Using U-Pb Dating of Detrital Zircons to Determine Major Ice Stream Flow History in the Weddell Sea Embayment, Antarctica

• Main Author: Agrios, Liana Marie
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IUPUI University Library 2018
• Subjects: Zircons; Provenance; U-Pb Dating; Ice Streams; Weddell Sea; Antarctica; Weddell; Berkner Island; Foundation Ice Stream; Institute Ice Stream; Slessor; Antarc*
• Online Access: https://dx.doi.org/10.7912/c2/554; https://scholarworks.iupui.edu/handle/1805/17426

Indiana University-Purdue University Indianapolis (IUPUI) : Tills from major ice streams (Institute, Foundation, Academy, Recovery, and Slessor) of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a provenance tool to better understand ice stream dynamics. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks, and 12 samples of offshore till. Grains were analyzed by LA-ICPMS at the University of Arizona (n=5447). Relative probability U-Pb age density plots of till in moraines along the Institute Ice Stream have dominant Grenville (1070 Ma) and secondary Ross/Pan-African peaks (560 Ma, 630 Ma). The Foundation and Academy show prominent Ross/Pan-African peaks (500-530 Ma and 615-650 Ma). The Recovery transports zircons with prominent 530 Ma and 635 Ma peaks along the southern margin, and 1610 and 1770 Ma along the northern margin. The Slessor carries zircons with prominent populations at 1710 Ma and secondary 2260-2420 Ma. U-Pb ages in zircons from offshore till samples show a general trend of fewer Mesozoic ages from west to east. The western most core, PS 1423, has dominant Jurassic populations while cores 1197 and 1278 have a high proportion of early Ross/Pan-African ages relative to Grenville ages. The similar zircon age distributions between PS 1278 and the Foundation Ice Stream tills suggest that the Foundation switched to an easterly flow path around Berkner Island (BI) at some point during the LGM. In the eastern Weddell Sea (PS 1400), there was a near absence of Proterozoic zircon age populations carried by the Slessor and northern side of the Recovery. Another unexpected find was a lack of Grenville ages in PS 1423 relative to the Institute tills. The U-Pb data in this study provides a basis for two possible LGM ice flow reconstructions. In the first, the Institute flowed west around the unnamed isolated bedrock highs, deposited tills between PS 1423 and PS 1197, providing a westerly flow path around BI for the Foundation. In the second, the Institute flows over the subglacial topography and deposited till closer to PS 1197, forcing the Foundation east around BI.