| 现代板块运动驱动地幔块体置换度及地幔混合的研究 |
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| 引用本文： | 傅容珊,韩力波,黄建华,单斌,刘军.现代板块运动驱动地幔块体置换度及地幔混合的研究[J].地球物理学报,2007,50(5):1409-1417. |
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| 作者姓名： | 傅容珊 韩力波 黄建华 单斌 刘军 |
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| 作者单位： | 中国科学技术大学地球和空间科学学院，中国科学院壳幔物质与环境重点实验室，合肥 23;0026 |
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| 基金项目： | 国家自然科学基金(40574043)资助 |
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| 摘 要： | 定义了描述地幔混合程度的新的统计学量度——地幔块体对流置换度和对流混合扩散度.地幔块体对流置换度等于至少被置换一次的块体数与地幔总块体数之比，对流混合扩散度等于示踪元初始体密度与示踪元终体密度之比.本研究假设地幔对流是稳定的，上地幔和下地幔的黏滞性存在差异，其驱动力为板块运动或地幔中密度异常分布.实验中地幔被划分为20736 个块体（5°×5°×300 km），2376个示踪元被放置在地幔顶部100 km深度或底部100 km高度的5°×5°的网格点上.模型计算表明， 地幔块体对流置换度随运转时间变化.就全地幔而言，在系统运行四十亿年后，大多数模型对应的块体对流置换度均超过80%，而上地幔块体置换度则达到90%.这预示大多数的地幔块体将被来自其他位置的块体所取代.对于放置在地幔顶部或底部，浓缩于很小空间10°×10°(间距0.25°) 中的两组1681个示踪元而言，尽管其对流混合扩散度在开始有较大的差异，但是在运行一段时间之后，此两组对应的对流混合扩散度均趋于常数，示踪元比较均匀地分布于全地幔之中.由以上的结果可以推断，在经历了四十五亿年的演化过程后，由于对流的作用使地幔基本上已经均匀混合，地幔中不大可能存在尺度大于5°×5°×300 km的异常块体.
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| 关 键 词： | 地幔混合 示踪元 块体置换度 混合扩散度 |
| 文章编号： | 0001-5733（2007）05-1409-09 |
| 收稿时间： | 2007-1-4 |
| 修稿时间： | 2007-01-04 |
Study of the mantle mixing driving by plate motions |
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| FU Rong-Shan,HAN Li-Bo,HUANG Jian-Hua,SHAN Bin,LIU Jun.Study of the mantle mixing driving by plate motions[J].Chinese Journal of Geophysics,2007,50(5):1409-1417. |
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| Authors: | FU Rong-Shan HAN Li-Bo HUANG Jian-Hua SHAN Bin LIU Jun |
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| Institution: | CAS Key Laboratory of Crust Mantle Materials and Environments School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China |
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| Abstract: | Two new quantitative terms are employed to investigate the problem of the mantle mixing in this paper,Box Replacement Degree of convective mantle ixing and pervasion degree of convective mantle mixing. The first term is to count statistically the percent of the mantle boxes that have been replaced by other mantle boxes. The second term is to evaluate the pervasion degree for a roup of fine mantle elements confined in a small space. In this study we assume that there is a stable convection system in the mantle, which drives by plate motions and density distribution anomaly. In our numerical experiment the mantle is divided into 20736 boxes（5°×5°×300 km）and there are 2376 tracers placed on 5°×5° grids at 100km depth and 100 km above CMB. The results show that the Box Replacement Degree of convective mantle mixing is over 80% for the whole mantle and is over 90% for upper mantle after 4 billion years. It infers that most mantle boxes have been replaced. For two groups of 1681 tracers in a small space 10°×10° placed at the top and bottom of the mantle their pervasion degree approaches a constant and the initial tracers become widely distributed in the mantle after 3 billion years. These results infer that the Earth's mantle, excepting lithosphere and “D" layer, has been mixed very well in the past 4 billion years. There are not much initial heterogeneity boxes with a size more than 5°×5°×300 km present in our mantle now. |
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| Keywords: | Mantle mixing Tracer Box replacement degree Pervasion degree of mixing |
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