Geochronology, geochemistry and Hf-O isotopes of Late Archean meta-mafic volcanics in the Jiaobei Terrane

The Jiaobei Terrane is situated in the eastern part of the Shandong Province in eastern China, experiencing multi-stage magmatism during the Mesoarchean (~2.9Ga) and Neoarchean (~2.7Ga and ~2.5Ga). It consists dominantly of granitoid gneisses and meta-gabbros with minor Neoarchean supracrustal rocks enclaves or lenses. This study presents new zircon SHRIMP U-Pb dating, whole-rock geochemical and Hf-O isotopic data for the Late Archean meta-basic volcanic rocks from the Jiaodong Terrane in order to constrain their petrogenesis and tectonic setting. Magmatic zircon SHRIMP U-Pb dating yielded an age of 2524±22Ma for the meta-basic volcanic rocks, which was influenced by the Late Neoarchean (2494±9Ma) tectonic thermal events. This constrains the formation age of the meta-basic volcanic rocks to 2494~2507Ma, attributing them to the Late Neoarchean Jiaodong Group. These rocks display tholeiitic basaltic composition, which has underwent olivine and clinopyroxene fractional crystallization during protolith magmatic evolution. Whole-rock composition analysis indicates low to moderate SiO2 (50.39%~52.01%) and high MgO (Mg#=41~67) contents. They are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) Rb, Ba, Pb, depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE) Nb, Ta and Ti, with no significant Eu anomalies. The εHf(t) and δ18O values range from +1.22 to +6.0, and 3.46‰ to 6.59‰, respectively. These geochemical features show typical subduction-related arc signature, indicating that the meta-basic volcanic rocks were derived from partial melting of a depleted mantle. In the Late Neoarchean(~2.5Ga), a combination of TTGs, sanukites and potassium-rich granites emerged, reflecting strong crust-mantle interactions and crustal recycling, signifying the initial carbonization of the North China Craton was completed.