滇西双江县清平地区斜长角闪岩年龄与地球化学特征及其对昌宁-孟连洋演化的制约  

The evolution of Changning-Menglian Ocean in the Qingping area of Shuangjiang County,western Yunnan:Constraints from age and geochemistry of plagioclase amphibolite

作　　者：彭智敏[1] 关俊雷[1] 付于真[2] 胡金锋 张璋[1] 王国芝[2] 任飞[1] 张向飞 PENG Zhimin;GUAN Junlei;FU Yuzhen;HU Jinfeng;ZHANG Zhang;WANG Guozhi;REN Fei;ZHANG Xiangfei(Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China;Chengdu University of Technology,Chengdu 610059,Sichuan,China;Institute No.280,CNNC,Guanghan 618300,Sichuan,China)

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]成都理工大学地球科学学院,四川成都610059 [3]核工业二八〇研究所,四川广汉618300

出　　处：《地质通报》2021年第11期1905-1919,共15页Geological Bulletin of China

基　　金：国家自然科学基金项目《特提斯构造域地质构造编图及区域对比研究》(批准号:92055314);中国地质调查局项目《三江造山带昌都—澜沧地区区域地质调查》(编号:DD20190053);《中国大地构造演化和国际亚洲大地构造图编制》(编号:DD20190363)。

摘　　要：近年,昌宁-孟连结合带已获得了大量早古生代残余洋壳年龄及与之对应的弧岩浆记录,但晚古生代大洋演化相关的记录较少,缺乏高精度的年代学数据,制约了对昌宁-孟连洋演化的认识。通过对双江县清平地区2件斜长角闪岩LA-ICP-MS锆石U-Pb定年研究,获得^(206)Pb/^(238)U年龄加权平均值分别为442±3 Ma、410±6 Ma、365±6 Ma,其中410±6 Ma为继承年龄,其余代表岩浆结晶年龄。斜长角闪岩样品地球化学特征显示,SiO_(2)含量为47.28%~48.18%,平均为47.90%,K_(2)O/Na_(2)O值小于1,具有富钠贫钾的特征。轻稀土元素富集,重稀土元素亏损,富集大离子亲石元素Ba,高场强元素Nb、Ta无明显的亏损,Ti、Zr呈弱的负异常,总体特征具富集型洋中脊玄武岩的性质。(^(87)Sr/^(86)Sr)t=0.705288~0.705750,(^(143)Nd/^(144)Nd)t=0.512373~0.512424,ε_(Nd)(t)值为4.01~5.00,平均值4.72。Sr-Nd-Pb同位素组成表明,斜长角闪岩岩浆主要来源于富集型地幔(EMII)并具DUPAL异常的特征。综合分析认为,清平地区在442~365 Ma发育洋盆,表明昌宁-孟连结合带经历了原-古特提斯洋的演化过程。A large number of data about ages of Early Paleozoic relict oceanic crust and corresponding arc magma records of the Changning-Menglian suture zone in recent years have been obtained.However,there are relatively few records related to the Late Paleozoic oceanic evolution and lack of high-precision chronological data,which severely constrains the understanding of the Changning-Menglian oceanic evolution.LA-ICP-MS zircon U-Pb dating of two plagioclase amphibolite samples in the Qingping region of Shuangjiang County yields the weighted average ages of 442±3 Ma,410±6 Ma and 365±6 Ma respectively,of which 410±6 Ma is the inheritance age,and the rest represents the magmatic crystallization age.Geochemical characteristics show that the content of SiO_(2)is 47.28%~48.18%(sample D6164,t=365 Ma),averaging 47.90%,and the ratio of K_(2)O/Na_(2)O is less than 1,rich in sodium and poor in potassium.It is characterized by LREE enrichment,HREE depletion,enrichment of large ion lithophile element Ba,no obvious loss of high field strength elements of Nb and Ta,weak negative anomalies of Ti and Zr,indicating the overall characteristics of E-MORB.Sr-Nd-Pb isotopic compositions,(^(87)Sr/^(86)Sr)t=0.705288~0.705750,(^(143)Nd/^(144)Nd)t=0.512373~0.512424,ε_(Nd)(t)=4.01~5.00,averaging 4.72,indicate that the magma source of amphibolite was mainly derived from the enriched mantle(EMII)with DUPAL anomaly.The comprehensive analysis shows that the ocean basin was developed in the period of 442~365 Ma in the Qingping area,and the Changning Menglian suture zone once experienced the evolution of Proto-Paleo Tethys Ocean.

关 键 词：斜长角闪岩 原-古特提斯 锆石U-PB年龄 SR-ND-PB同位素 昌宁-孟连结合带 

分 类 号：P588.12[天文地球—岩石学] P597[天文地球—地质学]