Iranian Journal of Geology
Year:2020 | Volume:13 | Issue:52 |Papers Count:10

Gneisses from Gol-e-Gohar metamorphic complex in the south Kerman province and in the south-east of the Sanandaj-Sirjan metamorphic zone with granitoid protolith represent the green schist to lower amphibolite facies as a result of early Cimmerian orogenic phase. The studied gneisses are composed of potassium feldspar, plagioclase, biotite, quartz and garnet as main mineralogical composition. In addition, apatite, ilmenite, titanite, chlorite and muscovite are accessory phases in gneisses. Geothermobarometric calculations estimate a temperature of 600 to 610° C, with a pressure of 8 to 10Kbar. This is in accordance with the lower amphibole facies. The partial enrichment of the LREE relative to HREE and the lack of depletion in HREE of the samples, the values of YbN greater than 10 (average 12. 70), combined with the alkali nature of the primary magma, indicate an intra-plate garnet-free crustal source for the gneisses. In addition, the metamorphic processes gave them gneissic nature, however, features of the primary igneous rock are recognizable. This situation is consistent with the extensional rifting environment developed in the southern part of the Sanandaj-Sirjan zone in the lower Paleozoic era in the early stages of the Paleo-Tethys formation.

The Takab-Qorveh magmatic lineament between the Urumieh-Dokhtar and the Sanandaj-Sirjan zones contains important gold mines such as Dashkasan and Zarshuran. The Dashkasan deposit is located in the Kurdistan province and is one of the largest gold deposits in the Middle East domain. The gold is mainly hosted by porphyritic dacite and breccia. In spite of detailed previous studies, there is still debate regarding the genesis of the Dashkasan. Herein, this study present the source and evolution of the mineralizing fluids using the fluid inclusion and stable isotopic investigations. At Dashkasan, the breccia and mineralization are constrained by the steep NNE-SSW-trending faults. Alteration zones on the surface are phyllic, silicification, tourmalinization, argillic and minor propylitic. Sulfide minerals consist of pyrite, marcasite, arseno-pyrite, stibnite, chalcopyrite and to lesser amounts of bornite, sphalerite and galena associated with quartz, tourmaline, sericite, calcite and chalcedony. Result of microthermometry measurements shows a range of homogenization temperatures between 183-260 ° C with salinities of 15. 97 to 17. 06 wt % NaCl equiv. The oxygen isotope composition of fluid in quartz ranges from 6. 6 to 9. 9 ‰ , while, the tourmaline has δ 18Ofl uid values are in the ranges of 8. 5 to 12. 3‰ . Also, the δ Dfl uid values of the quartz and tourmaline ranges between-51 to-81 and-93 to-111‰ , respectively. Integrating with previous studies, all these data, suggest a migration from a porphyry gold system (stage-I) with a magmatic source to a low-sulphidation epithermal (stage-III). Stage-II occurred simultaneously with the collapse and eruption of crater.

In this paper the fractal dimension of the aftershocks of the 2013 M 7. 8 Gosht-Saravan earthquake and their relationship with the seismicity parameters (such as the b-value) and also the released seismic energies of the main shocks and the aftershocks are investigated. The Gosht-Saravan main shock is an intraslab event with normal mechanism. No relationship between the Saravan fault and the main shock is observed. By examining the fractal dimension of the aftershocks and their relationship with the b-value it is confirmed that a linear seismic source (such as a subduction zone) exists. The slip ratio between the primary and secondary faults can be estimated by the fractal dimension. The calculated slip ratio indicates that a low portion of the slips may be related to the near surface fractures which can be verified by the shallow depth aftershocks. The earthquake occurrence in the intermediate depth, releases seismic energy and migrates to the near surface faults and fractures. The occurrence of aftershocks both near the hypocenter and at shallow depths can confirm the activity of these faults. The ratio of the total radiated seimic energy of the aftershocks to the radiated seimic energy of the main shock indicates that a high fraction of the energy related to the main shock and just a small fraction of the energy related to the aftershocks.

The study area is located in the southern boundary of the Eastern Alborz range between North Shahroud Fault and Astaneh Fault. The exposed formations are from Paleozoic to Cenozoic in age. Several structural surveys such as geometrical analysis of folds and geometrical and kinematical analysis of faults were studied. Field observations and software analysis revealed that most folded structures show a northeast-southwest trend in the eastern area and an east-west axis in the western area. Due to location of E-W trending mesoscopic folds on the hanging-wall of Tazareh thrust fault, these mesoscopic folds are fault-related folds. Axes and axial plane of folds revealed that macroscopic folds with a tendency toward south-east, are consistent with flower structure of the Alborz range. Available faults in the area have two trends: northeast-southwest in the eastern part and east-west trend in the western area, and their arrangements give a scaly situation to the area. Therefore, due to existence of east-west compressional structures, it could be suggested that Dehmolla contractional duplex is developed as a result of strike-slip faulting between Shahroud and Astaneh faults.

The Kavand area is located in the southwest of Zanjan, in Soltanieh district in Central Iran zone. Mineralization is hosted by upper Precambrian-lower Cambrian sedimentary sequences, and it is mainly associated with the dolomitic rocks of the Soltanieh Formation. Mineralization appears as massive, vein-veinlets and karst open space filling. Dominant alterations include iron-oxide, carbonate and silicic types. The ore minerals conist of hematite, specularite, gold, chalcopyrite pyrite, chalcocite, covellite, malachite, azurite, goethite and limonite, while quartz, barite, calcite and dolomite are gangue minerals. The Fe and Au are important ore-forming elements in this area. The average content of Fe and Au in the Kavand mineralization is 15. 7% (Max. 28. 4%) and 1. 3 ppm (max. 14. 6 ppm), respectively. Geochemical data represent a high positive correlation between Au with Ag, As, Sb, Cu, Zn, Cd, and Ba. Fluid inclusion studies on quartz from samples with quartz+sulfide+gold and iron oxides+barite+quartz+gold mineral associations indicate that average temperature was 277. 84 º C and salinity was 3. 67 wt. % NaCl. Mineralization is likely formed under pressures below than 200 bars and a depth over than 700 m. The multi-element microprobe analyses of gold grains from stream sediments demonstrate that Au and Ag contents are dominant in the composition of Kavand gold index. The chemical composition of the Kavand gold particles compared with those from various gold deposits proves their epithermal source. The Kavand mineralization can be considered as a carbonate rock-hosted epithermal gold deposit.

Karstic aquifers are vital water resources which are used for irrigation and drinking purposes in arid and semi-arid regions. Understanding of the hydrogeological behavior of these springs and the qualitative tracing of these water resources are the first step in their better management. There are wide outcrops of Tirgan karstic formation in the study area, in the north of Khorasan province. In this area, there are a few karstic springs the discharge rate ranges from 50 to 500 lit/s. The recharge area characteristics of these springs vary significantly with their elevation, catchment size, thickness of epikarst and degree of karstification. In this study, temporal and spatial hydrogeochemcal variations of the five karstic springs including Arnaveh, Rezghaneh, Estarkhi, Ghordanlo and Sarani and 3 rain stations are investigated during one year period. The effects of both precipitation and lithology on the chemistry of these karstic springs are also considered. The dominant rain water types are Ca-SO4-Cl and Ca-HCO3 which change into Ca-Mg-HCO3 type during ground water flow in karstic system. This karstic aquifer is recharged during winter snowfall. The EC values of the rainfall vary from 70 µ mohs/cm in Namanloo station to 100 and 150 µ mohs/cm in Estarkhi and Ghale Barbar stations, respectively. The summer precipitations have more EC value than winter precipitations. This is due to long trajectory of air masses through arid regions with dust particles. The time series variations of discharge value are negligible in some karstic springs except for Sarani and Estarkhi springs. Hydrochemical composition of Sarani, Ghordanlo and Estarkhi springs are mostly affected by precipitation; while, Arnaveh and Rezghaneh springs with the same precipitation composition in this area have higher EC values. This is due to soil cover in catchment area, dissolution of clay minerals and diffusion.

Travertine deposits in Azarshahr, NW Iran, are one of the most extensive travertine deposits in the world. The process of travertine deposit is currently active in the several springs. It was used a multidisciplinary approach to determine the source of fluids and structural characteristics of travertine springs. Results of in-situ measurements and type of travertine deposits, demonstrate that the springs are of thermogenic type with hydrothermal sources. Hydrogeochemical diagrams and ionic ratios represent that the type of spring waters are calcium carbonate, with increased sodium and chloride ions levels due to mixing with brine waters. Geophysical studies showed that these brines originated from the Urmia Lake or related brines, which are intruded through fracture systems to relay zones of faults and mixed with hydrothermal bicarbonate-saturated fluids. This phenomenon shows that hydrochemistry of travertine springs are affected by Urmia Lake or related brines.

The Piranshahr ophiolitic complex is located in NW Iran and in the north west of Piranshahr town. Tectonically, the NW Piranshahr ophiolitic complex is severely mingled and the boundary of different units in this complex is indistinguishable. Piranshahr ophiolite includes ultramafic, mafic, sedimentary and metamorphic rocks. Basic rocks with basalt and diabase compositions are exposed in several parts of the region. In this paper, whole rocks geochemistry and petrogenesis of basic rocks were studied in the Piramshahr ophiolite (in the Mashkan and Gerdikavalan areas) and were compared with the geochemistry of basic rocks located in the west of Mawat ophiolite in Iraq (in the Hasanbag, Walash and Neopurdan regions). Composition of basic rocks of Mashkan area in Piranshahr ophiolite and Hasanbag area in Iraq ophiolite is calc-alkaline in nature and depleted with respect to MREE, HREE, Zr, Hf, Y, Ti elements and enriched in Rb, Cs, Ba, U, Th, Pb, LREE elements with negative Ta, Nb anomalies. These geochemical features show that the source of magma was generated in the supra-subduction zone tectonic settings. Composition of basic rocks of Gerdikavalan area in Piranshahr ophiolite and similar rocks in the Walash-Neopurdan areas in Iraq ophiolite represent tholeiitic nature. Tholeiitic nature in these areas show both MORB and volcanic arc affinity. It seems that the tholeiitic magma was probably generated in the lithospheric extension over on subduction zone and these features conform asupra-subduction setting for basic rocks in Piranshahr ophiolite and similar rocks in western continuation of Iraq ophiolitic complex.