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Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge

机译：北极超慢Gakkel中洋洋脊上熔体产生减少的地球物理证据

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Most models of melt generation beneath mid-ocean ridges(1-3) predict significant reduction of melt production at ultraslow spreading rates ( full spreading rates < 20 mm yr(-1)) and consequently they predict thinned oceanic crust. The 1,800-km-long Arctic Gakkel mid-ocean ridge is an ideal location to test such models, as it is by far the slowest portion of the global mid-ocean-ridge spreading system, with a full spreading rate ranging from 6 to 13 mm yr(-1) ( refs 4, 5). Furthermore, in contrast to some other ridge systems, the spreading direction on the Gakkel ridge is not oblique and the rift valley is not offset by major transform faults. Here we present seismic evidence for the presence of exceptionally thin crust along the Gakkel ridge rift valley with crustal thicknesses varying between 1.9 and 3.3km ( compared to the more usual value of 7 km found on medium- to fast-spreading mid-ocean ridges). Almost 8,300 km of closely spaced aeromagnetic profiles across the rift valley show the presence of discrete volcanic centres along the ridge, which we interpret as evidence for strongly focused, three-dimensional magma supply. The traces of these eruptive centres can be followed to crustal ages of &SIM;25 Myr off-axis, implying that these magma production and transport systems have been stable over this timescale. [References: 19]
机译：大多数洋中脊以下的熔体生成模型（1-3）预测超低扩散速率（全扩散速率<20 mm yr（-1））时熔体产量将显着减少，因此，他们预测洋壳将变薄。 1800公里长的北极Gakkel中海脊是测试此类模型的理想地点，因为它是全球中海脊扩散系统中最慢的部分，全扩散率范围为6到13毫米yr（-1）（参考文献4、5）。此外，与其他一些山脊系统相比，Gakkel山脊上的扩展方向不是倾斜的，并且裂谷也不会被主要的变形断层抵消。在这里，我们提供了地震证据，证明了在Gakkel脊裂谷处存在极薄的地壳，地壳厚度在1.9至3.3 km之间变化（相比之下，在中等至快速扩散的中洋海脊中发现的更常见的值为7 km） 。纵裂谷上近8300公里的紧密间隔的航空磁廓表明，沿山脊存在离散的火山中心，我们将其解释为强烈集中的三维岩浆供应的证据。这些喷发中心的踪迹可以追溯到地壳年龄为＆SIM; 25 Myr轴外，这意味着这些岩浆的生产和运输系统在这段时间内一直稳定。 [参考：19]

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