Musgrave Block - Granites and Calderas

Granites and Calderas

There are three main phases of granite intrusion into the Musgrave Block;

• Kulgera Suite at 1200 Ma
• At ~1080Ma synchronous with the Giles Complex
• Winburn Suite at ~1050Ma postdating the Giles Complex.

The Kulgera Suite is a widespread, voluminous suite of fractionated amphibole-bearing plagioclase rich tonalite to granodiorites of an I-type affinity (Stewart, 2003). They are dated at ~1200 Ma and are considered to be related to melting of the lower crust during the ~1200 Ma Musgravian Orogeny. The Windburn Suite is considered to be an anorogenic A-type granite suite produced by anatexis of the lower crust at ~1080 to 1050 Ma by the injection of the mafic Giles Complex intrusions. They are in most cases poorly fractionated, biotite-muscovite granites, with little hornblende, a high radiometric count and the presence of fluorine. The 1080 Ma granites and 1050 Ma granites can be distinguished on geochemical grounds, the latter is perhaps created by th above process, and the earlier suite a hybrid between A-type and I-type granites formed by assimilation and mixing.

There are also significant granite caldera complexes, of many hundred square kilometres in area, which intrude the Musgrave Block. These are of the ~1050 Ma age, and are subvolcanic, possibly related to some of the ~1050 Ma volcanic rocks.