oa South African Journal of Geology - The Proterozoic Hatches Creek Group, an ensialic sandstone-bimodal volcanic association in central Australia

Volume 89 Number 2
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590



The recently investigated 10 km-thick Hatches Creek Group is exposed over 15 000 km2 in the southern part of the Proterozoic Tennant Creek Inlier, central Australia. It unconformably overlies the 1870 Ma old Warramunga Group to the north, and was deformed and later intruded by post-tectonic granite plutons, one of which has been dated at about 1640Ma. Rock types include quartzose, lithic, and feldspathic sandstones, basaltic and dacitic to rhyolitic lavas and pyroclastics, and subordinate pebbly sandstone, conglomerate, siltstone, shale, mudstone, and carbonates which in places are stromatolitic. Sedimentary structures indicate fluvial to shallow marine deposition, with rapid sedimentation keeping pace with subsidence. The volcanics are largely subaerial. Granophyre and dolerite sills, probably comagmatic with the volcanics, intrude the lower part of the sequence. The felsic volcanics and associated intrusives (63-77 % Si02) are potassic. The basalt lavas and dolerite sills ( 44-57 % Si02) have continental tholeiite affinities.

The Hatches Creek Group has been compressed into major upright anticlines and synclines, mostly concentric in style, and regionally metamorphosed to mainly greenschist facies. It is cut by gold-bearing quartz veins, which are possibly syntectonic, and by tungsten-bearing quartz veins containing minor copper, bismuth, and molybdenum, probably related to post-tectonic granites.

The prevalence of shallow-water sediments and subaerial volcanics and the bimodal composition of the volcanics indicate crustal downwarping and thinning during a tensional regime. Underlying sialic rocks indicate an intracratonic setting. Sedimentation and volcanism do not appear to be associated with rift structures, and the middle and upper parts of the group were probably laid down in an extensive epicontinental sea.

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