Characterising the Magmatic Activity of the Bight Basin Igneous Complex of the Australian Southern Margin.

Monday, 30 January 2017
Marina/Gretel (Hobart Function and Conference Centre)
Joanna M Parr1, David Robert Mole2, Andrew Ross3, Asrarur Rahman Talukder3, Richard Kempton3, Emmanuelle Frery3 and April Picard3, (1)CSIRO, Mineral Resources, North Ryde, Australia, (2)CSIRO, Minerals Resources, Perth, Australia, (3)CSIRO, Energy, Perth, Australia
Abstract:
Although the southern margin of Australia has been classified as a “non-volcanic” margin, a growing number of volcanic cones and volcanic edifices have been identified in the Great Australian Bight (GAB) using seismic and bathymetric surveys. These volcanoes are believed to have formed during the Cretaceous-mid Paleogene breakup of Gondwana. Earlier surveys identified alkali basalts and amygdaloidal (possibly pillow) basalts; however the paucity of samples means that we know little of the provenance, mechanisms of formation, precise timing and impact of this magmatic activity on the host sedimentary rocks. These attributes are not only important in terms of hydrocarbon potential for the basin, but are also fundamental to understanding the breakup between Australia and Antarctica.

This study forms part of the multifaceted Great Australian Bight Deepwater Marine Program that aims to build a comprehensive regional understanding of the deep water GAB geology (source rocks, seeps and volcanic seamounts), and its benthic ecology. During November 2015, the RV Investigator and a support vessel for an AUV spent combined 34 days in the deep GAB, mapping 10,225 km2 of seabed in detail and completing a complementary program of physical geological and biological sampling. A surprisingly complex deep water environment was revealed, including several previously unmapped deep water canyons and ten previously unmapped volcanic seamounts. Approximately 1.3 t of volcanic and sedimentary rocks and over 25,553 biological specimens were collected from 700 m to 4800 m water depths.

Here we present descriptions of some of the igneous rocks observed and sampled, including reworked and in-situ hyaloclastites as well as lesser vesiculated lavas. Locally we observe complex interaction between seafloor sediments and magma including hydrobreccias, peperites, fluidised-carbonate and xenoliths. Unravelling the nature of the magmatic activity in the GAB will give us greater insight into the mechanisms and characteristics of submarine magmatism and has significant implications for understanding the tectonic evolution of Australia’s southern margin.

The Great Australian Bight Deepwater Marine Program is a public good research program led by CSIRO, and sponsored by Chevron, with data generated to be made publically available.

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