مقایسه نتایج دما-فشارسنجی دگرگونی با استفاده از ترموکالک و تریاک دومینو جهت مطالعه هورنفلس های کالک-سیلیکات منطقه چشین، همدان

منطقه مورد بررسی در اطراف روستای چشین و جنوب همدان واقع‌ شده است. هورنفلس‌های کالک-سیلیکات در نتیجه نفوذ باتولیت الوند در سنگ میزبان آهکی تشکیل‌شده است. این پژوهش با هدف مقایسه نتایج دما فشارسنجی حاصل از دو نرم‌افزار تریاک دومینو و ترموکالک انجام‌شده است. داده ‌های مورد‌ استفاده در نرم ‌افزار تریاک دومینو شیمی‌کل سنگ است که به‌وسیله آن به بررسی روابط فازی به‌روش شبه مقاطع پرداخته‌شده است و فشار دگرگونی برای هورنفلس‌های کالک سیلیکات مورد بررسی تخمین‌زده شده است. با استفاده از نرم‌افزار ترموکالک نیز تعادلات ترمودینامیکی کانی ‌ها و واکنش ‌های تعادلی چندگانه بررسی و فشار و دمای دگرگونی محاسبه‌شده است. مدل‌سازی انجام‌شده با استفاده از این دو نرم‌افزار، ضمن تایید یکدیگر، دما را در حدود 500 تا 550 درجه سانتی ‌گراد و فشار را در حدود 2.5 تا 3.5 کیلوبار نشان می ‌دهد. دما و فشار دگرگونی بر اساس کسر مولی کلسیم و منیزیم برای گارنت و کلینوپیروکسن، دمای محاسبه‌شده را تایید می‌کند.

Comparison of the ThermometeryBarometery methods by using Thermocalc and Theriakdomino to study Calc silicate Hornfelses in Cheshin, Hamedan

Introduction;The pseudosection method, first proposed by Hensen (1971), is used today by scientists to determine the thermodynamic conditions of mineral crystallization and modeling in metamorphic lithology (Hoschek, 2004; Omrani et al., 2013). The principle of this method is based on the fact that in order to have a complete chemistry of a rock sample with certain minerals in equilibrium, only one equilibrium pressure and temperature can be considered. However, the whole rock chemistry is fixed, mineral changes show some changes in temperature and pressure and new thermodynamic conditions. The superiority of using the pseudosection method of temperature and pressure calculation is knowing the composition of minerals (microprobe data). By knowing the whole chemistry of the rock and the type of minerals found in the rock, the range of temperature and the pressure of rock formation can be determined. However, possession of mineral chemistry data and microprobe data can help us in more advanced computing and modeling. Accessing the whole rock 's chemistry data is easier and calculating the temperature and pressure by pseudosection methods has high capabilities (Moazzen et al., 2015). This paper investigates the results of this method for calcsilicate hornfelses of the Cheshne area of Hamedan. In this study, the theriakdomino program and the thermodynamic data database of minerals (Powell and Holland, 1988) have been used. In this research study, we tried to determine the temperature and the pressure for the studied rocks by using the two software: Thermocalc and Theriakdomino. Furthermore, the zoning of garnet and clinopyroxene have been studied by the pseudosection method.;  ;Materials and methods ;After a careful examination of the area, a number of samples were taken. Sampling was done based on the collection of the best samples that represent the whole of the studied rocks. After the preparation of thin sections of suitable samples, according to the objective of the study, three samples of calcsilicate hornfels of Hamedan area were selected for chemical decomposition of the main elements. During the sampling, samples were taken from fresh and nonrough sections of the rock and were selected such as to represent the actual changes in their chemical composition and mineralogy. These samples were sent to Kanpajoh for analysis. The main elements were analyzed by the Xray fluorescence (XRF) method. In addition, it should be noted that the data from chemical minerals, which was presented in the article by Ghorbani et al. (2016)+, was used in this study (Ghorbani et al., 2016).;  ;Results;The major oxidative disintegrations in three samples of calcsilicate hornfelses show that the most abundant oxide in these samples is SiO2, which averages about 45.04. Decreasing calcium in the Grossular garnets can indicate a decrease in pressure. In fact, by describing the garnet in calcsilicate rocks in the Hamedan area, a prograde metamorphism has been created that has reduced the amount of this element after decreasing the temperature and pressure due to the retrograde metamorphism and the uplift and removal of pressure of the upper floors and the influence of the fluids. The combined variations of the garnets are in the Grossular range.   The Garnets are the ultimate members of the Pyrope, the Almandine and the Spessartine poor (Ghorbani et al., 2016). The combination of clinopyroxenes in the EnWoFs graph shows that most of the analyzed points are located within the diopside (Ghorbani et al., 2016).;  ;Discussion;We supposed that all solid solution minerals were pure final members, and unit activity for solid solution phases (such as diopside and garnet) and pure phases (such as quartz). Then, the equilibrium reactions at 3.3 kb pressure were calculated by the Thermocalc software and plotted on PT charts. The calculated temperature for the garnet and clinopyroxene minerals was calculated to be about 550 ° C and the calculated pressure was 2.5 to 3.5 kb. In this paper, using the whole rock chemistry and minerals chemistry, the method of calculating the temperature and pressure was applied to the pseudosection method. For this purpose, the percentage of the main oxides was calculated as the molar percentage of the elements, then molar percentage of the elements was used as input for the Theriakdomino program. The pressure and temperature calculated by the Theriakdomino software package are from 2.5 to 3.5 kb and 500 to 550 degrees C, respectively.;References;Ghorbani, H., Moazzen, M. and Saki, A., 2016. Investigate the Mineral Chemistry and PT Estimation of Formation of Diopside, Garnet and Coexisting Minerals in the Calc silicate Hornfelses from the Alvand Metamorphic Aureole, Hamadan, West of Iran. Journal of Earth Science, 26(101): 139–146. (in Persian with English abstract);Hensen, B.J., 1971. Theoretical phase relations involving cordierite and garnet in the system MgOFeO Al2O3SiO2. Contributions to Mineralogy and Petrology, 33(3): 191–214.;Hoschek, G., 2004. Comparison of calculated PT pseudosections for a kyanite eclogite from the Tauern Window, Eastern Alps, Austria. European Journal of Mineralogy, 16(1): 59–72.;Moazzen, M., Torabi Asl, S. and Omrani, H., 2015. Temperature and pressure of metamorphism, phase stability and chemical zoning in garnet and biotite of metamorphic rocks of Jandag region using quasisectional method. Iranian Journal of Crystallography and Mineralogy, 23(4): 651–660. (in Persian with English abstract);Omrani, H., Moazzen, M., Oberhänsli, R., Tsujimori, T., Bousquet, R. and Moayyed, M., 2013. Metamorphic history of glaucophaneparagonitezoisite eclogites from the Shanderman area, northern Iran. Journal of Metamorphic Geology, 31(8): 791–812.;Powell, R. and Holland, T.J.B., 1988. An internally consistent thermodynamic dataset with uncertainties and correlations. III. Application methods, worked examples and a computer program. Journal of Metamorphic Geology, 6(2): 173–204.