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首页> 外文期刊>Journal of Volcanology and Geothermal Research >The Cerro Chopo basaltic cone (Costa Rica): An unusual completely reversed graded pyroclastic cone with abundant low vesiculated cannonball juvenile fragments
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The Cerro Chopo basaltic cone (Costa Rica): An unusual completely reversed graded pyroclastic cone with abundant low vesiculated cannonball juvenile fragments

机译：塞罗·乔波（Cerro Chopo）玄武岩锥（哥斯达黎加）：一种不寻常的完全颠倒的渐变火山碎屑锥，上面有丰富的低泡炮弹少年碎片

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摘要

Cerro Chopo is a partially dissected, asymmetric, isolated Pleistocene pyroclastic cone, located in front of the Cordillera de Guanacaste, in northern Costa Rica. The cone consists of ～0.09 km3 of basaltic tephra, as well as ～0.14 km3 of lateral lava flows. Tephras are tholeiitic, high-alumina, olivine basalts, and represent minor degrees (≤5%) of crystal fractionation. Major and trace element compositions are consistent with minor fractionation from a mixture of E-MORB and OIB magmas. The cone walls consist of alternating coarser- and finer grained well-sorted beds, containing continuous spectra from breadcrust to smooth surface cannonball bombs, but also less frequent cylindric fragments and broken dasts. Cerro Chopo is unique compared to other typical scoria cones because it contains ubiquitous reversely-graded layers, scarcity of scorias, and instead a wide range of dense (1.54-2.49 g/cm3) poorly vesicular (5-40 vol.%) juvenile clast morphologies, including abundant cannonball juvenile bombs and lapilli. These are bombs with concentric layers surrounding vesiculated, dense and lapillistone cores and are interpreted to have repeatedly recycled through the vent. The cannonball bombs and lapilli have been described in a few scoria cones but are much less abundant than in Chopo. The reverse graded sequences are interpreted to have resulted from decreasing explosivity at the vent, in addition to local failure of tephra on slopes as the consequence of grain flows. Elsewhere on the Earth, most of the poorly-vesiculated spherical bombs, particularly cannonball, accretionary, composite, and core bombs, and its equivalent lapilli size (pelletal, spinning droplets and ellipsoidal lapilli), are all related to mafic to ultramafic, low-viscosity magmas.
机译：Cerro Chopo是部分解剖的，不对称的，孤立的更新世火山碎屑锥体，位于哥斯达黎加北部的瓜纳卡斯特山脉前。圆锥体由〜0.09 km3的玄武特非拉和〜0.14 km3的横向熔岩流组成。特弗拉斯是可塑的高铝橄榄石玄武岩，代表次要程度（≤5％）的晶体分馏。主要和微量元素组成与E-MORB和OIB岩浆混合物的次要馏分一致。锥壁由交替排列的粗粒和细粒排列良好的床组成，包含从面包壳到光滑的表面炮弹炸弹的连续光谱，还包含较少见的圆柱形碎片和破碎的碎屑。 Cerro Chopo与其他典型的圆锥sco相比具有独特之处，因为它包含无处不在的反渐变层，稀有的圆锥and，而是各种各样的稠密（1.54-2.49 g / cm3）的水泡不佳（5-40 vol。％）的少年碎屑形态，包括大量的炮弹，少年炸弹和lapilli。这些是炸药，其炸药的同心层围绕着囊状，致密和拉米石的核心，并被解释为通过发泄口反复回收。弹丸炸弹和拉皮球已经在一些炸炉锥体中进行了描述，但数量远不及Chopo。反向坡度序列被认为是由于喷口处爆炸性的降低，以及边坡中特非拉因谷物流而导致的局部破坏之外的结果。在地球的其他地方，大多数气泡较疏的球形炸弹，特别是炮弹，增生，复合和核心炸弹及其等效的lapilli大小（弹丸，旋转液滴和椭圆形lapilli）都与铁镁合金，超镁铁合金，粘性岩浆。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2011年第4期|p.163-177|共15页
  • 作者

    Guillermo E. Alvarado; Wendy Pérez; Thomas A. Vogel; Heike Groeger; Lina Patino;

  • 作者单位

    Area de Amenazas y Auscultation Sismovolcanica, Institute Costarricense de Electricidad, San Jose, Costa Rica,Escuela Centroamericana de Ceologia, Universidad de Costa Rica, Apdo. 35, Sanjost, Costa Rica;

    Escuela Centroamericana de Ceologia, Universidad de Costa Rica, Apdo. 35, Sanjost, Costa Rica,RD4- Dynamics of the Ocean Floor, IFM-CE0MAR, Wischhofitr., 1-3, 24148 Kiel, Germany;

    Department of Geological Sciences, Michigan State University, East Lansing, MI 48824- 1115, USA;

    Statoil ASA, Forusbeen 50, NO-4035 Stavanger, BS, Norway;

    Department of Geological Sciences, Michigan State University, East Lansing, MI 48824- 1115, USA;

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  • 正文语种 eng
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  • 关键词

    pyroclastic cone; reverse grading; cannonball bombs; cerro chopo; costa rica;

    机译：火山碎屑锥;反向分级;炮弹;塞波罗;哥斯达黎加;

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