A numerical model of hydrothermal cooling and crustal accretion at a fast spreading mid‐ocean ridge
A numerical model of hydrothermal cooling and crustal accretion at a fast spreading mid‐ocean ridge
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DOI：
10.1029/2001gc000215
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发表时间：
2003-09
期刊：
影响因子：
3.7
通讯作者：
A. Cherkaoui;W. Wilcock;R. Dunn;D. Toomey
中科院分区：
文献类型：
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作者：
A. Cherkaoui;W. Wilcock;R. Dunn;D. Toomey
对于快速扩张脊的下地壳吸积，有两种相互竞争的模式。在辉长岩冰川模型中，所有的下地壳在岩脉/辉长岩边界的岩浆透镜中凝固，然后流向最终的水平。在片状基岩模型中，下地壳是由位于不同深度的基岩形成的。我们提出了一个明确包括热液循环的静止模型的稳态数值表示。地壳在所有深度的脊轴上均匀地增生，热液循环发生在冷却到阈值温度以下的地壳岩石中。结果表明，当渗透率超过一个阈值（在800℃开裂温度下渗透率均匀时为~ 4 × 10−14 m2）时，热液循环可以使整个地壳在脊轴附近降温，在地壳下部产生垂直等温线。在较低渗透率下，海水的特性导致了双峰冷却，最底部的地壳冷却速度比较浅的要慢。这些结果与东太平洋隆起的地震构造和阿曼辉长岩中斜长石晶粒尺寸分布的研究结果基本一致。我们推断，由于热原因，薄板基板模型不能被抛弃。
There are two competing models for lower crustal accretion at fast spreading ridges. In the gabbro glacier model, all the lower crust solidifies in a magma lens at the dike/gabbro boundary and then flows to its final level. In the sheeted sill model, the lower crust is formed by sills emplaced at a variety of depths. We present a steady state numerical representation of the sill model that explicitly includes hydrothermal circulation. The crust is accreted uniformly at the ridge axis at all depths and hydrothermal circulation occurs in crustal rocks that have cooled below a threshold temperature. The results show that when the permeability exceeds a threshold value (∼4 × 10−14 m2 for a cracking temperature of 800°C and a uniform permeability), hydrothermal circulation can cool the entire crust near the ridge axis, producing vertical isotherms in the lower crust. At lower permeabilities, the properties of seawater lead to bimodal cooling with the lowermost crust cooling more slowly than shallower depths. These results are reasonably consistent with studies of the seismic structure of the East Pacific Rise and of plagioclase crystal size distributions in gabbros from Oman. We infer that the sheeted sill model cannot be discarded on thermal grounds.