The Jabal Aja Ring Complex (ARC) is a late Ediacaran composite pluton of postcollisional A-type granites in the northeastern part of the Arabian Shield. It is an elliptical body with discontinuous ring-shaped outcrops due to later faulting. Field relationships enable the recognition of two main phases of magmatic activity in the ARC. The early phase represents the core of the intrusion (monzogranite, syenogranite, granophyre, and alkali feldspar granite) surrounded by the last phase (alkali volcanics and alkaline/peralkaline granites). The contacts between two phases are gradational and/or sharp, indicating their emplacement within a very short time period before the complete crystallization of the earlier phase. The ARC is alkaline to peralkaline rare-metal granites with the common geochemical characteristics of postcollisional intraplate A-type rocks. The pronounced negative Eu anomalies (Eu/Eu*=0.14−0.25) reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interaction. All A-type rocks of the ARC retain a positive Nb-Ta anomaly that increases from the early phase to the most evolved alkaline/peralkaline granites. They define geochemical signatures reflecting their derivation from the same magma sources that evolved through fractional crystallization with crustal contamination. The geochemical characteristics of the A-type granites of ARC reflect remelting of previously formed arc material. The mafic microgranular enclaves represent metamorphic rocks derived from or in the deeper part of the crust and represent the source rocks from which the granitic magma was generated by partial melting. The early phase of magmatism of the ARC represents melts derived from partial melting of lower or middle crustal sources during the postcollisional stage that fractionated to give the various granitic rocks. The absence of mafic xenoliths in the late stage of the ARC indicates that the contribution of crustal sources to magma generation is absent in the late stage.

中文翻译：

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阿拉伯地盾碰撞后含稀有金属花岗岩的成因和岩石学：以沙特阿拉伯北部 Aja 环杂岩为例

Jabal Aja Ring Complex (ARC) 是阿拉伯地盾东北部碰撞后 A 型花岗岩的晚期埃迪卡拉复合岩体。它是一个椭圆体，由于后来的断层作用，具有不连续的环形露头。场关系能够识别 ARC 中岩浆活动的两个主要阶段。早期阶段代表侵入体的核心（二长花岗岩、正长花岗岩、花岗岩和碱性长石花岗岩），被最后阶段（碱性火山岩和碱性/过碱性花岗岩）包围。两相之间的接触是渐变的和/或尖锐的，表明它们在早期相完全结晶之前的很短的时间内就位。ARC 是碱性至过碱性的稀有金属花岗岩，具有碰撞后板内 A 型岩石的共同地球化学特征。显着的负 Eu 异常 (Eu/Eu*=0.14−0.25) 反映了极端的岩浆分馏以及晚期流体-岩石相互作用的影响。ARC 的所有 A 型岩石都保留了 Nb-Ta 正异常，该异常从早期阶段增加到最进化的碱性/过碱性花岗岩。他们定义了地球化学特征，反映了它们源自相同的岩浆源，这些岩浆源是通过带有地壳污染的分步结晶演化而来的。ARC A型花岗岩的地球化学特征反映了先前形成的弧形物质的重熔。镁铁质微粒包体代表源自地壳或地壳较深部分的变质岩，代表部分熔融产生花岗质岩浆的烃源岩。ARC 岩浆活动的早期阶段代表了碰撞后阶段下地壳或中地壳源的部分熔融产生的熔体，这些熔体分馏成各种花岗岩。ARC 晚期没有镁铁质捕虏体，表明晚期没有地壳源对岩浆生成的贡献。