Fast kimberlite ascent rates estimated from hydrogen diffusion profiles in xenolithic mantle olivines from southern Africa
Fast kimberlite ascent rates estimated from hydrogen diffusion profiles in xenolithic mantle olivines from southern Africa
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DOI：
10.1016/j.gca.2008.03.019
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发表时间：
2008-06
影响因子：
5
通讯作者：
A. Peslier;A. Woodland;J. Wolff
中科院分区：
文献类型：
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作者：
A. Peslier;A. Woodland;J. Wolff
傅里叶变换红外光谱（FTIR）分析橄榄岩捕虏体中的橄榄石在非洲南部金伯利岩中发现0至80 ppm的H2O浓度。OH的吸收曲线在橄榄石颗粒显示均匀的H含量从核心到边缘的大多数样品。在一个样本中的橄榄石是H-免费的，而另一个橄榄石的特点是较低的H含量在晶粒边缘的核心相比，表明H损失过程中的捕虏体的表面。平坦或近平坦的H配置文件放置从橄榄石颗粒的H损失的持续时间的严重限制，与金伯利岩岩浆上升率的影响。扩散方程被用来估计约4 h的橄榄石H含量不均匀的样品的H损失的时间。由此产生的金伯利岩上升速率被计算为5- 37 ms − 1最小值，尽管这些估计高度依赖于寄主金伯利岩岩浆的挥发物含量和脱气行为。碱性玄武岩中的捕虏体橄榄石一般具有较低的H含量和更明显的H扩散配置文件比金伯利岩。这种差异可能是由于碱性玄武岩的岩浆温度高于金伯利岩，上升速率低于金伯利岩。
Fourier transform infrared spectrometry (FTIR) analyses of olivines from peridotite xenoliths found in southern African kimberlites indicate 0 to 80ppm H2O concentrations. OH absorbance profiles across olivine grains show homogeneous H contents from core to edge for most samples. In one sample the olivines are H-free, while another has olivines characterized by lower H contents at the grain edges compared to the cores, indicating H loss during transport of the xenolith to the surface. Flat or near-flat H profiles place severe constraints on the duration of H loss from olivine grains, with implications for kimberlite magma ascent rates. Diffusion equations were used to estimate times of H loss of about 4h for the sample with heterogeneous olivine H contents. Resulting kimberlite ascent rates are calculated to be 5–37ms−1minimum, although these estimates are highly dependent on volatile contents and degassing behavior of the host kimberlite magma. Xenolithic olivines from alkali basalts generally have lower H contents and more pronounced H diffusion profiles than do those from kimberlites. This difference is likely caused by higher magma temperatures and lower ascent rates of alkali basalts compared to kimberlites.