Magmatic relationships between depleted mantle harzburgites, boninitic cumulate gabbros and subduction-related tholeiitic basalts in the Puerto Plata ophiolitic complex, Dominican Republic: Implications for the birth of the Caribbean island-arc

The Lower Cretaceous Puerto Plata ophiolitic complex (PPC) occurs west of the main collisional suture between the Caribbean and North American plates in the northern Dominican Republic, and imposes important constraints on the geochemical and tectonic processes associated with the birth of the Caribbean island-arc. The PPC exposes a tectonically dismembered 3.0-km-thick section of upper mantle harzburgites, lower crustal cumulate gabbroic rocks and upper crustal basaltic pillow lavas, volcanic breccias and pelagic sediments. The harzburgites exhibit a highly depleted signature in terms of their modal compositions, mineral chemistry and whole rock major and trace element contents, suggesting that they are residues after high-degrees of partial melting. Melt modeling suggests that they were similar in trace element characteristics to a boninite. In the crustal sequence, three magmatic episodes have been recognized based on field, mineral and geochemical data. The first phase is composed of the lower layered gabbronorites, which are variably deformed and recrystallized at high-temperature conditions. Trace element modeling suggests that the gabbronorites crystallized from LREE-depleted island-arc tholeiitic (IAT) melts. The second phase is composed of the intermediate layered troctolites (126. Ma), which are undeformed and preserve igneous cumulate textures. Modeling indicates that the troctolites crystallized from boninitic melts. The gabronorite-troctolite substrate was intruded by a third, supra-subduction zone tholeiitic magmatic phase at <. 126. Ma, which formed the upper olivine gabbros and gabbronorites. These gabbroic rocks formed from melts similar in composition to the IAT basalts and basaltic andesites of the overlying Los Caños Fm. Contemporaneous Aptian to lower Albian mafic volcanic rocks of the Los Ranchos Fm and Cacheal complex have comparable IAT geochemical and isotopic signatures, suggesting that all of them may have erupted over a single piece of the Caribbean oceanic lithosphere.The Lower Cretaceous PPC is interpreted to have formed during initiation of W/SW-directed subduction in an intra-oceanic island-arc setting. Fast rollback of the subducting slab would have induced extension in the Caribbean upper plate, and upwelling of mantle already depleted by the generation of oceanic crust. Aided by fluid expelled from the downgoing plate, the decompression melting of this previously depleted mantle at shallow levels yielded boninitic melts. The supra-subduction zone tholeiite sequence would have formed from ascending fertile mantle fluxed with subduction-related fluids as rollback continued. This model constrains the initiation and early evolution of a SW-dipping subduction zone that was responsible for the formation of the primitive Caribbean island-arc/back-arc system currently preserved in several locations in the Greater Antilles. © 2014 Elsevier B.V.The research has been funded by Spanish MECD, through the PRX12/00152 grant of the National Program of Human Resources Mobility to the first author. Funding by the CGL2009-08674/BTE and CGL2012-33669/BTE projects is gratefully acknowledged.Peer Reviewe