High- and low-K granites and adakites at a Palaeoproterozoic plate boundary in northwestern Australia

The Lamboo Complex is one of several Palaeoproterozoic terrains in northern Australia that is intruded by high-ii, I-type granites. The oldest granite s in the complex consist of the high-Ii 1865-1850 hla Paperbark supersuite with initial epsilon (Nd) values between -2.7 and -4.0. Tonalite sheets of the c, 1850 hla Doupalls suite have high Al2O3, Na2O, Sr, Sr/Y and La/Yb, a nd low Y and HREE, and initial e,, values between +1.4 and +0.7. The rocks have compositions similar to adakites that form by melting of mafic rocks i n the deep crust with garnet in the residue. Granites of the 1835-1805 Ma S ally Downs supersuite range from high-K types through to crustally derived adakites, all with initial epsilon (Nd) values between +0.1 and -1.2. The t wo supersuites and the Dougalls suite were intruded into different tectonic settings, previously all of the granites in the Lamboo Complex were interp reted as partial melts of a chemically and isotopically uniform underplate beneath a rifted Archaean craton. However, their spatial and temporal distr ibution, and their varied compositions, are best explained by large-scale h orizontal plate motions and subduction of oceanic crust.