Geochemical constraints on the origin of the late Jurassic proto-Caribbean oceanic crust in Hispaniola

Abstract

The nature of the oceanic crust produced through rifting and oceanic spreading between North and South America during the Late Jurassic is a key element for the Caribbean plate tectonic model reconstruction. Located in the Cordillera Central of Hispaniola, the Loma La Monja volcano-plutonic assemblage (LMA) is com- posed of gabbros, dolerites, basalts, and oceanic sediments, as well as metamorphic equivalents, which represent a dismembered fragment of this proto-Caribbean oceanic crust. Petrologic and geochemical data show that the LMA have a relatively broad diversity in composition, which represent the crystallization products of a typical low-pressure tholeiitic fractionation of mid-ocean ridge basalts (MORB)-type parental magmas, ranging from N- to E-MORB. Three geochemical groups have been dis- tinguished in the volcanic sequence: LREE-flat to slightly LREE-enriched basalts of groups II and III occur inter- layered in the lower stratigraphic levels; and LREE- depleted basalts of group I in the upper levels. Mantle melt modeling suggests that group III magmas are con- sistent by mixing within a mantle melt column of low- degree (\1%) melts of a deep garnet lherzolite source and high-degree ((15%) melts of a shallow spinel source, and groups II and I magmas are explained with moderate to high (14-18%) and very high ((20%) fractional melting degrees of a shallower spinel mantle source, respectively. Thus, upward in the volcanic sequence of the LMA, the magmas represent progressively more extensive melting of shallower sources, in a plume-influenced spreading ridge of the proto-Caribbean oceanic crust. Nb/Y versus Zr/Y systematics combined with recent plate tectonic model reconstructions reveal that Caribbean Colombian oceanic plateau fragments in Hispaniola formed through melting of heterogeneous mantle source regions related with distinct plumes during at least from Aptian-Albian ((96 Ma) to Late Campanian.