Minor elements and isotopic compositional characters of amphibolite from Song Ma suture zone in Northern Vietnam

Abstract

Song Ma suture zone is a metamorphic complex developed between the South China and the Indochina Blocks, and composed of greenschist to amphibolite facies metamorphic rocks. Analytical results of whole rock compositions of amphibolites are reported for considering the origin of metamorphic rocks in the suture. The amphibolite show basaltic compositions with slightly enriched incompatible elements, especially HFS elements as Y and Zr from the primitive mantle composition. Almost amphibolites show nearly flat REE patterns with restored high Nd isotopic compositions. Such compositional characters of HFSE and REE are equivalent to those of basalt originated from depleted mantle. On the other hand, an amphibolite with LREE-enriched composition was also found. This has comparatively much LILE. Protolith of the amphibolite was possibly originated from enriched mantle. Based on such compositional evidence, amphibolites in the Song-Ma suture zone were probably metamorphosed mid-ocean ridge basalt with a few ocean island basalts.