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The Petrological and Geochemical Evolution of Ediacaran Rare‐Metal Bearing A‐type Granites from the Jabal Aja Complex, Northern Arabian Shield, Saudi Arabia
Acta Geologica Sinica-English Edition ( IF 3.5 ) Pub Date : 2020-06-26 , DOI: 10.1111/1755-6724.13825 Shehta E. ABDALLAH 1 , Mokhles K. AZER 2 , Abdullah S. AL SHAMMARI 3
Acta Geologica Sinica-English Edition ( IF 3.5 ) Pub Date : 2020-06-26 , DOI: 10.1111/1755-6724.13825 Shehta E. ABDALLAH 1 , Mokhles K. AZER 2 , Abdullah S. AL SHAMMARI 3
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New fieldwork, mineralogical and geochemical data and interpretations are presented for the rare‐metal bearing A‐type granites of the Aja intrusive complex (AIC) in the northern segment of the Arabian Shield. This complex is characterized by discontinuous ring‐shaped outcrops cut by later faulting. The A‐type rocks of the AIC are late Neoproterozoic post‐collisional granites, including alkali feldspar granite, alkaline granite and peralkaline granite. They represent the outer zones of the AIC, surrounding a core of older rocks including monzogranite, syenogranite and granophyre granite. The sharp contacts between A‐type granites of the outer zone and the different granitic rocks of the inner zone suggest that the AIC was emplaced as different phases over a time interval, following complete crystallization of earlier batches. The A‐type granites represent the late intrusive phases of the AIC, which were emplaced during tectonic extension, as shown by the emplacement of dykes synchronous with the granite emplacement and the presence of cataclastic features. The A‐type granites consist of K‐feldspars, quartz, albite, amphiboles and sodic pyroxene with a wide variety of accessory minerals, including Fe‐Ti oxides, zircon, allanite, fluorite, monazite, titanite, apatite, columbite, xenotime and epidote. They are highly evolved (71.3–75.8 wt% SiO2) and display the typical geochemical characteristics of post‐collisional, within‐plate granites. They are rare‐metal granites enriched in total alkalis, Nb, Zr, Y, Ga, Ta, REE with low CaO, MgO, Ba, and Sr. Eu‐negative anomalies (Eu/Eu* = 0.17–0.37) of the A‐type granites reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interactions. The chemical characteristics indicate that the A‐type granites of the AIC represent products of extreme fractional crystallization involving alkali feldspar, quartz and, to a lesser extent, ferromagnesian minerals. The parent magma was derived from the partial melting of a juvenile crustal protolith with a mantle contribution. Accumulation of residual volatile‐rich melt and exsolved fluids in the late stage of the magma evolution produced pegmatite and quartz veins that cut the peripheries of the AIC. Post‐magmatic alteration related to the final stages of the evolution of the A‐type granitic magma, indicated by alterations of sodic amphibole and sodic pyroxene, hematitization and partial albitization.
中文翻译：
沙特阿拉伯北部盾构Jabal Aja矿区Ediacaran稀有金属A型花岗岩的岩石学和地球化学演化
给出了阿拉伯盾北段Aja侵入带（AIC）的稀有金属的A型花岗岩的新的野外工作，矿物学和地球化学数据和解释。这种复合体的特征是后来断层将不连续的环状露头切开。AIC的A型岩石是新元古代晚期碰撞后的花岗岩，包括碱长石花岗岩，碱花岗岩和碱土花岗岩。它们代表了AIC的外部区域，围绕着一些较老的岩心，包括单长花岗岩，正花岗岩和花岗石花岗岩。外部区域的A型花岗岩与内部区域的不同花岗岩岩石之间的尖锐接触表明，在早期批料完全结晶之后，AIC在一定的时间间隔内以不同相的形式存在。A型花岗岩代表了AIC的晚期侵入相，其在构造伸展过程中就位了，如与花岗岩位相同步的堤坝位和碎裂特征的存在所表明。A型花岗岩由钾长石，石英，钠长石，闪石和钠辉石组成，还含有多种辅助矿物，包括铁钛氧化物，锆石，尿石，萤石，独居石，钛矿，磷灰石，哥伦比，异诺时间和埃皮多。它们高度演化（71.3–75.8 wt％SiO 闪石和苏打辉石以及各种辅助矿物，包括Fe-Ti氧化物，锆石，滑石，萤石，独居石，钛矿，磷灰石，co石，异诺时间和埃迪波德。它们高度演化（71.3–75.8 wt％SiO 闪石和苏打辉石以及各种辅助矿物，包括Fe-Ti氧化物，锆石，滑石，萤石，独居石，钛矿，磷灰石，co石，异诺时间和埃迪波德。它们高度演化（71.3–75.8 wt％SiO2）并显示板后花岗岩内部碰撞后的典型地球化学特征。它们是富含总碱，Nb，Zr，Y，Ga，Ta，REE的稀有金属花岗岩，CaO，MgO，Ba和Sr均为Eu负异常（Eu / Eu *= 0.17–0.37）的A型花岗岩反映了岩浆的极端分馏，可能反映了后期流体-岩石相互作用的影响。化学特征表明，AIC的A型花岗岩代表了极端分步结晶的产物，涉及碱性长石，石英以及较小程度的铁锰矿。母岩浆来自具有地幔贡献的幼年地壳原石的部分熔融。在岩浆演化的后期，残留的富含挥发性的熔体和溶解的流体的积累产生了伟晶岩和石英脉，从而切割了AIC的外围。岩浆后蚀变与A型花岗岩岩浆演化的最后阶段有关，其特征是苏打闪石和苏打辉石的变质，血化和部分位化。
更新日期：2020-06-26
中文翻译：
沙特阿拉伯北部盾构Jabal Aja矿区Ediacaran稀有金属A型花岗岩的岩石学和地球化学演化
给出了阿拉伯盾北段Aja侵入带（AIC）的稀有金属的A型花岗岩的新的野外工作，矿物学和地球化学数据和解释。这种复合体的特征是后来断层将不连续的环状露头切开。AIC的A型岩石是新元古代晚期碰撞后的花岗岩，包括碱长石花岗岩，碱花岗岩和碱土花岗岩。它们代表了AIC的外部区域，围绕着一些较老的岩心，包括单长花岗岩，正花岗岩和花岗石花岗岩。外部区域的A型花岗岩与内部区域的不同花岗岩岩石之间的尖锐接触表明，在早期批料完全结晶之后，AIC在一定的时间间隔内以不同相的形式存在。A型花岗岩代表了AIC的晚期侵入相，其在构造伸展过程中就位了，如与花岗岩位相同步的堤坝位和碎裂特征的存在所表明。A型花岗岩由钾长石，石英，钠长石，闪石和钠辉石组成，还含有多种辅助矿物，包括铁钛氧化物，锆石，尿石，萤石，独居石，钛矿，磷灰石，哥伦比，异诺时间和埃皮多。它们高度演化（71.3–75.8 wt％SiO 闪石和苏打辉石以及各种辅助矿物，包括Fe-Ti氧化物，锆石，滑石，萤石，独居石，钛矿，磷灰石，co石，异诺时间和埃迪波德。它们高度演化（71.3–75.8 wt％SiO 闪石和苏打辉石以及各种辅助矿物，包括Fe-Ti氧化物，锆石，滑石，萤石，独居石，钛矿，磷灰石，co石，异诺时间和埃迪波德。它们高度演化（71.3–75.8 wt％SiO2）并显示板后花岗岩内部碰撞后的典型地球化学特征。它们是富含总碱，Nb，Zr，Y，Ga，Ta，REE的稀有金属花岗岩，CaO，MgO，Ba和Sr均为Eu负异常（Eu / Eu *= 0.17–0.37）的A型花岗岩反映了岩浆的极端分馏，可能反映了后期流体-岩石相互作用的影响。化学特征表明，AIC的A型花岗岩代表了极端分步结晶的产物，涉及碱性长石，石英以及较小程度的铁锰矿。母岩浆来自具有地幔贡献的幼年地壳原石的部分熔融。在岩浆演化的后期，残留的富含挥发性的熔体和溶解的流体的积累产生了伟晶岩和石英脉，从而切割了AIC的外围。岩浆后蚀变与A型花岗岩岩浆演化的最后阶段有关，其特征是苏打闪石和苏打辉石的变质，血化和部分位化。
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