Ultra-high temperature overprinting of high pressure pelitic granulites in the Huai'an complex,North China Craton: Evidence from thermodynamic modeling and isotope geochronology |
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| Affiliation: | 1. Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology, Qingdao 266590, China;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;3. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia;1. School of Earth Sciences and Resources, China University of Geosciences, Beijing, 29 Xueyuan Road, Beijing 100083, China;2. Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia;3. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea;1. Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China;2. Department of Geosciences, University of Mainz, D-55099 Mainz, Germany;1. Department of Earth and Environmental Sciences, The Earth and Environmental Science System Research Center, Chonbuk National University, Jeonju 561–756, Republic of Korea;2. Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, South Korea;3. Divisions of Earth and Environmental Sciences, Korea Basic Science Institute, Ochang 363–883, Republic of Korea;1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;2. College of Earth Science & Engineering, Shandong University of Science and Technology, Qingdao 266590, China |
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| Abstract: | Paleoproterozoic granulite facies rocks are widely distributed in the North China Craton (NCC). The Huai'an terrane, located within the northern segment of the Trans-North China Orogen (TNCO), a major Paleoproterozoic collisional belt in the central NCC expose mafic and pelitic granulites as well as TTG (tonalite-trondhjemite-granodiorite) gneisses. Here we investigate the pelitic granulites from this complex and identify four distinct mineral assemblages corresponding to different metamorphic stages. The prograde metamorphism (M1) is recorded by relict biotite and the compositional profile of Xca (grt) isopleths. The Pmax (M2) is distinguished by the Xca (grt) isopleths, which corresponds to the kyanite stable area with an inclusion mineral assemblage of Grt-c–(Ky)-Qz-Rt-Kfs-liq suggesting that the pressures were higher than 12 kbar with a temperature below 900 °C. However, kyanite is absent in thin sections suggesting its consumption during later stages. The Tmax metamorphism (M3) is characterized by the assemblage: Grt-m-Qz-Pl-Rt-Kfs-Sil-liq in the garnet mantle and also reflected in the compositional profile. Two-feldspar geothermometry yields a P-T range of 940 °C–950 °C and 9.5–10.5 kbar, indicating ultra-high temperature (UHT) metamorphic overprinting. The subsequent retrograde metamorphic stage (M4) is characterized by Grt-r-Bt-Sil-Kfs-Pl-Qz ± Rt ± Ilm with symplectites of Bt-Sil-Qz in the garnet rim suggesting garnet breakdown with P-T conditions estimated as 770 °C–840 °C and 6.5–8 kbar. The pelitic granulites show a clockwise path, with P-T estimates higher than those in estimated in previous studies using conventional techniques.LA-ICP-MS U–Pb analysis of metamorphic zircon grains yield two groups of ages at 1972.9 ± 8.1 Ma and 1873.3 ± 9.9 Ma. We suggest that the protoliths of the Manjinggou HP-UHT granulites were deep subducted where they experienced HP metamorphism associated with the collision of the Ordos and Yinshan blocks at ca. 1.97 Ga. Subsequently, the UHT metamorphic overprint occurred during the assembly of the unified Western and Eastern Blocks of the NCC along the TNCO at ca. 1.87 Ga. |
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