Zircon ages, mineralogy, and geochemistry of ophiolitic mafic and island-arc rocks from central Cuba: Implications for Cretaceous tectonics in the Caribbean region

Abstract

Ophiolite-related rocks and volcanic-arc rocks are the main geological components in Cuba; deciphering their origin and evolution is fundamental in interpreting and reconstructing the tectonic processes for the Caribbean region. In this paper, we report new zircon U Pb chronology, mineralogy, and geochemistry of ophiolitic metadiabase dikes and island-arc rocks in central Cuba, and discuss their origin and petrogenesis. The metadiabase dikes have a zircon U Pb age of 135.0 ± 1.7 Ma; they are low-K tholeiites , and have geochemical characteristics intermediate between those of typical normal mid-ocean ridge basalt (N-MORB) and island-arc tholeiites (IAT), suggesting that they were formed in a back-arc basin. The investigated island-arc rocks, including amphibolite from the Mabujina amphibolite complex (MAC), plutonic diorite and their mafic enclaves, and volcanic dacite, have zircon U Pb age of 93.53 Ma, 92.31 Ma, 94.35 Ma and 83.60 Ma, respectively, recording different phases of island-arc magmatism. The amphibolite samples have geochemical compositions suggesting that the protolith of the amphibolite was basaltic igneous rocks that originated from a depleted mantle source mildly modified by fluids from a subducting slab, and that the mantle source might be deep and garnet-bearing. Microstructures and elemental geochemical data reveal that the mafic enclaves and diorites represent distinct island-arc magma pulses that originated from partial melting of depleted mantle which had been previously modified by subduction-related mobile elements. The dacites are evolved island-arc volcanic rocks that formed through fractional crystallization of hydrous basaltic magmas that originated from a strongly depleted mantle source. Above data support such a tectonic model, that is, during the Early Cretaceous (from ~135 Ma or even earlier), a typical trench–arc–basin system developed in the Caribbean region as a result of southwest-directed subduction of the Proto-Caribbean plate beneath the Caribbean plate; after that time, uninterrupted Proto-Caribbean plate subduction occurred, generating quasi-continuous arc magmatism from before ~135 to 81 Ma, and gradually consuming the Proto-Caribbean Ocean. • A diabase dike in the ophiolite in central Cuba has a zircon U Pb age of 135.0 ± 1.7 Ma. • A typical trench–arc–basin system developed in the Caribbean region during the Early Cretaceous. • The arc rocks have highly diverse major and trace elemental and isotopic compositions.