PROVENANCE OF THE MIDDLE–LATE ORDOVICIAN CLASTIC WEDGE IN THE ARGENTINE PRECORDILLERA
Late Mesoproterozoic (10001200 Ma) ages are documented in basement of the Precordillera and of the Sierra de Pie de Palo and other massifs east of the Precordillera, as well as older (~1370 Ma) basement clasts in the Precordillera. More importantly, quartzite in Pie de Palo has detrital-zircon age peaks at 10001200 and 13001450 Ma. The abundance of 10001200 Ma zircons in the clastic wedge is compatible with a source in the Pie de Palo and other massifs (basement and cover), which may have been incorporated into a complex accrectionary prism and backthrusted during subduction. The 10001500 Ma grains could be from a primary Sunsás or Rondonian source or from recycling of pre-Ordovician sedimentary cover on the upper plate; however, the relative abundance of these grains favors the basement and cover of Pie de Palo and other nearby massifs. Neoproterozoic ages (515800 Ma) are compatible with upper-plate (e.g., Pampean and Brasiliano) rocks or, alternatively, Iapetan synrift igneous rocks, which have been recognized in Pie de Palo. The distinct Paleoproterozoic grains (20002200 Ma) suggest a primary source in Amazonia or Rio de La Plata basement or cover.