MANTLE DEGASSING AND TRAVERTINE DEPOSITS AS NEOTECTONIC INDICATORS IN THE GREAT ARTESIAN BASIN OF AUSTRALIA

Endogenic fluids and the travertine mound spring deposits of the western Great Artesian Basin provide underutilized and sensitive gauges of neotectonics in Australia, one of the oldest, flattest, and least tectonically active of the continents. At continental scale, the locus of mound spring discharge follows lithosopheric zones of weakness (Tasman line and Torrens hinge zone). These were established in the Neoproterozoic but are currently being reactivated as the boundary between high velocity mantle in western Australia and lower velocity mantle in eastern Australia, and as zones of concentrated microseismicity in the upper crust. At intermediate scale, travertine deposits offer the potential to quantify rates and locations of neotectonic uplift/subsidence. They are located at the broad hinge region separating actively uplifting mountain ranges (Flinders and Dennison ranges) from subsiding areas (Lake Eyre). A U-Series date of 250 ± 4 ka from near the top of an elevated extinct travertine mound at Beresford Hill (base of travertine ~ 42 m elevation, sample ~ 53 m elevation) indicates rapid denudation rates (relative to the present ~16 m elevation of the Bulldog Shale surface) of 100-150 m/Ma likely driven by uplift. A date on the platform near Elizabeth Spring of 372 ± 14 ka (~34 m elevation relative to surrounding surface of ~14 m elevation) gives lower but still appreciable denudation rates of 54 m/Ma. Elevated ³He/⁴He of 0.16 to 0.81 R_A in mound springs that are aligned on faults supports the model that the fluid conduit system for the endogenic fluids involves mantle degassing associated with basalt transfer in the lower lithosphere and microseismicity and faults as fluid conduits in the upper lithosphere. The lowest elevations in the Australian continent, the mound springs lineaments, and the resulting locations of the main discharge areas of the Great Artesian Basin are seen as a product of interacting scales of active tectonism. Our goal is to understand the sources of the deep fluid inputs, their conduit systems through the lithosphere, and the surface record of neotectonic activity through time preserved in the travertine mound and platform deposits.