Episodic magmatism and serpentinized mantle exhumation at an ultraslow-spreading centre
Episodic magmatism and serpentinized mantle exhumation at an ultraslow-spreading centre
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DOI：
10.1038/s41561-018-0124-6
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发表时间：
2018-06-01
影响因子：
18.3
通讯作者：
Papenberg, Cord
中科院分区：
文献类型：
--
作者：
Grevemeyer, Ingo;Hayman, Nicholas W.;Papenberg, Cord
以小于20 mm Yr(-1)的超低速率展开的大洋中脊可以将蛇纹状地幔折返到海底，或者它们可以产生岩浆壳。然而，超低扩张中心的地震成像并不能解决蛇纹岩化地幔折返的丰度，而是支持2至5公里的地壳。大多数地震地壳厚度估计都反映了超过7.1kmS(-1)P波速度的深度。然而，利用P波与S波速度(V-p/V-S)之比可以更可靠地推断大洋岩石圈的真实性质。本文报道了在超低伸展的中开曼扩张中心沿较老的大洋岩石圈的离轴剖面获得的地震资料。我们认为，高的V-p/V-S比值大于1.9，纵波速度持续增加，从海底的4公里S(-1)到2~4公里处的大于7.4公里的S(-1)，表明强烈的蛇纹岩橄榄岩折返到海底。在其他地方，要么是岩浆地壳，要么是蛇纹岩地幔在海洋核心杂岩中变形和抬升，位于高水深区域。因此，开曼海槽提供了一扇了解大洋中脊动力学的窗口，大洋中脊动力学在富含岩浆和缺乏岩浆的大洋地壳增长之间切换，包括覆盖该地区约25%海底的蛇纹岩地幔折返。
Mid-ocean ridges spreading at ultraslow rates of less than 20 mm yr(-1) can exhume serpentinized mantle to the seafloor, or they can produce magmatic crust. However, seismic imaging of ultraslow-spreading centres has not been able to resolve the abundance of serpentinized mantle exhumation, and instead supports 2 to 5 km of crust. Most seismic crustal thickness estimates reflect the depth at which the 7.1 km s(-1) P-wave velocity is exceeded. Yet, the true nature of the oceanic lithosphere is more reliably deduced using the P-to S-wave velocity (V-p/V-s) ratio. Here we report on seismic data acquired along off-axis profiles of older oceanic lithosphere at the ultraslow-spreading Mid-Cayman Spreading Centre. We suggest that high V-p/V-s ratios greater than 1.9 and continuously increasing P-wave velocity, changing from 4 km s(-1) at the seafloor to greater than 7.4 km s(-1) at 2 to 4 km depth, indicate highly serpentinized peridotite exhumed to the seafloor. Elsewhere, either magmatic crust or serpentinized mantle deformed and uplifted at oceanic core complexes underlies areas of high bathymetry. The Cayman Trough therefore provides a window into mid-ocean ridge dynamics that switch between magma-rich and magma-poor oceanic crustal accretion, including exhumation of serpentinized mantle covering about 25% of the seafloor in this region.