U-PB DETRITAL ZIRCON COMPARISON OF WESTERN SIERRA NEVADA METAMORPHIC PENDANTS WITH THE GOLCONDA ALLOCHTHON: IMPLICATIONS FOR THE PRE-MESOZOIC ASSEMBLY OF CENTRAL CALIFORNIA

Uranium-lead geochronologic analysis of detrital zircon is employed to reveal the identity of metasedimentary pendants forming the western framework of the Sierra Nevada batholith with the goal of reconstructing the pre-Mesozoic crustal structure. The SCICON pendant (near Springville, CA) is composed of amphibolite facies calc-silicate rocks, quartz amphibolite, quartzite, and lesser marble, whereas phyllite, schist, and marble comprise the South Fork pendant (SW Sequoia N.P.). Despite polymetamorphic recrystallization and isoclinal folding, crinoid fossils are preserved in the SCICON pendant. After excluding high U/Th Mesozoic metamorphic grains, zircon from the SCICON-South Fork pendants define large 1.7-1.8 Ga and 2.4-2.5 Ga age peaks, whereas the neighboring Sequoia and Slate Mountain pendants exhibit large 1.0-1.1 Ga, moderate 1.4 Ga, and small 1.7-1.8 Ga age peaks. Detrital zircon ages, rock types and fossil data support correlation of these two pendant groups with post-early Cambrian passive margin strata and with Neoproterozoic-early Cambrian passive margin strata, respectively. Previous statistical analysis, using two published detrital zircon samples (n~20, 21), suggested a strong correlation between the SCICON pendant and Mississippian marine sediments of the Golconda allochthon (GA). Three large grain (n~114-303) detrital zircon samples of the Schoonover Sequence (north-central Nevada) were analyzed to test whether the western Sierra Nevada pendants were offset equivalents of the Golconda allochthon. Though the preliminary hypothesis is not supported by the expanded detrital zircon database, the new data provides insight regarding the provenance of quartz-rich and volcanic lithic strata of the Schoonover Sequence. Specifically, a narrow and robust (n=63) 354.2 ± 1.2 Ma age peak provides an Early Mississippian maximum age (Tournaisian) for deposition of the lower Schoonover Sequence, confirming previous age constraints provided by radiolaria. These new detrital zircon U-Pb data will be used to evaluate whether the Schoonover Sequence could have been derived by erosion of the Antler orogenic highlands, or whether additional, extra-regional sources are required.