DETRITIAL ZIRCON CHARACTERIZATION OF METASEDIMENTARY UNITS OF SIERRA DE MAZ, WESTERN SIERRAS PAMPEANAS, ARGENTINA

Sierra de Maz, western Sierra Pampeanas of central Argentina, is underlain by metamorphic rocks included in the MARA block (Casquet et al., 2012, Geosci. Frontiers). The range is transected by the near vertical Maz shear zone which separates complexes with differing metamorphic histories and was active at least at 425-405 Ma (see abstract Houlihan et al., 2017). Samples for detrital zircon geochronology were analyzed (Arizona LaserChron Center) to evaluate potential protolith differences across the structure. Cm-bedded quartzite interlayered with metapelite west of the Maz shear zone defined major peaks at 1085 and 1225 Ma within a population ranging from 1000-1500 Ma and 1860 Ma. Minor peaks occur at 2615 and 725 Ma. The detrital zircon population lacks evidence of the prograde 420 Ma metamorphism recorded by the metapelites (see abstract Tholt et al., 2017). Two samples with different protolith lithology were collected immediately east of the Maz shear zone. A m-thick quartzite layer yielded a large peak at 1055 Ma in a population ranging from 1000 to 1500 Ma and minor peaks at 835, 910, 980, 1660, 1860, 1920 Ma. A sample of metagraywacke defined a broad distribution from 1000-1500 Ma with major peaks at 1090 and 1230 Ma and a small peak at 1430 Ma, and minor peaks at 840, 1820 and 1870 Ma. Both samples have grains with low Th/U rims that yield metamorphic ages of ca 420 Ma. All of the samples have similar detrital zircon signatures that are consistent with igneous ages observed east of the Maz shear zone (see abstract Webber et al., 2017). Neoproterozoic grains in all 3 samples provide single grain maximum depositional ages ranging from 529 to 717 Ma. Maximum depositional ages defined by multiple grains are ca 720 Ma and ca 820 Ma west and east of the Maz shear zone respectively. The detrital zircon spectra from all samples are similar to those observed in the Difunta Correa sequence in the eastern Sierra Pie de Palo (Ramacciotti et al., 2015, Precambrian Research). However along-strike variations in Ordovician-Silurian magmatic, metamorphic and structural history of the Proterozoic metasedimentary units west of the Famatina arc reflects sinistral displacement and juxtaposition of different units or blocks along the Famatina arc margin in Late Silurian – Devonian.