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The role of ridges in the formation and longevity of flat slabs

机译：脊在平板的形成和寿命中的作用

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Flat-slab subduction occurs when the descending plate becomes horizontal at some depth before resuming its descent into the mantle. It is often proposed as a mechanism for the uplifting of deep crustal rocks ('thick-skinned' deformation) far from plate boundaries, and for causing unusual patterns of volcanism, as far back as the Proterozoic eon(1). For example, the formation of the expansive Rocky Mountains and the subsequent voluminous volcanism across much of the western USA has been attributed to a broad region of flat-slab subduction beneath North America that occurred during the Laramide orogeny (80-55 million years ago)(2). Here we study the largest modern flat slab, located in Peru, to better understand the processes controlling the formation and extent of flat slabs. We present new data that indicate that the subducting Nazca Ridge is necessary for the development and continued support of the horizontal plate at a depth of about 90 kilometres. By combining constraints from Rayleigh wave phase velocities with improved earthquake locations, we find that the flat slab is shallowest along the ridge, while to the northwest of the ridge, the slab is sagging, tearing, and re-initiating normal subduction. On the basis of our observations, we propose a conceptual model for the temporal evolution of the Peruvian flat slab in which the flat slab forms because of the combined effects of trench retreat along the Peruvian plate boundary, suction, and ridge subduction. We find that while the ridge is necessary but not sufficient for the formation of the flat slab, its removal is sufficient for the flat slab to fail. This provides new constraints on our understanding of the processes controlling the beginning and end of the Laramide orogeny and other putative episodes of flat-slab subduction.
机译：当下降板在下降到地幔中之前恢复到一定深度时，平板俯冲发生。人们经常提出将其作为一种机制来使深部地壳岩石抬升（远离“厚皮”形变）远离板块边界，并引起远古时代的火山爆发，从而引起异常的火山活动（1）。例如，膨胀的落基山脉的形成以及随后在美国西部大部分地区爆发的大量火山活动，都归因于拉拉米德造山运动（80-5500万年前）发生在北美下方的宽平板俯冲区域（2）。在这里，我们研究了位于秘鲁的最大的现代平板，以更好地了解控制平板形成和程度的过程。我们提供了新的数据，这些数据表明俯冲的纳斯卡海脊对于发展和持续支撑约90公里深度的水平板是必要的。通过将瑞利波相速度的约束与改善的地震位置结合起来，我们发现平坦的板块沿着山脊最浅，而到山脊的西北部，该板正在下垂，撕裂并重新开始正常俯冲。根据我们的观察，我们为秘鲁平板的时间演化提出了一个概念模型，其中由于沿秘鲁板块边界的沟槽退缩，吸力和山脊俯冲的综合作用而形成了平板。我们发现，虽然脊对于形成平板来说是必要的，但并不足够，但将其移除足以使平板失败。这为我们对控制Laramide造山带的开始和结束以及平板俯冲的其他假定事件的过程的理解提供了新的限制。

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  • 来源
    《Nature》 |2015年第7564期|212-215|共4页
  • 作者

    Antonijevic Sanja Knezevic; Wagner Lara S.; Kumar Abhash; Beck Susan L.; Long Maureen D.; Zandt George; Tavera Hernando; Condori Cristobal;

  • 作者单位

    Univ N Carolina, Dept Geol Sci, Chapel Hill, NC 27599 USA;

    Carnegie Inst Sci, Dept Terr Magnetism, Washington, DC 20015 USA;

    Univ N Carolina, Dept Geol Sci, Chapel Hill, NC 27599 USA;

    Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA;

    Yale Univ, Dept Geol & Geophys, New Haven, CT 06511 USA;

    Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA;

    Inst Geofis Peru, Lima 15012, Peru;

    Inst Geofis Peru, Lima 15012, Peru;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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