Musgrave Block
The Musgrave Block (also known as the Musgrave Province) is an east-west trending belt of Proterozoic granulite-gneiss basement rocks approximately long. The Musgrave Block extends from western South Australia into Western Australia. The Musgrave Block is primarily exposed through the actions of the Petermann Orogeny at c. 535-550 Ma, which exhumed the orogenic belt along the Woodroffe Thrust. Geomorphology of Quaternary deposits The Musgrave Block is currently passive geologically, with surficial processes described as residual erosion. The area currently experiences on average less than 150mm (6 inches) of rainfall per annum, which provides little surface runoff and hence virtually no erosion. The landforms of the area are primarily composed of wide calcrete plains, often covered by Pleistocene Age aeolian deposits of sand dunes, sometimes reworked into ephemeral sheetwash fans. Outcrop is rare, restricted primarily to the igneous rocks of the Giles Complex and several granite domes, gneiss domes and isolated outcrops. This area is also a distinct physiographic province of the larger West Australian Shield. Palaeozoic rocks Several Palaeozoic to neoproterozoic sedimentary basins onlap the Musgrave Block, and are exposed mostly around its edges. These were derived from erosion of the Musgrave Block basement during the neoproterozoic to Permian. Proterozoic basement The Proterozoic of the Musgrave Block is composed of seven main classes of rocks: Surficial volcanics of c.1050 to 1080 Ma, both mafic (Mummawarrawarra Basalt) and andesitic to rhyolitic (Tollu, Smoke Hill Volcanics) and the Bentley Supergroup volcanics and sediments of c. 1080 Ma Large intrusive caldera type granite intrusive complexes (Palgrave, Skirmish Hill, Smoke Hill), possibly of c. 1050 and likely no older than 1080 Ma Partly metamorphosed, rarely dissected c. 1080 Ma granite Usually unmetamorphosed, rarely dissected granites of a c. 1050 intrusive suite Partly metamorphosed, dissected intrusive rocks of the mafic-ultramafic c. 1080 Ma Giles Complex Highly metamorphosed metagranites of the c. 1200 Ma suite High-grade crystalline metamorphic basement rocks of c. 1550-1300 Ma age The Musgrave Block is flanked by several Proterozoic to Palaeozoic sedimentary basins, whose sedimentary history can elucidate the timing of tectonic events in the Musgrave Block post-1080 Ma. These include the Proterozoic Amadeus and Officer Basins. Events The most illustrating way of considering the Musgrave Block is as part of a time-space plot in which geological events are arrayed in time against rock units, stratigraphic relationships and for correlative purposes. The key events in the Musgrave Block are: Protolith formation ~1550 Ma. Formation of crustal rocks of the Birksgate Complex, which are both mafic and felsic in composition. Igneous event and orogeny ~1300 Ma inferred from geochronology and distribution of felsic “volcanic” supracrustal sequence of the high grade gneisses Musgravian orogeny at ~1200 Ma including generation of voluminous Kulgera Suite of granites and metamorphosis of the Birksgate Complex and ~1300 supracrustal sequence to amphibolite-granulite facies Warakurna Large igneous province at 1076 ± 6 Ma including the intrusion of the Giles Complex and the Winburn Suite of granites, plus deposition of the Bentley Supergroup (including Tollu and Smoke Hill Volcanics) Amata Dyke