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首页> 外文期刊>Geochemistry, geophysics, geosystems >Along-axis variation in crustal thickness at the ultraslow spreading Southwest Indian Ridge (50 degrees E) from a wide-angle seismic experiment
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Along-axis variation in crustal thickness at the ultraslow spreading Southwest Indian Ridge (50 degrees E) from a wide-angle seismic experiment

机译：来自广角地震实验的西南印度洋超慢蔓延（50度）的地壳厚度沿轴向变化

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摘要

The Southwest Indian Ridge (SWIR) is characterized by an ultraslow spreading rate, thin crust, and extensive outcrops of serpentinized peridotite. Previous studies have used geochemical and geophysical data to suggest the presence of a thicker crust at the central and shallowest portions of the SWIR, from the Prince Edward (35 degrees 30E) to the Gallieni (52 degrees 20E) fracture zones. Here we present a new analysis of wide-angle seismic data along the ridge 49 degrees 17E-50 degrees 49E. Our main conclusions are as follows: (1) we find an oceanic layer 2 of roughly constant thickness and steep velocity gradient, underlain by a layer 3 with variable thickness and low velocity gradient; (2) the crustal thickness varies from approximate to 5 km beneath nontransform discontinuities (NTDs) up to approximate to 10 km beneath a segment center; (3) the melt supply is focused in segment centers despite a small NTD between adjacent segments; (4) the presence of a normal upper mantle velocity indicates that no serpentinization occurs beneath this thick crust. Our observation of thick crust at an ultraslow spreading ridge adds further complexity to relationships between crustal thickness and spreading rate, and supports previous suggestions that the extent of mantle melting is not a simple function of spreading rate, and that mantle temperature or chemistry (or both) must vary significantly along axis.
机译：西南印第安海岭（SWIR）的特征是超低的铺展速率，薄的地壳以及蛇纹石化橄榄岩的大量露头。以前的研究已经使用地球化学和地球物理数据表明，从爱德华王子（35度30E）到加利尼（52度20E）断裂带，SWIR的中央和最浅部分都存在较厚的地壳。在这里，我们介绍了沿49度17E-50度49E脊的广角地震数据的新分析。我们的主要结论如下：（1）我们发现了一个厚度大致恒定且速度梯度陡的海洋层2，下面是厚度可变且速度梯度低的层3。 （2）地壳厚度从非转换间断点（NTD）下约5 km到段中心以下约10 km不等; （3）尽管相邻段之间的NTD较小，但熔体供应仍集中在段中心; （4）正常的上地幔速度表明在该厚地壳下未发生蛇纹石化。我们对超慢扩散脊厚壳的观察进一步增加了地壳厚度和扩散速率之间关系的复杂性，并支持先前的建议，即地幔融化的程度不是扩散速率的简单函数，而且地幔温度或化学性质（或两者兼而有之） ）必须沿轴明显变化。

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