| 云南澜沧发展河花岗岩体成因研究——锆石U-Pb年龄、地球化学及Sr-Nd-Pb同位素制约 |
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| 关键词:Fazhanhe zircon U-Pb Paleo-Tethys geochemistry post-collision |
| 基金项目:本文由中国地质调查局地质调查项目(编号: DD2016008005; DD20220987; DD20240207101)资助。 |
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| Petrogenesis of the Fazhanhe Granitoids in Lancang, Yunnan, China: Constraints from Zircon U-Pb Dating, Geochemistry, and Whole-rock Sr-Nd-Pb Isotopes |
| During the subduction of the oceanic slab, collision between the Baoshan Terrane and Simao Terrane, and post-collision extension of the Paleo-Tethys Ocean, a large number of Mesozoic magmatic activities occurred in the Sanjiang area, southwest China. Based on petrologic, whole-rock geochemical, zircon U-Pb geochronological, and whole-rock Sr-Nd-Pb isotopic analyses, we conducted systematic studies on the identified Fazhanhe granitoids in the Changning–Menglian suture zone to evaluate their petrogenesis and magma sources. LA-ICP-MS zircon U-Pb analyses indicated a crystallization age of (237±2) Ma for the Fazhanhe biotite monzogranite, and the crystallization age of the monzogranite is between (228±2) Ma and (224±5) Ma, belonging to the Middle–Late Triassic magmatic activity. Geochemical analyses revealed that the granitic samples exhibit relatively high SiO2, aluminum, and alkali concentrations and have metaluminous to peraluminous chemical compositions, belonging to the high-K calc-alkaline series. They are enriched in Rb, Th, U, and light rare earth elements and depleted in Ti, P, Sr, and Nb, with a significant negative Eu anomaly. The granites display a high differentiation index (74.39–94.86), indicating predominant crystallization differentiation processes. Most samples exhibited S-type granite characteristics, but a small number of rocks were I-type granites. The granite samples had high initial ??Sr/??Sr ratios (0.705 85–0.720 36) and low εNd(t) values (–12.83 – –11.70), with a two-stage Nd model age ranging from 1.96 to 2.23 Ga, which is quite similar to the age of Proterozoic crustal basement in the region. Whole-rock Pb isotopic compositions (2??Pb/2??Pb)i =18.682–18.751, (2??Pb/2??Pb)i=15.769–15.780, (2??Pb/2??Pb)i=38.436–38.872) indicate that the sourced material came from the upper crust. Integrating regional tectonic evolution, we propose that the Fazhanhe granitoids formed in the Middle–Late Triassic post-collision extension environment. These geochronological and geochemical data indicate that the Changning–Menglian Paleo-Tethys Ocean closed prior to 224 Ma. |
| LAN Kaijun,WU Liang,CHEN Qingsong,LIU Junping,SUN Jianxun,WEI Jie,ZHU Enyi.2026.Petrogenesis of the Fazhanhe Granitoids in Lancang, Yunnan, China: Constraints from Zircon U-Pb Dating, Geochemistry, and Whole-rock Sr-Nd-Pb Isotopes[J].Acta Geoscientica Sinica,47(5):1097-1115. |
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