جستجوی مقالات مرتبط با کلیدواژه "پوسته زیرین" در نشریات گروه "زمین شناسی"

Granitoid bodies of west of Zanjan with Precambrian age are located in northwest of central Iranian structural zone. Based on field observations and microscopic studies, these bodies contain tonalite, granodiorite and monzogranite. Tonalite are I-type, calc-alkaline, and peraluminous (206Pb/238U age of 576±13 Ma) which base on isotopic studies (87Sr/86Sr (i) and εNd (i) values equal to 0.710544, -7.01), and geochemistry of major and trace elements, can concluded that they were resulted from melting of amphibolitic crust that generated from thickened mafic crust or under plate basalts (with presence of plagioclase in source area) in low pressures and depth in an active continental margin. Monzogranites are S-type, peraluminous and calc-alkaline, which is plotted in collision zone. These rocks were generated from melting of crustal rocks (melt derived from pelitic rocks with high plagioclase). Granodiorite are I-type, calc-alkaline and Weakly peraluminous (206Pb/238U age of 548±27 Ma). They have value of 87Sr/86Sr (i) more than 0.705, negative value of εNd (i), and geochemical data, which is generated from partial melting of lower to middle crust, because of thickening and shortening due to continental- continental collision. With respect of geographical location of granitoid bodies of Mahneshan and age of their units, it seems that these granitoid rocks have formed in an active continental margin during convergence of Central Iran and Alborz-Azarbayjan with Arabian platform during Precambrian

The Moghanlu granitoid was located in the northwest of central Iranian structural zone with a Precamberian age. Based on field observations and microscopic studies, this body includes tonalite, monzogranite and granodiorite. Based on geochemical studies, tonalites are I-type, calc-alkaline, and weakly peraluminous. Based on isotopic studies [(87Sr/86Sr (i) and εNd (i) values equal to 0.710544, -7.01 respectively)], low values of La/Yb, Sr/Y , Nb/Ta, Ni and Cr, low fractionated patterns (flat pattern) of rare earth elements (REE) and negative anomaly of Eu, it can be concluded that they were resulted from melting of amphibolitic thickened mafic crust or under plate basalts (in the stability field of plagioclase) in low pressures and low depth in volcanic arc granitic area. Monzogranites are S-type, peraluminous and calc-alkaline, which are plotted in collision zone. These rocks are enriched in LILE and LREE and also depleted in HFSE, which represent negative anomaly of Ba, Ti, Nb, Sr with Mg number about 11-20. On the basis of this result, it can be concluded that the granitoids were generated from melting of crustal rocks (melt derived from pelitic rocks with high plagioclase content). Granodiorite are I-type, calc-alkaline and peraluminous. They have 87Sr/86Sr (i) and εNd(i) values of 0.71713, -10.55, Mg number between 31-33, negative anomaly of Sr and Nb, and also positive anomaly of La and Th, which represent that these rocks were generated from partial melting of lower to middle crust. These granodiorites were formed because of thickening and shorting due to continental- continental collision (collision of Iranian-Arabian plates). With respect to geographical location of Moghanlu body and the age of this units, it seems that these granitoide rocks formed on active continental margin during convergence of Central Iran and Alborz-Azarbayjan plates to Arabian platform during Precambrian.

Study area located on N to NW of Rabor city in Kerman province that belong to Uromieh-Dokhtar Magmatic Belt (UDMB). Most of rock lithology in this area including diorite, granodiorite and granite which have been exposed in volcanic sequences. Based on geochemical studies all of rocks in this area classified in two groups: (1) some igneous rocks show adakitic affinity with high SiO2 (61.49–66.78 wt. %), Al2O3 (15.72–17.74 wt. %), Sr (374–602 ppm), Sr/Y (34–53), (La/Yb) N (8.35–16.88) and low Y values. (2) another rock group that distinguished in study area including various granitiods rocks with typical calc-alkaline characteristics that distinct from adakitic types such as: SiO2 (63.07–72.32 wt. %), lower Sr/Y (3.8–13.2) ratio and higher Y (21.7–31.6 ppm) and Yb (2.29–3.26 ppm) contents, and the lowest Sr (119–297 ppm) and (La/Yb)N (3.02–11.13) values relative to adakitic groups, with distinctly negative Eu [(Eu/Eu*)N= (ave. 0.49)] anomalies.The adakitic rocks most probably originated from thickened mafic lower crust (garnet amphibolite) with garnet rutile ± plagioclase as residual minerals in the source corresponding to depths of >50 km, and calc-alkaline rocks were probably generated in shallow depth than adakitic groups in mid-lower crust (dominant amphibolite) correlating to depths of

Quaternary volcanic activities in Alamut Valley occurred in three stages and covered Neogene red sedimentary rocks. The volcanic rocks are intermediate in composition and are classified as hornblende trachyandesite. The SiO2 content of the rocks varies in a range from 55.48-61.88 wt%. Chondrite normalized REE patterns exhibit a steep arrangement of LREEs and MREEs (La/Ho)N =85 and a relatively flat HREE (Ho/Lu)N =1.3., Large ion lithophile elements (LILE) do not show strong enrichment compared to LREEs in mantle normalized multi-element spider diagrams. Nb andTa are slightly depleted compared to neighboring light rare earth elements. These rocks have high Sr/Y (140-205), La/Yb (113-142) ratios, accompanied by high K2O/Na2O (0.7-0.9) and resemble C-Type adakites. Geochemical evidence suggest that these rocks are resulted from partial melting of thickened eclogitic lower crust in presence of abundant residual garnet. Partial melting of lower continental crust probably triggered by thickening of crust as a result of late Cenozoic orogenic phases especially the Passadenian Orogenic phase.

The Darvazeh pluton is located in the south of Qorveh. Olivine gabbro, diorite, quartz monzonite and granite rocks are rock forming of this body, but this paper is focused on the leucocratic to mesocratic rocks (quartz monzonitic and granitic rocks). These rocks were effected by dynamic tectonic activity during the intrusion and according to the distance of shear zone; deformation can be classified to cataclastic, protomylonite and mylonite. Microstructure evidences including the presence of porphyroclasts, bending of crystals and their twining, myrmekitic and pertite textures which caused by stress. Based on the microstructure features, deformations occurred at temperature of about 500-600 ° C. The geochemical data suggested that the felsic rocks belong to calc-alkaline, ferroan, I-type and metaluminous to slightly peraluminous series. Enrichment in LREE/HREE; negative anomalies of Ba, Ti, P, Sr, Nb and U, Th, Pb positive anomalies and Th/Ta ratios indicate continental arc setting. The presence of mafic enclaves, high volume of granite and negative trend of Zr versus SiO2, all suggest that the felsic rocks were generated via partial melting process. According to geochemical characteristics, the studied granitoid was originated by partial melting of meta basaltic rocks in the lower crust.

The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town¡ Qazvin province. This Pluton which intruded the Eocene volcano-sedimentary rocks of the Urumieh-Dokhtar Magmatic assemblage (UDMA)¡ is mainly composed of granodiorite and produced narrow thermal metamorphic contact aureoles surrounding the intrusion. The body is characterized by SiO2 content ranging from 64.2 to 66.9 wt%¡ high-k calc-alkaline nature and metaluminous character (A/CNK