What constitutes ‘emplacement’ of an ophiolite?: Mechanisms and relationship to subduction initiation and formation of metamorphic soles
What constitutes ‘emplacement’ of an ophiolite?: Mechanisms and relationship to subduction initiation and formation of metamorphic soles
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DOI：
10.1144/gsl.sp.2003.218.01.22
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
J. Wakabayashi;Y. Dilek
中科院分区：
文献类型：
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作者：
J. Wakabayashi;Y. Dilek
摘要蛇绿岩一直被认为是化石海洋岩石圈的陆上碎片，当它通过一个复杂的“侵位”过程进入大陆边缘时，就成为蛇绿岩。蛇绿岩侵位的一个基本问题是致密的洋壳如何侵位在大陆边缘或俯冲-增生系统的低密度物质之上。在未来的蛇绿岩之下俯冲较低密度的物质是克服不利的密度反差所必需的。俯冲作用与蛇绿岩侵位的关系是蛇绿岩与造山带形成的重要联系。虽然蛇绿岩的侵位机制明显不同，但大多数现有的侵位模型和定义都涉及特定类型的蛇绿岩（即阿曼或特罗多斯），并不适用于世界上许多蛇绿岩。根据不同的侵位机制，我们定义了四种原型蛇绿岩：（1）“特提斯”蛇绿岩，由于碰撞事件侵位于被动大陆边缘或微大陆之上，（2）“科迪勒拉”蛇绿岩，通过增生过程逐步侵位于俯冲杂岩之上;（3）“脊-沟交汇”（RTI）蛇绿岩是通过扩张脊与俯冲带相互作用的复杂过程形成的;（4）麦夸里岛蛇绿岩，由于板块边界形态沿沿着大洋中脊系统发生变化而暴露于地表下。某些洋盆的原始演化历史以及俯冲带走向的沿着变化可能导致蛇绿岩的侵位机制更为复杂。没有一个单一的侵位定义是没有缺点的;然而，我们可以考虑俯冲的开始，冲断大陆边缘或俯冲复合体，以及陆上暴露作为蛇绿岩侵位的关键阶段。
Abstract Ophiolites have long been recognized as on-land fragments of fossil oceanic lithosphere, which becomes an ophiolite when incorporated into continental margins through a complex process known as ‘emplacement’. A fundamental problem of ophiolite emplacement is how dense oceanic crust becomes emplaced over less dense material(s) of continental margins or subduction-accretion systems. Subduction of less dense material beneath a future ophiolite is necessary to overcome the adverse density contrast. The relationship of subduction to ophiolite emplacement is a critical link between ophiolites and their role in the development of orogenic belts. Although ophiolite emplacement mechanisms are clearly varied, most existing models and definitions of emplacement concern a specific type of ophiolite (i.e. Oman or Troodos) and do not apply to many of the world’s ophiolites. We have defined four prototype ophiolites based on different emplacement mechanisms: (1) ‘Tethyan’ ophiolites, emplaced over passive continental margins or microcontinents as a result of collisional events; (2) ‘Cordilleran’ ophiolites progressively emplaced over subduction complexes through accretionary processes; (3) ‘ridge-trench intersection’ (RTI) ophiolites emplaced through complex processes resulting from the interaction between a spreading ridge and a subduction zone; (4) the unique Macquarie Island ophiolite, which has been subaerially exposed as a result of a change in plate boundary configuration along a mid-ocean ridge system. Protracted evolutionary history of some ocean basins, and variation along the strike of subduction zones may result in more complicated scenarios in ophiolite emplacement mechanisms. No single definition of emplacement is free of drawbacks; however, we can consider the inception of subduction, thrusting over a continental margin or subduction complex, and subaerial exposure as critical individual stages in ophiolite emplacement.