Origin and Petrogenetic Implications of Spessartine Garnet in Highly‐Fractionated Granite from the Central Eastern Desert of Egypt,Acta Geologica Sinica-English Edition

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Origin and Petrogenetic Implications of Spessartine Garnet in Highly‐Fractionated Granite from the Central Eastern Desert of Egypt
Acta Geologica Sinica-English Edition ( IF 3.5 ) Pub Date : 2020-06-26 , DOI: 10.1111/1755-6724.13883
Mabrouk SAMI _{1,

2} , Theodoros NTAFLOS ₂ , Haroun A. MOHAMED ₁ , Esam S. FARAHAT ₁ , Christoph HAUZENBERGER ₃ , Nasser M. MAHDY ₄ , Khaled M. ABDELFADIL ₅ , Douaa FATHY ₁

Affiliation

A highly‐fractionated garnet‐bearing muscovite granite represents the marginal granitic facies of the Abu‐Diab multiphase pluton in the Central Eastern Desert of Egypt. New electron microprobe analyses (EMPA) and laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) data from garnets are reported, in order to constrain their origin and genesis. Garnet in the Abu‐Diab host granite is euhedral to subhedral, generally homogeneous and, in rare cases, it shows weak zonation. The garnet contains appreciable amounts of MnO and FeO, with lesser amounts of MgO and CaO, yielding an end‐member formula of Sps_61–72Alm_25–35Prp_1–4Adr_0–1. Moreover, it is depleted in large ion lithophile elements (LILE) with lower values of Ba, Nb and Sr relative to the primitive mantle. Additionally, it contains high concentrations of HREE and Y and their REE pattern shows strong negative Eu anomalies. The garnet was crystallized under relatively low temperature (646°C–591°C) and pressure (< 3 kbar) conditions. The textural and chemical features indicate that the garnet is magmatic in origin and is chemically similar to that from highly‐fractionated A‐type granite. It was probably formed at the expense of biotite in a highly‐evolved MnO‐rich magma and/or by hydroxyl complexing of Mn during the ascending fluid phases.

中文翻译：

埃及中部东部沙漠中高度分馏的花岗岩中斯佩莎汀石榴石的成因及岩石成因意义

含石榴石的高分馏白云母花岗岩代表了埃及中部东部沙漠中阿布迪亚多相岩体的边缘花岗岩相。报告了石榴石的新电子微探针分析（EMPA）和激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）数据，以限制其起源和成因。Abu-Diab宿主花岗岩中的石榴石是从正面到背面的，通常是均质的，在极少数情况下，其带状分布较弱。石榴石中含有大量的MnO和FeO，而MgO和CaO的含量较少，最终的分子式为Sps _61–72 Alm _25–35 Prp _1–4 Adr _0–1。此外，相对于原始地幔，它被贫化了具有较低Ba，Nb和Sr值的大型离子亲石元素（LILE）。此外，它含有高浓度的HREE和Y，并且其REE模式显示出强烈的Eu负异常。石榴石在相对较低的温度（646°C–591°C）和压力（<3 kbar）的条件下结晶。质地和化学特征表明，石榴石起源于岩浆，化学性质与高度分离的A型花岗岩相似。它可能是在高度演化的富含MnO的岩浆中以黑云母为代价而形成的，和/或是在上升的液相中通过Mn的羟基络合而形成的。

更新日期：2020-06-26

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