Paper No. 43
Presentation Time: 8:00 AM-4:45 PM
Nd Isotope Provenance Signatures from Atlantic Coast of Tierra Del Fuego
Drake Passage forms a gateway connecting the Pacific and Atlantic Oceans between southernmost South America and the Antarctic Peninsula. Its tectonic opening has long been considered critical due to its relations with southern ocean circulation and thermal isolation of Antarctica as a result of the need for such a passageway for the development of the Antarctic Circumpolar Current (ACC). However, proxy data for Antarctic glaciation, inter-ocean water-mass penetration, and plate kinematic changes have led to a wide range of interpreted timings of passage opening. As a result, the relative importance of Drake Passage in Cenozoic glaciation and global climate is poorly understood. Although influx of Pacific sector water into the Atlantic is evidence of gateway opening, great debate persists over the coincidence of seawater penetration and the onset of the ACC that could cause glaciation with requisite opening to admit Pacific water sufficiently for the development of the ACC. Temporal variations in geochemical and mineralogical composition data of sediment provenance from both limbs of the Scotia Arc, however, would be a useful means of reconstructing the kinematic history of the associated orogenic systems. Nd isotope composition data from strata of the Magallanes foreland basin of Argentine Tierra del Fuego indicate a prolonged history of late Jurassic to early Neogene orogenesis and episodic volcanism in the Fuegian Andes that contributed sediments to the Magallanes foreland basin. Whereas the late Cretaceous to late Eocene sediments from Atlantic coast of Tierra del Fuego show εNd values ranging from moderately negative (~-3.5) to progressively higher (~+2.5) values, Oligocene sediments show a strongly negative value (~-7.0) indicating a shift in provenance. This provenance shift approximately coincides with water-mass provenance data indicating at least shallow-water opening of Drake Passage.