Lower Sequence Metavolcanic Rocks

Abstract

AbstractThe lower sequence metavolcanic rocks consist primarily of biotite two-pyroxene plagioclase gneisses, clinopyroxene hornblende plagioclase gneisses, amphibolites, hornblende plagioclase gneisses, and biotite plagioclase gneisses, which were metamorphosed primarily under amphibolite to granulite facies. These metavolcanic rocks were erupted during 2558–2536 Ma and can be subdivided into a basaltic-andesitic group, a high-MgO dacitic group, and a low-MgO dacitic group based on their distinct geochemical characteristics. The basaltic-andesitic samples exhibit calc-alkaline affinities with high MgO contents, and were most likely generated by the partial melting of mantle wedge materials metasomatized by dehydration fluids and partial melts derived from subducted slabs and sediments. The high-MgO dacitic samples display chemical affinities to high-SiO2 adakites and were probably derived from the partial melting of descending slabs and sediments, with the ascending melts contaminated by the overlying mantle wedge materials. The low-MgO dacitic samples show high SiO2 and low MgO contents, and were likely derived from the partial melting of lower crustal high-K mafic rocks and metasedimentary rocks.KeywordsLate NeoarcheanMetavolcanic rocksMetasomatized mantle materialsHigh-SiO2 adakitesLower crustal materials