The Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an exposure of juvenile continental crust on the eastern side of the Red Sea rift. Gabbroic intrusions in Saudi Arabia constitute a significant part of the mafic magmatism in the Neoproterozoic Arabian Shield. This study records the first detailed geological, mineralogical and geochemical data for gabbroic intrusions located in the Gabal Samra and Gabal Abd areas of the Hail region in the Arabian Shield of Saudi Arabia. Geological field relations and investigations, supported by mineralogical and geochemical data, indicate that the gabbroic intrusions are generally unmetamorphosed and undeformed, and argue for their post-collisional emplacement. Their mineralogical and geochemical features reveal crystallization from hydrous, mainly tholeiitic, mafic magmas with arc-like signatures, which were probably inherited from the previous subduction event in the Arabian–Nubian Shield. The gabbroic rocks exhibit sub-chondritic Nb/U, Nb/Ta and Zr/Hf ratios, revealing depletion of their mantle source. Moreover, the high ratios of (Gd/Yb)N and (Dy/Yb)N indicate that their parental mafic melts were derived from a garnet-peridotite source with a garnet signature in the mantle residue. This implication suggests that the melting region was at a depth exceeding ∼70–80 km at the garnet stability field. They have geochemical characteristics similar to other post-collisional gabbros of the Arabian–Nubian Shield. Their origin could be explained by adiabatic decompression melting of depleted asthenosphere that interacted during ascent with metasomatized lithospheric mantle in an extensional regime, likely related to the activity of the Najd Fault System, at the end of the Pan-African Orogeny.

中文翻译：

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沙特阿拉伯阿拉伯地盾辉长岩侵入体的成因：新元古代弧岩浆作用的矿物学、地球化学和构造指纹

沙特阿拉伯的阿拉伯地盾是阿拉伯-努比亚地盾的一部分，在红海裂谷东侧形成了幼年大陆地壳的暴露。沙特阿拉伯的辉长岩侵入体构成了新元古代阿拉伯地盾镁铁质岩浆作用的重要组成部分。本研究首次记录了位于沙特阿拉伯阿拉伯地盾冰雹地区 Gabal Samra 和 Gabal Abd 地区辉长岩侵入体的详细地质、矿物学和地球化学数据。由矿物学和地球化学数据支持的地质现场关系和调查表明，辉长岩侵入体通常未变质和未变形，并证明它们在碰撞后就位。它们的矿物学和地球化学特征揭示了含水结晶，主要是拉斑沸石，具有弧形特征的镁铁质岩浆，可能是从先前的阿拉伯-努比亚地盾俯冲事件中继承下来的。辉长岩表现出亚球粒状 Nb/U、Nb/Ta 和 Zr/Hf 比率，揭示了它们的地幔源耗竭。此外，(Gd/Yb) 的高比率ñ和 (Dy/Yb)ñ表明它们的母体镁铁质熔体来自石榴石 - 橄榄岩源，在地幔残留物中具有石榴石特征。这一暗示表明，在石榴石稳定场，熔化区的深度超过了 70-80 公里。它们具有与阿拉伯-努比亚地盾的其他碰撞后辉长岩相似的地球化学特征。它们的起源可以通过耗竭软流圈的绝热减压熔融来解释，该软流圈在上升过程中与伸展状态的交代岩石圈地幔相互作用，可能与泛非造山运动结束时的内志断层系统的活动有关。