From rift to drift: Mantle melting during continental breakup
From rift to drift: Mantle melting during continental breakup
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DOI：
10.1029/2003gc000662
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发表时间：
2004-07
期刊：
影响因子：
3.7
通讯作者：
T. Nielsen;J. Hopper
中科院分区：
文献类型：
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作者：
T. Nielsen;J. Hopper
火山裂陷边缘显示了火成岩地壳厚度的时间演化，因此与大洋中脊的稳态情况相比，提供了对地幔动力学的更多见解。虽然不同省份之间的细节有所不同，但火山裂陷边缘通常显示出短暂的极端岩浆活动脉冲，并迅速减弱为稳定状态的洋中脊。在火山裂陷边缘产生厚的火成岩地壳需要热地幔物质的熔融程度高于在洋中脊观察到的程度，或者需要比板块驱动的上涌更大量的地幔物质的熔融。为了评估在何种条件下，裂谷板块边界的强制驱动的上涌或小规模对流是重要的，开发了一个具有非牛顿粘度的流体动力学模型，该模型包括熔融对地幔物理性质的反馈。为了产生高岩浆生产的脉冲，需要一种粘度和密度结构，这种结构也会导致岩浆生产力的过度波动，或者在分裂后很长一段时间内持续的高生产力。由于融化引起的脱水而导致的粘度增加有效地抑制了深度以上的浮力上涌至干固相线，从而将浅层流动限制为板块驱动的上涌。虽然这稳定了时间依赖性，并迫使生产力达到与洋中脊增生一致的值，但这是以消除解体不稳定性为代价的。假设裂谷前岩石圈厚度突然变化的模型也存在同样的缺陷。然而，包括一个岩石圈下的热层导致一个模型，可以预测从格陵兰岛东南部火山裂谷边缘的折射地震数据中观察到的火成岩地壳厚度的时间演变。
Volcanic rifted margins show a temporal evolution in igneous crustal thickness and thus provide additional insights into mantle dynamics compared to the steady state situation at mid‐ocean ridges. Although details between different provinces vary, volcanic rifted margins generally show a short‐lived pulse of extreme magmatism that quickly abates to a steady state mid‐ocean ridge. The generation of thick igneous crust at volcanic rifted margins requires either melting of hot mantle material to higher degrees than observed at mid‐ocean ridges or melting of larger amounts of mantle material than would be the case for plate‐driven upwelling. To assess under what conditions buoyantly driven upwelling or small‐scale convection at rifting plate boundaries is important, a fluid dynamical model with non‐Newtonian viscosity that includes the feedback from melting on the physical properties of the mantle is developed. To generate a pulse of high magmatic production requires a viscosity and density structure that also leads to excessive fluctuations in magmatic productivity or a sustained high productivity that continues long after breakup. A viscosity increase due to dehydration caused by melting effectively suppresses buoyant upwelling above the depth to the dry solidus, thereby restricting shallow flow to plate‐driven upwelling. While this stabilizes the time dependence and forces the productivity to values consistent with mid‐ocean ridge accretion, it does so at the expense of eliminating the breakup instability. Models that assume an abrupt change in prerift lithospheric thickness suffer from the same deficits. However, including a sublithospheric hot layer leads to a model that can predict the temporal evolution of igneous crustal thickness observed in refraction seismic data from the southeast Greenland volcanic rifted margin.