Petrogenesis and tectonic implications of the Neoarchean North Liaoning tonalitic-trondhjemitic gneisses of the North China Craton, North China. (1st December 2016) - Wang, Maojiang
Graphical abstract: Highlights: High- and Low-MgO tonalitic and trondhjemitic gneisses in the Tangtu-Majuanzi area. Partial melting of the subducted slabs and the juvenile lower crust. Three episodes of magmatism at ∼2680 Ma, ∼2600–2570 Ma and ∼2550–2510 Ma. A Neoarchaean active continental margin in the North Liaoning area. Abstract: Tonalitic-trondhjemitic-granodioritic (TTG) gneisses are dominant lithological assemblages in Archean high grade metamorphic terranes in the world. These TTG gneisses preserve important information in formation and evolution of Archean continental crust. Tangtu-Majuanzi microblock in North Liaoning Province (NLP) is one of the major Neoarchean metamorphic basement terranes in the northeastern margin of the North China Craton (NCC). The Tangtu-Majuanzi microblock is composed mainly of Neoarchean tonalitic-trondhjemitic (TT) gneisses, subordinate granodioritic to monzogranitic association (GMA) and minor supracrustal rocks. The tonalitic-trondhjemitic gneisses are divided into high MgO Group (HMG) and low MgO Group (LMG) based on their chemical compositions. Detailed petrogenetic investigations suggest that the magmatic precursors of the HMG samples were derived from partial melting of subducted slabs and contaminated by the overlying mantle wedge during its ascent; whereas, magmatic precursors of the LMG samples were derived from the juvenile lower crust. LA-ICPMS zircon U-Pb isotopic dating analyses reveal that the magmatic precursors of the HMG samples were formed at 2553–2531 Ma. An older HMG tonalitic gneiss sample was discovered at Sandaoguan in the southmost of the studied area, with its magmatic precursor emplaced at 2680 Ma. The magmatic precursors of the LMG samples emplaced at 2595–2583 Ma. Combined with previous credible chronological data, our newly obtained zircon U-Pb dating and Lu-Hf isotopic data indicate that three episodes of magmatism at ∼2700–2680 Ma, ∼2600–2570 Ma and ∼2550–2510 Ma occurred in the Tangtu-Majuanzi microblock, and the TT gneisses in this microblock were subjected to generally amphibolite-facies metamorphism at ∼2520–2470 Ma. Based on the above Neoarchean crust-mantle thermal-dynamic processes, we propose that the Neoarchean magmatism and metamorphism in the Tangtu-Majuanzi microblock of North Liaoning Province occurred in an active continental margin.