闽中南平—宁化构造带南华纪陆缘弧岩浆活动:对武夷造山带构造演化的新启示  

Neoproterozoic continental margin-arc magmatic activity of the Nanping-Ninghua tectonic belt, South China: Implications for tectonic evolution of the Wuyi orogenic belt

作　　者：姜杨[1] 赵希林[1] 李龙明 潘桂棠[3] 徐敏成 黄文成[1] 刘欢 JIANG Yang;ZHAO Xilin;LI Longming;PAN Guitang;XU Mingcheng;HUANGWencheng;LIU Huan(Nanjing Center,China Geological Survey,Nanjing 210016,Jiangsu,China;Hefei University of Technology,Hefei 230009,Anhui,China;Chengdu Center,China Geological Survey,Chengdu 610081,Sichuan,China)

机构地区：[1]中国地质调查局南京地质调查中心,江苏南京210016 [2]合肥工业大学,安徽合肥230009 [3]中国地质调查局成都地质调查中心,四川成都610081

出　　处：《中国地质》2020年第4期1010-1024,共15页Geology in China

基　　金：国家重点研发计划(2016YFC0600210);中国地质调查局(DD20190045,DD20160037)联合资助。

摘　　要：南平—宁化构造带沿线出露着以万全岩群和楼前组、西溪组等为代表的一系列新元古代火山-沉积岩系。系统的岩石学、年代学和地球化学研究表明,福建明溪和江西瑞金地区的楼前组浅变质英安岩和晶屑凝灰岩分别形成于(729±4)Ma和(735±6.7)Ma(LA-ICP-MS锆石U-Pb法),SiO2含量变化在65.22%~74.54%,相对富Al2O3(11.05%~16.80%)富碱(Na2O+K2O=4.88%~10.19%)而贫CaO、MgO和FeOT,ANK值和A/CNK值分别为1.23~1.78和0.98~1.57,Nb/Ta=12.44~17.28,Nd/Th=2.07~3.51,Ti/Zr=6.08~10.37,Ti/Y=68.51~154.71,属过铝质S型火山岩;明显富集大离子亲石元素(Ba、Rb等)而亏损高场强元素(Nb、Ta、Ti、P等),Zr/Nb=16.65~24.07,Th/Ta=12.94~16.93,δEu呈现明显负异常(0.33~0.62),显示岛弧岩浆岩的地球化学特征。综合区域地质资料及前人研究结果提出,南平—宁化一线在713 Ma前为活动大陆边缘环境,洋壳俯冲引发的岩浆活动形成了沿南平—宁化—瑞金一线展布的陆缘弧中酸性火山岩带,暗示此时南、北武夷之间尚未拼合形成统一的武夷地块,因而华夏地块不存在统一的前南华纪结晶基底。Numerous Neoproterozoic volcanic-sedimentary rocks, e.g., Wanquan Group, Louqian and Xixi Formation, are outcropped along the Nanping-Ninghua tectonic belt, South China. This paper presents a systematic petrological, geochronological,and geochemical study of metamorphic rocks from the Louqian Formation in Mingxi County of Fujian and Ruijin County of Jiangxi Province. Zircons from meta-dacite in Mingxi County and meta-crystal tuff in Ruijin County yielded U-Pb weighted mean ages of(729 ± 4)Ma and(735 ± 6.7) Ma(by LA-ICP-MS), respectively. The SiO2 values of these meta-volcanic rocks range from65.22% to 74.54%, and they have high Al2 O3(11.05%-16.80%) and Na2 O + K2 O content(4.88%-10.19%) but low CaO, MgO, and FeOTcontent. Their ANK values and A/CNK ratios are 1.23-1.78 and 0.98-1.57 with Nb/Ta being 12.44-17.28, Nd/Th being 2.07-3.51, Ti/Zr being 6.08-10.37 and Ti/Y being 68.51-154.71, implying the S-type igneous rocks. All samples are enriched in large-ion lithophile elements(LILE;e.g., Ba and Rb) and depleted in high-field-strength elements(HFSE;e.g., Nb, Ta, Ti, and P)with Zr/Nb being 16.65-24.07 and Th/Ta being 12.94-16.93. Marked negative Eu anomalies 0.33-0.62 are similar to those in arc igneous rocks. Based on regional geological data and previous studies, the authors hold that the Nanping-Ninghua tectonic belt had been in an active continental margin setting until 713 Ma. The magmatism was caused by the subduction of oceanic crust and formed an intermediate-acid volcanic belt along the Nanping-Ninghua-Ruijin continental margin, which indicates that the collision between the North and South Wuyi blocks did not form a unified Wuyi Block before 713 Ma, and the Cathaysia Block had not a unified pre-Nanhua crystalline basement.

关 键 词：陆缘弧岩浆活动 南华纪 南平—宁化构造带 武夷地区 华夏地块 地质调查工程 

分 类 号：P618.51[天文地球—矿床学]