Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield
Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield
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DOI：
10.1016/j.lithos.2020.105720
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发表时间：
2020-11
期刊：
影响因子：
3.5
通讯作者：
Heba S. Mubarak;M. Azer;A. A. Surour-A.;H. E. Moussa;P. Asimow;M. Kabesh
中科院分区：
文献类型：
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作者：
Heba S. Mubarak;M. Azer;A. A. Surour-A.;H. E. Moussa;P. Asimow;M. Kabesh
我们在埃及东部沙漠的Um Rashid研究了蛇纹岩超镁铁岩序列和蛇绿混杂岩中的橄榄石和类似橄榄石的岩石。乌姆拉希德蛇绿岩经蛇纹岩化、碳酸盐化、片麻岩化、橄榄岩化和硅化作用强烈变形、变质和蚀变。新鲜原生矿物遗迹的结构、全岩化学和成分分析表明，蛇纹岩原岩为强烈熔融亏损的方辉橄榄岩和少量纯橄榄岩，为典型的超俯冲带弧前环境。根据野外关系、矿物组合和地球化学特征，将取代辉长岩的浅色岩石划分为典型的辉长岩和似辉长岩。典型的橄榄石呈块状分布于蛇绿混杂岩中，呈块状，边缘为绿泥石，含有石榴石、透辉石、透辉石和绿泥石，并有少量的先驱石和不透明矿物。蛇纹岩中发现的似罗丁石的岩石由钙铝榴石、一水硬铝石、珍珠岩、刚玉、钠长石、钠长石、安山石、斜长石和一水硬铝石组成。一些类似辉长岩的岩石样品保留了残存的辉长岩矿物和结构，而典型的辉长岩则被完全取代。罗丁石高度富含CaO、Fe_2O_3、MgO及相容的微量元素，类罗丁石强烈富含Al_2O_3及不相容的微量元素。根据地球化学和岩石学证据，这两种类型的褐斑岩很可能是从紧邻蛇纹岩的镁铁质原岩中发育出来的，但受到不同流体相互作用的影响，很可能是在不同的时间。典型的橄榄石发育可能伴随着蛇纹岩作用，在300℃左右表现出低硅高钙流体渗入的矿物组合特征，而类罗丁石岩石则可能是海水渗入形成的。
We studied rodingite and rodingite-like rocks within a serpentinized ultramafic sequence and ophiolitic mélange at Um Rashid, in the Eastern Desert of Egypt. The Um Rashid ophiolite is strongly deformed, metamorphosed, and altered by serpentinization, carbonatization, listvenitization, rodingitization and silicification. The textures, whole-rock chemistry, and composition of fresh primary mineral relics show that the serpentinite protoliths were strongly melt-depleted harzburgite and minor dunite, typical of a supra-subduction zone fore-arc setting. The light-colored rocks replacing gabbro are divided on the basis of field relations, mineral assemblages and geochemical characteristics into typical rodingite and rodingite-like rock. Typical rodingite, found as blocks with chloritite blackwall rims within ophiolitic mélange, contains garnet, vesuvianite, diopside and chlorite with minor prehnite and opaque minerals. Rodingite-like rock, found as dykes in serpentinite, consists of hercynite, preiswerkite, margarite, corundum, prehnite, ferropargasite, albite, andesine, clinozoisite and diaspore. Some rodingite-like rock samples preserve relict gabbroic minerals and texture, whereas typical rodingite is fully replaced. Rodingite is highly enriched in CaO, Fe2O3, MgO, and compatible trace elements, whereas rodingite-like rock is strongly enriched in Al2O3and incompatible trace elements. Based on geochemistry and petrographic evidence, both types of rodingitic rocks likely developed from mafic protoliths in immediate proximity to serpentinite but were affected by interaction with different fluids, most likely at different times. Typical rodingite development likely accompanied serpentinization and shows mineral assemblages characteristic of low-Si, high-Ca fluid infiltration at about 300 °C. Rodingite-like rock, on the other hand, likely developed from seawater infiltration.