TWO-STAGE SUBDUCTION INITIATION AROUND THE CARIBBEAN PLUMEHEAD PLATE

Caribbean lithosphere is unique in 2 ways: 1) it formed mainly by Cretaceous igneous activity above the Galapagos plumehead, and 2) it was surrounded by subduction zones that dipped towards the plate interior (until continental interactions disrupted this regime). This uniqueness encourages a search for links between Caribbean plume activity and subduction initiation. NE-dipping subduction initiation at a mechanically weakened flank of the SW Caribbean plume edge (Costa Rica-Panama) at ~85 Ma was first suggested by Pindell & Kennan (GSL SP328 2009) and further developed with integrated geologic–chemical–chronological (Whattam & Stern GondwanRes 2014) and geodynamic (Gerya et al. Nature 2015). It may be that SW-dipping subduction at the NE Caribbean flank began earlier when the plume head first impinged on the Proto-Caribbean Seaway. The composite plume head is preserved, mostly buried but sometimes exposed, as the Caribbean Large Igneous Province (CLIP). This was an unusually hot & long-lived (~70 m.y. duration) plumehead. We argue that CLIP emplacement was accompanied by mechanical weakening & thinning of the lithosphere, which resulted in subduction zones forming by lithospheric collapse around the margins of the plume head. This Plume-Induced Subduction Initiation (PISI) may have been how plate tectonics started (Gerya et al. Nature 2015). We suggest that PISI around the CLIP occurred in 2 phases; first at ~130 Ma around the NE margin to form the Greater Antilles–Aves Ridge/Tobago Arc (GAA) followed ~90 Ma to form the Central American subduction zone. Evidence is greater for the second PISI episode, and the long-held idea of a transform-related initiation for the GAA may yet be more satisfactory. We suggest that during both episodes, subduction initiation & associated rapid trench rollback resulted in strong extension in the newly-formed CLIP lithosphere, producing an extended LIP basin. Formation of the NE Caribbean subduction zone and associated rollback allowed the CLIP to migrate NE relative to North America ~2000 km at 130-85 Ma at ~ 45 mm/y. Formation of the SW Caribbean subduction zone at 85-90 Ma isolated the Caribbean Plate and anchored it near its present position relative to the mantle, while the Americas passed westward around it. Further work is needed to test & refine the Caribbean PISI hypothesis.