Cromititas podiformes en la Faja Ofiolítica Mayarí-Baracoa (Cuba)

Abstract

The Mayarí-Baracoa Belt occupies the easternmost part of the east-west-trending Cuban ophiolitic belt. It comprises t wo large, chromite-rich massifs: Mayarí-Cristal and Moa-Baracoa. Chromite deposits can be grouped into tree mining districts according to the chemistry of chromite ore: the Moa-Baracoa district (Al-rich chromite), the Sagua de Tánamo district (Al- and Cr-rich chromite) and the Mayarí district (Cr-rich chromite). Al-rich, Ti-rich chromites occur in the mantle crust transition (associated with harzbu rgites, dunites, plagioclase-bearing peridotites, gabbro sills and gabbro dikes), while Cr-rich, Ti-poor chromites occur in the deeper portions of the ophiolitic sequence (associated with harzbu rgites and dunites). The melts in equilibrium with the Al-rich chromites are close to the composition of the back-arc basin basalts (BABB), whereas the melts in equilibrium with the Cr-rich chromites are similar that of the boninite andesite. Chromite from Mayarí-Baracoa Ophiolite Belt formed when cal-alkaline melts (C), formed by melt-rock reactions, percolated through subhorizontal, porous dunitic channels and mixed with oxidized melts (H) in suprasubduction zone mantle. Mixing of these two melts generated a hybrid melt whose bulk composition fell within the chromite liquidus field in the P-T- fO2 space (Hill and Roeder, 1974). Percolation of the hybrid melt through the dunitic channels promoted dissolution of preexisting silicate minerals and chromite crystallization. Al-rich chromite from Moa-Baracoa should be formed in the distal parts of percolation channels at high fO2 , whereas Cr-rich chromite from Mayarí formed toward the proximal parts of the percolation channels under more reducing conditions.