Subalkaline picrobasalts and plateau basalts from putorana plateau (siberian cfb province). I. Mineral compositions and geochemistry of major and trace elements

We report in this article the results of the investigation'of trace and major element contents and compositions of minerals for the representative collection of the subalkaline picrite basalts from Putorana plateau and for tholeiite plateau basalts sampled from the same locality. Subalkaline picrite basalts (SAPB) are characterized by significant enrichment in highly incompatible trace elements and steep LREE enriched rare earth element patterns, whereas tholeiitic flood basalts (TFB) show only mild enrichment in incompatible elements and flatter REE patterns. High levels of incompatible elements in SAPB is reflected in the abundance of accessory apatite, baddeleite and altered zirconolite in them. Minerals of armalcolite - pseudobrookite series are present in solidified melt inclusions in olivine phenocrysts. Olivine phenocrysts in SAPB contain crystalline inclusions of Ti-rich chrome-spinel with significant fraction of magnetite component which points to the high values of oxygen fugacities. Certain geochemical features of SAPB (high values of Ti/Na and Lu/La ratios, negative K and P anomalies on BSE normalized diagrams) show that their primary magmas formed at very, high pressures. TFB lack these high pressure characteristics. TFB are characterized by distinct Nb-Ta negative anomalies, which imply certain level of crustal contamination, whereas in MgO-rich SAPB Nb-Ta anomaly is absent. Œ2001 r.