SEM-EDS HEAVY MINERAL PROVENANCE ANALYSIS OF MAGALLANES FORELAND BASIN SANDSTONES, ARGENTINA

Phanerozoic subduction-related continental orogens typically involve the formation, deformation and/or uplift & exhumation of common tectonostratigraphic elements, including magmatic arcs, precursor basins, metamorphic basement and accretionary assemblages. Because of their different petrogeneses, rocks of these tectonostratigraphic elements are known to have different mineralogical, elemental, and isotopic compositions, making associated foreland basins a useful resource for kinematic reconstructions. The development of the southern Andean orogen involved uplift and exhumation of many of these elements, making them possible contributors to the overall detrital composition of the adjacent Magallanes foreland basin. As a result, compositional analysis of Magallanes basin detrital strata and their candidate source units should reveal the mineralogic, elemental and/or isotopic signatures of these tectonostratigraphic domains and their possible provenance. Preliminary EDS-assisted detrital heavy mineral and sandstone-petrography provenance data from the Patagonian Andes and Tierra del Fuego suggest that uplift and exhumation of each of the tectonostratigraphic elements contributed sediment to the Magallanes foreland basin system at different times during the late Cretaceous and Cenozoic. Whereas the Paleogene sediments received a major contribution from the Patagonian and Antarctic Peninsula batholiths as indicated by the presence of volcanic and plutonic minerals (sphene, apatite, zircon), an increased abundance of titanium-bearing minerals (chrome-spinel, ilmenite, titano-magnetite) in Miocene strata indicate unroofing of marginal marine and ophiolitic complexes in the southern Andes. The increased abundance of volcanic (Lv) and metamorphic (Lm) lithic constituents in the central domain of southern Patagonia during Miocene time further supports this interpretation.