Petrology
Abdolsamad pourmohammad; Ahmad Ahmadi khalaji; Masoud Homam; Zahra Tahmasbi; Mohammad Ebrahimi
Abstract
Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature – low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. ...
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Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature – low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. These rocks belong to medium to high potassium calc-alkaline series, low temperature I type granite and are poorly peraluminous. The Chondrite-normalized REE patterns show that the rocks are enriched incompatible elements, with negative anomalies in Nb, Ta, Sr, P, Ti and Ba and strong enrichment in Rb, K and Th. These patterns are in perfect harmony in granodiorite, microgranular enclave (MME) and microgranite specimens. This harmony also has in upper, middle continental crust and greywackes. Positive anomalies in Rb, Th, Sm and negative anomalies in Ba are prominent in the composition of the crust. Based on the integration of these patterns with the pattern of upper continental crust (UCC) elements and greywackes and adaptation to laboratory work, the Geysour granitoid originated from crustal materials and a little mantle component. The temperature of granitoid formation was estimated based on the Zircon saturation temperature of 748-790 ֯C. Microgranular enclaves have rounded and oval shapes, mixed areole around them, fine grained texture, quartz and plagioclase eyes, bladed biotite, needled apatite, oxide phases in biotite, and the presence of a simple mixed – hyperbolic curve between MME and granodiorite. Field, petrography and geochemistry of the major and rare earth elements data suggest mixing/ mingling (partial melting) processes for the origin of enclaves and the rare earth elements patterns indicates the relationship between Geysour granitoid with the subduction system. Analysing its data, based on logarithmic ratios, show collision tectonic environment. Also, the tectonic-chemical distinctive diagrams suggest a syn-collision to post-collision tectonic type that is interpreted in connection with the collision of the Afghan Block with the Lut Block.
