Episodic Paleoarchean-Paleoproterozoic (3.3-2.0 Ga) granitoid magmatism in Yangtze Craton, South China: Implications for late Archean tectonics

The Archean Kongling Terrane preserves voluminous Paleoarchean-Paleoproterozoic granitoids, recording the early formation and evolution history of the Yangtze Craton, South China. We present petrography, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes of twelve gneissic granitoids from this terrane, including trondhjemites, biotite-granites, and two-mica granites. Magmatic zircons in these granitoids yield emplacement ages of 3.31-3.29 Ga for trondhjemites, 2.81-2.78 and 2.66 Ga for biotite-granites, as well as 2.70-2.64, 2.42, and 2.00 Ga for two-mica granites. The 2.8-2.6 Ga granites contain minor 3.4-2.9 Ga inherited zircons and 2.0 Ga metamorphic zircons that formed mainly by recrystallization. Major and trace element compositions of the trondhjemites suggest a garnet amphibolite-facies low-K mafic source, similar to the typical Archean medium-pressure trondhjemitetonalite-granodiorites (TTGs), whereas those of the biotite- and two-mica granites indicate tonalitic and tonalitic-sedimentary sources, respectively. The Lu-Hf data (chondritic epsilon(Hf)(t) values -0.8 to 0 and Eoarchean two-stage Hf model ages 3.75-3.70 Ga) for the trondhjemites support partial melting of a long-lived ancient depleted-mantle-derived or a juvenile lower-mantle-derived mafic crust. The Lu-Hf data and inherited zircon ages also suggest that the 2.8 Ga granites were derived from the local 3.4-2.9 Ga TTGs. Together with previously addressed 3.2 and 3.0-2.9 Ga TTG magmatism, a remarkable change is observed at 2.8 Ga in the petrology, geochemistry, and petrogenesis of the episodic 3.3-2.0 Ga granitoid magmatism from TTG- to granite-dominated in the Kongling Terrane, which may reflect a transition from subduction- to collision-related tectonics. In addition, we note that the 2.70-2.64 Ga biotite- and two-mica granites (this study) as well as 2.67-2.62 Ga A-type granites (published data) were emplaced shortly after a 2.75-2.72 Ga high-grade metamorphic event (published data) in the Kongling Terrane. These granites could be generated as a result of orogenic root collapse and subsequent mantle upwelling, implying a 2.7 Ga orogenic event in the Yangtze Craton. (c) 2015 Elsevier B.V. All rights reserved.