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

Abstract

Till 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.

Exhumation history along the eastern Amundsen Sea coast, West Antarctica, revealed by low‐temperature thermochronology

“…Some of the analyzed samples do, however, record rapid cooling as early as 120 Ma. A similar timing has been identified by Welke et al [] in the Ross Sea embayment of West Antarctica from zircon helium dating of detrital samples, which show a dominant age population of 180 to 130 Ma. Based on that, Welke et al [] infer a Gondwana breakup related exhumation event for this section of the Transantarctic Mountains.…”

“…A similar timing has been identified by Welke et al [] in the Ross Sea embayment of West Antarctica from zircon helium dating of detrital samples, which show a dominant age population of 180 to 130 Ma. Based on that, Welke et al [] infer a Gondwana breakup related exhumation event for this section of the Transantarctic Mountains. At that time, the Zealandia crustal blocks (including Campbell Plateau, Chatham Rise, North Island, and South Island; Figure S1) were still contiguous with West Antarctica and subduction of Phoenix Plate beneath the eastern Gondwana margin was still ongoing.…”

Analysis of Antarctic glacigenic sediment provenance through geochemical and petrologic applications

“…Interpretations of Beacon sediment provenance were initially derived from paleocurrent indicators, and subsequent work on detrital zircon U-Pb ages in these rocks have confirmed inputs from both East and West Antarctic sources (Elliot and Fanning, 2008;Elsner et al, 2013;Elliot et al, 2014). Beacon-derived zircons appear to constitute a significant fraction of zircons in Quaternary tills from the Transantarctic Mountains (Licht et al, 2014;Welke et al, 2016).…”

“…The double-or triple-dating of individual detrital zircon grains provides powerful insight into the geologic history of sediments' sources (e.g., Reiners, 2005;Tochilan et al, 2012;Thomson et al, 2013;Welke et al, 2016). No single grain of sand in glacigenic sediment must be from the same source as any other single grain, but any chronometer or geochemical tracer in a single grain must have experienced the same geological history.…”

Evidence for Extending Anomalous Miocene Volcanism at the Edge of the East Antarctic Craton

“…Palmer et al (2012) showed that nunatak moraines can be valuable repositories of previously unknown bedrock buried beneath the ice sheet. The erratics and detrital minerals transported by ice and finally deposited in moraines can be used to make inferences about unexposed geologic terrains (e.g., Welke et al, 2016).…”