobilized from migmatites in the deep crust during melt extraction and emplacement. The Pan Tak Granite formed by fluid-deficient melting and mica dehydration melting of meta-igneous protoliths, including Jurassic arc rocks. The characteristics and petrologic processes that created the Pan Tak Granite are strikingly similar to intrusive suites in the Himalayan leucogranite belt and suggest that the Laramide/Mexican orogeny was a major orogenic and thermal event in the southern U.S. Cordillera.