| 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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| 引用本文：兰开军,吴亮,陈庆松,刘军平,孙建勋,魏杰,朱恩异.2026.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[J].地球学报,47(5):1097-1115. |
| DOI：10.3975/cagsb.2026.012722 |
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| 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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| 中文摘要:在古特提斯洋洋壳俯冲、保山地块与思茅地块碰撞和后碰撞伸展演化过程中, 西南三江地区发育有大量的中生代岩浆岩。本文以昌宁—孟连缝合带内规模较大的发展河花岗岩体为对象, 通过系统的岩石学、地球化学、锆石U-Pb年代学及全岩Sr-Nd-Pb同位素分析, 研究其成因类型及源区信息。研究取得以下认识: (1)发展河花岗岩体主要由黑云二长花岗岩和二长花岗岩组成, 其中黑云二长花岗岩锆石U-Pb年龄为(237±2) Ma、二长花岗岩锆石U-Pb年龄为(228±2) Ma和(224±5) Ma, 表明其形成时代为中—晚三叠世。(2)地球化学分析显示岩石具有富硅铝、高碱特点, A/CNK为0.89~1.57, 为高钾钙碱性-准铝到过铝质花岗岩。岩石富集Rb、Th、U及轻稀土元素, 而相对亏损Ti、P、Sr、Nb等元素, 并呈现显著的负Eu异常。岩石具有较高的分异指数(74.39~94.86), 岩浆演化以结晶分异为主, 多数属于S型花岗岩, 少量岩石有I型花岗岩的特征。(3)岩石具有高的(87Sr/86Sr)i值(0.705 85~0.720 36)和较低的εNd(t)值(–12.83 ~ –11.70), 二阶段Nd模式年龄为1.96~2.23 Ga, 与区内元古宙地壳基底较为相似。全岩铅同位素(206Pb/204Pb)i在18.682~18.751之间, (207Pb/204Pb)i值为15.769~15.780, (208Pb/204Pb)i在38.436~38.872之间, 表明其物质来源以上地壳为主。综合区域构造演化特征, 认为发展河花岗岩体形成于中—晚三叠世昌宁—孟连古特提斯洋后碰撞伸展环境, 限定了区内后碰撞岩浆活动的起始时间不晚于224 Ma, 为古特提斯洋闭合提供了重要的年代学约束和地球化学证据。 |
| 中文关键词:发展河 锆石U-Pb 古特提斯 地球化学 后碰撞 |
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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 |
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| Abstract: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. |
| keywords:Fazhanhe zircon U-Pb Paleo-Tethys geochemistry post-collision |
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