Segmentation of mid-ocean ridges attributed to oblique mantle divergence
Segmentation of mid-ocean ridges attributed to oblique mantle divergence
复制标题
地幔倾斜分歧导致的大洋中脊分段
DOI：
10.1038/ngeo2745
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发表时间：
2016
影响因子：
18.3
通讯作者：
Wilcock, William S.
中科院分区：
文献类型：
--
作者：
VanderBeek, Brandon P.;Toomey, Douglas R.;Hooft, Emilie E.;Wilcock, William S.
大洋中脊分段的起源--构造和岩浆过程中沿轴线的系统变化--仍然存在争议。通常认为地幔流动是板块分异的被动响应，转换断层之间的岩浆供应控制着分段性。利用地震层析成像，我们约束了胡安德富卡山脊中伸展的奋进段之下地幔流动的几何形状和地幔熔体的分布。我们的结果，结合以前的研究，建立了地幔发散和板块扩张方向之间的系统偏差。在所研究的所有三种情况下，地幔散布相对于板块扩展方向的新变化而被推进，并且随着扩展速率的减小，流场被推进的程度也增加。此外，地震图像显示，大炮检距、未转换的不连续面是地幔熔体保持作用增强的区域。我们认为，大洋中脊之下的斜地幔流动是扩张段重新定向和形成脊轴不连续面的驱动力。由此产生的构造不连续降低了向上熔体输送的效率，从而定义了岩浆过程的区段尺度变化。我们预测，跨扩张速率的大洋中脊分段受控于软流圈流动的演化模式和岩石圈裂谷的动力学。
The origin of mid-ocean ridge segmentation—the systematic along-axis variation in tectonic and magmatic processes—remains controversial. It is commonly assumed that mantle flow is a passive response to plate divergence and that between transform faults magma supply controls segmentation. Using seismic tomography, we constrain the geometry of mantle flow and the distribution of mantle melt beneath the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge. Our results, in combination with prior studies, establish a systematic skew between the mantle-divergence and plate-spreading directions. In all three cases studied, mantle divergence is advanced with respect to recent changes in the plate-spreading direction and the extent to which the flow field is advanced increases with decreasing spreading rate. Furthermore, seismic images show that large-offset, non-transform discontinuities are regions of enhanced mantle melt retention. We propose that oblique mantle flow beneath mid-ocean ridges is a driving force for the reorientation of spreading segments and the formation of ridge-axis discontinuities. The resulting tectonic discontinuities decrease the efficiency of upward melt transport, thus defining segment-scale variations in magmatic processes. We predict that across spreading rates mid-ocean ridge segmentation is controlled by evolving patterns in asthenospheric flow and the dynamics of lithospheric rifting.