The petrogenesis of komatiites and related rocks as evidence for a layered upper mantle

摘要: Abstract Although the CaO/Al 2 O 3 ratio of komatiites has been regarded as one distinguishing features these rocks, a comparison various komatiite and oceanic tholeiite analyses suggests that there is continuum ratios between two. The extremely high MgO values peridotitic suggest they are result degrees partial melting mantle, leaving harzburgitic residuum depleted in CaO Al , hence preserving melt original parental material. Available chemical models mantle have too low to explain origin by such process. Shallow-level layered which clinopyroxene content decreases garnet increases with depth, may chemistry related ultrabasic lavas.