INVESTIGATION OF MELT ADDITION IN MANTLE PERIDOTITES FROM THE GAKKEL RIDGE
University of Delaware
Peridotites dredged from the ocean floor along the ultra-slow spreading Gakkel Ridge have been found to have varying compositions, suggesting that the Arctic upper mantle is heterogeneous in composition. This heterogeneity is likely formed as a result of ancient melting, followed by later melt percolation and entrapment (D’Errico et al., 2016). D’Errico presented data on only a subset of samples from this ridge; my research attempts to fill in the gaps left by earlier investigations, to provide better resolution for these processes along Gakkel Ridge. Trace elements in pyroxene grains from these samples are reported for 10 dredged peridotite samples that include both harzburgite and lherzolite lithologies. Rare earth element (REE) compositions indicate varying degrees of fractional mantle melting. Enrichments in incompatible light REE concentrations in several samples indicate additional interaction with an intruding melt. Several clinopyroxene-free harzburgite samples show low concentration, shallow-sloped REE trends indicating open-system melting involving interaction with a percolating melt. Zoning of spinel chrome number (Cr/(Cr+Al)) further supports the theory that geochemical heterogeneity exists beneath the ridge and is driven by melt addition. My findings broadly agree with conclusions drawn in D’Errico et al., 2016. This study suggests that heterogeneity in the upper mantle beneath the Gakkel Ridge is driven by complex melt-interaction processes and is the consequence of melting with subsequent melt addition.
geology,melt addition, perodotites