Duncan Keller

Abstract Massif-type anorthosites, enormous and enigmatic plagioclase-rich cumulate intrusions emplaced into Earth’s crust, formed in large numbers only between 1 and 2 billion years ago. Conflicting hypotheses for massif-type anorthosite formation, including melting of upwelling mantle, lower crustal melting, and arc magmatism above subduction zones, have stymied consensus on what parental magmas crystallized the anorthosites and why the rocks are temporally restricted.

Abstract Large igneous province volcanism represents extensive mantle melting that has contributed to Earth’s chemical differentiation and lithospheric and climatic changes. Compositional heterogeneities in the mantle, such as accumulated recycled crust, may make key contributions to large igneous province activity. One class of rocks capable of producing distinctive mantle heterogeneities is the iron formations, uniquely dense Fe-rich sedimentary rocks formed in Earth’s early oceans.