An Ultra-Depleted Mantle Component in the Ontong Java Plateau Revealed by Major, Trace and Volatile Element Abundances in Olivine-Hosted Melt Inclusions

Wednesday, 17 December 2014
Matthew G Jackson, University of California Santa Barbara, Department of Earth Sciences, Santa Barbara, CA, United States, Rita Ann Cabral, Boston University, Boston, MA, United States, Estelle F Rose-Koga, Univ. Blaise Pascal-OPGC-CNRS, Clermont-Ferrand, France, Kenneth T Koga, University Blaise Pascal Clermont-Ferrand II, Clermont-Ferrand, France, Allison A Price, University of California Santa Barbara, Santa Barbara, CA, United States, Erik H Hauri, Carnegie Inst Washington, Washington, DC, United States and Peter J Michael, University of Tulsa, Tulsa, OK, United States
The Ontong Java Plateau (OJP) represents the most voluminous large igneous province (LIP) preserved in the geologic record. The most voluminous volcanic stages of the OJP—the Kroenke and Kwaimbaita stages, which dominate the accessible portions of the plateau—have relatively flat primitive mantle normalized rare earth element (REE) patterns, or spidergrams. With the exception of relatively small volumes of late-stage melts—referred to as the Singgalo stage—that are characterized by slightly enriched REE spidergrams, the volcanic stages 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 OJP. We show that the melt inclusions have two clear populations defined by having distinct trace element characteristics. The first population has relatively flat trace element patterns that are similar to that observed in whole rock lavas from the most voluminous volcanic stages (Kroenke and Kwaimbaita stages) recorded in the OJP. In contrast, a second group of melt inclusions, referred to as UDM (ultra-depleted melt) inclusions, exhibit strikingly depleted REE spidergrams; 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 assimilation of hydrothermally-altered oceanic crust or 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 of a previously unrecognized ultra-depleted component hosted in the OJP mantle source.