Neoproterozoic basalts of the Paleo-Asian Ocean (Kurai accretionary zone, Gorny Altai, Russia): geochemistry, petrogenesis, and geodynamics

Late Neoproterozoic (Late Vendian) basalts of the Paleo-Asian Ocean are found as fragments incorporated in the Kurai accretionary zone, Gorny Altai, Russia. Detailed study of their geochemistry and relationships with associated sedimentary rocks allowed us to recognize three types of basalts: (1) lavas depleted in REE, Nb and Ti, compositionally similar to N-MORB and associated with thin-bedded oceanic siliceous sediments; (2) basalts of transitional compositions, and (3) basalts enriched in the above elements; basalts of types 2 and 3 are similar to Pacific intraplate basalts and are associated with carbonate "cap" sediments. The N-MORB-type basalts generated from a depleted upper-mantle source, whereas the transitional and enriched ones from a heterogeneous mantle source. Their crystallization temperatures were estimated from the experiments on homogenization of melt microinclusions hosted by clinopyroxene phenocrysts (1160-1190 °C) and from the composition of the latter (1100-1295 °C). The geological, lithological, petrological, and geochemical data show that the Kurai basalts were formed in the geodynamic settings of mid-oceanic ridges and oceanic seamounts/islands.