Urumieh-Dokhtar Magmatic Assemblage Research Articles

A new tectonic scenario for the Sanandaj–Sirjan Zone (Iran)

Recent geochemical studies of volcanic rocks forming part of the ophiolites within the Zagros and Naien-Baft orogen indicate that most of them were developed as supra-subduction ophiolites in intra-oceanic island arc environments. Intra-oceanic island arcs and ophiolites now forming the Naien-Baft zone were emplaced southwestward onto the northeastern margin of the South Sanandaj–Sirjan Zone, while those now in the High Zagros were emplaced southwestward onto the northern margin of Arabia. Thereafter, subduction continued on opposite sides of the remnant oceans. The floor of Neo-Tethys Ocean was subducted at a low angle beneath the entire Sanandaj–Sirjan Zone, and the floor of the Naien-Baft Ocean was subducted beneath the Central Iranian Micro-continent. The Naien-Baft Ocean extended into North-West Iran only temporarily. This failed ocean arm (between the Urumieh-Dokhtar Magmatic Assemblage and the main Zagros Thrust) was filled by thick Upper Triassic–Upper Jurassic sediments. The Naien-Baft Ocean finally closed in the Paleocene and Neo-Tethys closed in the Early to Middle Eocene. After Arabia was sutured to Iran, the Urumieh-Dokhtar Magmatic Assemblage recorded slab break-off in the Middle Eocene.

Integration and analysis of airborne geophysical data of the Darrehzar area, Kerman Province, Iran, using principal component analysis

This paper describes a methodology for the integrated interpretation of airborne magnetic and airborne γ-ray spectrometer data. The Darrehzar porphyry copper deposit is situated in the Urumieh–Dokhtar magmatic assemblage of Central Iran. Phyllic and propylitic alterations are pervasive in the area but potassic and argillic alterations are not readily recognized on the surface. The spatial distributions of geophysical data resemble the lithological and alteration patterns in the area. The Darrehzar porphyry copper deposit is considered as a control site for determination of the degrees that the geophysical data is correlated with the mineralization zone. Airborne magnetic/radiometric, and geochemical/alteration data sets have been integrated and analyzed using principal component analysis. This technique is found to be useful for the delineation of hydrothermally altered areas and data compression.

Synergetic use of remote sensing and geophysical data for exploration of porphyry copper deposits, using GIS

Darrehzar porphyry copper deposit is situated in the Urumieh-Dokhtar magmatic assemblage of central Iran. In this paper, the integration of multiple geodata sets has been carried out using geographic information system for mapping lithology or hydrothermally altered rocks and also in selecting the best discriminating data elements for exploration of porphyry copper deposits located in areas with similar geological setting and climatic conditions. Principal component analysis is found useful for reducing large data sets into a few principal components. The integration of various geophysical data with SPOT image data through GIS has shown that the hydrothermal alteration and lithology can be mapped with more efficiency.

Tectonics of the zagros orogenic belt of iran: new data and interpretations

The Zagros orogenic belt of Iran is the result of the opening and closure of the Neo-Tethys oceanic realm, and consists, from northeast to southwest, of three parallel tectonic subdivisions: 1.(1) the Urumieh-Dokhtar Magmatic Assemblage;2.(2) the Sanandaj-Sirjan Zone; and3.(3) the Zagros Simply Folded Belt. Recent detailed and reconnaissance mapping and stratigraphie-structural analyses in various parts of the belt indicate that the tectonics of the Sanandaj-Sirjan Zone is dominated by either large-scale composite duplex structures or low- and high-angle NE-dipping imbricate systems. These thrust systems have transported numerous horses and sheets (nappes) of metamorphosed and non-metamorphosed Phanerozoic rocks for tens or possibly hundreds of kilometers. Stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the Late Cretaceous and has continued episodically since that time. Shear sense indicators in various parts of the zone reveal a NE-SW direction of transport. Thrust systems generated in each episode are superimposed upon the previous structures, cutting across and displacing them and producing complicated stacks of thrust sheets. Southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10–15 km in the thickness of the continental crust in the southwestern part of this zone.The so-called z“Main Zagros Thrust”, which has been traditionally considered as the boundary between the Sanandaj-Sirjan Zone and the Zagros Simply Folded Belt, is by no means a single “high-angle reverse fault”, nor is it a narrow zone of “crushed rocks” but a series of low-angle thrusts locally cut by normal faults. These thrusts are indistinguishable from those mapped in the Sanandaj-Sirjan Zone, and are geometrically part of the Sanandaj-Sirjan Zone structures. There is no single thrust among them that can be singled out and referred to as the “Main” one.The boundary of the Sanandaj-Sirjan Zone with the Urumieh-Dokhtar Magmatic Assemblage to the northeast is characterized by a series of structural depressions formed by compression. Rock sequences (including ophiolite complexes) exposed along this boundary are strongly dismembered, sheared and mylonitized. Shearing planes and foliations are either subvertical or dipping at high angles to the northeast. This zone is suggested to be the suture between the Afro-Arabian and the Iranian plates.Overall, the intensity of deformation increases northeastward from the Persian Gulf-Mesopotamian basin, where strata are undeformed and horizontal, through the Zagros Simply Folded Belt which is characterized by en échelon, doubly plunging flexural slip folds, gentle to open in the southwest and close to locally SW-overturned in the northeast. The intensity of deformation continues to increase further northeastward through the Sanandaj-Sirjan zone where thrust faulting is dominant. This pattern suggests that the deformational front has migrated through time from the northeastern part of the Sanandaj-Sirjan zone (i.e., the suture zone) to its present position in the central portion of the Persian Gulf-Mesopotamian foreland basin.

Spectrum loading fatigue crack growth life prediction: Anandan, K., Dash, P.K. and Brahma, K.K. Conf. Fatigue and Fracture in Steel and Concrete Structures, ISFF '91, Madras, India, Dec 1991 Vol 1 (Oxford & IBH Publishing Co. Pvt. Ltd, New Delhi, India, 1991) 243–252

In this work, the structural geology and the tectonic conditions of the Zagros orogeny along the route of Qom to Kermanshah cities were investigated using the combined geophysical methods of the airborne magnetometry and the ground-based gravity data. Airborne magnetometry data of Iran with a line space of survey, 7.5 km, were used to model the magnetic susceptibility property along the route. At first, the airborne magnetic data were stably 500-m downward continued to the ground surface in order to enhance minor changes of the Earth’s magnetic field over the studied region. Afterward, 3D inverse modeling of the magnetic data was implemented to the downward continued data, and subsequently the section of magnetic susceptibility variation along the desired route was extracted and imaged at depth. The acquired model could appropriately predict the observed magnetic data, showing low misfit values between the observation and the predicted data. The analytic signal filter was applied to the reduced-to-pole (RTP) magnetic data leading to the determination of the active and probable hidden faults in the structural zones of the Zagros, such as Sanandaj-Sirjan, Central Domain (CD) and Urumieh-Dokhtar based upon the generated peaks along the profile of analytic signal filter. In addition, the density variations of the subsurface geological layers were determined by 3D inverting of the ground-based gravity data over the whole study area, and extracting this property along the route. The joint models of magnetic susceptibility and density variation could appropriately localize the traces of faults along with the geologically and tectonically structural boundaries in the region. The locations of faults correspond well to the variation of geophysical parameters on the inverted sections. Probable direction, slope and extension at depth of these faults were also determined on the sections, indicating a high tectonized zone of the Sanandaj-Sirjan Zone (SSZ) parallel to the zone of the Urumieh-Dokhtar Magmatic Assemblage (UDMA). The UDMA zone increases the magnetic and the Bouguer anomalies by intruding into the CD zone as well.