The petrology of kimberlites from South Australia: Linking olivine macrocrystic and micaceous kimberlites

摘要: Abstract Kimberlites of Jurassic age occur in various parts South Australia. Thirty-nine these kimberlites, which are mostly new discoveries, were studied to characterize their structural setting, petrography, and the composition constituent minerals. Although some kimberlites Australia on Archean Paleoproterozoic Gawler Block, most part a northwest-trending, semi-continuous kimberlite dike swarm located Adelaide Fold Belt. The typically as dikes or sills, but diatremes also present. In Belt, restricted hinge zones regional-scale folds within thick sedimentary sequences Adelaidean Supergroup. Despite widespread severe alteration, coherent pyroclastic can be readily distinguished. U-Pb Sr/Nd isotopic compositions groundmass perovskite indicate that all belong same group (177–197 Ma) formed near-primitive mantle environment (87Sr/86Sr: 0.7038–0.7052, eNd: −0.07 +2.97). However, compositionally diverse, range from olivine-dominated varieties (macrocrystic kimberlites) olivine-poor, phlogopite-dominated (micaceous kimberlites). Macrocrystic contain magnesium-rich phlogopite spinel, they olivine macrocryst-rich. Micaceous contrast, more iron- titanium-rich less magnesian macrocrysts rare absent. Correlations between spinel with modal abundances olivine, contrast macrocrystic micaceous is primarily linked amount components incorporated into uniform parental mafic silicate melt. We propose assimilation xenocrystic magnesite incorporation dunitic source rocks key processes modified melt created unique hybrid (carbonate-silicate) character kimberlites. Based xenoliths xenocrysts, lithospheric sampled by Australian relatively uniform, extends depths 160–170 km, slightly below diamond stability field. Only beneath Eurelia area does lithosphere appear thicker (>175 km), consistent presence diamonds