Paper No. 81-17
Presentation Time: 9:00 AM-5:30 PM
USING U-PB DETRITAL ZIRCON AGES TO DISTINGUISH ICE STREAM TILLS IN THE WEDDELL SEA EMBAYMENT, ANTARCTICA
Till from major ice streams and glaciers of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a valuable provenance tool. Characterizing the U-Pb detrital zircon ages in till and rocks will (1) provide the zircon provenance signatures of the material carried by the ice stream – when these signatures are found in LGM and older deposits downstream they can enable interpretation of past ice flow history; and (2) constrain ice-covered upstream bedrock geology that supplies the till carried by ice streams and glaciers. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks. Grains were analyzed by LA-ICPMS at the University of Arizona (n=300). Relative probability U-Pb age density plots of till in moraines along the Foundation Ice Stream and Academy Glacier show prominent peaks at 500-530 and 615-650 Ma, which overlap with the timing of the Ross and Pan-African orogenies. Zircon ages of 1000-1095 Ma are also present. Local bedrock in the Patuxent Range has the most prominent peak at 510 Ma, suggesting the till is predominantly derived from local Patuxent Formation. However, local bedrock also has fewer grains at ~1030 Ma which suggests that this age population is carried in the till as well. Prominent peaks in U-Pb ages from till transported by the Recovery Glacier are 530, 635, 1610 and 1770 Ma. Bedrock of this area contains similar age peaks, with the exception of the 635 Ma peak, suggesting that this ice stream is carrying a signature from an unexposed source of this age completely buried by ice. The Slessor Glacier carries zircons with prominent populations at 1710 and 2260-2420 Ma, which overlap with a high-grade metamorphic event in the Shackleton Range between 1710-1680 Ma. These U-Pb ages will also be compared with zircon ages from the Ellsworth Mountains, and 40Ar/39Ar age dates of hornblende in these samples in order to obtain a more comprehensive dataset to characterize ice stream tills in the WSE.