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Geochemistry of Khor Um-Safi ophiolitic serpentinites, central Eastern desert, Egypt: Implications for neoproterozoic arc-basin system in the Arabian-Nubian shield
Geochemistry ( IF 2.6 ) Pub Date : 2020-10-15 , DOI: 10.1016/j.chemer.2020.125690
Shehata Ali , Theodoros Ntaflos , Mabrouk Sami

Serpentinites in the Eastern Desert of Egypt are the most distinctive lithological unit in the Arabian–Nubian Shield (ANS) ophiolite sequence which associated with major suture zones. Khor Um-Safi (KUS) serpentinites represent dismembered fragments of ophiolitic rocks located in the central Eastern Desert (CED) of Egypt.

KUS serpentinites exhibit affinity to the typical metamorphic peridotites with harzburgitic protolith compositions. Their opaque mineral assemblage (pentlandite, heazlewoodite and magnetite) is similar to that observed in oceanic serpentinites and implies serpentinization under highly reducing conditions. They have refractory major element compositions with Al2O3 contents comparable to oceanic and active margin peridotites as well as Pan-African serpentinites. The Cr and TiO2 contents reflect evolution within a supra-subduction zone (SSZ) environment. This implication is confirmed by the Al2O3/SiO2 and MgO/SiO2 ratios which akin to ANS ophiolitic peridotites in fore-arc setting. Their enrichment in compatible trace elements (Cr, Ni and Co) reveals a depleted mantle peridotite protolith.

Modelling trace elements indicates that they represent the mantle residues from 15 to 20 % melting of spinel peridotite at oxygen fugacity conditions of the QFM + 1 buffer. This range of melt extraction is consistent with the typical range of SSZ peridotite. Oxygen fugacity estimation suggests evolution under more oxidizing regime similar to modern fore-arc basin system. Moreover, this implication indicates that the KUS mantle represents arc lithosphere interacted with arc melt.



中文翻译:

埃及东部东部中部的Khor Um-Safi蛇纹岩蛇纹岩的地球化学:阿拉伯-努比亚盾构中的新元古代弧盆系统的意义

埃及东部沙漠中的蛇纹岩是阿拉伯-努比亚盾(ANS)蛇绿岩序列中与主要缝合带有关的最独特的岩性单元。Khor Um-Safi(KUS)蛇纹岩代表位于埃及东部东部沙漠(CED)中的碎石碎片。

KUS蛇纹岩对典型的变质橄榄岩具有亲和性的原石组合物表现出亲和力。它们的不透明矿物组合(戊二石,杂木和磁铁矿)与在海洋蛇纹岩中观察到的相似,暗示在高度还原条件下蛇纹岩化。它们具有难熔的主要元素组成,其Al 2 O 3的含量可与海洋和活动边缘橄榄岩以及泛非蛇纹岩相媲美。Cr和TiO 2的含量反映了超俯冲带(SSZ)环境中的演化。Al 2 O 3 / SiO 2和MgO / SiO 2证实了这一含义。与前弧环境中的ANS蛇绿橄榄岩类似。它们富含相容的痕量元素(Cr,Ni和Co)显示出贫化的幔橄榄岩原岩。

微量元素建模表明,它们代表了在QFM + 1缓冲液的氧气逸度条件下,尖晶石橄榄石熔融度为15%至20%的地幔残留。熔体萃取的范围与SSZ橄榄岩的典型范围一致。氧气逸度估计值表明在类似于现代前弧盆地系统的更多氧化条件下的演化。此外,这暗示着KUS地幔代表了与岩石融化相互作用的岩石岩石圈。

更新日期:2020-10-15
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