High-pressure greenschist to blueschist facies transition in the Maimón Formation (Dominican Republic) suggests mid-Cretaceous subduction of the Early Cretaceous Caribbean Arc
Abstract
The Maimón Formation (Cordillera Central, Dominican Republic) is formed of metamorphosed bi-modal mafic-felsic volcanic rocks and sedimentary horizons of Early Cretaceous age deposited in the forearc of the nascent Caribbean island arc. Two structural-metamorphic zones depict an inverted metamorphic gradient: the Ozama shear zone, which records intense mylonitic and phyllonitic deformation and ubiquitous metamorphic recrystallization, tectonically overlies the much less deformed and variably recrystallized rocks of the El Altar zone. The presence of ferri-winchite and high-Si phengite, first reported in this paper, in the peak metamorphic assemblage of rocks of the Ozama shear zone (actinolite + phengite + chlorite + epidote + quartz + albite ± ferri-winchite ± stilpnomelane) point to subduction-related metamorphism. Pseudosection calculations and intersection of isopleths indicate peak metamorphic conditions of ~ 8.2 kbar at 380 °C. These figures are consistent with metamorphism in the greenschist/blueschist facies transition, burial depths of ~ 25-29 km and a thermal gradient of ~ 13-16 °C/km. Our new data dispute previous models pointing to metamorphism of Maimón rocks under a steep thermal gradient related to burial under a hot peridotite slice. Instead, we contextualize the metamorphism of the Maimón Formation in a subduction scenario in which a coherent slice of the (warm) Early Cretaceous forearc was engulfed due to intra-arc complexities and regional-scale-driven tectonic processes operating in the late Early Cretaceous. Integration of our findings with previous studies on metamorphic complexes in Hispaniola suggests that a major tectonic event affecting the whole arc system took place at c. 120-110 Ma.Although the three deposits are classified as non-auriferous, significant Au contents are described in Cerro de Maimón ore (to 7.6 g/t) and in intermediate (to 1.44 g/t) and upper (to 0.88 g/t) mineralized zones of the San Fernando deposit. Gold, probably precipitated as invisible gold during exhalative mineralization, shows evidence for later metamorphism- and deformation-triggered remobilization and re-precipitation as subordinate electrum. Solid-state mechanical transfer was apparently the dominant upgrading mechanism in the Cerro de Maimón deposit whereas liquid-state chemical transfer would have governed the upgrading process in the San Fernando deposit.
Keywords: Blueschist; HP/LT metamorphism; Maimón Formation; Dominican Republic; Caribbean; Volcanic arc
----------------------------------------------------------------------------------------------------------
To Cite this article:
Torró,L., García-Casco, A., Proenza, J.A., Blanco-Quintero, I.F., Gutiérrez-Alonso, G., Lewis,J.F. (2016): High-pressure greenschist to blueschist facies transition in the Maimón Formation (Dominican Republic) suggests mid-Cretaceous subduction of the Early Cretaceous Caribbean Arc. Lithos, 266-267, 309-331.
