Another, one ofthe important evidence of all, hard to neglect is the uplift of thelithosphere, as hot mantle plume impacts its base. Andy Saunders et al. critically review the geological evidence forregional uplift in five continental flood basalt provinces (Emeishan Traps,North Atlantic, Deccan Traps, Siberian Traps, Yellowstone) as case study. Eachof these five provinces are associated with surface uplift. The authors believethat models which we try to explain for the formation of LIPs without hotmantle plumes have difficulties in explaining surface uplift, rifting andmagmatism. They conclude that start-up plume models remain the most convincingway of explaining the formation of LIPs. Saunders suggested that in Iceland plume is thecause of the large volumes of basalt, and it the only reason why oceanic crustis thick (30 km) despite its presence in MOR.The newlydeveloped Al-in-olivine geothermometer was used to find the olivine-Cr-spinelcrystallizatioin temperature of a suite of picrites spanning the spatial andtemporal extent of the North Atlantic Igneous Provinces (NAIP), which is widelyaccepted to be the result of deep-seated mantle plume that presently underliesIceland.
Iceland is the only part of the NAIP that remains active.Here theAl-in-olivine thermometer calibrated by Wan et al. (2008) and extended by Coogan et al. (2014) is used. The Al content of olivine phenocrysts wasmeasured using the Cameca SX100 electron microprobe at the University ofEdinburgh. The geothermometer is based solely on the temperature dependence ofAl exchange between olivine and Cr-spinel and is largely independent ofpressure and melt composition, and so an estimate of these parameters is notrequired in order to calculate olivine crystallization temperatures.
It isfound that large-scale changes in the crustal architecture of the NorthAtlantic region can be explained by long-term cooling of the Iceland plume to35 Ma, followed by a gradual increase in temperatures until the present day.This suggests that mantle plumes are susceptible to long-term (107 year)fluctuations in temperature throughout their lifetime.The Al-in-olivinethermometry data thus confirm that start-up plumes are associated with a pulseof anomalously hot mantle over a large spatial area before becoming focusedinto a narrow upwelling. These conclusions are independent of traditionalpetrologic approaches to mantle temperature estimation, and provide anotherstrong piece to the growing body of evidence indicating that the temperature ofthe mantle source region of LIPs is substantially higher than that beneath themid-ocean ridges. However, some authors have argued that amantle plume is not required to produce the enhanced melting beneath Iceland (Foulgerand Anderson, 2005; Foulger et al., 2005).
For LIPs Saunders suggested that their initialbursts are due to the sudden increase in mantle flux as the plume head starts.Their sudden bursts could also be the result of initial decompressionassociated with the lithospheric extension in the overlying plate. Relatedprocess is the Reunion hotspot which was beneath India in the Late Cretaceous formingDeccan traps.