Effect of latent heat of freezing on crustal generation at low spreading rates
Effect of latent heat of freezing on crustal generation at low spreading rates
复制标题
低扩散速率下冻结潜热对地壳生成的影响
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
J. Warren
中科院分区：
文献类型：
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作者：
N. Sleep;J. Warren
岩石圈结构在低扩展速率（<40 mm a−1）下发生变化，因此稳定状态的熔融岩石不可能存在于正常的莫霍面深度1.6 km以上。对回收的岩性的疏浚统计表明，与速度较快的海脊相比，玄武岩的百分比显著降低，结壳的生成方式也各不相同。对岩石圈结构的一个重要影响是玄武岩浆在地幔内冻结时释放的潜热，而不是一直被输送到地表。使用热模型，我们表明，冻结熔体在地幔深处的缓冲温度由于结晶潜热。该模型包含两种准稳定的海底扩张模式：（1）岩浆沿着一个狭窄的轴向带上涌;（2）在一个宽阔的带上纯剪切伸展。这些模型预测的地壳结构的变化解释了在8个慢速至超慢速扩张脊段的疏浚岩性统计数据中观察到的变化。例如，Gakkel东部火山带和稀疏岩浆带都以12 mm a−1的速度扩张，但前者由7%的橄榄岩组成，而后者由46%的橄榄岩组成。这种差异可以通过从1.2 km厚地壳的窄轴体制到壳幔混合的宽轴体制的变化来解释。总的来说，疏浚统计和热模型表明，一些，但不是全部，上升岩浆的潜热释放在地幔深处，各种脊轴形态可以发生。
Lithospheric structure changes at low spreading rates (<40 mm a−1), such that steady state molten rock cannot exist above the normal Moho depth of ∼6 km. Dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable. One important effect on lithospheric structure is the latent heat released when basaltic magma freezes within the mantle, instead of being transported all the way to the surface. Using thermal models, we show that freezing of melt at mantle depths buffers temperature due to the latent heat of crystallization. Two quasi‐stable seafloor‐spreading patterns are imposed on the model: (1) upwelling of magma along a narrow axial zone and (2) pure shear extension over a broad zone. The variability in crustal structure predicted by these models explains variability observed in dredge lithology statistics at eight slow to ultraslow spreading ridge segments. For example, the Gakkel Eastern Volcanic Zone and Sparsely Magmatic Zone are both spreading at 12 mm a−1, but the former is composed of 7% peridotite, whereas the latter is 46% peridotite. This difference can be explained by a change from a narrow axis regime with ∼2 km thick crust to a wide axis regime with a crust‐mantle mix. Overall, dredge statistics and thermal models suggest that some, but not all, latent heat of ascending magmas is released at mantle depths and that various ridge axial morphologies can occur.