R Samadi; H Mirnejad; A.A Baharifar; S.J Sheikh Zakariaee
Abstract
The fibrolite garnet staurolite mica schist and staurolite garnet mica schist cropped out around the northwest of Khalaj, south of Mashhad in a SE_NW direction along the metamorphic complex of Kuh-e-Majuni. They have similar mineralogy and consist of quartz, annite, staurolite, almandine, muscovite, ...
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The fibrolite garnet staurolite mica schist and staurolite garnet mica schist cropped out around the northwest of Khalaj, south of Mashhad in a SE_NW direction along the metamorphic complex of Kuh-e-Majuni. They have similar mineralogy and consist of quartz, annite, staurolite, almandine, muscovite, zircon, and ilmenite; however, fibrolite in fibrolite garnet staurolite mica schist, and chlorite and tourmaline in the staurolite garnet mica schist are additionally found. Application of garnet - biotite thermometry and GBMAQ barometry indicates the temperatures and pressures of 560 and 605 °C / 3.5 and 5 kilobar for fibrolite garnet staurolite mica schist and temperatures of 489 and 547 °C (in 3.5 to 5 kilobar) for the staurolite garnet mica schist. Pressure and temperature increasing during the garnet growth indicates the effect of regional and contact thermal metamorphism on these rocks. Based on mineral paragenesis in KFMASH system, the metamorphic degree of regional metamorphism was about lower amphibolite (in staurolite garnet mica schist) to middle amphibolite facies (in fibrolite garnet staurolite mica schist). Meanwhile, intrusion of the Khalaj granitoid and its thermal diffusion raised the metamorphic temperature up to lower amphibolite facies (in staurolite garnet mica schist) and middle amphibolite facies (in fibrolite garnet staurolite mica schist), and consequently, this caused the fibrolite formation in the sample close to the pluton (i.e. fibrolite garnet staurolite mica schist).
A. A. Baharifar
Abstract
Chloritoid as one of the common metamorphic mineral in low to medium grade metapelites, is absent in metapelitic rocks of Hamedan area. Comparing with geochemical limitations for Chloritoid appearance in metapelites, whole rock composition of the area is suitable for Chloritoid formation. Since P, T ...
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Chloritoid as one of the common metamorphic mineral in low to medium grade metapelites, is absent in metapelitic rocks of Hamedan area. Comparing with geochemical limitations for Chloritoid appearance in metapelites, whole rock composition of the area is suitable for Chloritoid formation. Since P, T and X are in appropriate range for Chloritoid, the role of fluid could be important. Microscopic investigations show that all metapelitic rocks are in equilibrium with graphite and fluid composition is combination of CO2 and H2O. Based on estimated P and T, highest portion of H2O in the fluid, could be 0.9. Although this is highest approximation, it can conclude that for Chloritoid appearance, XH2O in fluid must be more than 0.9. Since in the Hamedan area staurolite is widespread and Chloritoid is absent - considering almost same composition between chloritoid and staurolite - the composition of fluid is more important. There are many doubts in geochemical limitations for Chloritoid appearance. Considering the results of this study and in the case of attention to fluid composition, geochemical limitations will change and Chloritoid could appear in many rocks, as its higher temperature equivalent, staurolite.
A. Saki; M. Moazzen; M. Modjtahedi; R. Oberhänsli
Abstract
Mahneshan Complex in the northwest of Iran was affected by regional and contact metamorphism. Microstructural and petrographical features as well as field relations show that Mahneshan Metamorphic Complex has been affected by four episodes of metamorphism (M1 to M4) and at least two ...
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Mahneshan Complex in the northwest of Iran was affected by regional and contact metamorphism. Microstructural and petrographical features as well as field relations show that Mahneshan Metamorphic Complex has been affected by four episodes of metamorphism (M1 to M4) and at least two deformational phases (D1 and D2). The M2 metamorphic stage is characterized by a strong preferential orientation of minerals (S2) and development of a peak metamorphic assemblage. This metamorphismis temporally associated with D2 deformational phase. The M3 metamorphism was contact metamorphism and M4 metamorphism is retrograde. The mineral assemblages of peak metamorphism M2 are muscovite, biotite, garnet, staurolite, andalusite and sillimanite. Pressure and temperature of metamorphism in the Mahneshan Complex were estimated by multiple equilibria calculations, cation exchange reaction thermometry and net transfer reaction in order to determine the geothermal gradients and type of metamorphism. The temperature of M1 metamorphism is estimated 420-450ºC and pressure of 3-4 kbar. M2 (peak metamorphism) temperature is 600-620ºC and pressure of 5-7 kbar. The temperature of M3 metamorphism is 520-560 ºC and pressure of 2.-3.5 kbar. The Geothermal gradients for the peak of metamorphism show high value for the upper crust (33° C/ km) indicating a Barrovian type of metamorphism for the study area. Tectonic setting of metamorphism is related to continental crust and magmatic arc.
