Collaborative Research: The provenance of "Grenville" age detrital zircon in western North America and the Neoproterozoic to early Paleozoic evolution of southwestern Laurentia

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Collaborative Research: The provenance of "Grenville" age detrital zircon in western North America and the Neoproterozoic to early Paleozoic evolution of southwestern LaurentiaR. Lang Farmer, University of Colorado, EAR-1251851Christopher Fedo, University of Tennessee, EAR-1251869ABSTRACTDetrital zircon U-Pb age determinations have become a primary tool in siliciclastic sedimentary provenance studies due in part to the advent of rapid, in situ methods of obtaining isotopic data from individual zircon grains. However, the ability to collect such data is outstripping our understanding of the limitations of using U-Pb age spectra in interpreting continental tectonics and paleogeography. In this study, PIs are interested in assessing the significance, in terms of the sediment provenance, of variations in the age spread and relative peak height of specific detrital zircon age populations in siliciclastic sedimentary successions. Their approach is through combined in situ zircon U-Pb and Hf isotope analyses, data to be obtained using the laser ablation-multicollector ICPMS technique. PIs will target Mesoproterozoic to Cambrian sedimentary successions in the SW United States and northern Mexico, rocks that have been extensively used for U-Pb detrital zircon studies, but for which there is little detrital zircon Hf isotope data. Existing U-Pb age spectra reveal that a significant fraction of the detrital zircons in these rocks were derived from 1.0 Ga to 1.3 Ga ("Grenville") basement sources. The width and relative peak heights described by detrital zircon in this age range vary considerably both temporally and spatially within these sedimentary successions. Many samples are dominated by ~1.1 Ga detrital zircon, which on the basis of their U-Pb ages alone implies that these zircon were all derived from the same Mesoproterozoic basement source. However, PIs pilot Hf isotopic studies of "Grenville" detrital zircon show that the ~1.1 Ga grains vary by over 15 epsilonHf(0) units and reveal that these zircons do not all share the same provenance. This fact is not recognizable from the U-Pb age spectra alone. Based on this observation, it is suggested that combined U-Pb and Hf isotopic data can be used to explore how changes in the characteristics of the "Grenville" peaks in detrital zircon age spectra reflect changes in the ultimate bedrock source of these detrital grains. A better understanding of the basement provenance for Mesoproterozoic detrital zircons can, in turn, be used terms to refine models for the Precambrian to early Paleozoic tectonic and paleogeographic evolution of North America. PIs will conduct a broad survey of the U-Pb and Hf isotopic compositions of potential sources of "Grenville" zircon amongst 1.0 Ga to 1.3 Ga igneous rocks within the Grenville Orogen in the central and southern Appalachians, in the Llano Uplift in Texas, and among the ~1.1 Ga igneous rocks distributed throughout Paleoproterozoic crust of the SW U.S. and northern Mexico. They will apply this information, along with whole-rock Nd isotopic analyses on samples for which such data not already available, to assess the provenance of "Grenville" detrital zircon in siliciclastic sedimentary rocks in the Death Valley region and in the Caborca area of central Sonora (MX).