Cataclasis relicta en los mármoles de alta presión del complejo de Samaná, Noreste de la República Dominicana

Resumo

Cold-cathodoluminiscence (CCL) images have unmasked relict cataclastic microstructures in marbles and calc-schists of the higher-pressure units of the Samaná complex. The grain size of the cataclastic microstructures always has a self-similar distribution of power law type, with a slope break at log (ri)=1.7. The large grain size fraction (1.7<log (ri)<2.4) is characterized by fractal dimension D2=2.43 in the calcite-microstructures of the Punta Balandra unit and D2=2.72 in the Santa Bárbara unit. Both D-values are within the usual range of the carbonate-cataclasites and they are significant with the linear correlation of R2 =0.95 and 0.93, respectively. However, the finer grain size fraction (0.9<log (ri)<1.7) is characterized by D1<1 and this grain-size distribution is beyond the fractal-range for pure cataclastic-fabric, even though it has better fit power-law distribution. Microstructures such as dissolution-surfaces, interpenetrated particles and the higher roundness and lower irregularity of the boundary grain from fine fraction indicate that dissolution-precipitation creep was dominant after cataclasis. Clast size and stress reduction after cataclasis and the high fluid pressure provided favourable conditions to allow dissolution-precipitation creep. Transition from cataclastic flow to dissolution-precipitation creep was scale-dependent and it tended to homogenize and reduce the finer grain size fraction. Consequently, the slope break between D1 and D2 is interpreted as a record in the grain size distribution produced by a change in the dominant deformation mechanism.