Multi-dating single detrital mineral grains (U-Pb, (U-Th)/He, and fission track): a key to reconstructing East Antarctic subglacial landscape evolution

Abstract:

Dating of single detrital mineral grains (typically zircon and apatite) using geochronology and low-temperature (LT) thermochronology is now an established tool in the investigation of a range of geologic processes and problems. For example, detrital zircon U-Pb (DZ) geochronology can be applied to derive maximum depositional age, reconstruct sediment provenance and routing systems, correlate isolated stratigraphic horizons, and characterize remote source terrane geology. Detrital LT thermochronology (fission track and (U-Th)/He dating) can be applied additionally to reconstruct source region cooling and exhumation history through use of lag-time – the time taken between a mineral grain cooling below its closure temperature and its time of deposition. While each of these methods in isolation are very valuable tools, they do have some limitations. For example, DZ geochronology cannot differentiate different sources with the same crystallization age, the youngest DZ age population may be older than depositional age, large orogenic or metamorphic episodes may not produce much primary zircon, and recycling of zircon grains can lead to incorrect interpretation of syn-depositional versus primary sediment source. Detrital LT thermochronology has additional problems such as syn-depositional age volcanic grains leading to erroneous lag-time interpretation. Many of these issues can be overcome by obtaining combining multiple dating techniques on single grains, with the bonus of acquiring higher resolution provenance information. While multi-dating does present analytical challenges, a number of studies have explored this approach in recent years. Here we show how detrital apatite and zircon double- and triple-dating of sediments of varying age (Cretaceous to Holocene) from offshore Antarctica provides a novel new approach to reconstructing the pre-glacial and glacial landscape evolution of this hidden continent over the last few hundred million years. In addition it provided an opportunity to test the optimum methodological approach to triple-dating, particularly for apatite, as well as evaluate potential issues such uncertainties inherent in (U-Th)/He ages acquired from part-polished grains, and whether lasing and/or fission track etching influence age reliability and reproducibility.