滇西剑川正长斑岩的岩浆作用过程——来自锆石U-Pb-Hf同位素和元素地球化学约束  

MAGMATIC PROCESSES OF SYENITE PORPHYRY IN JIANCHUAN,WESTERN YUNNAN:CONSTRAINTS FROM ZIRCON U-Pb-Hf ISOTOPES AND ELEMENTAL GEOCHEMISTRY

作　　者：张露 龙小虎 赵甫峰[1] 杨蜜蜜 任科法[1] 楚亚婷[1,3] 曹可 张凡 ZHANG Lu;LONG Xiaohu;ZHAO Fufeng;YANG Mimi;REN Kefa;CHU Yating;CAO Ke;ZHANG Fan(Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation,Ministry of Natural Resources,College of Earth Sciences,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Mianyang Normal College,Mianyang,Sichuan 621000,China;CECEP Construction Engineering Design Institute Limited Company,Chengdu,Sichuan 610059,China)

机构地区：[1]自然资源部构造成矿成藏重点实验室、成都理工大学地球科学学院,四川成都610059 [2]绵阳师范学院,四川绵阳621000 [3]中节能建设工程设计院有限公司,四川成都610059

出　　处：《矿物岩石》2023年第1期28-41,共14页Mineralogy and Petrology

基　　金：国家自然科学基金项目(批准号:41403025);四川省教育厅项目(编号:17ZB0052,18ZA0056)。

摘　　要：剑川正长斑岩是滇西新生代富碱斑岩的典型代表;岩石中发育各类深浅不一的包体,暗示正长斑岩的形成和演化经历了复杂的壳幔混合作用。本次研究通过剑川正长斑岩的锆石地球化学方法确定锆石相对氧逸度和Ti温度,结合锆石U-Pb定年和Hf同位素,探讨滇西剑川新生代富碱岩浆演化与壳幔岩浆混合作用。研究表明:正长斑岩w(SiO_(2))为61.65%~63.03%,全碱质量分数为9.52%~10.38%,K_(2)O/Na2O比值介于1.62~1.68。纱帽山岩体(J1样品)的锆石U-Pb年龄为35.15±0.52 Ma,锆石Ti温度相对均一,为745~822℃;Ce^(4+)/Ce^(3+)比值为23~329(均值119),指示相对较低的氧逸度,并对应相对较高的εHf(t)值(-0.4~+1.5)。金华山岩体(J2样品)的锆石U-Pb年龄为35.90±0.20 Ma,锆石Ti温度更宽泛,为683~917℃;Ce^(4+)/Ce^(3+)比值为36~380(均值170),指示相对较高的氧逸度,同时对应相对较低的εHf(t)值(-3.7~+0.7)。随着岩浆的演化,J1和J2岩体都具备从高氧逸度向低氧逸度演化的趋势。综合认为:剑川地区经历了幔源岩浆脉动式上涌与底侵作用导致的壳幔岩浆混合作用,形成了相对高氧逸度的岩浆,随着低氧逸度幔源岩浆上升通量增大,壳源物质混染比例相对降低,岩浆氧逸度呈现降低的趋势。Jianchuan syenite porphyry is a typical example of Cenozoic alkali-rich porphyry in western Yunnan,and its evolution has undergone complex crust-mantle mixing.In this paper,zircon relative oxy-gen fugacity and Ti temperature of Jianchuan syenite porphyry are determined by zircon geochemical analy-sis.Through analysis of zircon U-Pb dating and Hf isotopes,the evolution of Cenozoic alkali-rich magmat-ic and crust-mantle magmatic mixing in Jianchuan are discussed.The results show that the SiO_(2)content of syenite porphyry is 61.65%to 63.03%,the total alkali content is 9.52%to 10.38%,and the K_(2)O/Na_(2)O ratio is 1.62 to 1.68.The zircon U-Pb ages of the Shamaoshan pluton(J1 sample)are 35.15 to 0.52 Ma,and the zircon Ti temperatures are relatively uniform,ranging from 745 to 822℃.Ce^(4+)/Ce^(3+)ratios ran-ging from 23 to 329(mean 119),indicating relatively low oxygen fugacity and corresponding to relatively highεHf(t)values(-0.4 to+1.5).Zircon U-Pb ages of Jinhua Huashan pluton(J2 sample)range from 35.90 to 0.20 Ma,and zircon Ti temperatures range from 683 to 917℃.Ce^(4+)/Ce^(3+)ratios range from 36 to 380(mean 170),indicating relatively high oxygen fugacity and corresponding to relatively lowεHf(t)values(-3.7 to+0.7).With the magmatic evolution,J1 and J2 samples display the tendency of evolution from high oxygen fugacity to low oxygen fugacity.It is considered that the Jianchhuan area experi-enced the mixing of crust-mantle magma caused by the pulsing upwelling and underplating of mantle-de-rived magma,and formed relatively high oxygen fugacity magma.As the ascending flux of mantlederived magma with low oxygen fugacity increased,the mixing proportion of crust-derived material decreased relatively,and the magmatic oxygen fugacity showed a decreasing trend.

关 键 词：正长斑岩 锆石地球化学 岩浆演化 壳幔混合 滇西剑川 

分 类 号：P579[天文地球—矿物学]