R. Hajialioghli; M. Moazzen
Abstract
The Takht-e-Soleyman metamorphic complex is located at NE of Takab town, West Azerbaijan province. This complex having Precambrian-Cambrian age has been formed from low to high metamorphic rock types. The retrograde granulites are subject of this project. The retrograde metamorphic assemblages of the ...
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The Takht-e-Soleyman metamorphic complex is located at NE of Takab town, West Azerbaijan province. This complex having Precambrian-Cambrian age has been formed from low to high metamorphic rock types. The retrograde granulites are subject of this project. The retrograde metamorphic assemblages of the granulites are including of Amp+Grt+Spl+Opaque phases. Amphibole overprinted primary mafic phases of clinopyroxene and orthopyroxene highly. Spinel at the klyphitic texture around garnet porphyroblast forms the main feature for retrograde metamorphism of granulites. Rutile occur as inclusion within amphibole. The compositional profile of garnet indicates chemical variations from the core to the rim. Compositional variations from the core to the mid is characterized with a minor increase in XMg but decrease in XCa and XMn. This characteristic of garnet is indicative of pressure decompression with small increasing of temperature. Due to complete overprinting of high temperature phases by the retrograde phases as well as lack of preserved pick metamorphic minerals it is indeterminate pick metamorphic P-T estimations for M1 stage. On the basis of chemical compositions of porphyroblasts, retrograde evolutions of investigated granulites have been estimated at two stages: (1) pressure decompression (M2-a) and (2) cooling and exhumation (M2-b). The retrograde P-T conditions are obtained as T=810±10°C at P=10.5±0.7kbar for the first and second retrograde stages, respectively. Relatively coarse grained size of phases at the klyphitic margin are indicative of low cooling rate during uplifting of rocks from lower to upper levels. Highly overprinting of high temperature phases by amphiboles support this idea. Time of pick and retrograde metamorphism for the investigated granulites are not clear accurately. It seems reasonable to attribute pick metamorphic and granulite formation time to Oligocene-Miocene related to crustal thickening due to collision between the Central Iran microcontinent and the Arabia plate. The granulites have been metamorphosed under retrograde conditions in relation with thrusting and post collisional extensions which caused to uplifting, crustal thinning and exhumation of rocks. However more conclusions on tectonometomorphic evolutions need to precise studies.
R Hajialioghli; H Fakharinezhad; M Moazzen
Abstract
The study area (Siyah-Cheshmeh), is located to the south Maku in the Khoy-Maku ophiolite zone. The various outcropped metamorphic rocks include serpentinites, metabasites (green schist, amphibolite) and meta-pelitic rocks (slate, mica-schist) with interlayers of marble and quartzite. The amphibolites ...
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The study area (Siyah-Cheshmeh), is located to the south Maku in the Khoy-Maku ophiolite zone. The various outcropped metamorphic rocks include serpentinites, metabasites (green schist, amphibolite) and meta-pelitic rocks (slate, mica-schist) with interlayers of marble and quartzite. The amphibolites can be classified as actinolite-amphibolite, epidote-actinolite- amphibolite, biotite-amphibolite, amphibolite and garnet-amphibolite. They have fine- to coarse-grained granoblastic texture. On the basis of whole rock chemistry, the protolith composition of the amphibolites has been determined as basalts with tholeiitic and less commonly, calc-alkaline affinities, developed in an island arc setting. The negative anomaly of Nb as well as small enrichments in LILE and LREE support arc related and tholeiitic signatures for the protolith. Considering the unknown age of the studied amphibolites, it is difficult to propose an appropriate tectonic model for formation of the investigated rocks. If the amphibolites are related to the Khoy-Maku ophiolitic complex, then they would be the result of subduction of the northern branch of the Neotethys ocean basin, development of an island arc and eventually metamorphism of the rocks due to closure and collision. Since the age is not clear, it is not possible to conclude unequivocally if the rocks are results of the Neotethys subduction system or they are related to an older, possibly a Precambrian subduction system. Dating the rocks will help to propose a suitable model for their formation.
