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首页> 外文期刊>Contributions to Mineralogy and Petrology >Geochemistry and tectonic significance of peridotites from the South Sandwich arc-basin system, South Atlantic
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Geochemistry and tectonic significance of peridotites from the South Sandwich arc-basin system, South Atlantic

机译：南大西洋南桑威奇弧盆系统橄榄岩的地球化学和构造意义

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摘要

Petrographic and geochemical studies of peridotites from the South Sandwich forearc region provide new evidence for the evolution of the South Sandwich arc-basin system and for the nature of interactions between arc magma and oceanic lithosphere. Peridotites from the inner trench wall in the northeast corner of the forearc vary from clinopyroxene-bearing harzburgites, through samples transitional between harzburgites and dunites or wehrlites, to dunites. The harzburgites are LREE depleted with low incompatible element abundances and have chromites with intermediate Cr# (ca. 0.40). Modelling shows that they represent the residues from 15-20 percent melting at oxygen fugacities close to the QFM buffer. The dunites have U-shaped REE patterns, low incompatible element abundances and high Cr# (0.66-0.77). Petrography and geochemistry indicate that the latter are the product of intense interaction between peridotite and melt saturated with olivine under conditions of high oxygen fugacity (QFM +2). The transitional samples are the product of lesser interaction between peridotite and melt saturated with olivine +- clinopyroxene. The data demonstrate that the harzburgites originated as the residue from melting at a ridge (probably the early East Scotia Sea spreading centre), and were subsequently modified to transitional peridotites and dunites by interaction with South Sandwich arc magmas. The second dredge locality, near the South Sandwich Trench-Fracture Zone intersection, yielded rocks ranging from lherzolite to harzburgite that could similarly have resulted from a two-stage melting and enrichment process, but involving a more fertile mantle residue and a reacting melt that is transitional between MORB and island arc tholeiite. The South Sandwich peridotites have a similar petrogenetic history to those from Conical Seamount in the Mariana forearc in the sense that both involved interaction between arc magma and pre-existing mantle lithosphere of different provenance. However, the precise compositions of the magma and mantle components vary from location to location according to the precise tectonic setting and tectonic history. Overall, therefore, data from the South Sandwich and Izu-Bonin-Mariana systems emphasise the potential significance of peridotite geochemistry in unravelling the complex tectonic histories of forearcs past and present.
机译：南桑威奇前陆地区橄榄岩的岩石学和地球化学研究为南桑威奇弧盆系统的演化以及弧岩浆与海洋岩石圈相互作用的性质提供了新的证据。前臂东北角内沟壁中的橄榄岩，从含斜ino石的哈氏石，到在哈氏石与榴辉岩或辉绿岩之间过渡的样品变化为榴辉岩。 harzburgite的LREE元素贫乏度低，并且铬铁矿的Cr＃含量中等（约0.40）。建模表明，它们代表了在接近QFM缓冲液的氧气逸度下15％至20％熔化的残留物。 dunits具有U形REE模式，不相容元素丰度低和Cr＃（0.66-0.77）高。岩石学和地球化学表明，后者是橄榄岩与橄榄石在高氧逸度（QFM +2）条件下饱和的熔体之间强烈相互作用的产物。过渡样品是橄榄岩和橄榄石+-斜向辉石饱和熔体之间较小相互作用的产物。数据表明，哈兹伯格岩的残余物来自山脊（可能是东斯科舍省早期扩散中心）的融化作用，随后通过与南桑威奇弧状岩浆相互作用而被改造成过渡橄榄岩和辉石。第二个挖泥机地点在南桑德威奇海沟-断裂带交叉点附近，产生了从钙绿岩到钙锌榴石的岩石，可能类似地由两个阶段的熔融和富集过程产生，但涉及更肥沃的地幔残留物和反应性熔体。 MORB和岛弧型变黄铁矿之间的过渡。南桑威奇橄榄岩的成岩史与马里亚纳前额的圆锥海山的成岩史相似，因为两者都涉及弧岩浆与不同来源的早先存在的地幔岩石圈之间的相互作用。然而，岩浆和地幔成分的精确组成根据精确的构造背景和构造历史而在不同位置之间变化。因此，总的来说，来自South Sandwich和Izu-Bonin-Mariana系统的数据强调了橄榄岩地球化学在揭示过去和现在的复杂构造历史方面的潜在意义。

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