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首页> 外文期刊>Contributions to Mineralogy and Petrology >Hydrothermal alteration of kimberlite by convective flows of external water
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Hydrothermal alteration of kimberlite by convective flows of external water

机译：外水对流对金伯利岩的热液蚀变

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Kimberlite volcanism involves the emplacement of olivine-rich volcaniclastic deposits into volcanic vents or pipes. Kimberlite deposits are typically pervasively serpentinised as a result of the reaction of olivine and water within a temperature range of 130-400 CC or less. We present a model for the influx of ground water into hot kimberlite deposits coupled with progressive cooling and serpenti-sation. Large-pressure gradients cause influx and heating of water within the pipe with horizontal convergent flow in the host rock and along pipe margins, and upward flow within the pipe centre. Complete serpentisation is predicted for wide ranges of permeability of the host rocks and kimberlite deposits. For typical pipe dimensions, cooling times are centuries to a few millennia. Excess volume of serpentine results in filling of pore spaces, eventually inhibiting fluid flow. Fresh olivine is preserved in lithofacies with initial low porosity, and at the base of the pipe where deeper-level host rocks have low permeability, and the pipe is narrower leading to faster cooling. These predictions are consistent with fresh olivine and serpentine distribution in the Diavik A418 kimberlite pipe, (NWT, Canada) and with features of kimberlites of the Yakutian province in Russia affected by influx of ground water brines. Fast reactions and increases in the volume of solid products compared to the reactants result in self-sealing and low water-rock ratios (estimated at <0.2). Such low water-rock ratios result in only small changes in stable isotope compositions; for example, δO~(18) is predicted only to change slightly from mantle values. The model supports alteration of kimberlites predominantly by interactions with external non-magmatic fluids.
机译：金伯利岩火山活动涉及将富含橄榄石的火山碎屑沉积物安置到火山喷口或管道中。由于橄榄石和水在130-400 CC或更低的温度范围内反应，金伯利岩沉积物通常普遍蛇纹石化。我们提出了一种模型，用于地下水流入热的金伯利岩矿床，并逐步进行冷却和蛇化作用。大压力梯度会导致水流入并加热管道内的水，同时在母岩中和沿管道边缘的水平会聚流以及管道中心内的向上流动。预计将完全蛇化，从而使宿主岩和金伯利岩沉积物具有广泛的渗透性。对于典型的管道尺寸，冷却时间长达几个世纪。蛇纹石的体积过多会导致孔空间填充，最终抑制流体流动。新鲜的橄榄石保存在最初孔隙度较低的岩相中，并在管道的底部，较深层的基质岩石的渗透性较低，并且管道较窄，导致冷却更快。这些预测与Diavik A418金伯利岩管（加拿大西北地区）中新鲜的橄榄石和蛇纹石分布以及受地下水盐水涌入影响的俄罗斯雅库提省金伯利岩特征一致。与反应物相比，快速的反应和固体产物体积的增加导致自密封性和低的水岩石比（估计<0.2）。如此低的水岩石比只会导致稳定同位素组成的微小变化;例如，据预测δO〜（18）与地幔值仅略有变化。该模型主要通过与外部非岩浆流体的相互作用来支持金伯利岩的蚀变。

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