中国大陆新生代上地幔铅同位素特征

路凤香; 李方林; 韩吟文; 侯青叶

中国大陆新生代上地幔铅同位素特征

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

基金项目:

国家自然科学基金项目 90714008

国土资源部基础研究专项计划 20001010203

详细信息

作者简介:
路凤香（1935-）, 女, 教授, 博士生导师, 从事岩石学研究.E-mail：lufx@263.net

中图分类号: P591; P597
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出版历程
- 收稿日期: 2008-10-18
- 刊出日期: 2009-01-25

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

1.
Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China
2.
School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China

摘要

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.
- 幔源玄武岩 /
- Pb同位素 /
- ²⁰⁶Pb/²⁰⁴Pb比值变化趋势
Abstract: 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 ²⁰⁶Pb/²⁰⁴Pb ratio of Cenozoic basalts 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.
- matle-derived basalt /
- Pb isotop /
- variety trend of ²⁰⁶Pb/²⁰⁴Pb

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图 1 中国大陆新生代玄武岩²⁰⁶Pb/²⁰⁴Pb比值变化趋势图

Fig. 1. Variety trend of²⁰⁶Pb/²⁰⁴Pb ratio of late Mesozoic-Cenozoic basalts derived from mantle in China Continent

下载: 全尺寸图片幻灯片

图 2 中国大陆晚中生代一新生代玄武岩ε_Nd-²⁰⁶ Pb/²⁰⁴Pb图解

1.五大连池; 2.东北; 3.华北; 4.苏鄂皖赣; 5.闽浙; 6.青藏周边; 7.西藏

Fig. 2. The diagram for ε_Nd-²⁰⁶ Pb/²⁰⁴Pb of Late Mesozoic Cenozoic basalts derived from mantle in continent of China

下载: 全尺寸图片幻灯片

图 3 中国大陆晚中生代一新生代玄武岩PbΔ8/4-²⁰⁶Pb/²⁰⁴Pb图解

Δ8/4= (²⁰⁸Pb/²⁰⁴Pb-²⁰⁸Pb/²⁰⁴ PbNHRL)X100;1.五大连池;2.东北;3.华北;4.苏鄂皖赣;5.闽浙;6.青藏周边;7.西藏

Fig. 3. The diagram for PbΔ8/4-²⁰⁶Pb/²⁰⁴Pb of Late Mesozoic Cenozoic basalts derived from mantle in Continent of China

下载: 全尺寸图片幻灯片

图 4 中国大陆岩石圈²⁰⁶Pb/²⁰⁴Pb比值变化趋势图

Fig. 4. Variety trend of²⁰⁶Pb/²⁰⁴Pb ratio of lithosphere in China Continent

下载: 全尺寸图片幻灯片

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