The genesis of oceanic crust: Magma injection, hydrothermal circulation, and crustal flow
The genesis of oceanic crust: Magma injection, hydrothermal circulation, and crustal flow
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DOI：
10.1029/92jb02650
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发表时间：
1993-04
影响因子：
--
通讯作者：
J. Morgan;Y. Chen
中科院分区：
文献类型：
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作者：
J. Morgan;Y. Chen
在这项研究中，我们建立了一个海洋地壳成因的热力学模型。当岩浆到达冻结层时，其在洋壳内的上升停止，在那里与岩浆冻结相关的膨胀体积变化导致有利于岩浆在冻结层附近积水的粘性应力。通过岩脉注入和枕流模拟地壳增生的稳态热影响，我们对待所有的地壳增生的岩石冷却器比岩浆“固相线”发生在一个狭窄的250米宽的岩脉状区域为中心的山脊轴。大洋地壳的其余部分被建模为直接位于“固相线”冻结层位下方的稳态岩浆透镜，其中稳态侵位率由该透镜供应所有未通过岩浆透镜上方的筑堤/挤压侵位的地壳的约束来确定。如果温度低于600°C的地壳岩石中的热液热传输的散热效率是热传导的8倍，那么我们发现，稳定状态的岩浆透镜将只存在于扩张速度超过25毫米/年的地壳中。岩浆透镜的深度依赖性与扩展速率是很好的协议与地震观测。这些结果表明，地壳增生过程中的岩浆热注入和热液热去除之间的平衡相当微妙，导致强烈不同的地壳热结构在快速和缓慢扩展的脊轴。我们的研究结果支持这样一个假设，即中央谷地形是由于强脊轴岩石圈的延伸造成的;正是热状态的差异直接导致了在缓慢扩张的脊（例如，大西洋中脊）和在快速扩张脊（例如，东太平洋隆起）。这种模式的起源中谷在一个缓慢扩张的山脊预测，沿轴的变化中谷地形的缓慢扩张中心反映了最近的岩浆热输入的变化沿着一段，也就是说，轴向地形是一个很好的时间平均指标的相对重要性的热液冷却和岩浆注入沿着一个给定的一段山脊。我们确定了累积的地壳应变与低地壳流支持的假设，即阿曼蛇绿岩地壳创建在一个快速扩展的脊古模拟，也表明地壳应变，而不是累积分层，可能是占主导地位的物理过程，产生“层状辉长岩”在阿曼蛇绿岩。
In this study we construct a thermal and mechanical model for the genesis of oceanic crust. Magma is halted in its ascent within the oceanic crust when it reaches a freezing horizon, where the dilational volume change associated with magma freezing leads to viscous stresses that favor magma ponding near the freezing horizon. To model the steady state thermal impact of crustal accretion via dike injection and pillow flows, we treat all crustal accretion in rocks cooler than a magma “solidus” to occur in a narrow 250-m-wide dike-like region centered about the ridge axis. The rest of the oceanic crust is modeled to be emplaced as a steady state magma lens directly beneath the “solidus” freezing horizon where the steady state emplacement rate is determined by the constraint that this lens supply all crust that is not emplaced through diking/extrusion above the magma lens. If hydrothermal heat transport within crustal rocks cooler than 600°C removes heat 8 times as efficiently as heat conduction, then we find that a steady state magma lens will only exist within the crust for ridges spreading faster than a 25 mm/yr half rate. The depth dependence of the magma lens with spreading rate is in good agreement with seismic observations. These results suggest that a fairly delicate balance between magmatic heat injection during crustal accretion and hydrothermal heat removal leads to a strongly different Crustal thermal structure at fast and slow spreading ridge axes. Our results support the hypothesis that median valley topography is due to extension of strong ridge axis lithosphere; it is the difference in thermal regime that is directly responsible for the striking difference between the typical median valley seen at slow spreading ridges (e.g., Mid-Atlantic Ridge) and the axial high seen at fast spreading ridges (e.g., East Pacific Rise). This paradigm for the origin of a median valley at a slow spreading ridge predicts that along-axis variations in median valley topography of a slow spreading center reflect variations in recent magmatic heat input along a segment, that is, that the axial topography is a good time-averaged indicator of the relative importance of hydrothermal cooling and magmatic injection along a given section of a ridge segment. We determine the accumulated crustal strain associated with lower crustal flow which supports the hypothesis that the Oman Ophiolite crust was created at a paleo-analogue to a fast spreading ridge and also suggests that crustal strain, and not cumulate layering, may be the dominant physical process that generates “layered gabbros” within the Oman Ophiolite.