Abstract Mesozoic ortho-amphibolites exposed in the SE Sanandaj-Sirjan metamorphic belt (Bahram-e-Gur area, south-central Iran), record medium to high-grade metamorphism. Based on mineral assemblages, three lithological types of amphibolites have been defined: plagioclase amphibolite, epidote amphibolite, and biotite amphibolite. Metamorphic geothermobarometry reveals temperatures of 548−710 °C at 3–6 kbar, corresponding to a geothermal gradient of ca. ∼28 °C/ km, for the peak metamorphism. 40Ar/39Ar stepwise heating analyses, performed on amphibole separates revealed a well-defined isochron with a cooling age of 169.35 ± 14.77 Ma and a plateau cooling age of 162.54 ± 1.97 Ma (Upper Jurassic). The protoliths of the studied amphibolites were basalts, which were formed in an active continental margin tectonic setting, due to an extensional regime, brought about by a probable steep slab subduction. The magma affected by crustal component, acquired calc-alkalic characteristics. The rocks were metamorphosed in a compressional event due to flat subduction following a steep slab subduction. The age of metamorphism was pre-Middle Jurassic (older than ca. 162 Ma). Similar age metamorphic and magmatic events in the Sanandaj-Sirjan zone indicate that peak metamorphism and magmatic cooling were chronologically close. The studied rocks are related to Jurassic compression at the southwest active continental margin of the Central Iranian microcontinent and early Cimmerian deformation and metamorphism in the southeast Sanandaj-Sirjan zone.

中文翻译：

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伊朗 Sanandaj-Sirjan 带 Sirjan 地区角闪岩的地球化学和年代学：阿拉伯和欧亚大陆碰撞前的侏罗纪变质作用

摘要 出露在 SE Sanandaj-Sirjan 变质带（Bahram-e-Gur 地区，伊朗中南部）的中生代正角闪岩记录了中至高级变质作用。根据矿物组合，已经定义了三种岩性类型的角闪石：斜长石角闪石、绿帘石角闪石和黑云母角闪石。变质地温气压测量法显示 3-6 kbar 时的温度为 548-710 °C，对应于约 1 的地温梯度。～28 °C/km，对于峰值变质作用。对闪石分离物进行的 40Ar/39Ar 逐步加热分析揭示了一个明确的等时线，冷却年龄为 169.35 ± 14.77 Ma，高原冷却年龄为 162.54 ± 1.97 Ma（上侏罗纪）。所研究角闪岩的原岩是玄武岩，由于伸展制度，它们形成于活跃的大陆边缘构造环境中，可能是由陡峭的板块俯冲引起的。岩浆受地壳成分影响，具有钙碱性特征。由于在陡峭的板片俯冲之后平坦俯冲，岩石在挤压事件中变质。变质作用的时代是早于中侏罗世（早于约 162 Ma）。Sanandaj-Sirjan 带类似时代变质和岩浆事件表明峰值变质作用和岩浆冷却在年代上接近。研究的岩石与伊朗中部微大陆西南活动大陆边缘的侏罗纪压缩和东南萨南达吉-锡尔詹地区的早期辛梅里期变形和变质作用有关。由于在陡峭的板片俯冲之后平坦俯冲，岩石在挤压事件中变质。变质作用的时代是早于中侏罗世（早于约 162 Ma）。Sanandaj-Sirjan 带类似时代变质和岩浆事件表明峰值变质作用和岩浆冷却在年代上接近。研究的岩石与伊朗中部微大陆西南活动大陆边缘的侏罗纪压缩和东南萨南达吉-锡尔詹地区的早期辛梅里期变形和变质作用有关。由于在陡峭的板片俯冲之后平坦俯冲，岩石在挤压事件中变质。变质作用的时代是早于中侏罗世（早于约 162 Ma）。Sanandaj-Sirjan 带类似时代变质和岩浆事件表明峰值变质作用和岩浆冷却在年代上接近。研究的岩石与伊朗中部微大陆西南活动大陆边缘的侏罗纪压缩和东南萨南达吉-锡尔詹地区的早期辛梅里期变形和变质作用有关。