Geochemistry and mineralogy of the Jebel Aja Igneous Intrusion and the associated exotic pegmatites, Arabian Shield, Saudi Arabia
Geochemistry and mineralogy of the Jebel Aja Igneous Intrusion and the associated exotic pegmatites, Arabian Shield, Saudi Arabia
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沙特阿拉伯阿拉伯地盾阿贾山火成岩和相关的奇异伟晶岩的地球化学和矿物学
DOI：
10.1016/j.lithos.2021.106395
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发表时间：
2021
期刊：
影响因子：
3.5
通讯作者：
Hakeem, Alaa Y.
中科院分区：
文献类型：
--
作者：
Gahlan, Hisham A.;Asimow, Paul D.;Azer, Mokhles K.;Ma, Chi;Al-Kahtany, Khaled M.;Hakeem, Alaa Y.
我们描述了Jebel Aja火成岩侵入（JAII），它位于沙特阿拉伯裸露的阿拉伯盾的最远东北边缘。JAII由晚新元古代后碰撞a型花岗岩组成，形成于构造伸展时期。它是一个由花岗质岩心（二长花岗岩、正长花岗岩和碱长石花岗岩）和后期碱性和过碱性花岗岩组成的复合岩体。伟晶岩在碱性/过碱性花岗岩与正长花岗岩的接触处形成袋状和脉状。伟晶岩与它们的寄主花岗岩有明显的接触，呈现出不同的颜色（主要是粉红色和白色）、粒度、质地和矿物组成。我们在此报告了白色伟晶岩的矿物学特征，包括在整个阿拉伯盾中首次观察到的辉石岩、钍云母岩和海杂石-(Y)，以及一种新颖的（Sc， Y，空位）富辉石岩和一种富含空位的富八面体Si的铜质岩。辉石锰矿为主的岩性还具有石英、钠长石、闪辉石、辉铬石、白云母和萤石等。辉石而非菱铁矿的存在，以及富空辉石和过量硅辉石，表明侵位压力升高。JAII花岗岩高度演化，经历了长石的极端分离结晶，导致残余熔体中挥发性和不相容元素的浓度增加，最终导致同时期伟晶岩注入到大部分凝固的寄主花岗岩中。JAII的正长花岗岩和碱性/过碱性花岗岩含钠角闪孔，具有板内含稀有金属a型岩石的地球化学特征。Nb-Ta正异常由正长花岗岩向碱性/过碱性花岗岩增加。粉晶岩矿化程度高，含有高浓度Nb （1540 ~ 1769 μg）、Ta （103 ~ 136 μg）、Y （1116 ~ 1616 μg）、Zr （6362 ~ 9707 μg）、Hf （215 ~ 264 μg）、Th （278 ~ 384 μg）、U （110 ~ 147 μg）和∑REE （2334 ~ 3251 μg）。
We describe the Jebel Aja igneous intrusion (JAII), which sits at the farthest northeastern edge of the exposed Arabian Shield in Saudi Arabia. The JAII consists of late Neoproterozoic post-collisional A-type granites, and was emplaced during tectonic extension. It is a composite pluton consisting of a granitic core (monzogranite, syenogranite and alkali feldspar granite) surrounded by a later phase of alkaline and peralkaline granites. Pegmatites occur as pockets and dykes at the contact between the alkaline/peralkaline granites and syenogranite. The pegmatites have sharp contacts with their host granites and show variable colors (principally pink and white), grain sizes, textures, and mineral compositions. We report here that the white pegmatites host pockets with a unique mineralogy that includes the first observation of pyroxmangite, thortveitite and thalénite-(Y) in the whole Arabian Shield as well as a novel (Sc, Y, vacancy)-rich pyroxenoid and a vacancy-rich bustamite with excess octahedral Si. The pyroxmangite-dominated lithology also features accessory quartz, albite, spessartine, pyrochroite, muscovite, and fluorite. The presence of pyroxmangite rather than rhodonite, together with vacancy-rich and Si-excess pyroxenes, suggests an elevated pressure of emplacement. The granites of the JAII are highly evolved and have undergone extreme fractional crystallization of feldspars, leading to increases in the concentration of volatile and incompatible elements in the residual melt, which resulted eventually in injection of coeval pegmatites into the mostly solidified host granite. The syenogranite and alkaline/peralkaline granite of the JAII contain sodic amphibole and have geochemical characteristics common among within-plate rare-metal bearing A-type rocks. They have positive Nb-Ta anomalies that increase from syenogranite to alkaline/peralkaline granite. The pink pegmatite is highly mineralized and contains high concentrations of Nb (1540–1769 μg/g), Ta (103–136 μg/g), Y (1116–1616 μg/g), Zr (6362–9707 μg/g), Hf (215–264 μg/g), Th (278–384 μg/g), U (110–147 μg/g), and ∑REE (2334–3251 μg/g).
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DOI：
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发表时间：
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期刊：
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