| 桂东南岑溪燕山期A型花岗岩年代学、地球化学特征及其构造意义 |
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| 关键词:granite Yanshanian Period zircon U-Pb age geochemistry southeastern Guangxi |
| 基金项目:本文由广东省区域地质调查成果更新与综合编图项目(编号: 2024-02)和云南省新一轮找矿暨地勘基金项目(编号: Y202401; Y202504)联合资助。 |
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| Geochronology, Geochemical Characteristics and Tectonic Implications of the Yanshanian A-type Granites in Cenxi, Southeastern Guangxi |
| The southeastern Guangxi region, a crucial tectonic junction between the Cathaysia and Yangtze Blocks, is essential for understanding the Mesozoic tectonic and magmatic evolution of the South China Block. The petrogenesis of the Yanshanian A-type granites in this region is key to revealing these processes. This study focused on the Cenxi granite body and applied systematic field geological investigations, zircon U-Pb dating, whole-rock geochemistry, and zircon Hf isotopic analyses to investigate its petrogenesis and tectonic context. The granite mainly comprises biotite monzogranite with minor quartz monzodiorite and widespread dark-colored monzodiorite enclaves. The geochemical characteristics include high silica content (SiO2 = 73.8%–77.0%), alkali enrichment (Na2O + K2O = 7.71%–8.82%), a metaluminous composition (A/CNK = 0.95–0.96), and a high-K calc-alkaline to shoshonitic series. Key parameters, including 10 000×Ga/Al, Zr+Nb+Ce+Y ratios, and zircon saturation temperatures (TZr = 826–846 ℃), indicate that the granite is a typical A-type granite. LA-ICP-MS zircon U-Pb dating yields a crystallization age of (156.4±1.1) Ma (MSWD = 1.9; n = 18), indicating formation during the Late Jurassic (Early Yanshanian). Geochemical analyses reveal light rare earth element (LREEs) enrichment [(La/Yb)N = 6.88–8.01] and negative Eu anomalies (δEu = 0.13–0.15). Primitive mantle-normalized diagrams show enrichment in large-ion lithophile elements (Rb, Th, U, K, and Pb) and depletion in high-field-strength elements (Nb, Ta, P, and Ti). Zircon in-situ Hf isotopic compositions (εHf(t) = ?2.84 to +2.84, average +0.035) and corresponding two-stage model ages (T2DM = 1.39–1.03 Ga; average 1.20 Ga) suggest that the magma source mainly involved partial melting of Mesoproterozoic continental crust, with contributions from mantle components. Petrographic and geochemical evidence indicates that the biotite monzogranite, quartz monzodiorite, and monzodiorite enclaves represent different evolutionary stages of a co-magmatic system formed through crystallization differentiation. Regional tectonic analysis indicates that the formation of the Cenxi A-type granite is closely linked to the extensional tectonic environment triggered by subduction of the Paleo-Pacific Plate. Slab rollback induced asthenospheric upwelling, providing heat for crustal melting and facilitating the mixing of mantle-derived materials with crustal melts. This process ultimately generated high-temperature, low-water-activity parental magmas that underwent significant fractional crystallization. This study provides new constraints on the dynamic mechanisms of Late Mesozoic magmatism in the South China Block. |
| SONG Xingwang,XIE Zhipeng,WANG Jianrong,ZHANG Yuan,DOU Lei,WANG Wei.2026.Geochronology, Geochemical Characteristics and Tectonic Implications of the Yanshanian A-type Granites in Cenxi, Southeastern Guangxi[J].Acta Geoscientica Sinica,47(4):750-769. |
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