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Presented By: Earth and Environmental Sciences

Smith Lecture: Eric Roberts

The Wandering Falklands: A geological odyssey in the South Atlantic

A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica
A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica
The Falkland Islands are an isolated micro-continent within the South Atlantic Ocean proximal to the South American continent and characterized by Paleozoic sedimentary successions for which connections with coeval depositional systems in southern Gondwana are debated. Two sets of mafic dikes cross-cut sedimentary units on the Falklands and represent the only volcanics in the islands. Aside from an isolated exposure of Proterozoic granite, no other plutonic rocks are known to exist. Here we report the presence of rare to abundant intermediate to felsic volcanic and plutonic pebbles/cobbles from beaches along the northern and southern margins of the Falkland Islands for which there is no obvious source in the islands today. U-Pb LA-ICPMS dating of zircon grains separated from numerous representative volcanic cobbles from the northern beaches demonstrates a Middle-Late Jurassic provenance source between ~165-151 Ma. These ages are comparable to silicic volcanics in Patagonia, South Africa and the Antarctic Peninsula of the Chon-Aike silicic large igneous province linked with initial Gondwanan break-up, suggesting that similar volcanics are likely present in the proximal (shallow) offshore portion of the north Falklands that will potentially help to better refine the pre-break up position/tectonics of the Falklands within Gondwana. Additional U-Pb dating of volcanic and plutonic cobbles from southern Falklands beaches indicates a different provenance source, as indicated by a broad range of Jurassic to Paleocene ages, which compare favorably with documented rocks from the islands, submerged banks and volcanic edifices of the North Scotia Arc (e.g., Burdwood, South Georgia). The timing and mechanisms for delivery of these large clasts to the Falkland Islands is confounding but may be related to large submarine slides off the Burdwood Bank and subsequent tsunami deposits during periods of lowered sea level during the Quaternary. Determining the provenance of these allochthonous clasts may help with understanding the complex tectonics of this region and timing of opening of the Scotia Arc and associated ocean currents.
A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica
A man in a striped hat an orange sunglasses stands in front of a barren landscape in Antarctica

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