Gas-fluidisation in an experimental tapered bed: Insights into processes in diverging volcanic conduits
Gas-fluidisation in an experimental tapered bed: Insights into processes in diverging volcanic conduits
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DOI：
10.1016/j.jvolgeores.2007.12.034
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发表时间：
2008-06-20
影响因子：
2.9
通讯作者：
Field, Matthew
中科院分区：
文献类型：
--
作者：
Gernon, Thomas M.;Gilbertson, Mark A.;Field, Matthew
气体流化通常被认为是发散金伯利岩管道中喷口充填矿床形成过程中的一个重要过程。在本研究中，我们进行了一系列实验室实验，以确定颗粒在密闭直边容器和锥形容器中的气体流化行为，作为在气流存在下填充金伯利岩管道的火山碎屑材料的模拟。我们研究了锥角、床层高度和气体流速对流化行为的影响，重点研究了中粗粒颗粒（106-212 μ m）。我们表明，直边容器中的床变得均匀流化，而锥形容器中的床变得不均匀，流化仅限于中心大致双曲面形状的区域。在混合良好的流化岩心两侧，边缘楔形区域保持未流化状态，且未流化区域的宽度随气体通量的增加而减小。未流化的楔块在内部分层，当床层的临界比例流化（类似于90%）时，楔块会向下滑动。这就产生了一种“传送带”式的粒子输运机制。这些实验观察表明，气体速度的波动如何在层状和混合良好的区域之间产生陡峭的内部边界。观测结果还显示了边缘向内倾斜的层状序列如何滑入金伯利岩管道的深处。我们的研究结果为解释金伯利岩管的火山碎屑岩相提供了一个框架。(c) 2008 Elsevier B.V.版权所有
Gas-fluidisation is commonly invoked as an important process during the formation of vent-fill deposits in diverging kimberlite pipes. In this study, we performed a series of laboratory experiments to determine the gas-fluidisation behaviour of particles in both confined straight-sided and tapered containers, as an analogue to volcaniclastic materials infilling a kimberlite pipe, in the presence of a gas flow. We investigated the effects of taper angle, bed height and gas flow rate on fluidisation behaviour, focusing on medium-coarse grained particles (106-212 mu m). We show that beds in straight-sided containers become homogeneously fluidised, whereas beds in tapered containers become heterogeneous, with fluidisation limited to a central roughly hyperboloid-shaped region. Either side of the well-mixed fluidised core, marginal wedge-shaped regions remain unfluidised, and the width of unfluidised regions decreases with increasing gas flux. The unfluidised wedges are internally laminated and slip downwards when a critical proportion of the bed is fluidised (similar to 90%). This generates a "conveyor-belt"-type mechanism of particle transport. These experimental observations demonstrate how fluctuations in gas velocity can produce steep internal boundaries between laminated and well-mixed regions. The observations also show how marginal inward dipping layered sequences could slip into deep parts of kimberlite pipes. Our results provide a framework for interpreting the volcaniclastic lithofacies of kimberlite pipes. (c) 2008 Elsevier B.V. All rights reserved.