中国大陆新生代上地幔铅同位素特征  

Characteristics of Pb Isotopic Composition in Upper Mantle Cenozoic for China Continent

作　　者：路凤香[1] 李方林[1] 韩吟文[1] 侯青叶[2] 

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074 [2]中国地质大学地球科学与资源学院,北京100083

出　　处：《地球科学（中国地质大学学报）》2009年第1期11-16,共6页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.90714008);国土资源部基础研究专项计划(20001010203)

摘　　要：收集了新生代(含少量晚中生代)301件幔源玄武岩的Pb同位素数据,编制了系统的Pb同位素变化趋势(等值线)图件,现仅提供"中国大陆新生代上地幔的206Pb/204Pb比值变化趋势图".图件显示,Pb同位素在南北方向的差异比较显著,南北的界线大体从合肥-郑州-银川-汗腾格里峰,结合Nd同位素的资料,以206Pb/204Pb比值为18～18.5作为分界,以北小于18～18.5;以南大于该值.此外初步辨认出该时期存在3种类型的地幔:造山带地幔、裂谷型地幔及"非典型地幔".与依据不同时代、各种类型的样品铅同位素的比值,统一编制的"中国大陆岩石圈206Pb/204Pb比值变化趋势图"进行比较,显示出在东北的西北部的206Pb/204Pb比值、南北向东经104°附近的高206Pb/204Pb比值区是否存在、渤海周边Pb异常区的强度以及华南DUPAL异常区问题等方面都有区别,表明晚中生代-新生代时期,中国大陆进入了一个新的软流圈地幔对流体系,近代地幔并没有完全继承老地幔的全部特征而是被注入了新的软流圈物质.此外,两张趋势图都显示了南北分块的特征,而东西向的系统变化,仅在近代Pb比值趋势图中华南块体的东南沿海地区出现,暗示太平洋板块俯冲对中国大陆的影响处于次要地位.301 Pb isotopic data of mantle-derived basalts for Cenozoic （contain few Late Mesozoic samples） were collected in this work. The variety trend （contour） maps of mantle Pb isotopic in China continent for Cenozoic were draw up systematically and the “variety trend of ^206 pb/^204Pb ratio of Cenozoic basahs derived from mantle in continent of China” is submitted in this paper only. The result shows that there is a difference between North China and South China on ^206pb/^204Pb ratio. The geographic boundary between two regions is from Hefei-Zhengzhou-Yinchuan-Hantenggeli peak and the ^206Pb/^204Pb ratio boundary is believed to 18-18. 5 approximately. The ^206Pb/^204Pb ratios in North China are 〈（18-18.5） and vice versa. Combining with Nd isotopic data, three mantle types can be identified, they are： mantle of orogenic belt; mantle of continental rifting; and mantle of non-typical region. The map of “variety trend of ^206Pb/^204Pb ratio of lithosphere in continental of China” is also showed in this paper. This is a comprehensive map, and compiled by the Pb isotopic data of samples which collected from different periods and different type of rocks. By comparison to these two maps, some differences and problems can be found such as： The values for ^206Pb/^204Pb ratio in northwestern of Northeast China; the intensity of Pb isotopic-anomaly in “Bohai basin” whether the high-value area of Pb isotopic appears in 104°E and adjacent or not; a problem about DUPAL anomaly in South China. Based on the differences, the compositions of mantle at present-day did not inherit the total characteristics of lithosphere before and injects the new asthenospheric material. It is referred that a new mantle convection system appears in China continent for Late-Mesozoic-Cenozoic. However, the difference of ^206Pb/^204Pb ratio between North and South China still exist in both maps implying that the effect of subduction from Pacific slab for China continent is not very important.

关 键 词：幔源玄武岩 PB同位素 ^206Pb/^204Pb比值变化趋势 

分 类 号：P591[天文地球—地球化学] P597[天文地球—地质学]