THE INFLUENCE OF CRYSTAL AND MELT COMPOSITIONS ON THE REE+Y PARTITIONING BETWEEN CLINOPYROXENE AND BASANITIC/TEPHRITIC MELTS OF CRETACEOUS ALKALINE MAGMATISM ON THE SOUTHEASTERN PART OF THE SOUTH AMERICAN PLATFORM, SOUTHEAST BRAZIL

摘要

The partition coefficients of trace elements between clinopyroxene and basanite/tephrite matrices representative of magmatic melts have been obtained from ultramafic alkaline dikes related to Cretaceous magmatism on the South American Platform. The four studied dikes, related to the Ponta Grossa Arch (APG) and the Serra do Mar (SM-U, SM-PN, SM-B) alkaline provinces, are porphyritic melanocratic bodies with fine-grained to very fine-grained matrices and are classified as lamprophyres (monchiquite or camptonite), with the exception of SM-B, which is classified as an olivine basalt. The rocks have potassic to ultrapotassic affinity and are tephrite or basanite. The respective melts of the last stage of magmatic differentiation (fine-grained to very fine-grained matrices) are also tephrite or basanite. In general, the composition of the matrices differs from the respective whole-rock compositions by enrichment in normative felsic minerals and incompatible elements and by depletion in normative mafic minerals.