Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge
Geophysical evidence for reduced melt production on the Arctic ultraslow Gakkel mid-ocean ridge
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DOI：
10.1038/nature01706
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发表时间：
2003-06-26
期刊：
影响因子：
64.8
通讯作者：
Snow, J
中科院分区：
文献类型：
--
作者：
Jokat, W;Ritzmann, O;Snow, J
大多数洋中脊下的熔体生成模型（1-3）预测，在超低扩展速率（完全扩展速率< 20毫米/年（-1））下，熔体产生将显著减少，因此它们预测海洋地壳将变薄。1800公里长的北极Gakkel洋中脊是测试这种模式的理想地点，因为它是迄今为止全球洋中脊扩展系统中最慢的部分，其完全扩展速度为6至13毫米/年（-1）（参考文献4,5）。此外，与其他脊系相比，Gakkel脊上的扩展方向不是斜向的，裂谷没有被大转换断层所抵消。在这里，我们提出了沿Gakkel山脊裂谷存在异常薄的地壳的地震证据，地壳厚度在1.9到3.3公里之间变化（相比之下，在中等到快速扩张的洋中脊上发现的更常见的值为7公里）。横跨裂谷的近8300公里紧密间隔的航空磁剖面显示，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。这些喷发中心的痕迹可以追溯到离轴约25迈的地壳年龄，这意味着这些岩浆的产生和运输系统在这个时间尺度上是稳定的。
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 ∼25 Myr off-axis, implying that these magma production and transport systems have been stable over this timescale.