| چکیده انگلیسی مقاله |
Introduction
Granitic to alkaline feldspar granitic masses of Mishu mountains, which are similar to them in the Moro mountains in the northwest of the country, are among the granitoid masses that are related to the Hercynian (Donian-Permian) orogenic cycle, and the study of their lithology and petrogenesis in order to complete the geological information. The northwest of the country is of particular importance and they contribute to our knowledge of the crustal formation of Iran during the Hercynian orogeny (Moayyed and Moazzen, 2002). Eftekharnejad et al. (1991) considered the mass of intrusive Shebster to be equivalent to Mishu granites. This massif has cut and transformed the Kahr and Dolomites of Sultanate. Permian base sediments were placed on the eroded surface of this intrusive mass and based on this, the age of this mass has been attributed to Post-Cambrian and Pre-Permian (Asadian et al, 1994). Due to the lack of determination of the A-type granites and the existence of some ambiguities about the Shabestar granitoid mass such as lithology and geochemistry (including the temporal relationship of the Shabestar granite mass with the adjacent masses and the orogenic phase of Iran), the Shabestar intrusive mass requires a comprehensive and comprehensive study to be a part of the history The geology of this area and the granite masses of the adjacent areas should be properly analyzed. Therefore, in this article, with the help of the results obtained from the study of the field relationships governing the different parts of the Shabaster intrusive mass, petrography and geochemical analysis of the main and rare elements, it has been tried to investigate the genetic relationship between the different parts of the mass, the origin of the magma that formed it, and the tectonic position of this intrusive mass. And finally, determine the A-type granites and compare them with S and I granites.
Materials and Methods
In general, conducting this research includes two stages of field visits and laboratory investigations.
In the first surveys and field visits, 150 stone samples were taken from the internal igneous (Granitoid) masses of Shabestar, and from these samples, 110 microscopic thin sections were prepared for petrographic studies. In the next step, 20 samples were sent to ACME laboratory in Canada for geochemical analysis by whole rock method. Oxide analysis of main elements was done by lithium borate fusion method and inductively coupled plasma emission spectrometer (ICP-ES). In this method, the amount of oxides of the main elements is measured based on weight percentage.
Results and Discussion
Alkaline mafic minerals such as ezirin-augeite and ribkeite-arphodsonite are not found in the examined granites, but all petrographic and geochemical data show that Harris granite rocks are of A-type nature. The comparison of the granite mass of East Mishu with the granite mass of Harris shows that this mass has a range of alkaline rocks of granite-monzogranite-siyenogranite. The dominant texture in these samples is fine-grained from the same dimension to the non-dimensional, perthitic and granophyric. The main minerals of these stones include quartz, potassium feldspar, plagioclase and minor and accessory minerals including biotite, amphibole, pyroxene, apatite, sphene and zircon, which are similar to the granites studied in this article. The negative anomalies of Ba, Nb, Ti, Sr, and Eu and the enrichment in LILEs, especially Rb and Thn, indicate the crustal origin of these rocks. Also, Ce and Sm show their enrichment compared to the adjacent elements. Such selective enrichment has been referred to as shell dominance (Pearce et al, 1984), and such a pattern is called shell dominance. In addition, these high values of HFSEs confirm the dry origin of the constituent magma (Bonin, 2007; Zhao and Zhou, 2007).
Conclusion
According to the field evidence, petrography, geochemistry and tectonic structure differentiation diagrams, Shabester granitoid mass is alkali feldspar granite. These rocks are covered by the Permian Formation and the Soltanieh Formation has recrystallized with it. Therefore, their relative age is attributed to Post-Cambrian and Pre-Permian. According to the alumina saturation index, the granitoid mass of Shabestar has peraluminous to weakly metaaluminous characteristics. Negative anomalies of Ba, Nb, Ti, Sr and Eu and enrichment in LILEs, especially Rb and Thn, indicate the crustal origin of these rocks. Therefore, Shabestar granitoid mass is A-type of in-plane granites of A-type, which is related to group A2 due to the depletion of Nb. In other words, it is very likely that A-type alkaline granites were created in this region after impact events, and during their emplacement, tensile tectonics prevailed. The REE diagram of these granites shows that the granitoid mass of Shabestar was probably due to partial melting of the lower crust with tonalitic-granodioric composition. The REE diagram of these granites shows that the granitoid mass of Shabestar was obtained from a plagioclase-containing source, or plagioclase was separated from the forming magma during the evolutionary process, so that it is probably due to partial melting of the lower crust with tonalitic-granodioric composition. |