赣南南迳盆地I型流纹岩年代学、地球化学特征及其地质意义  

Geochronology,geochemistry,and geological significance of I-type rhyolite in Nanjing basin,South Jiangxi Province

作　　者：刘帅[1] 马树松 黄美化[1] 巫建华[1] 郭恒飞 LIU Shuai;MA Shu-song;HUANG Mei-hua;WU Jian-hua;GUO Heng-fei(State Key Laboratory Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China;No.243 Geological Party of CNNC,Chifeng 024000,Inner Mongolia,China)

机构地区：[1]东华理工大学核资源与环境国家重点实验室,江西南昌330013 [2]核工业二四三大队,内蒙古赤峰024000

出　　处：《地球化学》2020年第4期404-421,共18页Geochimica

基　　金：国家自然科学基金(41662006,41862013)。

摘　　要：赣南南迳盆地位于武夷-云开造山带中部,南岭构造带东段;为了查明盆地内流纹岩岩浆源区及形成的构造背景,本文对该流纹岩进行了岩石学、年代学和地球化学研究。结果显示,盆地内流纹岩锆石U-Pb年龄为(436.2±2.4)Ma(n=18,MSWD=0.89),为晚奥陶世末-早志留世初期岩浆活动产物。该流纹岩具有富硅、高钾、富铝的特征;富集大离子亲石元素(如Rb、K)和轻稀土元素,Ta、Nb和Ti等高场强元素和重稀土元素相对亏损,具有岛弧岩浆的特征;稀土元素总量较低,轻重稀土元素分馏明显,(La/Yb)N为8.65~12.2,Eu/Eu^*=0.60~0.65,具有中等Eu负异常,暗示其主要来自地壳熔融,并在岩浆演化过程中经历了斜长石分离结晶作用;Sr-Nd-Pb-O同位素数据指示其来源于古元古代结晶基底;岩石学和地球化学特征显示南迳盆地流纹岩具有I型花岗岩的特征,形成于活动大陆边缘弧环境。综合研究表明,南迳盆地流纹岩可能形成于早古生代扬子板块和华夏板块洋陆俯冲向陆陆碰撞造山的过渡阶段,是早古生代洋壳俯冲-碰撞的地质记录。Nanjing basin is located in the middle of the Wuyi-Yunkai orogenic belt and the eastern part of the Nanling tectonic belt.This paper examines the geochronology,petrology and geochemistry of rhyolite in this basin,to determine its source area and tectonic background.Zircon SHRIMP U-Pb dating suggests that the rhyolite of Nanjing basin was emplaced at(436.2±2.4)Ma(n=18,MSWD=0.89),indicating a Late Ordovician-Early Silurian magmatic event.Whole-rock major and trace element analysis indicates high levels of silicon,potassium and aluminum.The rhyolite is characterized by relative enrichment in LILE(e.g.,Rb,K)and LREE,and pronounced depletion in HFSE(e.g.,Ta,Nb and Ti)and HREE.Such geochemical features are typical of subduction-related magmatic rocks.The total amount of REE is relatively low,showing distinct enrichment in LREE and(La/Yb)N values of 8.65~12.23.Furthermore,and there is an obvious negative Eu anomaly(Eu/Eu^*=0.60~0.65),suggesting that the rhyolite parent magma was derived from partial melting of the lower crust,and underwent fractional crystallization of plagioclase.In addition,petrological and geochemical characteristics suggest that the rhyolite belongs to an I-type granite.Sr-Nd-Pb-O isotopic data indicate that the rhyolite might have originated from Paleoproterozoic crustal materials.In combination with the regional tectonic evolution,we suggest that the rhyolite formed in a tectonically-active continental margin.We therefore conclude that the rhyolite of Nanjing basin was an important record of oceanic subduction and subsequent continental collision in the south China during Early Paleozoic time.

关 键 词：流纹岩 SHRIMP锆石U-PB定年 岛弧岩浆岩 早古生代 南迳盆地 

分 类 号：P595[天文地球—地球化学] P597.3[天文地球—地质学]