Episodic Mesozoic thickening and reworking of the North China Archean lower crust correlated to the fast-spreading Pacific plate |
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| Institution: | 1. Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China;2. State Key Laboratory of Continental Geodynamics, Northwest University, Xi''an, China;3. School of Resource and Environmental Engineering, Anhui University, Hefei, China;4. Department of Earth and Environmental Sciences, Albert-Ludwigs University Freiburg, 79104 Freiburg, Germany;1. Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits, Ministry of Land and Resources, Xi''an Center of Geological Survey, Geological Survey of China, Xi''an 710054, China;2. Research Center for Orogenic Geology, Xi''an Center of Geological Survey, Geological Survey of China, Xi''an 710054, China;3. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia |
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| Abstract: | A central target in Earth sciences is to understand the processes controlling the stabilization and destruction of Archean continents. The North China craton (NCC) has in part lost its dense crustal root after the Mesozoic, and thus it is a key region to test models of crust–mantle differentiation and subsequent evolution of the continental crust. However, the timing and mechanisms responsible for its crustal thickening and reworking have been long debated. Here we report the Early Cretaceous Yinan (eastern NCC) adakitic granites, for which major/trace elemental models demonstrate that they are complementary to the analogy of the documented eclogitic relicts within the NCC. Based on their Late Archean inherited zircons, depleted mantle Nd model ages of ～2.8 Ga, large negative εNd(t) values (?36.7 to ?25.3) and strongly radiogenic initial 87Sr/86Sr ratios (0.7178–0.7264), we suggest that the Yinan adakitic granites were potentially formed by the dehydration melting of a thickened Archean mica-bearing mafic lower crust during the Early Cretaceous (ca. 124 Ma), corresponding to a major period (117–132 Ma) of the NCC Mesozoic intrusive magmatism. Combined previous results, it is shown that the thickening and reworking of the North China Archean lower crust occurred largely as two short-lived episodes at 155–180 Ma and 117–132 Ma, rather than a gradual, secular event. These correlated temporally with the superfast-spreading Pacific plate during the Mesozoic. The synchroneity of these events suggests rapid plate motion of the Pacific plate driving the episodic NCC crustal thickening and reworking, resulting in dense eclogitic residues that became gravitationally unstable. The onset of lithospheric delamination occurred when upwelling asthenosphere heated the base of lower crust to form coeval felsic magmas with or without involvement of juvenile mantle material. Collectively, the circum-Pacific massive crustal production could be attributed to the unusually rapid motion of Pacific at 155–180 Ma and 117–132 Ma. |
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| Keywords: | Adakitic granite Archean lower crust Thickening Pacific plate Rapid spreading North China craton |
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