Abstract

Metapelitic migmatites in the Hamedan area of Sanandaj–Sirjan Zone, Iran, contain spinel + gedrite + cordierite (± biotite, ± staurolite, ± ilmenite) symplectite, replacing andalusite in metatexite and diatexite. P-T conditions of metamorphism for cordierite-hornfels, andalusite-cordierite-hornfels and migmatites were estimated as 600°C, 2.2 kbar; 645°C, 2.9 kbar and 760°C, 3.7 kbar respectively, using calculated pseudosections for an average composition in the NCKFMASH system. Calculated pseudosection is in accordance with field and petrographic observation, except that symplectite minerals does not appear in the model, suggesting that formation of symplectite was affected by effective bulk compositions (EBC), rather than whole-rock composition. So EBC model was calculated using modal abundance and average composition of symplectite minerals. In pseudosection calculated for EBC, spinel + gedrite + cordierite is stable over wide range of P and T. Peak metamorphic condition for symplectites are estimated as 750°C at 4.1 kbar. Staurolite-bearing symplectites appeared during retrograde isobaric path at 600°C and 4.1 kbar. Based on calculated pseudosections and estimated P and T, an isobaric retrograde anticlockwise P-T path is proposed for the Sarabi migmatites. Metamorphism and migmatization in the area is linked to the major plutonism phases of the Sanandaj–Sirjan Zone in Middle-Jurassic under high T-low P conditions, during the evolution of Neo-Tethys.

中文翻译：

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伊朗Sanandaj–Sirjan地区Sarabi地区Sarabi地区的芒格岩中尖晶石-堇青石-堇青石共沸石的岩石学

摘要

伊朗Sanandaj–Sirjan地区Hamedan地区的成岩成岩的辉石岩含有尖晶石+闪铁矿+堇青石（±黑云母，±星形陨石，±钛铁矿）共沸石，取代了变质岩和绿岩中的红柱石。PT堇青石-角铁，红柱石-堇青石-角铁和蒙脱石的变质条件估计为600°C，2.2 kbar；对于NCKFMASH系统中的平均成分，使用计算出的伪截面分别计算出645°C，2.9 kbar和760°C，3.7 kbar。计算的假断面与野外和岩石学观察一致，只是该模型中未出现闪锌矿矿物，这表明该闪锌矿的形成受有效散装成分（EBC）的影响，而不是整个岩石成分的影响。因此，使用模态丰度和球墨石矿物的平均组成来计算EBC模型。在为EBC计算的假断面中，尖晶石+菱铁矿+堇青石在宽的P和T范围内都稳定。在4.1 kbar的条件下，对折页岩的峰值变质条件估计为750°C。在600°C和4.1 kbar的逆向等压路径中，出现了含恒沸石的共沸物。基于计算的伪截面和估计的P和T，为撒拉米米非铁矿提出了等压逆时针逆时针PT路径。在新特提斯的演化过程中，该地区的变质作用和迁移作用与侏罗纪中南桑达尼－西尔詹地区的主要岩体阶段有关，在高T低P条件下。