Physical constraints on the migration of immiscible fluids through partially molten silicates, with special reference to magmatic sulfide ores
Physical constraints on the migration of immiscible fluids through partially molten silicates, with special reference to magmatic sulfide ores
复制标题
DOI：
10.1016/j.epsl.2009.05.041
复制
发表时间：
2009-08-30
影响因子：
5.3
通讯作者：
Mungall, James E.
中科院分区：
文献类型：
--
作者：
Chung, Hye-Yoon;Mungall, James E.
致密的富铁不混溶液体通过部分熔融的硅酸盐的迁移对于岩浆硫化物矿床的形成和类地行星中金属核的形成等问题是至关重要的。不混溶的致密液体的迁移可以认为是在三个不同的区域中发生的，这三个区域由致密液滴和构成硅酸盐晶体碎屑或部分熔融的硅酸盐岩石的晶体的相对大小决定。如果致密的微滴比硅酸盐晶体之间最窄的孔喉部分的直径小，那么向下运动是可能的。在松散堆积的晶体中，当液滴尺寸约为晶体尺寸的十分之一时，向下沉降的速率最大。只要晶体之间的硅酸盐熔体保持不变，微滴就能够通过包含在具有典型粒度的冷却堤坝中的晶体蘑菇垂直迁移数百到数千米的距离。与晶体大小相似的较大液滴的搁浅是由于毛细管力阻止液滴变形，因为它们试图进入比自身更窄的孔喉。只有在颗粒尺寸大于约2厘米的非常粗粒的浆料中，晶间气孔大小的液滴才能向下迁移。另一方面，许多微滴聚合成预先存在的绞合状液滴，可能会产生比糊状物的颗粒尺寸大许多倍的稠密液体的连通网状织构结构域。当连通区域的垂直高度足够大时，致密相内部的压力梯度超过了阻碍通过狭窄孔喉向下运动的毛细管力，不混溶相能够沿垂直方向的网络向下移动。这些网络在到达坚固的层或入侵的基础之前不应受困。我们认为，在大多数情况下，在大型岩浆体中，由分馏形成的硫化物液滴应停留在晶堆的顶部，而细粒硫化物沉积物同化进入岩浆中的硫化物应能够向下穿过结晶泥，在部分熔融带底部形成块状或网状堆积。(C)2009爱思唯尔B.V.保留所有权利。
The migration of dense Fe-rich immiscible liquids through partially molten silicates is of critical importance to several issues including the formation of magmatic sulfide ore deposits and the formation of metallic cores in terrestrial planets. The migration of immiscible dense liquids can be considered to occur in three distinct regimes dictated by the relative sizes of the dense liquid droplets and the crystals making up the silicate crystal mush or partially melted silicate rock. If dense microdroplets are smaller than the diameter of the narrowest portions of pore throats between silicate crystals then downward motion is possible. The maximum rate of downward settling in loosely packed crystal mushes occurs when the droplet size is approximately one tenth the crystal size. As long as the silicate melt between crystals remains, microdroplets are capable of migrating distances of hundreds to thousands of meters vertically through crystal mushes contained in cooling dikes with typical grain sizes. Stranding of larger droplets similar in size to the crystals results from capillary forces preventing droplet deformation as they attempt to pass into pore throats narrower than themselves. Only in very coarse-grained mushes with grain sizes greater than about 2 cm can droplets the size of intergranular pores migrate downwards. On the other hand, coalescence of many microdroplets into pre-existing stranded droplets may generate connected net-textured domains of the dense liquid that are many times larger than the grain size of the mush. When the vertical height of the connected domain is great enough, the pressure gradient inside the dense phase exceeds the capillary force impeding downward motion through narrow pore throats and the immiscible phase is able to move down along vertically-oriented networks. These networks should not suffer stranding until they reach a solid layer or the base of the intrusion. We suggest that, in most cases, sulfide droplets formed by fractional segregation in large magma bodies should come to rest at the top of the crystal pile, whereas sulfides introduced to magmas by assimilation of fine-grained sulfidic sediments should be capable of passing downward through crystal mushes to form massive or net-textured accumulations at the bottom of the partially molten zone. (C) 2009 Elsevier B.V. All rights reserved.