Iranian Journal of Geology
Year:2013 | Volume:7 | Issue:27|Papers Count:8

Boroujerd plutonic complex is one the largest intrusive complexes located in the structural zone of Sanandaj-Sirjan in west of Iran. It is mainly composed of granodiorite which are accompanied with small quartzdiorite and monzogranitie stocks. Average magnetic anisotropy parameters were studied by using AMS studies. Anisotropy of magnetic susceptibility data analysis on 95 stations of the Boroujerd region rocks was compared by means of biotite alteration. The average magnitude of magnetic susceptibility is between 14 and 921 mSI. The results show that the relation between alteration of biotite and Km parameter is inverse. It means that, wherever in Boroujerd granotoid complex the intensity of alteration of mineral biotite is high, the amount of Km parameter decreases. Finally considering theKm data classification results determines that Boroujerd plutonic complex are paramagnetic rock. Also according to previous studies, we can say that the range of values of the average anisotropy of magnetic sensibility in Northern Sanandaj-Sirjan zone is 200 mSI, Thus all granitoid complexes in the Northern Sanandaj-Sirjan zone are paramagnetism. Finally all granitoid complexes set in the Northern Sanandaj-Sirjan zone, are an inverse between the amount of biotite alteration with anisotropy of magnetic sensibility. In other words, anywhere all Granitoid complexes are located in the Northern Sanandaj-Sirjan zone, if biotite alteration is increased anisotropy of magnetic sensibility is reduced.

The alkaline basic rocks in the base of the Shemshak Formation scattered mainly as intrusive and occasionally as extrusive, in some areas of the eastern Alborz zone. Their petrological compositions range from olivine gabbro to monzonite in intrusives and are olivine basalt in extrusives. Intracontinental settings of these rocks have been confirmed in various tectonomagmatic diagrams. Geochemical and petrogenetical investigations show that magma forming of these rocks, originated from 10-15 of percentages partial melting of an enriched subcontinental lithospheric mantle source with garnet-lherzolitic composition. This alkaline magma has been formed at 25-30 kbar pressures in 90-100 km depths and contaminated by continental rocks in small amounts, during rising and emplacement.

Fresh water carbonates are different in geochemical characteristics, especially in isotopic geochemical characteristics. Stable carbon and oxygen isotopes of carbonates such as travertine is one of the most important methods of carbonate study. Mahallat area with large travertine deposits, is very important for geochemical studies. This area is located in the south-east of Arak and this is a part of central Iran structural zone. Based on stable isotope studies, there are two types of travertine: thermogene and meteogene. Thermogene C-isotope composition range between -4 ‰ and 8 ‰. However, d13C value for meteogene type range between -11 ‰ and 0 ‰. In Mahallat area, travertine C-isotope composition range between 1.69 ‰ and 9.70 ‰ which indicate thermogene type. In addition, another way to distinguish the type of travertine, is determination of carbon dioxide source. Low values of d13CCO2 water shows to thermogene type and Mahallat area travertine show -8.47‰ and this confirm thermogene type for these deposits. Also, water temperature during the travertine precipitation can calculated by oxygen isotope study. The temperature in Abegarm travertine is 43oC which indicate it thermogene type.

Three deformation and two metamorphic phases are examined in the Shurow metamorphic complex located in SE of the Sanandaj-Sirjan zone. All deformation and metamorphic phases are produced during post-middle Jurassic and are studied in three areas of Chah Gaz, Chah Anjir and Dochah Zahra based on trends of the second generation map-scale folds. The first generation of folds are NW and SE shallow to moderately plunging isoclinal folds associated with continuous axial plane foliation, shallow to moderately dipping to NE. The second generation of folds are NE and SW shallow plunging open to close folds associated with axial plane crenulation foliation, steeply dipping to N and S. A NE -SW trending vertical compositional foliation is also developed in Cah Gaz metamorphic rocks. Local dextral strike-slip ductile shear zones are generated sub-parallel to the compositional foliation. Muscovite is crystalized along the axial plane foliations of the first and second generation of folds indicating low T and P green-schist facies condition. The third generation of folds are upright NW shallow (Chah Anjir area) to moderately (Chah Gaz area) plunging folds. The first deformation phase in Dochah Zahra area is identified by E -W oriented ductile shear zones, including syn-tectonic granite intrusion that are folded along the stretching lineation by NW-SE shallow plunging folds containing moderately to steeply dipping axial plane foliation.

The Amiran Formation (Upper Cretaceous-Paleocene) has an excellent exposure in the Lurestan Province in the Zagros basin. In order to interpret depositional environment of this interval, two stratigraphic sections (type and Pirshamsedin section) were measured and sampled. The thicknesses are 890 and 920 in these two sections, respectively. The lower boundeary of the Amiran Formation at the type section is sharp with Gurpi Formation and Upper boundeary is gradual with the Talezang Formation. This formation is composed of lithofacies conglomerate, sandstone, mud rocks, and carbonates. The Amiran Formation in the study area is composed of two units, carbonate (in the basal and upper parts) and siliciclastic facies (in the middle and upper parts). Based on petrographic studies, 8 silisiclastic petrofacies and 18 carbonate microfacies have been identified. The carbonate microfacies are deposited in 3 facies belts including open marine, barrier and Lagoon in a carbonate ramp system. Most of the identified rudists in this formation are elevator, horizontal and individual types constratal fabric and are usually present in the lagoonal deposits. Based on dictyoptychus genera, especially luftusia general, Maastrichtian age is suggested for this unit. Siliciclastic rocks in this formation consist of shale, siltstone, calclithite, lithic graywacke, chert arenite and ortho-micro conglomerate petrofacies. Based on the petrography and present of the sedimentary structures such as gradded-beds, Bouma sequence etc. they are deposited by turbidity currents in the slope and sub marine fans.

The Kuh-Gabbri granitoid is located at 42 Km east of Rafsanjan in Kerman provincs. This region is small part of Urumieh-Dokhtar magmatic belt of Iran. Intrusive of two granitoid stocks into Upper Crataceous limestone and Lower Paleocene polygenetic conglomerate, produced contact metamorphism. These rocks contain major minerals such as quartz, alkali feldspar and plagioclase; minor minerals as biotite, zircon and opaque. The SiO2 contents range from 75.57 to 76.83 wt%. The majority of the Kuh-e-Gabbri rocks show similar patterns in the trace element plots normalized to primitive mantle and condrite. These rocks are generally enriched in Rb and Th, and depleted in Ba, Sr and Eu. Condrite-normalized REE patterns are moderately LREE enriched whit pronounced negative Eu anomalies. The Nb anomaly implies a crustal component. Moreover all data belong to the within-plate granite field in the tectonic discrimination diagram and those are I- type granite. Field, petro raphic and geochemical characteristics suggest magmatic origin and crustal source rock under low pressure conditions. Petrographic and chemical variations were mainly the result of fractional crystallization.

Tertiary volcanic rocks of Damash area have outcraps about 70km for from east of Roudbar in Guilan province. From geochemical point of view, negative anomaly of P, Ba, Zr, Ti, Ta, Nb and positive anomaly of K, Th, Pb, Rb indicate crustal contamination.The ratios of (Tb/Yb) N, Nb/Yb, Zr/Yb, Zr/Y, Zr/Nb, Y/Nb show that the MORB-like depleted mantle source with spinel Facies. Study of the range of incompatible elements pattern and compare with the crustal data range and incompatible elements ratios show that the volcanic rocks have to intra-continental rift magmatism which are contaminated with continental crust. As a result of the crustal contamination, the original geochemical properties of the volcanic rocks were changed untruthly, these show subduction zones geochemical features.