The difference between metamorphic series in the metapelitic rocks of south and north of Alvand Batholith, Hamadan
Subject Areas :Keywords: Alvand Batholite Hamadan area multiple equilibrium reaction Barrow and Buchan metamorphic series. ,
Abstract :
Field relations and petrographical features show that formation of the metapelitic rocks in Western Iran were influenced by different metamorphic conditions in south and north of Alvand Batholite (Jurassic age). The intrusion of the Batholith into pelitic host rocks in the northern area (Cheshin Village) produced hornfelsic metamorphic rocks which contain staurolite, kyanite, garnet and sillimanite, whereas in the southern area (Tuyserkan city) these rocks contain, cordirite, andalusite, garnet and sillimanite. Mineral assemblages in the metapelitic rocks in two areas (in the north and south) are different. Using multiple equilibria temperature, pressure and fluid composition have been calculated for the formation of both northern and southern rocks respectively, as temperature (~600-630 ºC), pressure (~2-4 kbar), and fluid composition (XCO2 as low as 0.17) for northern rocks and temperature (~600-750 ºC), pressure (~4 kbar) and low (άH2O) for southern rocks. P-T results indicate that geothermal gradients in two areas (North and South) are respectively 42.5 and 58 ºC/km which conform Barrow and Buchan metamorphic series. Pseudosections were constructed using the Theriak/Domino program. Results of this method are in good agreement with other methods. Therefore, the Hamadan metamorphic rocks have experienced multiple episodes of metamorphism driven by burial and heating during arc construction and collision during subduction of a Neo Tethyan seaway in the Jurassic-Cretaceous, and these events are associated with different metamorphic series in parts of metamorphic aureole of the Alvand complex
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