Lithosphere thickness controls the extent of mantle melting, depth of melt extraction and basalt compositions in all tectonic settings on Earth – A review and new perspectives

Abstract Basalts and basaltic rocks are the most abundant igneous on earth their petrologic geochemical studies have formed our knowledge base thermal structure composition of mantle with which we developed workable models chemical differentiation earth. All this would not been possible without innovative painstaking experimental petrology peridotite melting, magma generation evolution largely done in period 1960s -1980s. However, ~30 year lively debate nature “primary magma” among petrologists community during time had inadvertently shelved development consensus melting context plate tectonics. Continued parallel worldwide sampling study mid-ocean ridge basalts (MORB) brought about new insights, culminating a model 1980s that potential temperature (TMP) variation controls extent pressure basalt compositions. The tenet is hotter rising begins to melt deeper thus has greater decompression depth interval more having petrological signature higher than cooler mantle. This gained wide acceptance MORB also invoked intra-plate ocean basins continental settings. Basalt above subduction zones, other hand, generally accepted as resulting from slab-dehydration induced wedge since early 1980s, but recent advocate primary control melting. these views laudable merits paradigm magmatism. In paper, I review historical developments towards demonstrate simple clarity it lithosphere thickness, TMP, extraction compositions, i.e., lid effect. lithospheric caps mantle, limiting equilibrium pressure/depth extraction, well registered compositions MORB, island (OIB), volcanic arc zones (VAB) interiors (CIB). Hence, thickness governing variable all tectonic settings Major element (e.g., Si-Mg-Fe) erupted no memory initial because effective efficient melt-solid olivine [Mg,Fe]2SiO4) equilibration Therefore, basalt-olivine based thermobarometry, albeit useful, supplies information TMP. It whether “mantle plumes” can surface or large provinces (LIPs) serve manifestations for thin thinned at emplacement. understanding global observations, well-understood rigorous analysis fundamental requires major change current paradigm.