مجله زمین ساخت
پیاپی 20 (زمستان 1400)

Porphyry copper and molybdenum deposits in metallogenic belts are formed following the infiltration of susceptible hydrothermal fluids in the direction of secondary tectonic structures. Therefore, in this study, in order to show the role and importance of these structural controllers in the formation of storage and distribution of mineralizing fluids, in parallel with petrographic and geochemical studies, various Remote sensing methods were used. Also, by examining the results of analysis of 174 soil samples in the region, the presence of four geochemical paragenesis in the secondary halos of the mineral block was detected. The way of grouping the elements and the values obtained from the ratio of compound halos related to different horizons indicated the correlation of the axial distribution with the vertical direction. This indicates the role of steeply sloping faults in the distribution of mineralizing fluid in the region As copper and molybdenum deposit elements show the highest concentration in the center of the system and super-deposit elements in the direction of faults and in the periphery of the region. On the other hand, the significant presence of tectonized joints and microstructures in the western part has prepared the conditions for the impact of mineralizing factors as well as erosion. As we see more concentrated anomalies of deeper element molybdenum than copper in the western half. This is also true for the geochemical paragenesis of lead and zinc elements relative to arsenic and antimony. anomalous areas to structural elements, show the steep slope of deep faults

Inselbergs are special forms of desert areas that give a special face to the morphology of these areas. The study of these forms is essential in terms of tourism, climate change and regional development. Among the factors influencing the formation of inselbergs the role of tectonics seems to be important. In this study, which was conducted by field and library studies with the aim of studying the inselberg of Safi Abad plain, we identified 20 inselbergs and concluded that the activity of regional faults in the Miocene period, the heights Poshte Bahram, the primary nucleus of inselberg in this plain Has created. In this plain, there were six thrust faults along the northwest-southeast and a slope between 30 and 50 degrees. These faults have provided the initial conditions for the formation of inselberg by moving and giving height to geological formations. The effect of faults in the formation of inselberg of this plain is not the same, in the northern part due to the confrontation of faults and erosion processes, the typical inselberg has been formed. In the middle part, due to the superiority of tectonic activity, the inselbergs have a rough and unglazed state, and in the southern part, due to the superiority of erosion, polished inselbergs have formed. In addition to the faults of Safi Abad plain, the activity of Aladagh highlands faults in the northern neighborhood of this plain, by affecting the catchment area of the Grati River, has been applied to the inselberg of this plain.

The southern section of the Caspian Sea convexity is included in the Central Alborz, which stretches from Semnan to Qazvin. The Central Alborz zone is the focus of the research because of the strong association between lead and zinc mineralization and tectonics, as well as the great potential of this zone. The major horizons of lead and zinc mineralization, as well as the location of these horizons with orogenic events, have been investigated in this study, based on fieldwork and office studies as well as previous research. According to this research, there are eight lead and zinc mineralization horizons in Central Alborz, ranging from old to recent, including the mineralization horizon of Soltanieh Formation associated with Zaygonin orogeny, the mineralization horizon of Mila Formation associated with Caledonian orogeny, the mineralization horizon of Mubarak Formation With Alborz orogeny, Mineralization horizon of Ruteh Formation related to Hercynian orogeny, Mineralization horizon of Elika Formation related to Early Cimmerian orogeny, Mineralization horizon of Lar Formation related to Middle Cimmerian orogeny, Cretaceous mineralization horizon related to Laramid orogeny and Mineralization within the Karaj Formation is related to the Eocene age in the Pyrenean orogen. According to mathematical modeling in the Central Alborz area, the lead and zinc mineralization controls by thrust faults and reverses-strike slip faults. According to the findings of this study, more than 60% of mineralizations connected to structures occur in the Mesozoic. Triassic mineralizations occurred along with extention tectonics, while Cretaceous mineralizations formed under a compressive regime.

The study area is located in the northeast of the Lut block between Nehbandan and Nayband fault zones; that in addition to sedimentary units and Cretaceous ophiolites, a wide range of Paleogene and Neogene sedimentary facies and pyroclastic sediments have been affected by deformation. Structural trends of the study area include two main groups with north-south and northwest-southeast trends. Structural data were collected in the direction of north-south trends (including Gazik, Afzalabad and east of Sahlabad) and northwest-southeast (including Birjand and Zahan); the deformed regions can be divided into three groups. Deformation in the direction of north-south zones (such as Gazik and Afzalabad stations) is mostly done as transpersonal zones. In the distance between the left-lateral en-echelon faults with north-south trend (such as Cheshmezangi, Chakhoo, and Asakoohak), according to the type of their overlap, pressure zones (such as Kasrab and Torshab) have been formed. In the mentioned compressive zones due to the operation of the thrust faults, ophiolite units have been exposed in these regions. The existence of thrust faults in the end of strike-slip faults (such as South Birjand), which are due to the interaction of the main trends in the region, has caused ophiolite outcrops in the direction of northwest-southeast trends.

The vein-type Qole-Kaftaran Pb-Zn and Cu deposit with middle Eocene volcanic host rock, located at the easternmost edge of the Toroud-Chah Shirin metallogenic belt, is chosen to characterize its structural architecture and further investigate the linkage between structures and ore-mineralization. The Qole-Kaftaran deposit is also situated at 20 km north of the active basement Toroud fault zone. To this end, field base structural study is integrated with remote sensing and ICP-OES geochemical analysis is used. Variable strikes of faults and fractures are propagated in the study area while a NE-SW strike as the significant fault trend is identified in the frequency aspect. This kind of propagation of diverse fault strikes can be interpreted as relatively tectonic maturity in the study area. Brittle and ductile derived- Paleo-stress results suggest an old almost vertical maximum compression direction (with possible age of post-Eocene- Early Miocene) and a post-Early Miocene horizontal NW-SE- directed maximum compression direction. Our result also points to the direct controlling impact of brittle structures on the distribution of alteration and Pb-Zn and Cu mineralization. In which, alteration and vein-type Pb-Zn and Cu mineralization are arranged along and at the hanging wall of the NE-SW extensional faults and grabens.

Differences in the estimation of an earthquake body-wave (mb) and surface-wave (Ms) magnitudes, and the possibility of magnitude saturation, can lead to incorrect measurements of the energy released during an earthquake. In the present research empirical regional relationships for conversion between earthquake magnitude scales in Iran have been studied. The magnitude values of 622 earthquakes reported in both the ISC-EHB and GCMT databases during the period from June 1976 to the end of December 2019 have been used. The moment magnitudes of these events are from 4.7 up to 7.8. The least-squares linear regression method was used to obtain relations for conversion of Mw-Ms, Mw-mb, and Ms-mb magnitudes, in six major seismotectonic provinces of Iran: Zagros, Kopet Dagh, Alborz, Azerbaijan, East-Central Iran, and Makran. These relations are very useful tools in regional homogenization of earthquake catalogs. The conversion relations between body wave and surface wave magnitudes and moment magnitude are important in correct energy estimation and as well as immediate earthquake damage assessment. Although the results for the conversion of Ms to Mw in different regions of Iran show a good agreement with the global model, the differences in the regression lines for the mb to Mw conversion may indicate different patterns of the body wave attenuation in the seismotectonic regions of Iran.