The Late Cretaceous Duarte Complex and Siete Cabezas Formation (Hispaniola): Caribbean Oceanic Plateau

Abstract

The Core of the Central Cordillera in Dominican Republic is composed of oceanic crustal fragments which form three distinct assemblages: the Duarte complex, the Siete Cabezas Formation and the serpentinized ultramafic belt. Three units are recognized in the Duarte complex: (i) basalts interbedded with Late Jurassic ribbon cherts; (ii) picrites and ankaramites, (iii) amphibolites and gneissic amphibolites. The Siete Cabezas Formation is composed of pillow basalts and pillow breccias associated with Upper Cretaceous pelagic sediments. Finally, the serpentinites are intruded by deformed diabase dykes. The Upper Jurassic pillow basalts and diabase dykes have major, trace element and lead isotopic compositions that are consistent with those of NMORB. However, the basalts differ from typical NMORB by lower ~Nd ratios which plot within the range of Ocean Island Basalts (OIB). The basalts and massive diabase of the Rio Verde complex are geochemically similar to the Upper Jurassic basalts and dykes. Thus, these rocks likely represent remnants of the Caribbean Jurassic oceanic crust formed from an oceanic ridge possibly close to a hotspot. The Duarte picrites and olivine-free ankaramites are generally intensely deformed and metamorphosed to greenschist facies. When devoided of any deformation, these rocks show preserved igneous textures and mineralogy with augite-diopside sometimes rimmed by Mg-hastingsite. Ar-Ar ages on separate Mg-hastingsite gave 86 4-1.4 Ma. This age is perfectly consistent with those of the basalts drilled from the Caribbean floor. The Duarte rocks are enriched in Nb-, Ta-, Ti-, and LREE like the Dumisseau tholeiites (Haiti) and the enriched basalts of Gorgona. Their eNd(T 86Ma) ratios range from +5.7 to 8.3 and are similar to those of OIB. Their eSr ratios (-17.7 to -4.6) are less homogeneous due to the hydrothermal alteration. Finally, their Pb isotopic ra t ios [(2~176 = 18.966-19.537] reflect the contribution of an HIMU-like enriched component. These isotopic ratios show that the Duarte picrites and the ankaramites are isotopicallyt similar to mafic lavas from previously described occurences of the Caribbean plateau (Costa Rica, Ha'it, Curagao and Gorgona). The amphibolites and gneissic amphibolites are composed of hornblende + plagioclase + epidote 4quartz. Most of the rocks have flat