Volume 10, Issue 2 (Autumn & Winter 2024)
KJES 2024, 10(2): 465-490 |
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Fazlnia A, Miri M M. Metamorphic conditions of dolomitic marbles from the Qori metamorphic complex, southern Sanandaj-Sirjan zone, using phase thermodynamic diagrams. KJES 2024; 10 (2) :465-490
URL: http://gnf.khu.ac.ir/article-1-2922-en.html
URL: http://gnf.khu.ac.ir/article-1-2922-en.html
1- Urmia University , a.fazlnia@urmia.ac.ir
2- Shahid Chamran University of Ahvaz
2- Shahid Chamran University of Ahvaz
Abstract: (295 Views)
The Barrovian-Qori metamorphic complex, which is exposed in the southern part of the Sanandaj-Sirjan zone, has a succession of metaultramafic, metabasite, metapelite, metacalcic silicate, and marble lithological diversity. The investigation of the types of dolomitic marbles in this complex, based on phase thermodynamic diagrams and petrographic studies, showed that the parageneses of amphibole + calcite + dolomite, amphibole + clinopyroxene + garnet + calcite + dolomite, clinopyroxene + garnet + calcite + dolomite, clinopyroxene + garnet + olivine + calcite + dolomite, clinopyroxene + olivine + calcite + dolomite and olivine + calcite + dolomite + gahnite + brucite were recognizable in the types of outcrops. In all samples, olivine crystals have been partially or completely converted into antigorite (a type of serpentine). Using thermodynamic phase diagrams drawn based on the chemical analysis of the whole rock and matched with petrographic and fabric evidence, it was determined that the calc-silicate samples of Qori, which recorded the highest degrees of metamorphism, underwent two stages of metamorphism, M1 and M2. The first stage of crystal growth, which was accompanied by maximum pressure, had the metamorphic paragenesis of clinopyroxene + garnet + calcite + dolomite, and the second stage of crystal growth was accompanied by an increase in temperature and a slight decrease in the temperature. These two stages of metamorphism are in thermodynamic agreement with the two previous ages reported for the complex (187 and 147 Ma). It seems that the different stages of the Neotethys subduction beneath the Sanandaj-Sirjan zone were the factors that increased the geothermal gradient and metamorphic pressure for the evolution of the growth of equilibrium metamorphic mineral assemblages. The different performance of thrust faults in the western and eastern parts of the Qori metamorphic outcrops has led to the creation of different paths of retrograde metamorphism; thus, in the western part, the intense performance of thrust faults has led to the creation of retrograde metamorphism with a sudden decrease in pressure at an almost constant temperature, in contrast, the western part displays retrograde metamorphism with a normal decrease in pressure and heat caused by the erosion of the upper parts of the crust.
Keywords: Dolomitic marbles, phase thermodynamic diagrams, Qori metamorphic complex, Southern Sanandaj-Sirjan zone.
Type of Study: Original Research |
Subject:
Petrology
Received: 2024/10/4 | Accepted: 2024/12/5 | Published: 2024/12/28
Received: 2024/10/4 | Accepted: 2024/12/5 | Published: 2024/12/28
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