Alkaly pyroxenite xenoliths from three volcanic fields in Uganda are largely composed of clinopyroxenite (cpx) and phlogopite-biotite (together>70% of mode). Inter-field compositional variation in these minerals, shown 749 cpx analyses and 237 mica analyses from 34 xenoliths, indicate bulck-chemical lateral variation in the xenoliths source. the ubiquitous presence of alkali clinopyroxenite xenoliths in all the fields suggests this litology is widespread beneath Uganda's Western Rift. Nd-Sr and Pb isotopes systematics indicate that the xenoliths are not cumulate from their host kamafugites, while P-T experiments indicate that the kamafugites were in equilibrium with clinopyroxewnite at >60Km depth. It is argued therefore that the xenoliths are fragments of a laterally variable clinopyroxenite layer in Uganda's Westren Rift deep crust-mantle.
Rift valley magmatism - is there evidence for laterally variable alkali clinopyroxenite mantle?
STOPPA, Francesco;
1999-01-01
Abstract
Alkaly pyroxenite xenoliths from three volcanic fields in Uganda are largely composed of clinopyroxenite (cpx) and phlogopite-biotite (together>70% of mode). Inter-field compositional variation in these minerals, shown 749 cpx analyses and 237 mica analyses from 34 xenoliths, indicate bulck-chemical lateral variation in the xenoliths source. the ubiquitous presence of alkali clinopyroxenite xenoliths in all the fields suggests this litology is widespread beneath Uganda's Western Rift. Nd-Sr and Pb isotopes systematics indicate that the xenoliths are not cumulate from their host kamafugites, while P-T experiments indicate that the kamafugites were in equilibrium with clinopyroxewnite at >60Km depth. It is argued therefore that the xenoliths are fragments of a laterally variable clinopyroxenite layer in Uganda's Westren Rift deep crust-mantle.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
