Hot or fertile origin for continental break-up flood basalts; insights from olivine systematics

The break-up of supercontinents is often temporally and spatially associated with large outpourings of basaltic magmas in the form of large igneous provinces (LIPs) and seaward dipping reflectors (SDRs). A widespread view is that the upwelling of hot mantle plumes drives both continental break-up and generation of associated LIPs. This is supported by petrologic estimates of the temperature from olivine-melt thermometers applied to basaltic magmas. These thermometers must be applied to a primary mantle-derived magma, requiring the selection of an appropriate primitive magma and an assumption of how much olivine is to be back-added to correct for fractional crystallization. We evaluated the effects of these assumptions on formation temperatures by compiling and analyzing a database of North Atlantic igneous province (NAIP) and Central Atlantic magmatic province (CAMP) lavas and olivines. Ni and FeOT systematics suggest that many picrite magmas have undergone olivine addition and are not true liquids, requiring careful selection of primitive magmas. The maximum amount of back-added olivine was determined by constraining mantle peridotite melt fractions for a range of possible mantle potential temperatures and continental lithosphere thicknesses. Using an empirical relationship between melting degree and forsterite (Fo) content, we show that the possible maximum olivine forsterite content in equilibrium with NAIP magmas is 90.9, which is lower than the maximum olivine forsterite content observed in the NAIP olivine population. We infer primary magmas that lead to mantle potential temperatures of 1420°C for the NAIP and 1330°C for CAMP. Using a similar approach for consistency, we estimate a mantle potential temperature of 1350°C for mid-ocean ridge basalts (MORB). Our results suggest that LIPs associated with continental break-up are not significantly hotter than MORB, which suggests that continental break-up may not be driven by deep-seated thermal plumes. Instead, we suggest that such voluminous magmatism might be related to preferential melting of fertile components within the lithosphere triggered by far-field extensional stresses.