Paper No. 8
Presentation Time: 10:00 AM
OVERVIEW OF PROVENANCE SIGNATURES, GEOLOGIC HISTORY, AND ICE SHEET STABILITY INDICATED BY DETRITAL ZIRCON U/PB AND (U-TH)/HE AGES FROM ANTARCTIC TILL
Over 3500 detrital zircons from the Ross Embayment were analyzed with U/Pb to characterize regional patterns in age distributions, assess provenance and constrain ice sheet history. Grains were isolated from a total of 21 high-elevation nunatak moraines and lateral moraines from major East Antarctic outlet glaciers, West Antarctic subglacial tills and offshore deposits in the Ross Sea from the Last Glacial Maximum (LGM). These analyses provide important new information about East Antarctic ice sheet stability, a distinctive West Antarctic ice sheet tracer, and the subglacial extent of geologic terrains. In particular, U/Pb ages from the Ross/Pan-African population (480-610) can be used to locate areas of glacial erosion. Younger grains from lateral moraines (500-550 Ma) reflect ages of locally derived material from the valley walls and older ages (550-610 Ma) indicate erosion and input upstream of the main outlet glacier valleys. The abundance of ages 550-610 Ma from moraines nearest the continental interior are consistent with zircon ages of magmatic growth and/or metamorphic overgrowth from Dronning Maud Land that are associated with the Pan-African Orogeny. Our data suggest that such materials and/or their erosional products must extend toward the interior of East Antarctica and into the catchments from at least the Byrd to Scott Glaciers. Second, East Antarctic ice sheet stability over multiple glacial cycles is reflected in invariant detrital zircon U/Pb signatures and moraine geomorphology of laterally extensive nunatak moraines on the inland side of the Transantarctic Mountains. This consistency in provenance is important for interpreting the origin of older offshore glacial deposits. Third, a distinct ~100 Ma age population present in U/Pb and (U-Th)/He from West Antarctica and eastern Ross Sea tills fingerprint a West Antarctic signature. Finally, ubiquitous U/Pb ages of 480-610 Ma can be subdivided with (U-Th)/He and reveal a widespread thermal event affecting the Beacon basin from ~180-110 Ma. This was likely the product of a combination of factors related to the breakup of Gondwana including local heating from intrusion of the Ferrar dolerite, subsidence and subsequent exhumation within the Beacon basin and a higher than normal geothermal gradient.