جستجوی مقالات مرتبط با کلیدواژه « binaloud » در نشریات گروه « زمین شناسی »

Geological events from Precambrian to Quaternary have played a very important role in producing magmatic rocks in Iran. However, magmatic rocks with the ages of Precambrian, early Cambrian and specially Tertiary are much more frequent (Aghanabati, 2004). In contrast, magmatism and plutonism in Iran with Paleozoic age considered to be very rare. Volcanic rocks with the age of Ordovician-Silurian have been reported from some restricted areas of Iran such as Soltan Meydan near Shahroud (Derakhshi and Ghasemi, 2015) and Abyaneh near Kashan (Ayati et al., 2011). Volcanic and volcanoclastic rocks from the North of Neyshabour extend with a linear trend from Garineh to Bojan. In the lack of geochronological data and on the basis of stratigraphical evidence, the age of Ordovician-Silurian has been suggested for these rocks. A detailed study on petrology and geochemistry of north Neyshabour volcanic and volcanoclastic rocks can help us reconstruct the evolution of Iran bed rock during the early Paleozoic Era. The aim of this study includes petrology and major and trace element geochemistry to present critical keys to obtain some knowledge about tectono-magmatic situation of Iran during the early Paleozoic Era, especially in the Binaloud structural zone. 

This study was carried out in two parts including field and laboratory works. Sampling and structural studies were carried out during field work. The petrographic studies were performed on 45thin and polished thin sections. Geological map for the study area was also prepared. Whole-rock chemical analysis of 7 samples for major, minor, trace and rare earth elements were performed at the ACME Laboratory in Canada, by using the 4AB1 method using ICP-MS and the major oxides of six basalt samples were analyzed by X-ray fluorescence (XRF) at the Zarazma Laboratory.

The study area is located in the Northeast of Iran 15 Km NE of Neyshabour city and 7 Km NE of Bojan village. The Bojan area consists of Paleozoic sedimentary rocks (Limestone, sandstone, Dolomite) and volcanic-volcanoclastic rocks (basalts, andesit-basalts, andesite, trachyte, agglomerate and tuff). Petroghraphic studies showed that major minerals in Bojan basalts are plagioclase, pyroxene and olivine and secondary and accessory minerals are apatite, ilmenite, magnetite, chlorite, calcite and epidote. The texture of the Basalts is porphyritic, glomeroporphyric and trachytic.Based on geochemical data, the TAS diagram shows that the Basalts fall within the fields of tephrite to trachyte and belong to alkaline series with sodic nature. MgO# is varied from 20.13 to 38.62 which can be interpreted on the basis of crystal differentiation in magma chamber. The low value of compatible elements such as nickel and descending trend of MgO versus SiO2 can clearly be explained in terms of olivine fractionation. In addition, the nearly constant ratios of incompatible elements such as Nb/Zr, Ce/Zr, La/Zr, and Rb/Zr in rocks with different SiO2 content can reveal the importance of primitive magma differentiation. In contrast, these ratios suggest that crustal assimilation plays no important role in changing primitive magma composition. Enrichment of LREE compared with HREE in the studied basalts can be explained by low degrees of partial melting. Chondrite-normalized REE patterns for basalts from the Bojan area show a very similar pattern with those from transitional - mildly alkalic basalts from the Eastern branch of the East African Rift. Spider diagram patterns for Bojan basalts normalized according to Thompson (1982) and Sun and Mc Donough (1989) show a clear enrichment of all trace elements compared with those from chondorite and primitive mantel. On the basis of tectonic setting discrimination diagrams the study area basalts fall in within plate alkaline domain. According to petrographical and geochemical data of Bojan volcanic rocks it can be concluded that magmatism in the Bojan area has been formed as a result of a cycle of within plate rifting when the Palaeo-Tethys Ocean started to open during the Ordovician-Silurian time. AcknowledgmentsThe Research Foundation of Ferdowsi university of Mashhad, Iran, supported this study (Project 3/50860, 08/09/ 2019). We thank the university authorities for funding. The authors also would like to thank Professor Gültekin Topuz at the Eurasian Institute of Earth Sciences, Istanbul Technical University (Turkey) for his kind support and valuable comments.

Continuation of the compressional regime within the convergence zone between the Central Iran and Turan rigid blocks caused thrusting of old rock complexes over the recent sediments. As a result of multiple thrusts and folds, the area uplifted at the same time and the Binalud range have been shortened. This study attempts to evaluate the amount of shortening of the Binalud mountains by reconstruction of a balanced cross-section. Field data from the Dulat-Abad-Neyshbur transect, study of the geological units and décollements along the section, and the Move® software environment are used as the basis for this research. Based on these information, four tests were carried out for balancing the cross section in question. The first test, which used the arc and polygon method for the horizons and a listric fault without floor thrust, failed to display the deformed section. In the second test the section was drawn, however the deformed structure did not balance the section in the process of unfolding the fault bend folds. In the third and fourth tests, we used the kink method to restore the deformed state to an undeformed section. For the third test, deformation was proceeded from the hinterland, and in the process of restoration, a shortening of about 65% was revealed. The fourth test was proceeded from the foreland, and taking into account both the foreland uplifts and shortening, the amount of shortening of Binalud range was estimated to about 26%. The final structural model defined a thin-skinned fold and thrust belt which included fault-bend-folds with out-of-sequence and in sequence duplexes. Major décollement horizons defined in the region include: 1) shale horizons within the Silurian-Devonian rock units, 2) medium-bedded dolomite and limestone layers within the Bahram Formation, and 3) evaporitic layers in the Eocene sediments.

In this paper, the feedback or interaction between tectonic and surface processes in the Binaloud Mountains and Neyshabour plain has been investigated. To achieve this, we have used topographic data, recorded earthquake data provided by the Geophysical Institute of Tehran University (Mashhad center) and field surveying results. Surface processes affect the propagation of tectonic thrust wedges in orogenic belts. In regions tectonic processes have led to an increase in the surface slopes due to development of mountain highs, surface processes will justify the uplifted areas by smoothing the slopes, eventually shedding off a massive load of clastic sediments into the foreland basin. Because of their huge weight and volume, these sediments prevent the forward propagation of the wedge and therefore increase the accumulation rate of stress in the orogenic wedge. Also the increase of fault-plane dips in the orogenic wedge will make the slip along the fault planes hard or even impossible. Formation of out-of-sequence faults and back-rotation of preexisting thrust faults may be considered as results of these accumulated stresses. North Neyshaboor thrust fault is a later or secondary structure and can be considered as an out-of-sequence thrust because it cuts other thrust sheets and limbs of folds. Our research shows that the high volume of Paleogene/Neogen sediments in the Neyshabour foreland basin has prevented the forwards (southwestward) propagation of the Binaloud mountain range as the orogenic wedge. Releasing of the accumulated forces has therefore led to the development of the North Neyshaboor out-of-sequence fault and back-rotation of former thrust faults.

The Dalichai Formation is among marine deposits in Jurrasic period that has a geographic expansion in north of Iran. In order to palynological studies in eastern part of the Binaloud Mountains an outcrop of this formation, in the bar village was selected. The thickness in bar village section is 255 meters includes dark gray shales. The study of 112 slides of 28 samples taken from this formation showed that the most of the samples contain palynomorphs specifically dinoflagellates. 53 species belonging to 27 genera of dinoflagellates were identified. According to dinoflagellates, a middle Jurassic age was determined for the Dalichai Formation in the Bar village section. Based on the study of three main groups of phytoclasts, marine palynomorphs and amorphic organic matters and result of the statistical studies of different factors, sedimentary environment of the Dalichai Formation in studied section was open marine basin with shallow and low oxygen condition.