A group of εNd-La/Nb, Ba/Nb, Nb/Th diagrams are used to study mantleheterogeneity. Island-arc basalts (IAB) are distributed in a triangle of these diagrams.Three end-member components (the MORB-type depleted mantle, ...A group of εNd-La/Nb, Ba/Nb, Nb/Th diagrams are used to study mantleheterogeneity. Island-arc basalts (IAB) are distributed in a triangle of these diagrams.Three end-member components (the MORB-type depleted mantle, the fiuid released fromsubducted oceanic crust and the sediments from the continental crust) of the source ofIAB may be displayed in these diagrams. Two types of IAB are identified. They areof the two-component type (with little continental sediments), such as the basalts fromAleutians and New Britain, and the three-component type, such as those from Sunda,Lesser Antilles and Andes. In addition, the EMII type mantle-derived rocks may alsobe divided into two groups. One is exemplifled by continental flood basalts and someperidotite xenoliths, similar to IAB, with high La/Nb and Ba/Nb and low Nb/Th ratios.The other includes the Samoa-type oceanic island basalts, with low La/Nb and Ba/Nband high Nb/Th ratios. The corresponding two sub-components of EMII are EMIIM,which is related to the metasomatism of lithosphere mantle by fluids released from thesubducted oceanic crust, and EMIISR, related to the intervention of recycling continentalsediments into the convective mantle.展开更多
文摘A group of εNd-La/Nb, Ba/Nb, Nb/Th diagrams are used to study mantleheterogeneity. Island-arc basalts (IAB) are distributed in a triangle of these diagrams.Three end-member components (the MORB-type depleted mantle, the fiuid released fromsubducted oceanic crust and the sediments from the continental crust) of the source ofIAB may be displayed in these diagrams. Two types of IAB are identified. They areof the two-component type (with little continental sediments), such as the basalts fromAleutians and New Britain, and the three-component type, such as those from Sunda,Lesser Antilles and Andes. In addition, the EMII type mantle-derived rocks may alsobe divided into two groups. One is exemplifled by continental flood basalts and someperidotite xenoliths, similar to IAB, with high La/Nb and Ba/Nb and low Nb/Th ratios.The other includes the Samoa-type oceanic island basalts, with low La/Nb and Ba/Nband high Nb/Th ratios. The corresponding two sub-components of EMII are EMIIM,which is related to the metasomatism of lithosphere mantle by fluids released from thesubducted oceanic crust, and EMIISR, related to the intervention of recycling continentalsediments into the convective mantle.