Plume-related, syn-rift, Neogene volcanism, the interplay with structure in Thailand and comparison with the East African Rift

Abstract

Structure-magma interactions in rifts, particularly those associated with mantle plumes, contain examples where structure predominantly controls magmatism and conversely examples where magmatism strongly controls structure. Contrasting examples of these cases from East Africa and SE Asia are discussed. These two regions illustrate that the starting conditions of the lithosphere are very important for how subsequent rift-plume interactions progress. In Thailand the subduction zone setting, and thin, young, hot crust of SE Asia minimised the impact of contemporaneous mantle plume activity on passive rifting, particularly in terms of upper crustal magmatic activity, and surface uplift. Rift structure exerts significant control on the timing and location of Neogene magmatic activity in the upper crust. At the largest scale this control varies according to rift mode (narrow vs wide) which in turn is related to large-scale pre-existing fabrics. Magma has been extensively emplaced in the lower crust since c. 24 Ma, yet only reached the surface after 6 Ma. Stress rotation, and a later change to strike-slip activity probably created dilatant pathways for the late (