Development of a heterogeneity in the lithosphere: Geochemical evidence

Abstract

Systematization of information on multivalent trace elements in peridotite xenoliths made it possible to reveal differences in the distribution of these elements in the subcontinental and suboceanic segments of the lithosphere, which reflects the development of a geochemical heterogeneity in the lithosphere during the early (Hadean) stage of its evolution. The vast extent of trace-element differentiation in Hadean peridotite xenoliths is most probably explained by the appearance of appreciable masses of condensed water and, consequently, active mantle metasomatism in the hydrated lithosphere. The latter formed the upper depleted (oceanic) zone underlain by an “undifferentiated” zone enriched in trace elements. The removal of trace elements from both zones, a process that does not rule out the participation of earlier accretion in it, gave rise to a crust strongly enriched in these elements. The existence of long-lived extensive lithosphere heterogeneity calls for revision of the concept of multistage crustal growth with a general tendency toward an increase in its bulk volume.