A PLATE MODEL FOR THE SIMULATION OF TRACE-ELEMENT FRACTIONATION DURING PARTIAL MELTING AND MAGMA TRANSPORT IN THE EARTHS UPPER-MANTLE

We propose a new plate model for the simulation of trace element trans fer during magmatic and metasomatic processes taking place in the Eart h'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-f low models for the simulation of fluid-rock interactions. Hence this a pproach may account for a wide range of mantle processes, including me lt extraction during compaction of molten peridotites, porous flow ass ociated with chromatographic effects, or fluid-rock reactions occurrin g upon melt infiltration at the base of the conductive mantle. The app lications 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 fo r (1) the ultra-rare-earth-element-depleted composition of peridotites and interstitial melts residual after mid-ocean ridge basalt extracti on, (2) the negative col relation between light rare earth element/hea vy rare earth element (LREE/HREE) ratio and refractory character of pe ridotites, as observed in several suites of mantle rocks, and (3) the origin of ultra-LREE-enriched metasomatic fluids infiltrated in the li thospheric mantle.