فصلنامه زمین شناسی ایران
پیاپی 21 (بهار 1391)

One of the most important effects of Manjil earthquake (M=7/7 20/6/1990) was triggering of the numerous landslides over an extensive area. To predict landslide locations for the future earthquakes, it is essential to map and analyze the distribution of landslides triggered by Manjil earthquake. In this paper, the most important parameters responsible for triggering Manjil earthquake landslides in the Chahar –Mahal and Chalkasar rectangles with an area of 309 km2 have been studied using GIS. Then Frequency Ratio Model has been used for rating the susceptibility of region to landslides and developing a predicting probability map. There is a good relationship between provided map and the inventory map of landslides occurred during Manjil earthquake. Based on the susceptibility map, the study area has been divided into five zones.

Kalkafi area is located about 76 km northeast of Anarak (Isfahan Province), in Central Iran structural zone. Based on field observations, petrographical and XRD examinations, three major alteration zones were identified in the studied area including potassic, phyllic-argillic, and silicic zones. Potassic alteration is characterized by orthoclase + biotite + quartz ± sericite assemblage. Phyllic alteration is composed of sericite + quartz + pyrite associated with clay minerals ± calcite, and argillic alteration is characterized by kaolinite + dikite + sericite + quartz + hematite + limonite + goethite. Two major ore mineralization were identified in the studied area: (1) Cu-Mo mineralization and (2) Au-Pb-Zn polymetallic mineralization. Cu-Mo mineralization is mainly related to porphyry quartz monzonites and granites. Chondrite normalized REE patterns of unaltered intrusive bodies (quartz monzonites) indicate a‎ strong LREE and a weak HREE differentiations. Lower content of total REEs in‎ the altered samples of the studied area indicates their mobility in hydrothermal environment. Microthermometric analysis of fluid inclusions of the studied samples indicates that salinity of mineralizing fluid ranges from 1.74 to 21.11 NaCl equivalent wt%. Collected homogenization temperatures confirm the existence of at least two generations of fluid inclusions or mineralizing fluids in this area.

The Siah Kuh anticline is located between Lorestan (in North) and Dezful Embayment (in South) zones in the Zagros fold-thrust belt. This anticline and adjacent anticlines are affected by the Balarud blind thrust fault zone, which is a part of Mountain Front Fault. The Mountain Front Fault is a major topographic front that is traced along the Zagros fold-thrust belt in the Izeh, Fars, Lorestan and Dezful Embayments. The field observations, analyses of the geometric parameters and comparison of the anticline with the theoretical fault-related folding models suggest that the Siah Kuh anticline, as a Transported Fault-Propagation Fold, is sheared by Balarud fault zone. The position of this anticline confirms this suggestion.

This research deals with the detection of the aquifer boundaries, depth to the water table, aquifer thickness, potential zones, source of salinity and subsurface geology of the Shirin Ab Basin by simultaneous use of electrical resistivity and borehole data. In this area, due to high population, demands for new water resources are increased and the current drinking and agricultural water resources are at risk. Hundred and seventy Vertical Electrical Sounding (VES) measurements were carried out in 19 profiles by Schlumberger array configurations. The maximum distance between current electrodes (AB) set is 1000 m. The following results have been achieved in this study. 1- Study area is an alluvial aquifer, divided into north and south parts by the Khohanak Anticline. 2- Interpretation of one-dimensional (1D) inversion of measured apparent resistivity curve was used for mapping fresh and brackish water, and separation of their boundaries. 3- Good agreement between conductivity and chloride concentration in water samples indicates that the salinity is the most important factors controlling resistivity. 4- Electrical resistivity of the aquifer was calculated and is about 13-380 Ohm-m in the northern part and 4-219 Ohm-m in the southern part of the aquifer. 5-Regarding the source and course of the Shoor Ab River, and ground water flow direction, it seems that the marly-sand of the Aghajari Formation is the main source of the salinity. 6- Transverse resistivity (RT) is calculated and interpreted in terms of the transmissibility and potentiality of the aquifer.

Potential field anomalies are usually superposed large-scale structures and small-scale structures anomalies. Separation of these two categories of anomalies is the most important step in the data interpretation. Different methods have been introduced for these types of work, but most of them are the semi-automatic methods. In this paper, empirical mode decomposition method is used to differentiate regional and residual anomalies. This automatic method is based on extraction of the intrinsic oscillatory modes of data. Efficiency of this method is investigated on both synthetic and real data acquired on Tromspberg area of South Africa. Different results show that this technique have higher accuracy than conventional methods like as polynomial fitting.

The Surgah Formation in Tang–e–Chenarbashi, with 15 meters thickness, encompasses Middle Torunian to Santonian planktonic foraminifera. Study of foraminiferal morphotypes in this formation show a moderately deep sedimentary environment, and replacement of heavy forms by light types indicate the rise of sea level. Their abundance depends on oxygen and other environmental factors such as salinity and temperature, and r-selected forms have more abundance and extensive stratigraphical distribution than K-selected forms.

Folding in the study area consists of refolded asymmetrical and concentric anticlines and synclines with fold axis of N51W, 0 and axial plane of N51W, 78SE. These folds are complex anticlines with oval shape and saddling form. They are “open fold” and can be classified as “1B classes”. Most important mechanism of folding, on the bases of evidence (parallel folds with interbedding slicken sides and decollement level in up and down of folds), is “flexural slip folding”. This style caused that the folds cannot to be very deep. Folding time can be considered to be the end of Pliocene. Joints in this area can be classified in 4 series. “a”&’b” series are extensional and have calcite veins and “c”&’d” series are compressional and have slicken sides. All joints are perpendicular to bedding planes, so they formed pre or syn-folding and there are no post-folding joints. On this basis, principal stresses are horizontal and all extensional and compressional joints produced vertical planes. Using folds and joints properties, stresses that resulted during compression between Iranian and Arabian plates are: δ1= N40E, 0- δ3= S50E, 0 and δ2 is vertical and intersection between joints. Faults are rare in this area and had short lengths with low displacements. Transverse and a few longitudinal faults are the most important faults in this area.

Deposition of organic rich black shale during Valanginian–Turonian, nearly all over the world, has marked oceanic anoxic events (OAEs). In Lorestan zone, black shale, marl, thin bedded argillaceous limestone and fissile limestone of Garau Formation, with bitumen, are deposited in correspondence to oceanic anoxic events. These complicate events cause frequent periods of radiation, variety, evolution and extinction in planktonic foraminifera. Planktonic foraminifera experienced their first major adaptive radiation and evolution nearly with the OAES onset. The most important character is the elongation of last whorl chambers and occurrence of species with twin chambers in last whorl in planktonic foraminifera that has been interpreted as an adaptation to low oxygen levels. The study of the Garau Formation (Early Aptian-Early Cenomanian in age) in subsurface section recorded widespread morphological changes in planktonic foraminifera in correspondence to deposition of organic rich argillaceous limestone and some marl intervals.