D, O and C isotopes in podiform chromitites as fluid tracers for hydrothermal alteration processes of the Mayari-Baracoa Ophiolitic Belt, eastern Cuba

Abstract

The Mayari-Baracoa Ophiolitic Belt (MBOB, eastern Cuba) is composed of two large, chromite-rich massifs: Mayari-Cristal and Moa-Baracoa. The chromitites and hosting dunites were firstly affected by a regional serpentinization event, a subsequent episode of hydrothermal alteration (chloritization mainly) and, finally, these already altered bodies were crosscut by thin calcite-dominated veins. Analysed serpentines from serpentinized chromitites and dunites present very similar isotopic compositions (delta(18)O= + 4.7 parts per thousand to + 6.3 parts per thousand and deltaD = - 67 parts per thousand to - 60 parts per thousand), suggesting that the serpentinization process took place at moderate temperatures, in an oceanic environment. Serpentine formation by interaction with ocean water is also supported by the isotopic composition of chlorite and calcite. These results suggest that the serpentinization, chloritization and fracture filling processes of the Mayari-Baracoa Ophiolite Belt took place in a subocean floor scenario and, thus, that the Mayari-Baracoa serpentines represent a good example of serpentine formed during interaction with seawater. The oceanic origin of the serpentines from serpentinized chromitites and dunites from the MBOB indicate that the serpentinization of the mantle sequence occurred pre-thrusting (pre-emplacement in age). (C) 2003 Elsevier Science B.V. All rights reserved.