Four distinct rock units have been recognized near El Aguacate, in the
Janico-Juncalito-La Vega area of the Duarte complex (Dominican
Republic): (1) serpentinites crosscut by numerous diabasic dikes, (2)
basalts interbedded with Late Jurassic ribbon cherts, (3) picrites and
ankaramites relatively enriched in incompatible trace elements, and (4)
amphibolites and gneissic amphibolites chemically similar to Oceanic
Plateau Basalts. Similar Ar-Ar ages of late magmatic amphibole from a
picrite, and hornblende from an amphibolite (86.1 +/- 1.3 Ma and 86.7
+/- 1.6 Ma, respectively), suggest that the Duarte picrites are
contemporaneous with the Deep Sea Drilling Program Leg 15 and Ocean
Drilling Program Leg 126 basalts drilled from the Caribbean oceanic
plateau. These basalts are associated with sediments containing Late
Cretaceous faunas. Sr, Nd, and Pb data show that enriched picrites and
amphibolites are isotopically similar to mafic lavas from previously
described Caribbean plateau and Galapagos hotspot basalts. Major
element, trace element, and lead isotopic features of Late Jurassic
basalts and diabases are consistent with those of normal oceanic crust
basalt. However, these basalts differ from typical N-MORB because they
have lower epsilon Nd ratios that plot within the range of Ocean Island
Basalts. These rocks appear to represent remnants of the Caribbean
Jurassic oceanic crust formed from an oceanic ridge possibly close to a
hotspot. Later, they were tectonically juxtaposed with Late Cretaceous
slices of the Caribbean-Colombian plateau.