COMPARISON OF DETRITAL ZIRCON POPULATIONS OF THE GOLCONDA ALLOCHTHON (NORTHERN NEVADA) WITH METAMORPHIC PENDANTS IN THE WESTERN SIERRA NEVADA FOOTHILLS (CENTRAL CALIFORNIA)

Uranium-lead (U-Pb) dates of detrital zircons from the SCICON metamorphic pendant in the western Sierra Nevada foothills are compared to zircon separated from the Schoonover Formation of the Golconda allochthon in order to test whether the SCICON protoliths might be offset equivalents of the Mississippian marine sediments that structurally overlie the Roberts Mountain allochthon. Pervasive deformation and amphibolite-grade recrystallization have obscured the protolith identity of the calcilicate rocks, quartz amphibolites, quartzites and lesser marbles that compose the recently discovered SCICON pendant. Further complicating protolith identification, the tiny, well rounded zircons separated from one calcsilicate sample define an age population that differs from both Neoproterozoic-Paleozoic passive margin sediments as well as from Mesozoic arc-related metasediments that are exposed in neighboring Sierra Nevada pendants. Instead, the SCICON detrital zircon population best matches the low-n detrital zircon samples reported for the Schoonover Formation exposed in northern Nevada (Riley et al., 2000). Models for the Permo-Triassic transition from a passive margin to a convergent margin seemingly predict translation of the southwestern terminus of the Golconda orogen southeastward along the truncated margin of Laurentia. High-n detrital zircon samples of quartz-rich and volcaniclastic facies of Schoonover sandstone will be statistically compared to high n-samples of quartzose meta-carbonate and quartz amphibolite SCICON rocks with the goals of (1) identifying the SCICON protoliths; and (2) testing models for the tectonic evolution of the southwestern margin of Laurentia. Detrital zircon separated from meta-sediments of the neighboring South Fork pendant (southwesternmost Sequoia National Park) will also be dated. Identifying the South Fork prototlith may additionally constrain models for the Permo-Triassic tectonic evolution of the Californian Cordillera.