Geothermobarometry of metapelites of southwest · PDF fileGeothermobarometry of metapelites of...

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Geothermobarometry of metapelites of southwest Mahneshan, using multiple equilibria curves and THERMOCALC program A. Saki, M. Moazzen, M. Moayyed Department of Geology, University of Tabriz, Tabriz, 51664, Iran Email: [email protected] Abstract: Pressure and temperature of metamorphism in the Mahneshan area were estimated in order to determine the type of metamorphism and tectonic setting of the rocks. Biotite, muscovite, plagioclase, garnet, quartz, andalusite and staurolite minerals are crystallized together in metapelites in the regional metamorphic rocks of southwest Mahneshan. Chemistry of coexisting minerals is studied using microprobe analysis. Using multiple equilibria calculations and THERMOCALC program, temperatures of ~520°C and pressure of ~3 kbar have been calculated for the formation of these rocks. Using these data, geothermal gradient of 60 °C/km has been calculated for the upper crust of the Mahneshan. Based on calculated geothermal gradient, the Buchan type metamorphism is suggested for the metamorphic rocks of southwest Mahneshan. Keywords: Geothermobarometry, metapelites, Buchan type, multiple equilibria, Mahneshan, THERMOCALC. Vol. 12, No. 2, 1383/2004 Fall & Winter (Received: 19/02/2004, received in revised form: 05/08/2004)

Transcript of Geothermobarometry of metapelites of southwest · PDF fileGeothermobarometry of metapelites of...

Geothermobarometry of metapelites of southwest Mahneshan, using multiple equilibria curves and

THERMOCALC program

A. Saki, M. Moazzen, M. Moayyed

Department of Geology, University of Tabriz, Tabriz, 51664, Iran Email: [email protected]

Abstract: Pressure and temperature of metamorphism in the Mahneshan

area were estimated in order to determine the type of metamorphism and

tectonic setting of the rocks. Biotite, muscovite, plagioclase, garnet, quartz,

andalusite and staurolite minerals are crystallized together in metapelites in

the regional metamorphic rocks of southwest Mahneshan. Chemistry of

coexisting minerals is studied using microprobe analysis. Using multiple

equilibria calculations and THERMOCALC program, temperatures of

~520°C and pressure of ~3 kbar have been calculated for the formation of

these rocks. Using these data, geothermal gradient of 60 °C/km has been

calculated for the upper crust of the Mahneshan. Based on calculated

geothermal gradient, the Buchan type metamorphism is suggested for the

metamorphic rocks of southwest Mahneshan.

Keywords: Geothermobarometry, metapelites, Buchan type, multiple

equilibria, Mahneshan, THERMOCALC.

Vol. 12, No. 2, 1383/2004 Fall & Winter

(Received: 19/02/2004, received in revised form: 05/08/2004)

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[8] Bucher K., Frey M., "Petrogenesis of metamorphic rocks", Springer Verlag (1994) p. 318. [9] Spear F.S., "Metamorphic phase equilibria and pressure-temperature time paths", Mineralogical Society of America. Monograph. (1993) p. 799. [10] Rios C., Garcia C., Takaus A. "Tectono-metamorphic evolution of the Silgara Formation metamorphic rocks in the southern Santander Massif, Colombian Andes", Journal of south American Earth sciences 16(2) (2003) 133-154. [11] Graeβner T., Schenk V., "Low-pressure metamorphism of Palaeozoic pelites in the Aspromonte, southern Calabria: constraints for the thermal evolution in the Calabrian crustal cross-section during the Hercynian orogeny", Journal of Metamorphic Geology 17 (1999) 157-172. [12] Holland T.J.B., Powell R., "An internally consistent thermodynamic data set for phases of petrological intrest", Journal of Metamorphic. Geology 16 (1998) 309-343. [13] Patino-Douce A.E., Johnston A.D., Rice J.M., "Octahedral excess mixing properties in biotite: a working model with application to geobarometry and geothermometry", American Mineralogist 78 (1993) 113-131.[14] Blümel P., Schreyer W., "Progressive regional low pressure metamorphism in Moldanubian metapelites of the Northern Bavarian Forest, Germany", Krystalinikum 12 (1976) 7-30. [15] Wagener-Lohse C., Blümel P., "Prograde metamorphose vom Niederdruck-Typ in der Grenzzone Saxothuringikum/Moldanubikum E’Tirschenereuth/NE-Bayern", Beiheft zu Fortschritte der Mineralogie 62 (1984) 254-255. [16] Miyashiro A., "Metamorphism and Metamorphic Belts", George Allen and Unwin Ltd., London (1973). [17] Hudson N.F.C., "Regional metamorphism of some Dalradian pelites in the Buchan area, N.E. Scotland", Contributions to Mineralogy and Petrology 73 (1980) 39-51.

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DJ Sanderson (eds) Variscan Tectonics of the North Atlantic Regional (Geol. Soc. London. Spes. Publ. no.14)", Blackwell Scientific, Oxford (1984) pp. 3-22.[20] Barton M.D., Hanson R.B., "Magmatism and the development of low-pressure metamorphism: Implications from thermal modelling at the western United States", Geol. Soc. Amer. Bull. 101 (1989) 1051- 1065. [21] De Yoreo J.J., Lux D.R., Guidotti C.V., "Thermal modelling in low-pressure/high-temperature metamorphic belts", Tectonophysics 188 (1991) 209-238. [22] Moazzen M., Droop G.T.R., Saki A., "Low pressure regional metamorphism in the Mahneshan area, Western Iran", Geophysical Research Abstracts 5 (2003) 1254.

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