Tracking the Transition From a Gondwana LIP to the South Atlantic Ocean With Geochronological and Geochemical Indicators

Abstract

The timing and mechanisms controlling the transition from large igneous provinces (LIPs) into oceanic crust during supercontinent breakup are poorly constrained. In the case of Pangea rifting and opening of the South Atlantic, the oldest seafloor magnetic anomalies usually postdate flood basalt extrusion by ∼20-30 Ma; however, geochronological evidence shows that minor mid-ocean ridge basalt (MORB)-like intrusions were almost coeval with late-stage flood basalt volcanism (e.g., Jagoutz et al., 2007;Jourdan et al., 2007). Little is known about the role and significance of this early MORB-like intrusive magmatism during rifting, and whether it marks a stepwise transition from a LIP into a passive margin, or whether it represents isolated asthenospheric upwellings still controlled by the LIP system.