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首页> 外文期刊>Journal of African Earth Sciences >The role of post-collisional mafic magmatism in the late stages of evolution of the northernmost Arabian-Nubian Shield (ANS): A case study from Isla Complex, Wadi Isla, South Sinai, Egypt
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The role of post-collisional mafic magmatism in the late stages of evolution of the northernmost Arabian-Nubian Shield (ANS): A case study from Isla Complex, Wadi Isla, South Sinai, Egypt

机译：碰撞后的铁镁质岩浆作用在最北端的阿拉伯-努比亚盾（ANS）演化的后期中的作用：以埃及西南部南部瓦迪岛的Isla Complex为例

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Isla complex is one of the late Neoproterozoic igneous complexes of the Arabian-Nubian Shield in southern Sinai. This research aims to examine the petrogenesis and tectonic setting of Isla complex, as well as inferring the P-T conditions of the parent magma and the depth of intrusion. A detailed field studies were carried out and representative samples for petrographic and geochemical studies were collected. Chemical analyses of major and trace elements for 18 samples and microprobe analyses for different mineral phases in olivine gabbro were performed. The Isla complex is distinguished into olivine gabbro, diorite and monzonite. The interrelationships between certain oxides and/or oxide ratios point to the important role of fractional crystallization process during the formation of the studied complex and the evolution of its mafic-intermediate rock units. The major fractionated phases were clinopyroxene, amphibole and plagioclase. The analyzed rocks show a gradual decrease in concentration of HFSE from olivine gabbro to monzonite via diorite suggesting overall co-magmatic origin. The low K content in plagioclase and low and constant Y/Nb, Nb/Zr, and K/Nb ratios in gabbroic rock relative diorites and monzonites suggest that during the formation of more evolved rock units, the crustal contamination process became more important. The rock varieties of the Isla complex are fresh and not deformed indicating post-collisional emplacement. The geochemical affinity of Isla complex is analogous to other within-plate postcollisional mafic magmatism of south Sinai. The subduction-related geochemical signature of the examined rocks can be interpreted by partial melting of an enriched lithospheric mantle source following an earlier subduction stage in the ANS. Based on hornblende-plagioclase thermometry, the gabbroic rocks of the Isla complex crystallized at a pressure of 5.5 kbar (similar to 20 km depth), the crystallization temperature was estimated at 823 to 967 degrees C. The model of lithospheric delamination is supposed to form the studied melt since the delamination of the lithospheric mantle caused the asthenosphere to rise rapidly initiating partial melting and creating the studied gabbroic melt, followed by the fractionation of this melt to form different rock varieties of the Isla complex. The melts then penetrated the crusts base to create the Isla complex in southern Sinai. The estimated age of crystallization and emplacement of the examined complex is < 590-610 Ma, as it invades the old calc-alkaline granites.
机译：Isla复合体是西奈半岛南部的新元古代火成岩复合体之一。这项研究旨在检查Isla复合体的岩石成因和构造背景，以及推断母岩浆的P-T条件和侵入深度。进行了详细的现场研究，并收集了用于岩石学和地球化学研究的代表性样品。进行了18个样品的主要元素和微量元素的化学分析，以及橄榄石辉长岩中不同矿物相的微探针分析。 Isla复合体分为橄榄石辉长岩，闪长岩和蒙脱石。某些氧化物和/或氧化物比率之间的相互关系指出了分步结晶过程在所研究的复合物的形成及其镁铁质中间岩石单元的演化过程中的重要作用。主要的分馏相为斜环，闪石和斜长石。经过分析的岩石显示，从橄榄石辉长岩到闪长岩，HFSE的浓度逐渐降低，这暗示着整个共岩浆成因。斜长石中的K含量低，辉长岩相对闪长岩和独居石中Y / Nb，Nb / Zr和K / Nb比值低且恒定，这表明在形成更多演化的岩石单元期间，地壳污染过程变得更为重要。 Isla建筑群的岩石种类新鲜，没有变形，表明发生了碰撞后的侵位。 Isla复合体的地球化学亲和力类似于南西奈的其他板块内碰撞后铁镁质岩浆作用。在ANS的较早俯冲阶段之后，富集的岩石圈地幔源的部分熔融可以解释所检查岩石与俯冲有关的地球化学特征。根据角闪石斜长石测温法，Isla配合物的辉长岩在5.5 kbar（约20 km深度）的压力下结晶，估计结晶温度为823至967摄氏度。自岩石圈地幔分层以来所研究的熔体导致软流圈迅速上升，从而引发了部分熔融并形成了所研究的辉长岩熔体，然后对该熔体进行分馏以形成Isla岩体的不同岩石变种。然后，熔体渗入地壳底部，在西奈南部建立了Isla建筑群。所检查的复合物的结晶和镶嵌的估计年龄是<590-610 Ma，因为它侵入了旧的钙碱性花岗岩。

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