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Spreading-rate dependence of melt extraction at mid-ocean ridges from mantle seismic refraction data

机译：来自地幔地震折射数据的中洋脊熔体提取物的扩散速率依赖性

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A variety of observations indicate that mid-ocean ridges produce less crust at spreading rates below 20 mm yr(-1) (refs 1-3), reflecting changes in fundamental ridge processes with decreasing spreading rate. The nature of these changes, however, remains uncertain, with end-member explanations being decreasing shallow melting(3) or incomplete melt extraction(2), each due to the influence of a thicker thermal lid. Here we present results of a seismic refraction experiment designed to study mid-ocean ridge processes by imaging residual mantle structure. Our results reveal an abrupt lateral change in bulk mantle seismic properties associated with a change from slow to ultraslow palaeo-spreading rate. Changes in mantle velocity gradient, basement topography and crustal thickness all correlate with this spreading-rate change. These observations can be explained by variations in melt extraction at the ridge, with a gabbroic phase preferentially retained in the mantle at slower spreading rates. The estimated volume of retained melt balances the similar to1.5-km difference in crustal thickness, suggesting that changes in spreading rate affect melt-extraction processes rather than total melting.
机译：各种观测结果表明，洋中脊在散布速率低于20 mm yr（-1）时产生的地壳较少（参考文献1-3），反映出随着散布速率降低，基本的山脊过程发生了变化。然而，这些变化的性质仍不确定，最终成员的解释是由于较厚的热盖的影响，浅熔（3）减少或熔体提取不完全（2）减少。在这里，我们介绍了一项旨在通过成像残留地幔结构来研究中洋海脊过程的地震折射实验的结果。我们的研究结果表明，整体地幔地震特性的突然横向变化与古扩展速率从慢到超慢的变化有关。地幔速度梯度，基底形貌和地壳厚度的变化都与这种扩展速率的变化相关。这些观察结果可以用山脊处熔体提取的变化来解释，辉长岩相优先以较慢的扩散速率保留在地幔中。估计的保留熔体体积平衡了地壳厚度相差约1.5公里，这表明扩展速率的变化会影响熔体提取过程，而不是总熔解。

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