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Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean

机译：北冰洋超慢扩展的加克尔山脊上的火山爆发

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Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m). A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85 ° E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limuo Pele), covering a large (>10km~2) area. At least 13.5 wt% CO_2 is necessary to fragment magma at these depths, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt. These observations raise important questions about the accumulation and discharge of magmatic vola-tiles at ultraslow spreading rates on the Gakkel ridge and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.
机译：地球外表面的大约60％是由洋中脊上的火山作用形成的洋壳组成。尽管只目视调查或取样了这片广阔火山地带的一小部分，但现有证据表明，在中海脊上很少发生爆发性喷发，尤其是在海水临界点以下（3,000 m）。从未在3,000 m以下的海床上观察到火山碎屑沉积，大概是因为中海脊玄武岩的挥发物含量通常太低，无法在如此高的静水压力下产生破碎岩浆所需的气体馏分。在国际极地远征队（北极圈）85°E的Gakkel山脊进行的一次国际极地探险中，我们采用了新的深层淹没技术，以在此偏远的冰雪覆盖的山脊上获取“零年龄”火山地形的照相和视频图像。在这里，我们提供的图像揭示了在4,000 m水深处的轴向山谷上覆盖着未固结的火山碎屑沉积物，包括气泡壁碎片（limuo Pele），覆盖了较大的区域（> 10km〜2）。在这些深度碎裂岩浆至少需要13.5 wt％的CO_2，这约为先前在洋中脊玄武岩中测得的最高值的十倍。这些观测结果提出了有关岩浆挥发物以超低扩散速率在Gakkel脊上的积累和排放的重要问题，并证明了甚至在全球中海脊火山系统的最深处也可能发生大规模的火山碎屑活动。

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  • 来源
    《Nature》 |2008年第7198期|1236-1238qt0003|共4页
  • 作者

    Robert A. Sohn; Claire Willis; Susan Humphris; Timothy M. Shank; Hanumant Singh; Henrietta N. Edmonds; Clayton Kunz; Ulf Hedman; Elisabeth Helmke; Michael Jakuba; Bengt Liljebladh; Julia Under; Christopher Murphy; Ko-ichi Nakamura; Taichi Sato; Vera Schlindwein; Christian Stranne; Maria Tausenfreund; Lucia Upchurch; Peter Winsor; Martin Jakobsson; Adam Soule;

  • 作者单位

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Marine Science Institute, University of Texas at Austin, Port Aransas, Texas 78373, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Swedish Polar Secretariat, 104 05 Stockholm, Sweden;

    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven 27570, Germany;

    Johns Hopkins University, Baltimore, Maryland 21218, USA;

    Goeteborg University, Goteborg 40530, Sweden;

    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven 27570, Germany;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    AIST, Tsukuba Central 7,1-1-1 Higashi, Japan;

    Ocean Research Institute, University of Tokyo,Minamidai, Nakano, Tokyo 164-8639, Japan;

    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven 27570, Germany;

    Goeteborg University, Goteborg 40530, Sweden;

    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven 27570, Germany;

    Marine Science Institute, University of Texas at Austin, Port Aransas, Texas 78373, USA;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

    Department of Geology and Geochemistry, Stockholm University, 106 91 Stockholm, Sweden;

    Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;

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