Tectonomagmatic evolution of the Caribbean plate: Insights from igneous rocks on Jamaica

The identification of post-Jurassic arc and plateau rocks in Jamaica has helped constrain the tectonic evolution of the Caribbean plate by identifying when, where and how the different volcanic rocks formed. This research therefore not only evaluates the existing models of Caribbean plate evolution, it also presents for the first time, a detailed gcochcmical and geochronolgical analysis of the igneous rocks on Jamaica. This study has focussed on the igneous rocks of the Blue Mountains, Central, Above Rocks and Benbow Cretaceous Inliers and the Tertiary Wagwater belt. Major and trace element data, Sr, Nd, Pb and Hf isotope analysis and argon radiometric ages have confirmed the presence of a Cretaceous oceanic plateau section within the Blue Mountains inlier and a number of primitive and evolved Cretaceous island arc sequences in the remaining inliers. Rare high-Nb basalts (HNB) and adakites have also been discovered in the Tertiary Wagwater belt. Many elements have been mobilised because of intense tropical weathering, and so the tectonic setting and petrogenesis of most of the analysed samples were interpreted using immobile trace elements which has led to the development of the Co- Th, Th/Zr-La/Yb. Cc/Lu-Sm/Yb, La'Hf-Sm/Y and Th/Hf-Sm/Yb discrimination diagrams. These diagrams have been used to classify the Jamaican volcanic arc rocks and thus identity their extent of fractionation and incompatible trace element enrichment. Immobile trace element and isotope geochemistry has identified at least 5 mantle wedge components and 8 slab components in the Jamaican island arc rocks. Additionally, the Bath-Dunrobin plateau lavas, the adakites and the HNBs represent at least three other chemically distinct source regions. The Bath-Dunrobin plateau lavas are derived from a - 90 Ma heterogeneous mantle plume source region which is distinct from the source regions for other Caribbean oceanic plateau lavas as it contains a larger HIMU component giving it more radiogenic Pb isotope ratios. The adakites have been derived from the combination of complex post-eruptive alteration, partial melting, fractional crystallisation and hybridisation processes. Rather than being related to a melt from a subducting slab, the Jamaican adakites appear to be derived from a melt of lower crustal garnet amphibolite with inter-bedded sedimentary material. The HNBs are derived from a HIMU-type source, which contained garnet and amphibole and so is distinct from the source region of the oceanic plateau. Using the new geochemical and geochronological data, together with the stratigraphic information and temporal location of the Jamaican igneous rocks, it is possible to place Jamaica in the Pacific model of Caribbean plate evolution. From 120- 75 Ma Jamaica formed the northernmost part of the Great Arc of the Antilles and erupted bimodal tholeiitic and calcalkaline magmas, which eventually evolved into calcalkaline and shoshonitic lavas after the collision of the Caribbean oceanic plateau -90 Ma. From -55 Ma Jamaica collided with the Yucatan peninsula and was subsequently tectonically transported to the east by transtensional opening of the Cayman Trough. This extension enabled decompression melting of the underlying asthenosphere to form the HNBs and adakites.