太平洋富稀土深海沉积物及黏土组分(<2μm)的Nd同位素特征及物源意义  

Nd Isotopes of the Pelagic Sediments and Clay Fractions(<2μm) from the Pacific Ocean and their Provenance Significance

作　　者：王汾连 何高文[1] 赖佩欣[1] WANG Fenlian;HE Gaowen;LAI Peixin(MNR Key Laboratory of Marine Mineral Resources,Guangzhou Marine Geological Survey,Guangzhou 510075,Guangdong,China;Key Laboratory of Mineralogy and Metallogeny,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China)

机构地区：[1]自然资源部海底矿产资源重点实验室广州海洋地质调查局,广东广州510075 [2]中国科学院矿物学与成矿学重点实验室,广东广州510640

出　　处：《大地构造与成矿学》2019年第2期292-302,共11页Geotectonica et Metallogenia

基　　金：国家青年自然科学基金项目(41702096);大洋"十三五"课题(DY135-R2-1-05;DY135-R2-1-04);国家自然科学基金项目(41803026);国土资源部海底矿产资源重点实验室开放基金项目(KLMMR-2015-A-06);中国地质调查局项目(DD20191009;DD20190629);中国科学院矿物学与成矿学重点实验室研究合作基金项目(KLMM20150201)联合资助

摘　　要：太平洋深海沉积物富含稀土元素(∑REY,REE+Y),稀土含量达到或超过中国南方离子吸附型稀土矿品位。富稀土沉积物类型主要为远洋黏土和(含)沸石黏土。为了解富稀土元素深海沉积物的物质来源及其对稀土富集机制的影响,本文对中、西太平洋远洋黏土和(含)沸石黏土分别进行了全岩和黏土组分(<2μm)的元素地球化学、Nd同位素及黏土矿物研究。结果表明,沸石黏土的∑REY最高,远洋黏土次之;全岩及黏土组分的∑REY与P_2O_5显示较好的正相关关系,且P_2O_(5全岩)/P_2O_(5黏土)和∑REY_(全岩)/∑REY_(黏土)正相关,说明不同类型沉积物黏土组分及全岩的稀土元素均主要由磷酸盐贡献;沉积物全岩ε_(Nd)值为-5.20～-6.02,表明其中的Nd来自火山源、陆源和自生源物质的混合源区;西太平洋含高REY的沸石黏土较中太平洋同类型沉积物具有较低的ε_(Nd)值,表明火山物质并不是沉积物中稀土元素富集的重要物源,但沸石含量对沉积物中稀土元素含量的高低具有一定指示意义;沉积物ε_(Nd)值接近海水ε_(Nd)值,表明稀土元素更多的直接来自于海水,但是成岩过程中可能受到其他物源或过程的影响。通过对比全岩及黏土组分的稀土元素特征,认为黏土矿物一定程度上可能承担了沉积物中稀土元素过渡载体相的作用。Deep-sea sediments in the Pacific Ocean are rich in rare earth elements(REY,REE+Y),where the rare earth-rich sediment types are mainly pelagic clay and zeolite clay,and their REY contents are similar or exceed that of the ion-adsorbed rare earth ores in South China.To investigate material sources of deep-sea sediments in the Pacific Ocean and mechanism of rare earth enrichment,the elemental geochemistry,Nd isotopes and clay minerals of the bulk samples and clay fractions(<2μm)from the western and central Pacific pelagic clays and zeolite clays were studied.The results show that REY concentration of the zeolite clay is higher than that of the pelagic clay,and REY and P2O5 contents are positively correlated in both the bulk rock and clay fractions.The ratios of P2O5 bulk-rock/P2O5 clay and∑REYbulk-rock/∑REYclay are also positively correlated,indicative of significant phosphates contribution to REY enrichment.TheεNd values in bulk sediments range from-5.20 to-6.02,indicating multiple Nd resources(terrigenous matter,volcanic materials,and autogenous materials),and predominantly terrestrial materials.TheεNd values of the REY-rich zeolite clays from the western Pacific Ocean are relatively lower than those from the central Pacific Ocean.It can be inferred that the volcanic materials contribute less to the enrichment of rare earths,however,but the zeolites content could be a significant to the amount of the rare earth elements in the sediment.The similarεNd values of the sediments and the seawater suggest that the rare earth elements in the sediment mainly come from the seawater.However,sediment source and sedimentation dynamics may also influence the REY enrichment.We propose that the clay minerals could be the front host of REY in the sediments.

关 键 词：ND同位素 稀土元素 物质来源 沸石黏土 远洋黏土 中、西太平洋 

分 类 号：P67[天文地球—海洋地质] P597[天文地球—地质学]