南大西洋中脊26°S玄武岩中斜长石化学成分变化对岩浆演化的启示  

Implications for magmatic evolution of changes in plagioclase composition in the 26°S basalts,Southern Mid-Atlantic Ridge

作　　者：雷庆[1] 王国芝 赵甫峰[1] 范蕾[4] 刘刚 王子昂[1] 胡起华 肖钰于 Lei Qing;Wang Guozhi;Zhao Fufeng;Fan Lei;Liu Gang;Wang Ziang;Hu Qihua;Xiao Yuyu(Faculty of Earth Sciences,Chengdu University of Technology,Chengdu 610059,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu 610059,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Chengdu University of Technology,Chengdu 610059,China;First Institute of Oceanography,Ministry of Natural Resources,Qingdao 266061,China)

机构地区：[1]成都理工大学地球科学学院,四川成都610059 [2]成都理工大学沉积地质研究院,四川成都610059 [3]成都理工大学油气藏地质及开发工程国家重点实验室,四川成都610059 [4]自然资源部第一海洋研究所,山东青岛266061

出　　处：《海洋学报》2023年第11期62-75,共14页

基　　金：大洋靶区多金属硫化物赋矿围岩包裹体特征与硫化物蚀变机制研究项目(DY135-S2-2-05)。

摘　　要：南大西洋中脊26°S热液区玄武岩中斜长石的成分和结构特征为研究岩浆演化特征提供了重要依据。在对玄武岩岩相学观察、斜长石成分分析的基础上,对不同阶段斜长石的结构及成分进行对比,探讨岩浆演化的过程。结果表明:研究区以斑状玄武岩为主,斜长石斑晶常见连晶结构、韵律环带、溶解与再吸收、生长结构,基质中的斜长石主要呈针状和燕尾状;南大西洋中脊26°S(SMAR-26°S)热液区玄武岩主要为钠质拉斑玄武岩,岩浆演化早期以形成培长石为主,晚期以形成拉长石为主,整个演化过程中CaO和Al2O3含量下降,而SiO2、Na2O、FeOT和MgO含量上升;从斜长石斑晶的核部→边部→基质中的斜长石微晶,An值整体下降,斜长石斑晶边部的An值与基质中斜长石微晶An值部分重合,形成温度总体有逐渐下降趋势。由此反映出地幔岩浆形成后在上涌过程中可能经历了减压挥发分逸出、晶体在深部的熔蚀、熔体过饱和结晶、低Si同源岩浆的混合、同喷发脱气岩浆迅速减压的过程。The composition and texture characteristics of plagioclase in basalt from the 26°S hydrothermal field of the Southern Mid-Atlantic Ridge provide an important basis for the study of magmatic evolution characteristics.On the basis of observing the petrography of basalt and analyzing the composition of plagioclase,the structure and composition of plagioclase at different stages are compared to explore the process of magma evolution.The results show that the study area is mainly composed of porphyritic basalt,and plagioclase porphyries are commonly charac-terized by glomerocryst structures,oscillatory-zoned,dissolved and resorbed rim,and growth structures.The pla-gioclase in the matrix is mainly acicular and swallow-tailed crystals;the basalts in the SMAR-26°S hydrothermal zone are mainly sodium tholeiitic basalts.In the early stage of magma evolution,bytownite was mainly formed,while in the late stage,labradorite was mainly formed.Throughout the entire evolution process,the content of CaO and Al2O3 decreases,while the content of SiO2,Na2O,FeO,and MgO increases;from the core to rim of plagioclase phenocrysts and then to plagioclase microcrystalline in the matrix,the An values decreases overall.The An values in the rim of plagioclase phenocryst partially overlaps with the An values of plagioclase microlites in the matrix,resulting in a gradual decrease in temperature.These represent the changes from the magma origin area to magma eruption.After the formation of mantle magma,it rapidly rises and erupts to form basalt.During the upwelling pro-cess,it may undergo the process of decompression accompanied by volatiles escaping,dissolving in the deep,super-saturated crystallizing of the melt,mixing of low-Si same sourced magma,and syn-eruptive fast decompression of degassed magma.

关 键 词：南大西洋中脊 玄武岩 斜长石斑晶 斜长石微晶 岩浆演化 

分 类 号：P736.211[天文地球—海洋地质]