Trace Element Characteristics of Ultramafic Xenoliths in Basaltic Rocks from Penghu Islands, Taiwan

Abstract

The trace and rare earth elements of ultramafic xenoliths from Peiliao area and combined with major elements proposed by Yang et al. (1987)[1] in order to understand the origin of these ultramafic xenoliths and the geochemical characteristics of the upper mantle. Spinel lherzolite mainly composed of olivine, orthopyroxene, clinopyroxene and spinel is the major rock type of ultramafic xenoliths found in Peiliao area, Penghu Islands, Taiwan. Based on major elements of ultramafic xenoliths analyzed in the present study (Yang et al., 1987)[1], we suggest that these xenoliths belong to the residual upper mantle after different degrees of partial melting. The ultramafic xenoliths have higher MgO content, but lower Al2O3, TiO2 and Na2O contents than primitive mantle proposed by Sun and McDonough (1989)[2], indicating that they represent residues formed by different degrees of partial melting from the upper mantle. Incompatible elements and LREEs tend to decrease with increasing MgO/ΣFeO ratios which may be related to the partial melting of the mantle source. These correlations mentioned above indicate that the ultramafic xenoliths from Peiliao area represent the residual materials after the primitive mantle had undergone partial melting. The spidergrams and the chondrite-normalized REE patterns reveal that ultramafic xenoliths from Peiliao area are depleted which indicate that the mantle beneath the study area had undergone relatively smaller degree of partial melting.KeywordsPartial MeltingMantle PlumeIncompatible ElementBasaltic RockPrimitive MantleThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.