Reconstructing the crustal section of the intra-oceanic Caribbean island arc: contraints from the cumulate layered gabbronorites and pyroxenites of the Rio Boba plutonic sequence, northern Dominican Republic
J. Escuder-Viruete 1, M. Castillo-Carrión1, F. Pérez Valera 2, P. Valverde-Vaquero 1, Á. Rubio Ordónez3, F.J. Fernández 3
1Instituto Geológico y Minero de España, C. La Calera 1, 28760 Tres Cantos, Madrid. Spain
2Departamento de Ciencias de la Tierra y del Medio Ambiente, Universidad de Alicante. 03080 Sant Vicent de Raspeig, Alicante. Spain
3Departamento de Geología, Universidad de Oviedo. C. Jesús Arias de Velasco, 33005 Oviedo. Spain
Corresponding author: Javier Escuder-Viruete (j.escuder@igme.es)
Key Points:
Abstract
Located in northern Dominican Republic, the Early Cretaceous Rio Boba mafic-ultramafic plutonic sequence constitutes a lower crust section of the Caribbean island arc, made up by gabbroic rocks and subordinate lenses of pyroxenite. Modal compositions, mineral chemistry, whole-rock compositions and thermobarometric calculations indicate that pyroxenites and gabbronorites represent a cumulate sequence formed by fractionation of tholeiitic magmas with initially very low H2O content in the lower crust of the arc (0.6-0.8 GPa). Melts evolved along a simplified crystallization sequence of olivine → pyroxenes → plagioclase → Fe-Ti oxides. The magmatic evolution of the Rio Boba sequence and associated supra-crustal Puerca Gorda metavolcanic rocks is multi-stage and involves the generation of magmas from melting of different sources in a supra-subduction zone setting. The first stage included the formation of a highly depleted substrate as result of decompressional melting of a refractory mantle source, represented by a cumulate sequence of LREE-depleted IAT and boninitic gabbronorites and pyroxenites. Sub-horizontal ductile stretching, deformation fabrics and recrystallization microstructures show that this substrate was variably deformed at upper amphibolite to mid-P granulite facies conditions. The second stage involved volumetrically subordinate troctolites and gabbros, which preserve cumulate textures and are not penetratively deformed. The mantle source was refractory and enriched by a LILE-rich hydrous fluid derived from a subducting slab and/or overlying sediments, and possibly by a LREE-rich melt. The third stage is recorded in the upper crust of the arc by the Puerca Gorda ‘normal’ IAT protoliths, which are derived from an N-MORB mantle source enriched with a strong subduction component. This magmatic evolution has implications for unravelling the processes responsible for subduction initiation and subsequent building of the intra-oceanic Caribbean island arc.