GLOBAL EOCENE TECTONICS, COLLISION-INDUCED VOLCANISM AND THEIR POTENTIAL EFFECTS ON CLIMATE

The global Eocene tectonics was controlled predominantly by continental collisions in Europe, Eurasia, Indochina, Australia–Papua New Guinea and North America that led to the closure of some major oceanic gateways (e.g. Tethys) and widespread post-collisional magmatism. These collisional events were responsible for slab detachment and asthenospheric heat input beneath the Eocene orogenic belts. Partial melting of the subcontinental lithospheric mantle and assimilation/FC processes produced evolved magmas that developed the widespread post-collisional magmatic units in discrete belts, straddling the early Eocene suture zones around the world. Geochemical characteristics of these slab breakoff magmatic assemblages display a major shift from early calc-alkaline to later shoshonitic affinities. The melt source of the former group was asthenospheric mantle that was modified by subduction-related components, whereas that of the latter group was a relatively deeper mantle source whose melt products were strongly affected by contributions from continental crust during magma ascent. Nearly coeval eruptions of volcanic fields at a global scale may have produced the carbon that triggered early warming in the form of exsolved magmatic CO₂, which in turn caused the Paleocene–Eocene Thermal Maximum. Alternatively, the clustering of bimodal eruptions in the early Eocene might have affected the incoming solar radiation via the continuous, widespread production of aerosol clouds and stratospheric dust that caused an episode of global cooling. These casual links between high-frequency volcanic eruptions and the global climate changes in the Eocene suggest that exceptionally large volumes of post-collisional volcanism played a significant role as a climate forcing effect.