A plate model for the simulation of trace element fractionation during partial melting and magma transport in the Earth's upper mantle

Abstract

We propose a new plate model for the simulation of trace element transfer during magmatic and metasomatic processes taking place in the Earth's upper mantle. As in previously published plate models, porous flow is accounted for by propagation of fluid batches through macrovolumes of mantle rocks. Being released from spatiotemporal constraints, the plate model allows much more freedom than the one-dimensional porous-flow models for the simulation of fluid-rock interactions. Hence this approach may account for a wide range of mantle processes, including melt extraction during compaction of molten peridotites, porous flow associated with chromatographic effects, or fluid-rock reactions occurring upon melt infiltration at the base of the conductive mantle. The applications presented in this study show several results consistent with published trace element data for mantle rocks and basaltic volcanism. In particular, the proposed models may provide simple explanations for (1) the ultrarare-earth-element-depleted composition of peridotites and interstitial melts residual after mid-ocean ridge basalt extraction, (2) the negative correlation between light rare earth element / heavy rare earth element (LREE/HREE) ratio and refractory character of peridotites, as observed in several suites of mantle rocks, and (3) the origin of ultra-LREE-enriched metasomatic fluids infiltrated in the lithospheric mantle.