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Recent mantle degassing recorded by carbonic spring deposits along sinistral strike-slip faults, south-central Australia

2016-11-15
Ring, Uwe
UYSAL, I. Tonguc
YUCE, Galip
UNAL-IMER, Ezgi
ITALIANO, Francesco
İmer, Ali
ZHAO, Jian-xin
The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle He-3 and CO2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50-70 km. U-series ages on 26 samples range from 354 +/- 7 to 1.19 +/- 0.02 ka (2 sigma errors) and suggest a clustering every similar to 3-4 ka since similar to 26 ka. Geochemical data demonstrate a remarkable mantle to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths >3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. He-3/He-4 isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60-70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure. (C) 2016 Elsevier B.V. All rights reserved.