The Greater Antillean Arc: Early Cretaceous origin and proposed relationship to Central American subduction melanges: implications for models of Caribbean evolution

We integrate known and suspected Meso-American plate motions with the geochronology of Caribbean arcs and Central American HP/LT belts to promote two primary concepts. The first is that the Greater Antillean Arc formed at about 135 Ma by inception of SW-dipping subduction along a sinistral 'inter-American transform' connecting the west-facing subduction zones of the North and South American Cordillera. Caribbean arc magmas date from 135 Ma and Caribbean HP/LT complexes from 118 Ma, and they were formed as the Caribbean lithosphere was engulfed between North and South America during westward drift of - and divergence between - the latter. Initial arc magmatism predates exhumation of HP/LT metamorphic rocks by 10-20 million years; that is, magmatism developed faster than refrigeration and recycling in the subduction zones. However, pre-130 Ma HP/LT melanges in Nicaragua (Siuna complex, 139 Ma 40Ar/39Ar) and in Guatemala both north and south of the Motagua fault zone (140-130 Ma Sm-Nd ages) require a different explanation. Therefore, our second concept is that these older rocks originated within a mature, west-facing Cordilleran subduction channel west of Mexico and/or the Chortis Block, and were subsequently dragged southeastward during sinistral subduction to a position along the NW portion of the 'inter-American transform'. Upon initiation of SW-dipping subduction along this transform at 135 Ma, these older HP/LT (and minor arc) rocks became entrained within the transpressive zone between the western end of the Caribbean Arc and the southeast-facing Proto-Caribbean passive margin of the Chortis and Maya blocks. They were obliquely and diachronously accreted along these margins in the Albian to Maastrichtian. Parts of these melanges are now exposed on both the northern and the southern flanks of the Motagua Valley of central Guatemala, and we further develop earlier suggestions that the southern Motagua melanges were emplaced there on Chortis basement units by mid-Tertiary south-vergent transpression along the Motagua Fault.