CRYSTAL CHEMISTRY OF CLINOPYROXENES IN SPINEL-PERIDOTITE MANTLE XENOLITHS FROM THE FERNANDO DE NORONHA OCEANIC ISLAND (NE-BRAZIL)

Six c2/c clinopyroxenes (cpx) of spinel peridotite mantle xenoliths enclosed in the alkali basalts from the Fernando de Noronha (FN) oceanic island (NE-Brazil) were studied by means of X-ray diffraction (single crystal) and electron microprobe analyses. Fn-cpx crystal chemistry was compared with those of clinopyroxenes of spinel-peridotite mantle xenoliths enclosed in alkali basalts related to continental extensional tectonics from NE-Brazil and Mt. Leura (Australia). The equilibration pressure estimates by FN-cpx crystal chemistry through cell and site volumes relationships evidences as the mantle xenoliths from Fernando de Noronha oceanic island were sampled at higher depth with respect to the continental analogues from NE- Brazil.