Melanges and olistostromes in the Puerto Plata area (northern Dominican Republic) as a record of subduction and collisional processes between the Caribbean and North-American plates
Résumé
The Cordillera Septentrional records the oblique subduction and collisional processes between the Caribbean and North American plates during Late Cretaceous to early Palaeogene times. The Puerto Plata basement complex of this range is considered to represent a fragment of the frontal part of the Great Arc of the Caribbean in Hispaniola that originated during thrusting of the Caribbean plate onto the North American shelf. This paper describes and interprets melange-type formations spatially related to this basement complex and its associated sedimentary cover, the Imbert Fm. Such formations include the San Marcos olistostromic Fm and a unit of Serpentinic Breccias located at the base and interbedded in the lower section of the former. Both units are Eocene in age, have been mainly deposited by syntectonic subaqueous mass-transport processes and typically host a varied mixture of blocks of known and unknown origin, including high-P metamorphic rocks (knockers). Cartoon models of palaeotectonic reconstructions depicting the final stages of subduction and the onset of collisional process in Early and Middle Eocene times respectively, are proposed in order to show the original relationships among all geological units involved in the study area. The Serpentinic Breccias are interpreted as being the result of extensive sedimentary recycling of peridotite and serpentinite massive bodies or subduction related melanges when exposed at the surface by return flow during early exhumation stages of the accretionary complex, coevally with the end of island-arc volcanism. This process is inferred to be the triggering mechanism for the feeding of originally deep-sited knockers, probably in combination with strike-slip tectonics and associated mud diapirism The slightly younger San Marcos Fm records the collision event and main exhumation stage, while displaying the typical features present in olistostromes and other mass-wasting, gravitationally-driven deposits recognized in extensive areas of forearc and accretionary complexes involved in arc-continent collisional processes.