A Detrital-Zircon Perspective of Antarctic Peninsula - South America Kinematics & Paleogeography – Results from Scotia

The Antarctic Peninsula's tectonic history of connection and disconnection with southernmost South America has profound implications for ocean circulation, Antarctic glaciation, and intercontinental biotic interchange. We compare the Paleogene compositional and exhumational histories of the northern Antarctic Peninsula and the Fuegian Andes via U-Pb detrital-zircon data for 20 samples collected from the Larsen and Magallanes basins. Detrital-zircon age spectra from late Paleocene, Eocene and Oligocene(?) strata of Marambio Island do not contain significant variation. Collectively, these strata are dominated by a 450-680 Ma population (51% of all grains, peak at 530 Ma), with lesser peaks at 95-145 Ma (14%, broad peak at 110-125 Ma), 1.0-2.0 Ga (10%, peak at 106 Ma), 160-195 Ma (6% of grains, peak at 180 Ma) and 200-230 Ma (4% of grains, peak at 220 Ma). Detrital-zircon age spectra from Coniacian-Oligocene Magallanes basin strata of Tierra del Fuego display slight diversification of source terranes between the Cretaceous and early Eocene, and a dramatic provenance shift in the late Eocene. The detrital-zircon age spectra of sampled Cretaceous-Danian strata are composed almost entirely of 60-110 Ma grains (peak at 79 Ma), whereas late Paleocene to middle Eocene strata contain a similar dominant population (57% of all grains, peaks at 77 and 103 Ma), but significant secondary peaks at 122-142 Ma (10%, peak at 130 Ma), and 138-181 Ma (7%, peak at 161 Ma). The late Eocene and Oligocene strata, however, are dominated by 140-195 Ma grains (47%) and have a striking dearth of pre-Jurassic grains (<10%). We interpret these results to suggest (a) different Paleogene sediment provenances for the northern and southern limbs of the Scotia Arc, and (b) a fundamental late Eocene reorganization of Fuegian Andes on the northern limb of the Scotia Arc, coincident with penetration of Pacific water-masses through the Drake Passage.