Abstract
New major, trace element and isotopic data for Jurassic basalts from SE Australia indicate that they resemble the Jurassic tholeiitic rocks of Tasmania and the Transantarctic mountains. The rocks are all characterized by low TiO (sub 2) , P (sub 2) O (sub 5) , Na (sub 2) O, Fe (sub 2) O (sub 3) , Ti/Zr, Ti/Y and epsilon Nd, and high SiO (sub 2) , Rb/Ba, Rb/Sr, (super 87) Sr/ (super 86) Sr and (super 207) Pb/ (super 204) Pb, relative to oceanic basalts, and therefore comprise a major province, the Ferrar magmatic province, which extended for 3000-4000 km across Gondwana. A review of the other Mesozoic low-Ti CFBs suggests that the Ferrar rocks are an extreme example of these magma types. The fact that both the major and trace element compositions differ from oceanic basalts suggests that these features are linked, and it is argued that they were derived from distinctive source regions in the sub-continental mantle. Such source regions were variably depleted in major and minor elements, and then relatively enriched in highly incompatible elements and Sr and Pb isotopes, which is best explained by the introduction of a small amount of subducted sediment. The tectonic setting of the Ferrar magmatism is poorly constrained, but at present there is no clear geochemical evidence for the involvement of asthenospheric plume material in the petrogenesis of these low-Ti CFBs.