Pegmatites and associated granitoids are integral parts of the Alvand plutonic complex in the Sanandaj–Sirjan zone, Iran. Whole rock major- and trace-element lithogeochemistry together with zircon U–Pb geochronology and zircon geochemistry are examined to evaluate the petrogenesis of sapphire-bearing pegmatites and other peraluminous pegmatites in the region. Pegmatites vary in their chemical compositions from mostly peraluminous, high-K calc-alkaline to shoshonitic signatures. A rare variety of extremely peraluminous sapphire-bearing syenitoid pegmatite (Al2O3> 30 wt %; A/CNK > 2) exists. This silica-undersaturated pegmatite and its sapphire crystals have a primary igneous origin. U–Pb zircon geochronology of three separate samples from this pegmatite indicates the following ages: 168 ± 1 Ma, 166 ± 1 Ma and 164 ± 1 Ma. The zircon grains have notable amounts of Hf (up to 17 200 ppm), U (up to 13 580 ppm), Th (up to 5148 ppm), Y (up to 4764 ppm) and ∑REE (up to 2534 ppm). There is a positive correlation between Hf and Th, Nb and Ta, U and Th, and Y and HREE and a negative correlation between Hf and Y values in the zircons. These zircons exhibit pronounced positive Ce anomalies (Ce/Ce* = 1.15–68.06) and negative Eu anomalies (Eu/Eu* = 0.001–0.56), indicative of the relatively oxidized conditions of the parent magma. Ti-in-zircon thermometry reveals temperatures from as low as ~683 °C up to ~828 °C (average = 755° ± 73 °C). Zircon and monazite saturation equilibria are also consistent with these temperatures. Zircon grains are magmatic (average La < 1.5, (Sm/La)N> 100 and Th/U > 0.7), with chemical characteristics similar to zircons from continental crust.

中文翻译：

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伊朗Sanandaj-Sirjan 带Hamedan 地区罕见的含蓝宝石正长岩伟晶岩和相关花岗岩：岩石学、岩石地球化学和锆石年代学/微量元素地球化学分析

伟晶岩和相关的花岗岩是伊朗萨南达杰-西尔詹地区阿尔万德深成杂岩的组成部分。研究了全岩主量元素和微量元素岩石地球化学以及锆石 U-Pb 年代学和锆石地球化学，以评估该地区含蓝宝石伟晶岩和其他过铝伟晶岩的岩石成因。伟晶岩的化学成分各不相同，从主要是过铝质、高钾钙碱性到玄武岩特征。一种罕见的极其过铝的含蓝宝石正长晶伟晶岩（Al2○3> 30 重量％；A/CNK > 2) 存在。这种二氧化硅不饱和伟晶岩及其蓝宝石晶体具有原生火成岩成因。来自该伟晶岩的三个独立样品的 U-Pb 锆石年代学表明以下年龄：168 ± 1 Ma、166 ± 1 Ma 和 164 ± 1 Ma。锆石晶粒具有显着量的 Hf（高达 17 200 ppm）、U（高达 13 580 ppm）、Th（高达 5148 ppm）、Y（高达 4764 ppm）和 ∑REE（高达 2534 ppm）。锆石中 Hf 与 Th、Nb 与 Ta、U 与 Th、Y 与 HREE 呈正相关，Hf 与 Y 值呈负相关。这些锆石表现出明显的正Ce异常（Ce/Ce* = 1.15-68.06）和负Eu异常（Eu/Eu* = 0.001-0.56），表明母岩浆的相对氧化条件。Ti-in-zircon 测温仪显示的温度从低至 ~683 °C 到 ~828 °C（平均值 = 755° ± 73 °C）。锆石和独居石饱和平衡也与这些温度一致。锆石颗粒是岩浆的（平均 La < 1.5, (Sm/La)ñ> 100 和 Th/U > 0.7)，化学特征类似于大陆地壳的锆石。