The hottest lavas of the Phanerozoic and the survival of deep Archaean reservoirs

Jarek Trela and co-authors report in the Journal Nature Geoscience that Large igneous provinces and some hotspot volcanoes are thought to form above mantle plumes. Petrological investigations that suppor t this model suggest that plume-derived melts originated at high mantle temperatures (greater than 1,500C) relative to those generated at ambient mid-ocean ridge conditions (about 1,350◦C). Earth’s mantle has also cooled appreciably during its history and the temperatures of modern mantle derived melts are substantially lower than those produced during the Archaean (2.5 to 4.0 billion years ago), as recorded by komatiites (greater than 1,700C). Trela et used geochemical analyses of the Tortugal lava suite to show that these Galapagos-Plume-related lavas, which formed 89 million years ago, record mantle temperatures as high as Archaean komatiites and about 400C hotter than the modern ambient mantle. These results are also supportd by highly magnesian olivine phenocrysts and Al-in-olivine crystallization temperatures of 1,570 ± 20C. As mantle plumes are chemically and thermally heterogeneous, theyinterpret these rocks as the result of melting the hot core of the plume head that produced the Caribbean large igneous province. Their results imply that a mantle reservoir as hot as those responsible for some Archaean lavas has survived eons of convection in the deep Earth and is still being tapped by mantle plumes.