Petrogenesis of eclogite and mafic granulite xenoliths from South Australian Jurassic kimberlitic intrusions: tectonic Implications

Jurassic kimberlites in South Australia have entrained sub lithospheric mafic granulites and eclogites from the eastern margin of the Australian Craton.This thesis looks at these rocks as a unique window into the sub-lithospheric mantle beneath the south eastern margin of Gondwana.Samples collected from Angaston, El Alamein and Pitcairn included eclogites, amphibole eclogites, amphibole granulites and feldspar rich granulites.These samples were prepared for analytical work at the University of Adelaide.Whole rock geochemistry was collected from x-ray fluorescence in the Mawson Laboratories.Mineral identification and geochemistry was determined by the Cameca SX 51 microprobe at Adelaide Microscopy.Geothermobarometry showed pressures between 6-30kbar, which represent 15-90km of depth and temperatures between 620-1200 o C.These rocks experience very high pressure and temperatures and show petrological evidence of isobaric cooling path from the adiabat to the stable geotherm.Magma crystallisation models using MELTS program helped to determine the protoliths that appear to represent mafic underplates.The cumulate and melts that make up these xenoliths have been shown in this thesis to most likely have been derived from a MORB source that crystallised at high pressures (up to 30kbar).Pseudosections produced with the Theriak-Domino program were used to produce a metamorphic path and show that rock type is closely linked to emplacement depth and bulk composition.Radiogenic dating using Neodymium and Samarium system created isochron's using IsoPlot and gave ages supporting protolith emplacement during the Neoproterozoic (≈670Ma) around the breakup Rodinia.