Musgrave Block - Bentley Supergroup

Bentley Supergroup

The Bentley Supergroup Volcanics are a sequence of bimodal supracrustal volcanic rocks formed during the ~1080 Warakurna Large Igneous Province, and are widely considered comagmatic with the mafic to ultramafic Giles Complex intrusions.

The Bentley Supergroup is composed primarily of bimodal volcanism, with several hundred-metres thicknesses each of alternating rhyolite and basaltic volcanism adding up to several kilometres true thickness in the area of the Warburton Range to the southwest of the Palgrave caldera. The Bentley Supergroup is divided into the Cassidy Group, Pussycat Group and Tollu Group.

The prevailing theory of the formation of the Bentley Supergroup is that the Warakurna Large Igneous Province, primarily represented by the Giles Complex intruding into the lower crust, breached the crust and erupted voluminous basaltic lava flows, and when enough heat had been added to the crust by the massive intrusions below, intracrustal felsic and intermediate melts were produced, forming A-type intracontinental granites of the Winburn Suite, and the felsic volcanic rocks.

This created the typical bimodal volcanic signature of the Cassidy Group and Pussycat Groups; the Tollu Group is a bit different, and it is considered the product of the large granite calderas which were formed immediately after the Giles Complex mamatism. Giles (1980) and earlier mappers have assigned the MacDougall Formation, overlying Mummawarrawarra Basalt, intermediate Smoke Hill Volcanics and the Tollu Volcanics to the Bentley Supergroup.

There has been little real study done on the Bentley Supergroup Volcanics since the 1960s. Geochemical and petrological observations are few and far between or lacking comprehensive rare earth and trace elements suites. The Bentley Supergoup is poorly exposed in South Australia (if at all).