REE chemistry of MORB and OIB explained by microchemical disequilibrium melting models

Abstract:

We have developed a two-dimensional numerical model of multi-phase coarsening, diffusive trace element partitioning, and near-fractional melting. The model is applied to decompression melting of MORB and OIB sources and the prediction of REE (La, Sm, and Yb) in erupted lavas. We show that the major features in global OIB REE systematics are easily explained via the so-called LID effect. The properties of models which do explain the data indicate that the OIB source cannot be hot (>1400°C) and may be compositionally similar to the MORB source. Moreover, our models predict that the thermo-mechanical LAB temperature is about 1225°C, average grain radii in the OIB source is on the order of 2-5 mm, and the bulk source compositions of REE are about 2-7 times higher than previous estimates.