Paleostress evolution during the exhumation of high-P marbles, Samaná Complex, northern Hispaniola

The marble of the Samaná complex presents a widespread foliation formed during its exhumation following a general decompressive strain path from high pressure (2.0>P>0.7 GPa) and low temperature (<500 ºC) conditions. The foliation is plano-linear and blastomylonitic. Deformation distribution is highly heterogeneous. Calcite preferred orientation is poor, even though the marble has a well-defined tectonic fabric. The blastomylonitic fabric is masking an earlier tectonic fabric. Cathodoluminiscence images reveal that intense fracturing formed prior to foliation development in the marbles. The thermodynamic modelling of mineral phase transformations during prograde metamorphism indicate an increase in water content (1.2%350 MPa during deformation. In contrast, mean flow stress during grain-boundary migration is estimated in |s1-s3| <150 MPa. The high paleostress record and microstructures of the marble are consistent with the high exhumation rate calculated (>110 MPa Ma-1). All of these data suggest that exhumation always occurred near the brittle-ductile regime of deformation.