Provenance of glacial tills in Ong Valley, Antarctica, inferred from quartz cathodoluminescence imaging, zircon U/Pb dating, and trace element geochemistry
Monday, 15 December 2014: 11:50 AM
An issue for interpreting exposure ages using cosmogenic nuclides is prior exposure (inheritance), especially for stable nuclides such as Ne-21. In this study we examine the reliability of provenance as a possible tool for determining the degree to which inheritance is an issue for a given sample. We use zircon U/Pb ages, quartz cathodoluminescence imaging, and trace element geochemistry from Antarctic glacial drifts and compare these to zircon, quartz, and trace elements from local bedrock in order to determine the drifts’ origins. This is potentially useful in Ong Valley in the Central Transantarctic Mountains, and likely elsewhere in Antarctica, as Antarctic glacial sediments are only derived either from sources that lie beneath the ice, where it likely had little prior exposure to cosmic rays, or from the relatively small amount of local, exposed bedrock, which would have inherited nuclides. Thus, sediment provenance is likely correlated with its inherited nuclide inventory. The bedrock of Ong Valley is composed of granite (Hope Granite, Granite Harbour Intrusives) and gneiss, and contains three glacial drifts. We collected samples from these three drifts and the surrounding bedrock. Cosmogenic nuclide dating using Ne-21 provides exposure ages for the quartz that can be used to constrain the timing of the glacier’s retreat from the three sites. The accuracy of these three exposure ages depends on the prior (or inherited) exposure of the sediment and its sources. The use of the use of multiple methods for determining provenance allows us to compare the results and see if they reach the same conclusion. If cathodoluminescence imaging proves to be a reliable method for establishing provenance it would provide complementary information for cosmogenic nuclide dating, especially because quartz is significantly more abundant and we would be obtaining coupled provenance information and exposure ages from a single mineral.