A PRELIMINARY METAMORPHIC PRESSURE-TEMPERATURE PATH FROM THE FUNERAL MOUNTAINS, CALIFORNIA: A RECORD OF THRUSTING AND EXHUMATION IN THE SEVIER OROGEN

Metamorphic rocks in the Funeral Mountains in southeastern California are ideal for studying orogenic processes due to excellent exposure, the presence of several thick pelitic units that developed garnet-bearing assemblages, and a Barrovian metamorphic field gradient. Regional metamorphism was the result of Late Jurassic to Late Cretaceous burial by thrusting in the Sevier orogen to depths more than double the thickness of the 13 km thick sedimentary package. The pelitic units are contained within a Mesoproterozoic to Neoproterozoic section of metasedimentary rocks in a tilted crustal section exposed beneath a Miocene detachment fault. Upper amphibolite facies assemblages are present in Monarch Canyon, at the northwest corner of the lower plate. The grade decreases upsection to the southeast across northwest dipping strata, to middle greenschist facies at Indian Pass, over a distance of ~40 km. Pressure-temperature (P-T) paths may be extracted from garnet that preserves growth zoning, which occurs in middle amphibolite facies assemblages at Chloride Cliff, ~15 km southeast of Monarch Canyon, and in middle greenschist facies assemblages at Indian Pass. Garnet grains in rocks from Monarch Canyon preserve little or no growth zoning due to temperatures that exceeded the threshold for cation diffusion, and so are not suitable for extracting P-T paths. A preliminary path from the Neoproterozoic Kingston Peak Formation at Chloride Cliff displays a pressure increase of 0.8 kb followed by a pressure decrease of 0.8 kb and a second pressure increase of 0.2 kb, all during a temperature increase of ~35°C. We interpret the pressure increases to represent burial by thrusting and the decrease to represent an episode of synconvergent exhumation. A P-T path containing similar alternations of burial and exhumation is documented from another exposure of metamorphic rocks in the Sevier hinterland ~700 km to the northeast, in the Raft River-Albion-Grouse Creek ranges of northwest Utah and southern Idaho.