Composition of megacrysts and evolution of primary melt for rocks of the rhyolite-basalt association of iceland

摘要

The peculiarities of the geological setting of Iceland and the structure of the Earth's crust (oceanic in composition, but with a slightly increased thickness) makes cesses of basaltic magma differentiation. magmatism of Iceland is of essentially mantle origin. Geophysical studies reveal the anomalous mantle beneth iceland.Two rock series of various alkalinity (tholeiitic and alkaline olivine basaltic) are distinguished among Quaternary volcanic rocks of the Iceland rift zone [1,2]. Cenozoic alkaline basalts usually contain megacrysts in association with xenoliths; those are large discrete isets of various rock-forming minerals, among which clinopyroxene, olivine,orthopyroxene, sanidine, and others are abundant. in contrast to the other rift zones and Cenozoic volcanic areas with anomalous mantle, no mantle xenoliths of spinel and garnet lherzolites have been found in the rocks from Iceland. We have found megacrysts (?) in Quaternary basalt with various alkalinities from western and southwestern parts of the Iceland rift zone (on the Reykjanes and Snaiefellsness Peninsulas). The material for our study was collected by A.I.Polyakov in 1982 during the work of a geological expedition of the USSR Academy of Sciences.