MELTING OF A SUBDUCTION-MODIFIED CONTINENTAL LITHOSPHERIC MANTLE - EVIDENCE FROM LATE PROTEROZOIC MAFIC DIKE SWARMS IN CENTRAL AUSTRALIA

Geochemical and Nd isotopic studies of two postorogenic, Late Proteroz oic (1083 +/- 23 Ma), high-Mg tholeiitic dike swarms in central Austra lia indicate that the dike swarms were derived by partial melting of t he continental lithospheric mantle, which was modified by subduction p rocesses during major crust-formation events in the region. Both dike swarms (Stuart and Kulgera, which intrude the Arunta and Musgrave inli ers, respectively) resemble island-arc tholeiites in terms of geochemi cal features. They yield whole-rock Sm-Nd ages of 1853 +/- 189 Ma with epsilon(Nd) = -4.2 +/- 4.2 (Stuart) and 1589 +/- 165 Ma with epsilon( Nd) = +1.7 +/- 3.6 (Kulgera). The two whole-rock ages and initial epsi lon(Nd) Values are remarkably similar to the oldest U-Pb zircon ages a nd initial epsilon(Nd) values obtained from the corresponding basement blocks. These isotopic data are interpreted as recording Sm-Nd fracti onation events in the continental lithospheric mantle associated with major episodes of crust formation in the Early Proterozoic.