Paper No. 11
Presentation Time: 10:50 AM
THE SECRET LIFE OF QUARTZ; SEM-CATHODOLUMINESCENCE ON QUARTZ FROM ANDRILL SMS CORE INDICATES RECYCLING OF GRAINS
BASSETT, Kari N., Geological Sciences, University of Canterbury, Christchurch, 8041, New Zealand, WILLIAMS, Tessa J., Geological Sciences, University of Canterbury, Prvt Bag 4800, Christchurch, 8053, New Zealand and STOREY, Bryan, Gateway Antarctica, University of Canterbury, Prvt Bag 4800, Christchurch, 8053, New Zealand, kari.bassett@canterbury.ac.nz
Scanning Electron Microscope-Cathodoluminescence combined with optical microscopy has been used to identify recycled quartz grains in the Andrill Southern McMurdo Sound drill core. The Victoria Land Basin is part of the West Antarctic Rift system, with sediment derived from the Transantarctic Mountains and local McMurdo Volcanics. Detrital quartz types have been identified following Bernet and Bassett (2005). The majority of the quartz grains are plutonic, making up 88%, which are evenly mixed between angular and well-rounded grains. 2% of plutonic grains show remnant silica cement. 4% of quartz grains are ambiguous with non-undulose extinction and generally featureless appearance with bright CL; they could be either volcanic or plutonic; 75% of which are well rounded. 8% of grains are identified as metamorphic, characterised by a dark, featureless appearance in CL, undulose extinction and polycrystallinity. Only 21% of the metamorphic grains are rounded.
The metamorphic grains were derived from the Proterozoic metasedimentary Koettlitz Group, making up the basement of the Transantarctic Mountains. The plutonic grains were derived from the Cambrian Granite Harbour Group, which intruded the Koettlitz Group. Preserved silica cement and well rounded texture of many quartz grains is indicative of sediment recycling. The well-rounded ‘ambiguous’ grains are likely to be the stronger cores of plutonic quartz grains that have not been broken during transport. The quartz and subfeldsarenites of the Lower Beacon Supergroup also are derived primarily from the Granite Harbour Group with a minor contribution from the Koettlitz Group. The high percentage of rounded grains suggests that ~50% of the quartz grains have been recycled through the sedimentary Beacon Supergroup before being eroded from the Transantarctic Mountains and deposited offshore in the Victoria Land Basin alongside angular grains, which have been derived directly from source. The identification of the prominance of recycling will have bearing on the interpretation of glacial advances and retreats based on sediment provenance.
