Heat Flow in Southern Australia and Connections With East Antarctica. (27th November 2019) - Pollett, Alicia
Key Points: First heat flow measurements from the Coompana Province, southern Australia, indicate values of 40–70 mW/m 2 (57 ± 3 mW/m 2 average) A tectonically reconstructed heat flow map constrains the thermal regime of geological provinces formerly contiguous with East Antarctica Geophysical models of Antarctic heat flow are likely underestimating crustal sources of radiogenic heat that influence subglacial melting Abstract: Viscosity and melt generation at the base of ice sheets are critically dependent upon heat flow. Yet subglacial heat flow is poorly constrained due to the logistical challenges of obtaining boreholes that intersect the bedrock beneath thick ice cover. Currently, continental estimates of Antarctic heat flow are derived from geophysical methods that provide ambiguous constraints of crustal heat sources, despite their demonstrated importance for accurate predictions of future ice sheet behavior. This study pursues an alternative approach by using heat flow measurements from rock units in the Coompana Province of southern Australia, which represent the geological counterparts of those beneath Wilkes Land in East Antarctica. We present nine new surface heat flow estimates from this previously uncharacterized region, ranging from 40 to 70 mW/m 2 with an average of 57 ± 3 mW/m 2 . These values compare favorably to recent geophysically derived estimates of 50–75 mW/m 2 for the Totten Glacier catchment of East Antarctica, and to the single in situ measurement of 75 mW/m 2 from the Law Dome deep ice borehole. However, they are appreciably lower than the range of 56–120 mW/m 2 (83 ± 13 mW/m 2 average) for the abnormally enriched Proterozoic terranes of the Central Australian Heat Flow Province. This study provides the first regional heat flow map of geological provinces formerly contiguous with East Antarctica through the application of continent‐scale heat flow data sets tied to a Jurassic plate tectonic reconstruction for Gondwana. Our approach reveals several discrepancies with current heat flow models derived from geophysical methods and provides a more robust analysis of subglacial heat flow using this plate tectonic synthesis as a proxy for East Antarctica. Plain Language Summary: The Antarctic ice sheet currently represents the largest source for potential sea level rise. Understanding Antarctic ice sheet behavior is important for predicting ice sheet movement and possible melting. Heat that flows from the crust to the base of the ice sheet is a significant contributor to ice sheet behavior. Obtaining estimates of heat flow across Antarctica are problematic due to the logistical challenges of accessing bedrock that lies beneath thick ice cover. Consequently, thermal conditions are currently estimated using geophysical data, from which temperatures beneath the ice extending into the crust and mantle are derived. However, large discrepancies exist between alternative geophysical models, and there remains the need to validate these models and assess their accuracy. This study takes a new approach by using heat flow estimates from southern Australia as a proxy for heat flow in East Antarctica. Plate tectonic reconstructions indicate that approximately 160 million years ago, Australia and East Antarctica were conjoined. We argue that the rocks and corresponding heat flow values of southern Australia are genuine counterparts to those beneath the ice in East Antarctica. If true, this suggests that existing geophysical models can be tested against our reconstructed heat flow maps of this shared tectonic margin.