Implications of εNd—La／Nb,Ba／Nb,Nb／Th Diagrams to Mantle Heterogeneity—Classification of Island—arc Basalts and Decomposition of EMII Component

A group of εNd/Nb,Ba/Nb,Nb/Th diagrams are used to study mantle heterogeneity.Island-arc basalts(IAB) are distributed in a triangle of these diagrams. Three end-member components (the MORB-type depleted mantle, the fluid released from subducted oceanic crust and the sediments from the continental crust) of the source of IAB may be displayed in these diagrams. Two types of IAB are identified .They are of the two-component type (with little continental sediments), such as the basalts from Aletians and New Britain ,and the three-compeonent type, such as those from Sunda, Lesser Antilles and Andes. In addition ,the EMII type mantle-derived rocks may also be divided into two groups. One is exemplified by continental flood basalts and some peridotite 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/Nb and 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 the subducted oceanic crust, and EMIISR, related to the intervention of recycling continental sediments into the convective mantle.

Implications of εNd–La/Nb,Ba/Nb,Nb/Th diagrams to mantle heterogeneity—Classification of island-arc basalts and decomposition of EMII component–La/Nb,Ba/Nb,Nb/Th diagrams to mantle heterogeneity—Classification of island-arc basalts and decomposition of EMII component

A group of ε_Nd–La/Nb, Ba/Nb, Nb/Th diagrams are used to study mantly heterogeneity. Island-arc basalts (IAB) are distributed in a triangle of these diagrams. Three end-member components (the MORB-type depleted mantle, the fluid released from subducted oceanic crust and the sediments from the continental crust) of the source of IAB may be displayed in these diagrams. Two types of IAB are identified. They are of the two-component type (with little continental sediments), such as the basalts from Aleutians 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 also be divided into two groups. One is exemplified by continental flood basalts and some periotite 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/Nb and 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 the subducted oceanic crust, and EMIISR, related to the intervention of recycling continental sediments into the convective mantle. This project was granted by the National Natural Science Foundation of China.