Geochemical mapping of a paleo-subduction zone beneath the Troodos Ophiolite
Geochemical mapping of a paleo-subduction zone beneath the Troodos Ophiolite
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特罗多斯蛇绿岩下方古俯冲带的地球化学测绘
DOI：
10.1016/j.chemgeo.2019.05.041
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发表时间：
2019
期刊：
影响因子：
3.9
通讯作者：
Regelous
中科院分区：
文献类型：
--
作者：
Woelki;Regelous
俯冲带上的蛇绿岩，如塞浦路斯的白垩纪Troodos蛇绿岩，是靠近俯冲带的海底扩张形成的洋壳碎片。它们的确切起源构造背景一直存在激烈的争论。虽然许多俯冲带上的蛇绿岩被认为是在俯冲开始时形成的弧前地壳，但其他蛇绿岩可能形成于俯冲脊，或弧后脊-海沟-海沟/转换三重连接或“板块边缘”环境。通过对特罗多斯熔岩序列7个详细剖面的515个新鲜火山玻璃样品进行主量元素和微量元素分析，确定特罗多斯岩浆作用成分的区域和时间变化，从而重建特罗多斯扩张轴相对于前俯冲带的距离和方向。Troodos玻璃的范围从玻安岩到拉斑玄武岩和安山岩到英安岩。与大洋中脊玄武岩（MORB）相比，所有的玻璃都富含流体流动的微量元素，并在高场强元素中亏损。因此，这些玻璃中没有一个具有与Izu-Bonin-Mariana弧前熔岩相同的成分，Izu-Bonin-Mariana弧前熔岩被认为是俯冲开始期间形成的熔岩的主要例子。玻安岩显然仅限于南部边缘的特罗多斯蛇绿岩，和玻璃从东南边缘的蛇绿岩是最耗尽，并包含最强的俯冲带流体和熔融签名输入。这些玻璃成分的地理变化表明，特罗多斯蛇绿岩形成的NW-SE方向的扩展（91 Ma）约100-120公里以上的向东倾斜的俯冲板块。Troodos扩张轴相对于前海沟的方向可以解释，如果Troodos蛇绿岩形成于弧前位置的俯冲开始在转换断层。然而，缺乏与弧前玄武岩成分的玻璃，和特罗多斯玻璃的微量元素组成之间的相似性，从Fonualei盆地和北方劳盆地在西南太平洋的建议，特罗多斯蛇绿岩形成在一个脊-沟-沟或脊-沟-转换三重连接设置，在弧后扩张中心，传播到弧和弧前地壳。
Supra-subduction zone ophiolites such as the Cretaceous Troodos Ophiolite of Cyprus are fragments of oceanic crust formed by seafloor spreading close to subduction zones. Their exact tectonic setting of origin has been intensively debated. Although many supra-subduction zone ophiolites are thought to represent fore-arc crust, created during subduction initiation, others may have formed at a subducting ridge, or in a back-arc, ridge-trench-trench/transform triple junction or ‘plate edge’ setting. We carried out major and trace element analyses of 515 fresh volcanic glasses from 7 detailed sections through the Troodos lava sequence in order to determine the regional and temporal variation in the composition of Troodos magmatism, and hence reconstruct the distance and orientation of the Troodos spreading axis relative to the former subduction zone. Troodos glasses range from boninite through tholeiitic basalt and andesite to dacite. All glasses are enriched in fluid-mobile trace elements, and variably depleted in the high-field strength elements compared to Mid-Ocean Ridge Basalt (MORB). None of these glasses therefore have compositions identical to Izu-Bonin-Mariana fore-arc lavas that have been proposed to be the prime example of lavas formed during subduction initiation. Boninites are apparently restricted to the southern margin of the Troodos Ophiolite, and glasses from the southeast margin of the ophiolite are the most depleted and contain the strongest input of subduction zone fluid and melt signature. These geographic variations in glass composition indicate that the Troodos Ophiolite formed by NW-SE directed spreading (at 91 Ma) approximately 100–120 km above an eastward-dipping subducting plate. The orientation of the Troodos spreading axis relative to the former trench could be explained if the Troodos Ophiolite formed in a fore-arc position by subduction initiation at a transform fault. However, the lack of glasses with fore-arc basalt composition, and similarities between the trace element compositions of Troodos glasses and those from the Fonualei basin and northern Lau Basin in the southwest Pacific suggest that the Troodos Ophiolite formed in a ridge-trench-trench or ridge-trench-transform triple junction setting, at a back-arc spreading centre that propagated into arc and fore-arc crust.
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DOI：
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发表时间：
1998
期刊：
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DOI：
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发表时间：
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期刊：
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