Structure and geochemistry of Tethyan ophiolites and their petrogenesis in subduction rollback systems
Structure and geochemistry of Tethyan ophiolites and their petrogenesis in subduction rollback systems
复制标题
DOI：
10.1016/j.lithos.2009.04.022
复制
发表时间：
2009-11
期刊：
影响因子：
3.5
通讯作者：
Y. Dilek;H. Furnes
中科院分区：
文献类型：
--
作者：
Y. Dilek;H. Furnes
造山带上俯冲带蛇绿岩代表了大陆碰撞前盆地闭合阶段俯冲回滚旋回洋壳的生成过程。地幔流动和板块回滚导致一个或多个事件的弧分裂和盆地开放，产生拼贴的“原弧和弧前海洋岩石圈”在俯冲带设置。东地中海地区（即米尔迪塔、平多斯、特罗多斯、克孜尔达格、阿曼）侏罗纪-白垩纪SSZ特提斯蛇绿岩一般具有彭罗斯型洋壳，并含有发育良好的席状岩墙杂岩，表明在海底扩张演化过程中，岩浆在狭窄裂谷带下方延伸。这些SSZ特提斯蛇绿岩的火成增生涉及上板的延伸和先进的熔融以前耗尽软流圈在主机盆地，表现出从MORB样IAT（岛弧拉斑玄武岩）玻安岩（极难熔）原弧组合的渐进演变。然而，这些特提斯蛇绿岩的地球化学演化存在一些明显的差异，这似乎是由于它们的俯冲带地球动力学的变化造成的。而克孜尔达格和Troodos熔岩的大部分显示岛弧的亲和力类似于他们的同行在Pindos和Mirdita蛇绿岩，阿曼熔岩的重要组成部分表明MORB的亲和力和大部分的克孜尔达格和阿曼的数据图内的地幔阵列之间的N-MORB和E-MORB的Nb/Yb-Th/Yb判别图。此外，特罗多斯和阿曼熔岩没有显示出任何特定的Th富集在其多元素模式，这表明流体/熔体输入俯冲沉积物是不是显着的，在他们的岩浆生成。虽然所有的蛇绿岩表现出地球化学特征，表明在熔融演化过程中，他们年轻的喷出序列和岩脉侵入体的俯冲影响增加，证明了他们的负Nd值，其整体特征的微量元素模式似乎已经受到强烈的影响，他们发展的俯冲系统的成熟度。
Suprasubduction zone (SSZ) ophiolites in orogenic belts represent oceanic crust generation in subduction rollback cycles during the closing stages of basins prior to terminal continental collisions. Mantle flow and slab rollback result in one or more episodes of arc splitting and basin opening, producing a collage of ‘protoarc and forearc oceanic lithosphere’ in suprasubduction zone settings. The Jurassic–Cretaceous SSZ Tethyan ophiolites in the eastern Mediterranean region (i.e. Mirdita, Pindos, Troodos, Kizildag, Oman) generally have Penrose-type oceanic crust and contain well-developed sheeted dike complexes indicative of magmatic extension beneath narrow rift zones during their seafloor spreading evolution. Igneous accretion of these SSZ Tethyan ophiolites involved upper plate extension and advanced melting of previously depleted asthenosphere in host basins, showing a progressive evolution from MORB-like to IAT (island arc tholeiite) to boninitic (extremely refractory) protoarc assemblages. However, there are some distinct differences in the geochemical evolution of these Tethyan ophiolites that appear to have resulted from variations in their subduction zone geodynamics. Whereas a major part of the Kizildag and Troodos lavas shows island arc affinity similar to their counterparts in the Pindos and Mirdita ophiolites, a significant component of the Oman lavas indicates MORB affinity and the majority of the Kizildag and Oman data plot within the mantle array between N-MORB and E-MORB on the Nb/Yb–Th/Yb discriminant diagram. Furthermore, the Troodos and Oman lavas do not show any particular Th-enrichment in their multi-element patterns, suggesting that fluid/melt input from subducted sediments was not that significant in generation of their magmas. Although all ophiolites exhibit geochemical features indicating increased subduction influence during the melt evolution of their younger extrusive sequences and dike intrusions, as evidenced by their negative ɛNdvalues, their overall characteristic trace-element patterns seem to have been strongly affected by the maturity of the subduction systems in which they developed.