A high-order numerical study of reactive dissolution in an upwelling heterogeneous mantle—I. Channelization, channel lithology and channel geometry
A high-order numerical study of reactive dissolution in an upwelling heterogeneous mantle—I. Channelization, channel lithology and channel geometry
复制标题
上涌非均质地幔反应溶蚀的高阶数值研究——I.
DOI：
10.1111/j.1365-246x.2011.05065.x
复制
发表时间：
2011
影响因子：
2.8
通讯作者：
E. Parmentier
中科院分区：
文献类型：
--
作者：
A. Schiemenz;Yan Liang;E. Parmentier
总结
高孔隙度通道是地幔熔体运移的重要通道。为了更好地了解高孔隙度熔体通道的岩性和几何形状，我们进行高阶精确的数值模拟反应溶解沿着溶解度梯度在一个上涌和粘性变形多孔柱。与以前的研究相比，我们假设溶解反应处于平衡状态，考虑有限的可溶性矿物丰度，并采用高阶精确的数值方案。使用持续的扰动在流入边界的孔隙度和可溶性矿物丰度，我们探讨了稳态高孔隙度熔体通道的结构及其相关的岩性在一系列参数，包括可溶性矿物丰度，溶解度梯度，幅度和横向变化的流入熔体通量，熔体分数和上涌速率。一般来说，高孔隙度纯橄榄岩通道是地幔熔体迁移通道的短暂和浅部。高孔隙度水道的下部是含斜方辉石纯橄榄岩、方辉橄榄岩和可能的二辉橄榄岩。一个宽的无斜方辉石纯橄榄岩通道可能包含两个或三个高孔隙度熔体通道。纯橄榄岩通道形成的深度取决于溶解度梯度、可溶矿物丰度、熔体流量、熔体抽吸速率和上涌速率。在上升柱底部的孔隙度和斜方辉石丰度的横向变化的幅度和长度尺度是重要的，在确定纯橄榄岩通道的大小和尺寸，熔体聚焦的强度和熔体抽吸速率，压实边界层的存在，以及在纯橄榄岩通道内的高孔隙度熔体分支的数量。在我们的数值模拟中记录的高孔隙度熔体通道，纯橄榄岩和harzburstan通道之间的空间关系可能会揭示一些领域，岩石学和地球化学观测有关的熔体在地幔中的迁移。
SUMMARY
High-porosity channels are important pathways for melt migration in the mantle. To better understand the lithology and geometry of high-porosity melt channels, we conduct high-order accurate numerical simulations of reactive dissolution along a solubility gradient in an upwelling and viscously deformable porous column. In contrast to earlier studies, we assume the dissolution reaction to be at equilibrium, consider a finite soluble mineral abundance, and employ a high-order accurate numerical scheme. Using sustained perturbations in porosity and soluble mineral abundance at the inflow boundary, we explore the structure of steady-state high-porosity melt channels and their associated lithologies over a range of parameters, including soluble mineral abundance, solubility gradient, amplitude and lateral variation in inflow melt flux, melt fraction and upwelling rate. In general, high-porosity dunite channels are transient and shallow parts of pathways for melt migration in the mantle. The lower parts of a high-porosity channel are orthopyroxene-bearing dunite, harzburgite and possibly lherzolite. A wide orthopyroxene-free dunite channel may contain two or three high-porosity melt channels. The depth of dunite channel initiation depends on the solubility gradient, soluble mineral abundance, inflow melt flux, melt suction rate and upwelling rate. The amplitude and length scale of lateral variation in porosity and orthopyroxene abundance at the base of the upwelling column are important in determining the size and dimension of dunite channels, the strength of melt focusing and the melt suction rate, the presence of compacting boundary layer, as well as the number of high-porosity melt branches within a dunite channel. The spatial relations among the high-porosity melt channels, dunite and harzburgite channels documented in our numerical simulations may shed new light on a number of field, petrological and geochemical observations related to melt migration in the mantle.