Iranian Journal of Earth Sciences
Volume:1 Issue: 1, Oct 2009

New simplified tectonic models and depositional history of Late Cretaceous rocks are established in a part of Zagros Orogenic Belt that is located in the Northeastern Iraq. These rocks constutes the most important Cretaceous oil reservoir in the Middle East. The dependent tools are petrography, field study and the concept of drowning phases. This concept is relatively new and accurate in explanation of development of carbonate sequences growth and termination. The columns of both carbonate and clastics rocks of the area are divided into three phases of drowning: 1- Pre-drowning phase of reefal limestone which is represented by Qamchuqa Formation which is equivalent to Mauddud and Shuaba formations (Early Cretaceous) in the south Iraq and in the Gulf. 2- Transitional phase of pelagic limestone and marl deposition which is transitional to post drowning phase during which Gulneri Shale and Dokan limestone Formations (Cenomanian- Turonian) are deposited. 3- Post drowning phase of deep carbonate sedimentation during which Kometan Formation (Santonian-Campanian) and 4- Burial Phase in which Shiranish and Tanjero Formations (Maasstrichtian) are deposited by which Arabian Platform was covered by siliciclastics sediments and main carbonate sedimentation was ended during Campanian. These phases, as resulted from tectonics of Zagros, can replace the complex previously assigned tectonic and depositional history of the area during Later Cretaceous. The application of the phases revealed nearly a continuous history of deposition in foredeep during Early Cretaceous and foreland basin during later ages. This continuous sedimentation is opposite to previously cited episodic sedimentation in the Cretaceous basins. Moreover than that, the occurrences of the previously mentioned subaerial cycles of erosion (unconformities) are not ascertained. The previous cycles had segmented the rocks and history of the area into several separated and unrelated tectonic events that occurred in different basins. According to the above cycles and unconformities the tectonic setting and depositional history of the whole northwestern Iraq assumed be violent during compete time span of the Late Cretaceous by which basin isolation and uplift and erosion occurred. The above ideas are amended and the unconformable boundaries are changed to conformable ones. Consequently, in the present study, a new tectonic history and model are established for Cretaceous which agree with field observation and existed lithofacies.

Principal Skarn deposits along the northern margin of the Ahar batholith from west to east include Mazraeh, Vine and Gowdoul skarn deposits. Among these skarn deposits, the Mazraeh Cu-Fe Skarn deposit is the most typical skarn deposit in the NW Iran. This skarn deposit is located 5 km. north of Mazraeh village and 20 km north of Ahar town. The origin and development of the skarn can be related to the granitic intrusion of Oligo- Miocene age which has intruded a sequence of calcareous rocks. On the basis of petrological considerations the skarn can be subdivided into Exoskarn, Endoskarn and Ore skarn. The main mineral constituents of the skarns are garnet, magnetite, calcite, chalcopyrite, epidote, hematite and pyroxene, accompanied by quartz, pyrite, bornite, coevalite, chalcocite, plagioclase and chlorite. The bulk chemistry and spatial variation characteristics indicate that the endoskarn was the result of interaction between Mazreah granodiorite with crystalline limestone and metasomatic alteration through hydrothermal fluid enriched in Mg, Fe, Cu, P, Ag, Zn, Pb, Cd, Mo, Mn, etc. These elements point toward a magmatic source, and have been contributed to the system from the magma as well as the host rock. The crystalline limestone was the source for Ca and Mg in case of endoskarn. The transformation of granodiorite into endoskarn was accomplished by addition of 1.4 to 15% CaO along with 7.17% of total iron into the granodiorite was accompanied by depletion of about 15.5% SiO2 (average 53.5%).

Adsorption capacity of Cr (VI) onto cousinia eryngioides boiss, activated carbon was investigated in a batch system by considering the effects of various parameters like contact time, initial concentration, pH, temperature, agitation speed, absorbent dose and particle size. Cr (VI) removal is pH dependent and found to be maximum at pH 2.0. The amounts of Cr (VI) adsorbed increased with increase in dose of both adsorbents and their contact time. A contact time of 30 min was found to be optimum. Experimental results show low cost biosorbent were effective for the removal of pollutants from aqueous solution. The Langmuir, Freundlich and Temkin isotherm were used to describe the adsorption equilibrium studies of agrowaste. Freundlich isotherm shows better fit than Langmuir and Temkin isotherm in the temperature range studied.

The most enigmatic problems with the nearly 200 salt domes pierced in the Persian Gulf and in the Zagros Mountain Ranges (ZMR) in southern Iran, a unique morphology in the world, have been the matter of this study, which is based on a combination of field work, enhancement of satellite and aerial photographs etc. In the ZMR, structural anomalies are frequently associated with similar facies distribution patterns. In the eastern portion of the region, emergent salt plugs of Infra-Cambrian age exhibit the same alignment patterns. Such trends bear no apparent genetic relationship to the Tertiary folding responsible for the present Zagros fold belt, but rather indicate their affinity with linear basement features which are readily observable on Land sat imagery and aerial photographs. Bending of anticlines in the competent cover rock, combined with minor strike-slip faults and horizontal displacements of parts of folded structures, strongly point to the presence of these basement faults. The salt plugs, which have pierced cover rocks of up to 10000 m thick, are distributed on the Arabian Platform along regional basement faults. The area of diapir outcrops is bounded by the Oman Line to the east and by the Kazerun fault to the west. Pieces of the basement have been brought up to the surface on some of the salt domes. The fragments were transported by rotational ascent of the Hormuz Salt Formation to the present and former land surfaces. The recognition of features related to basement tectonics and realization of their implication in the control and modification of geological processes are important adjuncts to the search for hydrocarbon accumulations in this region. To our best knowledge, data of basement faults in the study area are scarce. Therefore, this study was carried out to determine basement faults and their relation to salt dome distribution. Considering the fold axes bending, the trend of the salt plugs and also the distribution of epicenters of the last century, numerous new basement faults are introduced in this paper.

Different types of iron oxides deposits have been identified along the Khaf – Dorouneh volcanic and plutonic belt in north east of Iran. Kuh-e-Zar is one of these ore deposits known as Fe- oxide gold deposit. The main purpose of this paper is to detect and discriminate the iron oxide minerals in this area based on the ETM+ data. Data processing has been done by ENVI (Environment for Visualizing Images) software. Color Composites, Band Ratios, Principal Components (PC) analysis were used to delineate the associated zones of hydrothermal alteration and iron oxide minerals. Based on both field observations and the results of this satellite data processing, the area covered by secondary iron oxide (hematite, goethite and limonite mainly in soil) was enhanced very good, but the primary iron oxides (specularite) which are very fine grain and have a linear structure (mainly in mineralized veins) are not very clear in detail in these images.

The Bundelkhand-Aravalli craton is the most important lithotectonic unit in the central and western India where Paleoproterozoic Aravalli Supracrustal sequence has been deposited over an Archaean basement, the latter also known as the Banded Gneiss Complex (BGC). A NE-trending linear metasedimentary sequence, designated as the Jahazpur Belt occurs along the eastern fringe of the Aravalli Supergroup. This belt comprises low-grade metasedimentary assemblages of Hindoli (lower unit) and Jabhazpur (upper unit) Groups. Although predominantly pelitic in composition, both the groups show subtle variations in geochemical characteristics, such as in SiO2, Al2O3, TiO2 etc. and critical trace element (Th, Sc, Rb, etc.) characteristics. CIA (Chemical Index of Alteration) values vary from 73 to 79 in Hindoli metapelites and from 71 to 81 in Jahazpur metapelites indicating moderate to high degree of weathering and alteration in both the cases. The CIA data underline a granodioritic to tonalitic source composition for Hindoli metasediments and a relatively more felsic source (granitic) for Jahazpur metapelites. A probable and likely provenance for the Hindoli metapelites could be analogous to the Banded Gneiss Complex (BGC) which includes TTG gneisses as a major component.

Kuhbanan fault system, as one of the intracontinental faults of central Iran, is recognized by considerable seismogenic activities and modern morphotectonics evidences with a strike-slip (reverse component) motion. According to the geometric and kinematics data, Kuhbanan fault has been divided into 5 segments (S26, S27, S28, S29, S30) in Bahabad region. Measured geomorphic indices of ratio of valley-floor width to valley height (Vf) and morphology of the valley (V) manifest the maximum denudation rate for the S28 segment. The mean calculated values of mountain-front sinuosity (Smf) and %facet parameters for different segments of the fault are 1.1 and 83.16, consequently. Regarding to these geomorphic indices, a denudation rate of about 2-4 mmyr-1 is suggested for this region. According to reconstruction of Kuhbanan fault since 360 ka, minimum horizontal cumulative displacement of 750 m and minimum slip rate of about 2-1.4±0.1 mmyr-1 is inferred from well preserved geomorphology in the northern segment of the fault. Applying this horizontal cumulative displacement causes reconstruction of geomorphic markers such as drainages and shuttered ridges.