Kharazmi Journal of Earth Sciences

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Gabbroic bodies with NW-SE trend outcropped in the southwest of Sahneh in the north of Gamassiab River, W. Iran are part of Zagros ophiolite . This complex is separated from the other geological units by deep faults and cut by pyroxenitic dikes. The field evidences, petrographic, geochemical and mineral paragenesis of these rocks are completely different from the fresh and un-altered gabbroic rocks. Furthermore; the high ratios of ¹⁴³Nd/¹⁴⁴Nd (0.512945-0.513021) and low ratios of ⁸⁷Sr/⁸⁶Sr (0.70334-0.70656) indicate the sub-oceanic depleted mantle source for the origin of these rocks. Low variation of ¹⁴³Nd/¹⁴⁴Nd ratios, increasing of ⁸⁷Sr/⁸⁶Sr ratios, decreasing of SiO₂ and increasing of CaO and Al₂O₃ mainly concludes the high reaction of gabbroic rocks with seawater. The pargenetic assemblages of altered gabbros are grossular/hydrogrossular, anderadite, epidote, idocrase (vesuvianite) and diopside. The mineral paragenesis reveals that the rodingitization was occurred by reaction of gabbroic bodies with high alkali water at a shallow depth. 

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Majority of Iran’s anticline oil traps located in the Dezful Embayment in southwest of Iran and Zagros Fold and Thrust belt. These anticlines mostly have NW-SE trend and their southern limb have a steep to returned dip. In some cases, thrust faults and steep south west limb of anticlines caused thrusting of adjacent anticlines on the others and repetition of sequence stratigraphy. The study area covered by Aghajari and Marun anticlines in Dezful embayment and the Aghajari anticline is thrusting on the Marun. In this research, structural geometry of thrusting of Aghajari anticline on the Marun anticline were studied based on seismic reflection data and specified the repetition of sequence stratigraphy. These two anticlines have a NW–SE trends and the Marun anticline is developing in the south of the study area, and most of deformation is concentrated in Aghajari anticline. The Marun anticline formed in the middle of the study area without thrusting, while maximum amount of thrusting of Aghajari anticline on the Marun anticline occurred in this area. There is a shallow thrust in the south limb of two anticlines in the northern part and an upper thrust from Gachsaran formation exposed from progressive deformation. Finally, a shallow thrust propagates to surface in the end of NW parts and back thrusts separate from main shallow thrust. But unlike Aghajari anticline, an upper thrust from Gachsaran formation propagates to surface with continuation of deformation in the Marun anticline showing low depth of the Marun anticline.   

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Extending in the Zagros range, the Hormuz Series are known as the world's oldest evaporative unit. Movements related to the salt structures are one of the unique phenomena associated with Hormuz Series, which could be observed in different regions of the Zagros range. Owing to the poor outcrops of Hormuz Series, the surface evidence to assess effects of the salt tectonics is not enough, therefore subsurface data are very useful for in this regard. The isopach maps produced by the National Iranian Oil Company as well as the distribution maps of salt domes between the Kazerun and Minab faults are used to examine the effect of salt tectonics on the sedimentary setting of the Fars Basin and Bandar-Abbas hinterland from the Permian time up to the present. Accordingly, the Isopach curves are digitized in GIS environment, then the negative 3D map [before deposition] and positive [after deposition] are obtained in SURFER software. The study of changes in Late Permian to Miocene period sequences as results of salt dome activity shows that the first movements of salt domes in this area has incepted in Permo-Triassic time synchronous with the opening of Neotethys Ocean. During the period of Late Triassic to Early Cretaceous some of the salt domes have been buried and tangible actions that altered the sedimentary system, is not happening. The second main pulse of the salt dome activity coincides with the development of the Zagros foreland in the Upper Cretaceous. The peak activity of the salt domes and their impact on the sedimentary setting happened simultaneously with the final development of the Zagros foreland basin in the time frame of the Paleocene-Eocene. In Oligocene to Miocene times the salt domes were active, especially in the southeastern part of the range. This study seeks to investigate the salt domes and the result of their uplift on the sedimentary settings in the Fars basin.

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 Some Peridotite dismembered parts have outcropped in Southwest of Sahneh, as a part of Zagros ophiolite complex. These bodies contain olivine, pyroxene and spinel with some altered minerals such as serpentine and amphibole. Based on electron microprobe analyses, olivine composition is forsterite with Fo_88-94. The composition of pyroxenes is diopside and clino­enstatite with low contents of TiO₂ and Al₂O₃. The spinels are poor in Al₂O₃ with Cr# number between 0.41-0.51 which indicate the ophiolitic and depleted mantle origin. The serpentines have Al₂O₃ content in the range of 0.2 to 2.2 wt.% with SiO₂ content between 34.15 to 44.07 wt.%  and are chrysotile and lizardite. The low temperature of serpentine minerals (lizardite and chrysotile) and primary spinels indicates that the alteration was lower than 500 ºC. In the tectonic setting diagram, based on mineral chemistry, the higher content of Al₂O₃ and MgO in pyroxenes than to mid oceanic ridge ones and have the same properties with back arc basins. These evidences have been confirmed by spinel mineral chemistry. Accordingly based on the geodynamic situation of Kermanshah area and tendency of some samples to back arcs, it seems these peridotites have derived by high degree partial melting of depleted and sub-oceanic mantle in a supra-subduction zone-back arc and have same properties with residual mantle peridotites

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The East Darreh-Baneh anticline is located in the Lurestan structural zone, west of the Zagros fold and thrust belt. In this zone thrust faults and detachment horizons have a main role in geometry and kinematic of the folded structures. In this research, deformational pattern and structural geometry of the East Darreh-Baneh anticline have been studied using interpretation of five 2D seismic profiles, drawing of structural cross sections, drilling well data in the adjacent anticline and related analysis. Accordingly, the East Darreh-Baneh anticline is a detachment folding, in which two upper and middle detachment levels is affected its structural geometry. In the study area, the shaly Garu and the flysch Amiran formations caused deformations as a middle and upper detachment levels, respectively. The high thickness of the upper detachment level caused formation of the anticlines in surface with low wavelength and amplitude and formation of the surface disharmonic folding on deep-seated anticlines. Also, geometrical parameters analysis of the East Darreh-Baneh anticline indicate that this anticline is an asymmetric and noncylindrical fold and from tightness view is open to gentle with wide aspect ratio.

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The Dara anticline as one of the anticlinal oil structures in the Zagros fold-and-thrust belt within the Dezfol embayment (west of the Kazerun fault) has been carried out at this research. For this aim, after the determination of fold trend and mechanism, some sections at: NW nose, center and SE nose of anticline have been drown by using subsurface data. Analyses of folds exhibit the Dara anticline at Class 3 Ramsay classification. On the base of Fleuty classification, this fold is an open one. Fractures are at three main trends: E-W, N-S and NW-SE. Restoration sections indicate that the rate of shortening along the NW nose (A-A' section) is 6.5% and at B-B' section is 8.4% that illustrates on high folding rate at SE nose of the Dara anticline.
 
 

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Niabad-Qalaje ophiolitic complex is part of Sarvabad ophiolites in Kurdistan that exposed in northwest of Iran and the north of Kermanshah Ophiolites. The complex located in north of Zagros orogeny, consists of lens form, tectonically dismembered ophiolitic sequences located along the main Zagros trust. The ultramafic part includes serpentinized dunite and wherlite, serpentinite and chromitite that outcropped as consecutive lenses. Small lentiform chromitites present podiform and shear fabrics. The major minerals in peridotites are olivine (Fo= 88-91), clinopyroxene and chromian spinels.  Low Ti value and high content of Al and Cr# in peridotite chromian spinels reveal a high rate of partial melting (25-35%). Mineral chemistry and whole-rock chemistry clearly indicate that the Kurdistan ultramafic cumulates and chromitites record an episode of boninitic magmatism.  Boninitic melts in Niabad-Qalaje ophiolites were formed by partial melting of a depleted peridotite which made up the residual mantle after MORB-type melt extraction. The chemistry of peridotites shows the abyssal to supra-subduction zone source. Comparing the lithological and geochemical characteristics of the studied ophiolites with some other complexes in the world denotes that the Kurdistan ophiolitic complex formed in a fore arc basin close to the Sanandaj-Sirjan zone continental margin.

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The Gurpi Formation with a thickness of 190 m at the Kouh-e Sefid anticline is investigated based on the calcareous nannofossils. In this section, Gurpi Formation is mainly consists of shale, marls and argillaceous limestones. As a result of this study, 21 genera and 41 species of calcareous nannofossil have been recognized. Based on distribution of index species calcareous nannofossils CC16-CC25 biozones have been recognized, that is corresponding to UC12-UC20a^TP. According to the identified biozones, the age of the Gurpi Formation in this section is middle/late Santonian to early late Maastrichtian. This study in the Kouh-e Sefid anticline shows that the sedimentation of Gurpi Formation started at the middle/late Santonian and continued to the early late Maastrichtian

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In order to study of calcareous nannofossils biostratigraphy, the upper part of the Pabdeh Formation and the lower parts of the Asmari Formation were selected in one well in Parsi oil field in southwest of Iran. Investigation of calcareous nanofossils in this section resulted in detection of 16 genera and 39 species. According to the first occurrence of index species and distribution of fossil assemblages, four biozones including Helicosphaera reticulate Zone (NP22/ Rupelian), Sphenolithus predistentus Zone (NP23/Rupelian), Sphenolithus distentus Zone (NP24/ Rupelian- Chatian) and Sphenolithus ciperoensis Zone (NP25/ Chatian), which is equivalent to zones CP16c - CP19b, was recognized in the upper part of the Pabdeh Formation. As a result of this study, and based on the identified calcareous nannofossil biozones, the age of the uppermost part of the Pabdeh Formation is Rupelian to Chatian. In the basal anhydrite portion of the Asmari Formation, no biozone of calcareous nanofossils was determined. In this study, the dominant conditions of the sedimentary environment, were determined by the presence of calcareous nannofossils index species, so that the presence of these species confirms the warm climate and basin location at low latitudes.

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In this study, the sediments of Kazhdumi Formation were evaluated as a possible source rock in Ahwaz, Aghajari, Parsi, Kilorkrim and Masjed Soleiman oil fields in Zagros basin located in southwestern Iran. For this purpose, the Arrhenius kinetic model was used to evaluate the maturity of the source rock as well as to investigate oil generation. According to the information obtained, the dominant kerogen in the Kazhdumi Formation is type II. Also, based on the values obtained from the Rock-Eval pyrolysis, this Formation has fully entered the oil window and has a high­ . Therefore, the kerogen of this Formation was classified in very good source rock, which has a very good hydrocarbon potential. Similar results were obtained in this study based on the Arneus kinetic model. Accordingly, the Transformation rateof hydrocarbons in different oil fields were the range of 66 to 100%. These changes are mainly due to different burial history in the oilfields studied.
 

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