Back-arc spreading and mantle flow in the East Scotia Sea

Abstract

AbstractThe East Scotia Ridge exhibits systematic variations in axial morphology and basalt geochemistry. Central segments have morphology typical of intermediate-rate spreading centres and erupt mainly normal mid-ocean ridge basalt (N-MORB). Segments near the ridge ends exhibit anomalous, inflated, axial morphology and erupt more evolved basalts, influenced by the Bouvet plume in the north. As the end segments lie closer to the volcanic arc, these variations could be caused by coupled flow within the mantle wedge, as inferred from similar studies in the Lau Basin. Three of the four zones of crustal accretion defined from the Lau Basin may be identified in the East Scotia Sea, although there is no counterpart to a zone of diminished magma supply observed at the East Lau Spreading Centre. Superimposed on the pattern of plate-driven flow is a ridge-parallel flow related to inflow of Atlantic mantle into the East Scotia Sea back-arc region at both ends of the South Sandwich slab. The inflow causes enhanced magmatism and propagation of the end segments towards the middle of the back-arc region, and may be related to trench-parallel flow beneath the rapidly retreating slab. Alternatively, it may be driven by buoyancy flux from Atlantic hot spots. There is no evidence that retreat was ever driven by escape flow of Pacific mantle.