余江盆地铁镁质火山岩地球化学特征及其地质意义  

Geochemical characteristics of femic volcanic rocks in the Yujiang Basin and their geological significance

作　　者：郭佳磊 巫建华[1,2] 胡杰[3] 郭国林 刘帅[1,2] GUO Jia-lei;WU Jian-hua;HU Jie;GUO Guo-lin;LIU Shuai(State Key Laboratory of Breeding Base of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China;Collage of Earth Science,East China University of Technology,Nanchang 330013,China;West Jiangxi Geology Party,Jiangxi Bureau of Geology and Mineral Prospecting and Exploitation,Nanchang 330002,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培育基地,江西南昌330013 [2]东华理工大学地球科学学院,江西南昌330013 [3]江西省地质矿产勘查开发局赣西地质调查大队,江西南昌330002

出　　处：《地球化学》2018年第4期380-395,共16页Geochimica

基　　金：中国核工业集团公司项目"中国中-新生代内生铀矿成矿作用"(中核地计[2008]74号)

摘　　要：余江盆地位于赣杭铀成矿带中段的西端,盆地内出露的铁镁质火山岩主要为玄武岩和玄武质安山岩,全岩SiO_2含量为47.6%~52.1%(平均49.1%),全碱(Na_2O+K_2O)含量较低,变化范围为3.16%~4.11%(平均3.64%),K_2O/Na_2O比值高,变化于0.70~0.94之间(平均0.78),在TAS图解上落入亚碱性系列范围;TFeO含量为9.26%~11.2%(平均10.5%),且Fe_2O_3/FeO比值为0.30~0.59(平均0.43),MgO含量为6.39%~8.03%(平均7.34%),在AFM图解主要落入钙碱性系列范围。CaO含量为7.45%~8.89%(平均8.28%),Al2O3含量为14.3%~15.3%(平均15.0%)。稀土总量较低,变化范围为149~160μg/g(平均154μg/g),轻稀土富集明显,(La/Yb)N值变化范围为6.77~9.12(平均7.65),Eu和Ce异常不明显(δEu=0.86~1.09;δCe=0.89~1.00),富集大离子亲石元素Ba、K、Rb、Sr等,亏损高场强元素Nb、Ta、Zr、Ti、Y等。(87Sr/86Sr)_i值介于0.704634~0.705000之间(平均0.704741),(143Nd/144Nd)_i值介于0.512650~0.512674之间(平均0.512659),εNd(t)值变化范围是2.60~3.07,显示出亏损地幔源的特征;全岩δ18O值较高(6.99‰~9.90‰,平均8.21‰),可能与部分地壳物质的混入有关;(^(206)Pb/^(204)Pb)_i值介于17.659~17.875之间(平均17.768),(^(207)Pb/^(204)Pb)_i值介于15.255~15.292之间(平均15.272),(^(208)Pb/^(204)Pb)_i值介于37.854~37.994之间(平均37.933)。在(^(87)Sr/^(86)Sr)_i-(^(206)Pb/^(204)Pb)_i、(^(143)Nd/^(144)Nd)_i-(^(206)Pb/^(204)Pb)_i和(^(143)Nd/^(144)Nd)_i-(^(87)Sr/^(86)Sr)_i图解中位于亏损地幔端元和EMⅡ富集地幔端元之间,且更偏向于亏损地幔端元,表明源区可能有亏损地幔和EMⅡ富集地幔的贡献,且亏损地幔端元所占比例更高,暗示铀成矿作用与亏损地幔的关系比较密切,并且多类型的铁镁质岩浆活动可能有利于铀成矿作用。结合构造环境判别图分析,余江盆地铁镁质火山岩形成于板内伸展环境,由于岩石圈伸展减薄导致软流圈上涌所产生的结果,同时铀成矿作用可能与伸展构造环境有关。The Yujiang Basin is located in the western middle section of the Ganhang tectonic belt.The exposed femic volcanic rocks are primarily basalt and basaltic andesite;whole rocks span a SiO2 range of 47.6%–52.1%(average 49.1%),with low alkali(Na2O+K2O)contents,ranging from 3.16%to 4.11%(average 3.64%)and high K2O/Na2O ratios,between 0.70 and 0.94(average 0.78),which plot within sub-alkaline series field in the TAS diagram.The TFeO contents range from 9.26%to 11.2%(average 10.5%),Fe2O3/FeO ratios are 0.30–0.59(average 0.43),and MgO contents are 6.39%–8.03%(average 7.34%),which place them in the calc-alkaline series in the AFM diagram.The CaO contents are 7.45%–8.89%(average 8.28%)and Al2O3 contents are 14.3%–15.3%(average 15.0%).The total rare earth element contents are lower,ranging between 149μg/g and 160μg/g(average 154μg/g),with significant enrichment in light rare earth,(La/Yb)N is 6.77–9.12(average 7.65)and weak Eu(δEu=0.86–1.09)or Ce(δCe=0.89–1.00)anomalies.Samples are enriched in lithophile elements(Ba,K,Rb,Sr),but are depleted in high field strength elements(Nb,Ta,Zr,Ti,Y).(87Sr/86Sr)i ratios are between 0.704634 and 0.705000(average 0.704741)and(143Nd/144Nd)i ratios are between 0.512650 and 0.512674(average 0.512659).The whole rocks span anεNd(t)range of 2.60–3.07,showing characteristics of depleted mantle material(DMM).However,theδ18O range from 6.99‰to 9.90‰(average 8.21‰),which may indicate mixing with crustal material.(206Pb/204Pb)i ratios are between 17.659 and 17.875(average 17.768),(207Pb/204Pb)i ratios are 15.255–15.292(average 15.272),and(208Pb/204Pb)i ratios are 37.854–37.994(average 37.933).In the(87Sr/86Sr)i-(206Pb/204Pb)i,(143Nd/144Nd)i-(206Pb/204Pb)i and(143Nd/144Nd)i-(87Sr/86Sr)i diagrams,the values fall between the DMM and EMⅡpositions,which suggests that both mantle sources produced the femic volcanic rocks in the Yujiang Basin,with a higher proportion of DMM.Furthermore,the results suggest a close relationship between uranium mineralization and DMM,and

关 键 词：铁镁质火山岩 Sr-Nd-Pb-O同位素 亏损地幔 多类型 伸展构造 铀成矿作用 余江盆地 

分 类 号：P597[天文地球—地球化学] P581[天文地球—地质学]