Geochemistry and geochronology of I–type granites of the Feidong Complex, eastern China: Implications for the Paleoproterozoic tectonic evolution of the Yangtze Craton

Abstract

The early history of the Yangtze Craton is not well constrained as a result of the lack of outcropping Archean to Paleoproterozoic rocks. This study presents new elemental and Laser Ablation–(Multicollector)–Inductively Coupled Plasma–Mass Spectrometry (LA–(MC)–ICP–MS) zircon U–Pb geochronological and Hf isotopic data for Paleoproterozoic granites of the Feidong Complex, located within the northeastern Yangtze Craton. Zircon U–Pb dating yields 207Pb/206Pb ages of 2054 ± 22 and 1994 ± 26 Ma for granite and granitic gneiss units in this area, respectively, confirming the existence of middle Paleoproterozoic basement rocks within the Feidong Complex and the northeastern Yangtze Craton. Zircons from the granite and granitic gneiss units have εHf(t) values ranging from –13.02 to –6.91, corresponding to two–stage Hf model ages (TDM2) of 3.44–3.07 Ga. The granites have whole–rock εNd(t) values from –0.25 to + 0.14 whereas the granitic gneisses have εNd(t) values that range from –8.90 to –8.12. This suggests that the granitic magmatism in this area was resulted from reworking of ancient crustal components but that the granites and granitic gneisses are derived from different magma sources. This is consistent with the fact that the granites in this area have volcanic arc affinities whereas the granitic gneisses have syn-collisional granite affinities, although all are classified as I–type granites. Combining these data with previous research on Paleoproterozoic magmatic and metamorphic events recorded elsewhere in the Yangtze Craton suggests that a middle–late Paleoproterozoic geological transition from plate subduction to collision occurred at ca. 2.0 Ga in the northeastern Yangtze Craton. This tectonism caused the partial melting of ancient crustal material, generating both the granites and granitic gneisses in the study area.