Applications of detrital geochronology and thermochronology from glacial deposits to the Paleozoic and Mesozoic thermal history of the Ross Embayment, Antarctica

Abstract

AbstractTill from moraines at the heads of six major outlet glaciers in the Transantarctic Mountains (TAM) and from till beneath three West Antarctic ice streams have a ubiquitous zircon U‐Pb age population spanning the time of the Ross/Pan‐African Orogenies (610–475 Ma). Geochronology and thermochronology of detrital minerals in these Antarctic glacial tills reveal two different thermal histories for the central and southern TAM. Double‐dating of the zircons reveals a geographically widespread (U‐Th)/He (ZHe) population of 180–130 Ma in most of the till samples. Sandstone outcrops at Shackleton Glacier, and three Beacon Supergroup sandstone clasts from three moraines, have ZHe ages that fall entirely within this range. The similar population and proximity of many of the till samples to Beacon outcrops lead us to suggest that this extensive ZHe population in the tills is derived from Beacon Supergroup rocks and reflects the thermal response of the Beacon Basin to the breakup of Gondwana. A second population of older (>200 Ma) ZHe ages in tills at the head of Byrd, Nimrod, and Reedy Glaciers. For the tills at the head of the Nimrod and Byrd Glaciers, integrating the double‐dated zircon results with 40Ar/39Ar of hornblende, muscovite and biotite, and U‐Pb and (U‐Th‐Sm)/He double‐dates on apatite yields a typical pattern of early rapid orogenic cooling (∼4–10°C/Myr) 590–475 Ma after the emplacement of the Granite Harbour Intrusives. Low temperature thermochronometers at these sites yield variable but quite old ages (ZHe 480–70 Ma and AHe 200–70 Ma) that require a long history at low temperature.