Ultra-depleted melts in olivine-hosted melt inclusions from the Ontong Java Plateau

Abstract

The Ontong Java Plateau (OJP) represents the largest large igneous province (LIP) preserved in the geologic record. The most voluminous volcanic types of the OJP—the Kroenke and Kwaimbaita groups, which dominate the accessible portions of the plateau—have relatively flat primitive mantle normalized rare earth element (REE) patterns. With the exception of relatively small volumes of late-stage melts—referred to as the Singgalo group—that are characterized by slightly enriched REE patterns relative to a chondritic pattern, the volcanic groups that dominated the eruptive history of the OJP exhibit remarkably homogeneous, flat REE patterns. Here we isolate, for the first time, olivine-hosted melt inclusions from the OJP. We show that the melt inclusions have two clear populations defined by distinct trace element characteristics. The first population has relatively flat trace element patterns that are similar to those observed in whole rock lavas from the most voluminous volcanic groups (Kroenke and Kwaimbaita) recorded in the OJP. In contrast, a second group of melt inclusions, referred to as UDM (ultra-depleted melt) inclusions, exhibit (light-REE) LREE-depleted patterns relative to a chondritic pattern; these trace element patterns are far more depleted than any previously reported lava from OJP. The UDM have unique trace element signatures that preclude an origin by re-melting the depleted mantle source left over after melt extraction during construction of the OJP. We interpret the new UDM compositions to be the result of melting a previously unrecognized (in lavas) ultra-depleted component hosted in the OJP mantle source.