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首页> 外文期刊>Contributions to Mineralogy and Petrology >The Lyngen Gabbro: the lower crust of an Ordovician Incipient Arc
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The Lyngen Gabbro: the lower crust of an Ordovician Incipient Arc

机译：Lyngen Gabbro：奥陶纪初始弧的下地壳

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We present evidence for the origin of the Lyngen Gabbro of the Ordovician Lyngen Magmatic Complex in Troms, Northern Norway. The two magmatic suites of the Lyngen Gabbro strike parallel NNE-SSW, and have distinct magmatic signatures. We define these signatures by using major and trace-element analyses together with selected major- and trace-element mineral analyses and 143Nd/144Nd-isotope whole-rock analyses of gabbroic to tonalitic plutonic rocks from seven detailed cross-sections from this large gabbro-complex. The Western suite of the Lyngen Gabbro precipitated from magma that may have been derived from the same system as the associated volcanic rocks. The gabbros have high An-content (An>90) of their plagioclases relative to co-existing mafic minerals. Together with somewhat high ɛNd(t) values (+6), this implies that the parental magmas were hydrous tholeiites similar to those found in back arc basins today. The Eastern suite, on the other hand, consist of cumulates that were precipitated from melts resembling those of ultra-depleted high-Ca boninitic magmas found in fore-arcs. Extremely high-An plagioclases (An>95) co-exist with evolved mafic minerals and oxides, and the ɛNd(t) values are lower (+4) than in the Western suite. The Eastern suite has no volcanic counterpart, but dikes intersecting the suites have compositions that possibly represent its parental magma. The oceanic Rypdalen Shear Zone generally separates the two suites in the north, but several non-tectonic transitions from boninitic to tholeiitic signatures southwards advocate that the magmatism happened concurrently. The magmatic proximity between the suites, the hydrous magmatism and the absence of a silicic or calc-alkaline mature arc section, suggests that the Lyngen Gabbro formed in the Iapetus Ocean under conditions presently found in incipient arcs later emplaced as outer arc highs.
机译：我们提供挪威北部Troms奥陶纪Lyngen岩浆复合体的Lyngen Gabbro起源的证据。 Lyngen Gabbro的两个岩浆套件与NNE-SSW平行，并具有独特的岩浆特征。我们通过使用主要元素和痕量元素分析以及选择的主要元素和痕量元素矿物分析和143 Nd / 144 Nd同位素从辉长岩到成色质古生岩的全岩体分析来定义这些特征。这个大型辉长岩复合体的七个详细横截面。 Lyngen Gabbro的西部套件是从岩浆中沉淀出来的，岩浆可能来自与相关火山岩相同的系统。辉长岩相对于共存的镁铁质矿物具有较高的cla含量（An> 90 ）。再加上较高的ɛNd（t）值（+6），这意味着亲代岩浆是含水的辉母岩，类似于今天在后弧盆地中发现的。另一方面，Eastern suites由堆积物组成，这些堆积物是从熔体中沉淀出来的，类似于在前弧中发现的超贫化高钙贝氏体岩浆。极高的安氏斜纹岩（An> 95 ）与演化的铁镁质矿物质和氧化物共存，并且ɛNd（t）值比西方套房低（+4）。东部套房没有火山对应物，但与套房相交的堤防可能具有代表其父母岩浆的成分。大洋的Rypdalen剪切带通常将北部的两个套间分隔开，但是向南的几个从贝尼特性向沃利特性特征的非构造过渡都主张岩浆作用是同时发生的。套件之间的岩浆接近性，含水岩浆作用和不存在硅质或钙碱性成熟弧段，这表明在伊阿佩图斯海洋中形成的Lyngen Gabbro在目前处于初期弧中的条件下形成，后来被定位为外部弧高。

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