Australia: The Land Where Time Began

A biography of the Australian continent 

Kimberley Region, WA, Palaeoproterozoic Post-Collisional, High-K Felsic Igneous Rocks, Tectonic Implications

The Hooper and Lamboo Complexes, Kimberley Region, northwestern Australia, are dominated by high-potassium I-type granites, high-level porphyry intrusions, and felsic volcanic rocks of the Whitewater Volcanics. In the field the granites, porphyries and volcanic rocks grade into each other and they have the same mineralogy, abundances that are similar for major and trace elements, and SHRIMPU-Pb zircon ages that are indistinguishable of 1865-1850 Ma. Evidence of mingling between granites and gabbros that are coeval is widespread. The authors¹ suggest magma mixing may be important in some of the mafic granites, though most of the rocks formed from felsic parent magmas that underwent fractional crystallisation to varying degrees. It is suggested that partial melting of intermediate to felsic calc-alkaline rocks along the southern and eastern margins of the Kimberley Craton may have been responsible for the formation of the felsic igneous rocks, subsequent to accretion to the craton of various  terranes of earlier Palaeoproterozoic age. Models for Palaeoproterozoic high-potassium granites in northern Australia invoking intracratonic rifting of a stable craton from the Archaean may need to be revised.

Sources & Further reading

1. Griffin, T. J., R. W. Page, S. Sheppard, and I. M. Tyler. "Tectonic Implications of Palaeoproterozoic Post-Collisional, High-K Felsic Igneous Rocks from the Kimberley Region of Northwestern Australia." Precambrian Research 101, no. 1 (5// 2000): 1-23.