Oxides and Silicates in Gabbros Tell two Tales of the Mid-Cayman Rise Magma Chamber

Abstract

The Mid-Cayman Rise (MCR) is a l l0-km long spreading center in the Cayman Trough in the Caribbean. MCR glasses define major and trace element trends consistent with fractional crystallization of an olivine-plagioclase-clinopyroxene a s s e m b l a g e . T h e y have low 87Sr/S6Sr ( 0 . 7 0 2 4 8 0 . 7 2 6 0 ) and high 143Nd/144Nd (0.51311-0.51314). Major-element compositions of silicate minerals in MCR gabbros are compatible with their separation from mafic liquids to produce the glass trends (Elthon et al., 1995). More detailed study of minerals in the gabhros has revealed that they did not form as series of primocrysts from a liquid evolving in a closed system. We present the results of chemical study of spinel grains from several gabbros and show that these grains record a different evolution than that suggested by the silicate phases.