| 米仓山地块新元古代花岗类岩石成因及其对扬子克拉通西北缘大陆增生弧持续演化的制约 |
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| 关键词:Yangtze Craton Micangshan block adakitic granite granitic gneiss geochemistry geochronology |
| 基金项目:本文由国家自然科学基金面上项目(编号: 42472080)和山东省自然科学基金面上项目(编号: ZR2023MD058)联合资助。 |
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| Genesis of Neoproterozoic Granitoids from the Micangshan Block and Its Constraints on the Continuous Evolution of the Continental Accretionary Arc on the Northwestern Yangtze Craton |
| The Neoproterozoic magmatism that developed widely in the Micangshan and Hannan blocks of the northwestern Yangtze Craton is of considerable importance for investigating the tectonic–magmatic evolution of the Yangtze Craton during the Neoproterozoic and its role in the evolution of the Rodinia supercontinent. This study conducted detailed petrographic, zircon U-Pb geochronological, Lu-Hf isotopic, and geochemical analyses on the porphyritic granite and granitic gneisses in the Micangshan block to reveal their formation mechanisms and dynamic setting. Petrographic observations indicate that these rocks underwent intense regional metamorphism and deformation after their formation. LA-ICP-MS zircon U-Pb dating reveals that the porphyritic granites formed at (822±2) Ma, whereas the protoliths of the granitic gneisses formed between 838 and 852 Ma. Geochemical analyses show that the porphyritic granites exhibit high Sr, low Y and Yb, and high Sr/Y and La/Yb ratios, resembling typical adakitic rock. Their low MgO, Cr, and Ni contents, coupled with positive εHf(t) values, suggest derivation from partial melting of thickened juvenile basaltic crust. Conversely, the granitic gneisses showed low Mg#, Ni, and Zr concentrations, classifying them as I-type granites. Their primitive mantle-normalized trace element patterns are enriched in large-ion lithophile elements (Rb, Ba, U, and K), however, depleted in high-field-strength elements (Nb, Ta, Ti), indicative of arc-related magmatism. Combined with their positive zircon Hf isotopic compositions, these features imply formation via partial melting of juvenile crust. The northwestern Yangtze Craton was situated in a continental margin arc setting between 870 and 830 Ma due to oceanic subduction, generating arc-type magmatic rocks, such as the Zhengyuan gabbro, Shantan diorite, and Zhengyuan I-type granitic gneisses in the Micangshan region. During ~820 Ma, slab rollback led to the formation of adakitic granite in Micangshan and A-type granites in Xihe. Subsequently, between 770 and 707 Ma, the collision and amalgamation of the Hannan arc with adjacent continental blocks occurred, followed by orogenic collapse. This resulted in the widespread emplacement of adakites and A-type granites. In conclusion, the Micangshan and Hannan blocks likely represent a prolonged Neoproterozoic continental arc accretionary environment along the northwestern Yangtze Craton, evolving from the Micangshan arc to the Hannan arc during the assembly of the Rodinia supercontinent. |
| LI Yongpan,YUAN Mingkao,ZHANG Jiantai,XIAO Lingling,WANG Guodong.2026.Genesis of Neoproterozoic Granitoids from the Micangshan Block and Its Constraints on the Continuous Evolution of the Continental Accretionary Arc on the Northwestern Yangtze Craton[J].Acta Geoscientica Sinica,47(4):770-789. |
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