Petrogenesis of boninitic lavas from the Troodos Ophiolite, and comparison with Izu–Bonin–Mariana fore-arc crust
Petrogenesis of boninitic lavas from the Troodos Ophiolite, and comparison with Izu–Bonin–Mariana fore-arc crust
复制标题
DOI：
10.1016/j.epsl.2018.06.041
复制
发表时间：
2018-09
影响因子：
5.3
通讯作者：
Dominic Woelki;M. Regelous;K. Haase;R. H. Romer;C. Beier
中科院分区：
文献类型：
--
作者：
Dominic Woelki;M. Regelous;K. Haase;R. H. Romer;C. Beier
超俯冲带(SSZ)蛇绿岩，如塞浦路斯的特罗多斯蛇绿岩，被认为是在靠近俯冲带的扩张中心形成的。SSZ蛇绿岩熔岩与活动俯冲带弧前熔岩在地球化学上的相似性，以及两者中玻安岩的存在，导致了SSZ蛇绿岩代表了俯冲开始时形成的弧前地壳和地幔的碎片。本文介绍了特罗多斯蛇绿岩南缘熔岩堆中新鲜火山玻璃的主元素、痕量元素和锶、钕、铅同位素数据，并与伊豆-博宁-马里亚纳前弧的熔岩进行了比较。在特罗多斯，玻安岩和拉斑玄武岩是互层的，来自高度亏损的地幔来源，后来被流体和主要来自俯冲沉积物的熔体富集，然后在扩张轴以下熔融。与Izu-Bonin-Mariana玻安岩不同的是，Troodos玻安岩比伊祖-博宁-马里亚纳玻安岩具有更大的源区亏损、少量熔体对Nb的富集性以及相对于Sm缺乏对Zr的富集性。再加上特罗多斯缺乏弧前玄武岩，我们的资料表明特罗多斯蛇绿岩形成于弧后扩张中心的弧前位置，并传播到弧壳中。因此，特罗多斯蛇绿岩不是在俯冲开始时形成的，因此不能用作形成弧前玄武岩的类似物。
Supra-subduction zone (SSZ) ophiolites such as the Troodos Ophiolite of Cyprus are thought to have formed at spreading centres close to subduction zones. Similarities in the geochemistry between lavas from SSZ ophiolites and fore-arc lavas from active subduction zones, and the presence of boninites in both, have led to the suggestion that SSZ ophiolites represent fragments of fore-arc crust and mantle, formed during subduction initiation. Here we present major and trace element and Sr, Nd and Pb isotope data for fresh volcanic glasses from a section through the lava pile on the southern margin of the Troodos Ophiolite, and compare these to lavas from the Izu–Bonin–Mariana fore-arc. In Troodos, boninites and tholeiitic basalts are interbedded and were derived from a highly depleted mantle source that was later enriched by both fluids and melts derived largely from subducted sediment, before melting beneath the spreading axis. Troodos boninites differ from Izu–Bonin–Mariana boninites by their greater source depletion, enrichment in Nb by small degree melts, and lack of Zr enrichment relative to Sm. Together with the lack of fore-arc basalts in Troodos, our data imply that the Troodos Ophiolite was formed in a fore-arc location at a back-arc spreading centre that propagated into arc crust. The Troodos Ophiolite was thus not formed during subduction initiation and thus may not be used as analogue for the formation of fore-arc basalts.