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首页> 外文期刊>Ofioliti >THE AYLI DAG OPHIOLITE SEQUENCE (CENTRAL-NORTHERN TURKEY): A FRAGMENT OF MIDDLE JURASSIC OCEANIC LITHOSPHERE WITHIN THE INTRA-PONTIDE SUTURE ZONE
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THE AYLI DAG OPHIOLITE SEQUENCE (CENTRAL-NORTHERN TURKEY): A FRAGMENT OF MIDDLE JURASSIC OCEANIC LITHOSPHERE WITHIN THE INTRA-PONTIDE SUTURE ZONE

机译：AYLI DAG蛇绿岩序列（中北土耳其）：-壳内缝合带中的侏罗纪海洋卵石片段

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摘要

The Ayli Dag ophiolites occur as an independent tectonic unit within the Intra-Pontide suture zone, central-northern Turkey. They crop out, together with the other units of the Intra-Pontide suture zone, at the top of the Late Cretaceous-Middle Paleocene foredeep sediments of the Sakarya Terrane. The Ayli Dag ophiolites sequence include in its lower part a mantle sequence consisting of not less than 2-3 km-thick peridotites, topped by 500-600 m-thick layered gab-bros with alternating, dm- to m-thick layers of spinel-bearing dunites, melatroctolites, troctolites, ol-gabbros and leucogabbros. The gabbro sequence is overlain by a sheeted dyke complex, that shows a transition to 100-200 m-thick massive basaltic lava flows followed by 600-800 m-thick massive and pillow lavas and breccias alternating with ophiolite-bearing arenites and cherts. Geochemical evaluation of the mafic lavas and dykes reveals three distinct chemical groups that reflect melt generation within an intra-oceanic subduction system. Among these, the first group shows island-arc tholeiite (IAT)-like features, showing very-depleted characteristics (very high Zr/Nb, low Zr/Y and Nb/Y) ratios coupled with light rare-earth (LREE)-depleted chondrite-normalized patterns. The second group is more akin to back-arc basin basalts (BABB); it displays normal mid-ocean ridge basalt (N-MORB)-like high-field strength element (HFSE) distribution except for depletion in Nb, and flat REE patterns. The third group is somewhat similar to the second one, displaying BABB-like characteristics, but it is more enriched in terms of absolute trace element abundances. The radiolarian cherts sampled from the top of the pillow lavas yielded less-diverse but characteristic radiolarian assemblages indicating the middle Bathonian to early Callovian ages. The Ayli Dag Ophiolite is the first finding of back-arc type oceanic lithosphere in the Intra-Pontide suture zone. Together with previous data obtained from basalts in the melange from the Intra-Pontide suture zone, this finding represents a proof that an intra-oceanic subduction within the Intra-Pontide oceanic basin occurred in the Middle Jurassic time.
机译：Ayli Dag蛇绿岩以独立的构造单元出现在土耳其中北部土耳其境内的Intra-Pontide缝合带内。它们与Po内缝合线区的其他单元一起在萨卡里亚地带的晚白垩世-中古新世前缘深部沉积物顶部切出。 Ayli Dag蛇绿岩层序在其下部包括地幔层序，该层序由不少于2-3 km的橄榄岩组成，顶部是500-600 m厚的层状gab-bros，且具有从dm至m厚的交替尖晶石层轴承的dunites，黑闪石，斜闪石，ol-gabbros和leucogabbros。辉长岩层序被片状堤防复合体覆盖，表明向100-200 m厚的块状玄武岩熔岩流过渡，然后过渡到600-800 m厚的块状和枕状熔岩和角砾岩，以及含蛇绿岩的刚玉和石。对铁镁质熔岩和堤坝的地球化学评估显示出三个不同的化学基团，它们反映了海洋俯冲系统内熔体的生成。其中，第一组显示出类似岛弧状辉绿岩（IAT）的特征，显示出非常贫乏的特征（非常高的Zr / Nb，低Zr / Y和Nb / Y）比率以及轻稀土（LREE）-耗尽的球粒陨石归一化模式。第二类更类似于弧后盆地玄武岩（BABB）。它显示出正常的中洋洋脊玄武岩（N-MORB）状高场强度元素（HFSE）分布，除了Nb的损耗和平坦的REE模式。第三组与第二组有些相似，显示出类似BABB的特征，但在绝对微量元素丰度方面更加丰富。从枕形熔岩顶部取样的放射虫石产生的多样性较低但特征性的放射虫组合，表明中巴东期至早期卡洛维时期。 Ayli Dag蛇绿岩是在庞德特缝合线带内首次发现反弧型海洋岩石圈。连同先前从庞特德内缝合带的混杂岩中的玄武岩获得的数据，该发现代表了庞特德大洋盆地内洋内俯冲发生在中侏罗世的证据。

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