根据自扩散系数的基础,水对上层地幔质有很小的影响
Hongzhan Fei1, Michael Wiedenbeck, Daisuke Yamazaki
1Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth D95440, Germany. hongzhan.fei@uni-bayreuth.de
Nature
|June 15, 2013
概括
水对上层地幔的风湿有很小的影响,这与以前的看法相反. 新的研究表明,石中的扩散只受到水含量的轻微影响,这挑战了现有的构造板运动和地幔粘度模型.
科学领域:
- 地质物理学 地质物理学
- 矿物物理 矿物物理
- 地质化学 地质化学
背景情况:
- 水对地球内部动态的影响是显著的,之前的研究表明,即使在低水度下,橄石的爬行速率也有很大的提高.
- 然而,实验性变形研究在水度和应力水平方面存在局限性,可能会扭曲结果.
- 岩石变形与的自我扩散有关,这控制了与地球内部相关的高温下矿物质的爬行速率.
研究的目的:
- 通过实验确定在石中的自扩散系数 (DSi).
- 为了研究含水量 (CH2O) 和在高压和高温下自我扩散之间的关系.
- 重新评估水对上层地幔风学和相关地质现象的影响.
主要方法:
- 在石中实验确定自扩散系数 (DSi).
- 测量在8GPa下进行,温度在1600K至1800K之间.
- 分析DSi作为水含量 (CH2O) 的函数,从小于1到大约800ppm的重量.
主要成果:
- 的自扩散系数在石中显示出与含水量之间的关系:DSi ≈ (CH2O) ≈1/3).
- 这个指数 (1/3) 显著低于从先前的实验变形研究 (如1.2) 中得出的指数.
- 这些发现表明,在之前的湿变形实验中观察到的高爬行速率可能受到过多的谷物边界水的影响.
结论:
- 水对上层地幔风湿学的影响很可能很小.
- 天气层中的矿物质水合不太可能是平滑的板块运动的原因.
- 水含量差异不是热点不移的主要机制,也不能解释上层地幔的粘度最小区域.
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