Showing 6 results for Rahgoshay
Afsaneh Naseri Esfandagheh, Mohamad Rahgoshay, Sasan Bagheri, Iman Monsef,
Volume 31, Issue 2 (5-2023)
Abstract
The Faryab ophiolitic complex is located in Golashkard region, in the southeastern part of Sanandaj-Sirjan zone. This complex is mainly composed of the ophiolitic mantle part consisting of dunite, wehrlite, and pyroxenite, as well as chromitite and serpentinite, which was thrusted on the metamorphic rocks of the Bajgan complex. Dunites are found in the form of bodies sometimes containing thin layers of chromitite. Wehrlite and pyroxenite are also exposed as minor dykes in different parts of the complex. The main texture in the wehrlite and dunite is granular and cataclastics. The chromitites appear in both stratiform and podiform. Microscopic evidence indicates that the presence of lattice preferred orientation in minerals may be formed during recrystallization at high- temperature mantle. The chemistry of minerals in the peridotites shows that rocks including forsterite with low chromium and high nickel, diopside and magnesium-bearing Cr-spinel with small amounts of orthopyroxene were partially melted in the upper mantle up to 35 to 40%. Using tectonic setting discrimination diagrams led us to conclude that the Faryab complex peridotites are a part of the oceanic lithosphere which have emplaced in the supra-subduction zone, suffered partial melting evolutions and then tectonically emplaced in the crust in the form of ophiolitic remnants.
Afsaneh Naseri Esfandagheh, Mohamad Rahgoshay, Sasan Bagheri,
Volume 31, Issue 4 (12-2023)
Abstract
Metamorphic rocks in the Faryab complex are part of the Bajgan metamorphic complex with Upper Cretaceous age that crops out in the southeast of Sanandaj-Sirjan zone, south Iran. The metamorphic rocks of Faryab Complex have been metamorphosed in greenschist and amphibolite facies include garnet mica schist, epidote schist, epidote amphibole schist, amphibole schist, epidote amphibolite, amphibolite and garnet amphibolite. Minerals composing amphibolites are garnet, amphibole, epidote, plagioclase, quartz, chlorite and sphene as well as titanite and magnetite as secondary minerals. The composition of amphiboles in amphibolite and epidote amphibolite are made of calcic types and their chemistry varies from magnesio-hornblende through ferro-tschermakite-hornblende, ferro paragasite-hornblende, ferro edenite-hornblende to ferroedenite. The composition of plagioclas ranges from albite to oligoclase. The protolith of most amphibolites and epidote amphibolites in the Faryab complex are defined by the occurrence of key minerals in metabasites and are considered as basalt and gabbro. Several thermobarometeric calculation methods indicate that the highest temperature and pressure for the amphibolites, which were appeared adjacent to peridotites and located in the northern part of the complex, are about 700 °C and 9.7 kbar. By moving away from the peridotites into the lower structural units in the southern part of the Faryab complex, the temperature and pressure range in the amphibolite and epidote amphibolite and decrease to 510°C and 4.34 kbar on average, which is beginning of amphibolite and middle amphibolite facies. Investigation of the P-T pathes in conjunction with close associations of isograde lines show that geothermal gradients were high even at the beginning of metamorphism. Mineral chemistry and thermobarometric calculations along with consideration of the structural position of the Faryab complex indicate that the tectonic position of the Faryab complex in the Sanandaj-Sirjan zone may remined us an accretion-subduction complex. This complex was constructed in the north-dipping Neo-Tethyan subduction zone during the Late Cretaceous time, which caused the higher degree metamorphic rocks were thrusted onto the shallower ones.
Salimeh Dehghani Dashtabi, Mohammad Rahgoshay, Shahriyar Mohammadi,
Volume 31, Issue 4 (12-2023)
Abstract
Biotite is usually formed as a rock-forming mineral in a wide range of felsic to intermediate intrusive rocks. Due to complex crystal structure of biotite, different elements can substitute in this rock-forming mineral; therefore can record the physicochemical conditions of the source magma. Based on the chemical classification of mica, the biotites of the igneous rocks, investigated in the Hararan area, can be placed between the poles of phlogopite and annite, and are magnesium type, which indicates their formation in high oxygen fugacity, and according to the amounts of Mg, TiO2 and FeO oxides, these biotites are primary type. These biotites belong to the calc-alkaline magmatic series formed in the subduction environment. Based on the chemistry of biotites, oxygen fugacity in the source magma of Hararan granitoid is in the range of iron oxide. Geothermometry of biotites shows that these biotites formed at temperature ranging between 680 to 780 degrees Celsius and pressure of 2 (1-2) Kbars.
Salimeh Dehghani Dashtabi, Mohammad Rahgoshay, Shahryar Mahmoody,
Volume 32, Issue 1 (4-2024)
Abstract
The Lalezar igneous complex is located on the border of the Sanandaj-Sirjan zone and the southeastern parts of the Urmia-Dakhtar volcanic arc and in the northeast of Baft city in Kerman Province. In the northwestern and western boundaries of the intrusive body, there are relatively wide contact metamorphic carbonate rocks. In the southern part of Hararan, the Lalezar igneous body with the Oligo-Miocene limestone and marl complex (equivalent to the Qom Formation), as large contact with metamorphism halo (skarn and marble parts), is the most widespread. Based on microscopic studies, garnet, calcite, wollastonite, pyroxene, olivine, idocrase, and epidote minerals are formed in skarns. Different metamorphic zones including garnet-clinopyroxene, olivine-clinopyroxene, wollastonite-garnet, and garnet-epidote have appeared. Based on the geochemical analysis of the minerals (EPMA), the garnets contain more than 70% grossular (calcium-rich garnet) and less than 30% almandine (iron-rich garnet). The composition of clinopyroxenes belongs to the first group (calcium-iron and magnesium) and of the wollastonite-enstatite type, where the amount of wollastonite is more than 50%. Also, there is less than 10% ferrosilite in the composition of these clinopyroxenes. Based on the garnet-clinopyroxene temperature-pressure measurement, the temperature of skarn formation, based on various equations presented, is between 413 and 530 degrees Celsius and the pressure is 1.5 to 2.5 kbar. The existing paragenesis as well as thermodynamic conditions indicate oxygen fugacity greater than 0.2. This phenomenon indicates the activity of fluids rich in silicate-rich solutions in the formation of these skarns.
Salimeh Dehghani Dashtabi, Shahryar Mahmoody, Mohammad Rahgoshay,
Volume 32, Issue 1 (4-2024)
Abstract
The Laleh-Zar granitoid complex is one of the most important magmatic phases of the Urumieh-Dokhtar belt and is located in the southeast of this belt in Kerman Province, which has a combination of granite and gabbrodiorite. Parts of this vast complex is exposed in the southern part of Hararan region. Based on petrographic studies, these igneous rocks are granodiorite, diorite, and dacite with quartz, plagioclase, amphibole, biotite, pyroxene, and opac minerals. The secondary minerals of chlorite, calcite, epidote and sericite are also present in these igneous units. The results of mineral analysis, using microprobe method, showed that amphiboles are calcite and hornblende. these amphiboles are igneous and belong to the calc-alkaline magmatic series and are of S type (subduction Amphiboles), which are formed in the subductions environment. The pressure and temperature during the formation of these amphiboles were calculated by different methods, therefore the temperature was 650 to 798 degrees Celsius and the pressure was 0.9 to 2.3 kbar. In addition, these amphiboles have high oxygen fugacity and were created at the depths of 9 to 14 kilometers of the earth. Based on the relationships between different elements in these amphiboles, the conducted studies showed that tschermakite and adenitic successions occurred in these amphiboles, but glaucophane, riebeckite and richterite successions did not occur in these amphiboles.
Ayoub Veisinia, Dr Mohammad Rahgoshay, Dr Iman Monsef, Dr Bahman Rahimzadeh,
Volume 3100, Issue 1000 (1-2023)
Abstract
The Dalampar ophiolitic- metamorphic complex is is an unknown part of the Neo-Tethys ophiolite and is located NW of Iran in the south of Urmia city within the Sanandaj-Sirjan metamorphic belt. This complex consists of a variety of schist, gneiss, amphibolite rocks with serpentinite and tectonic slices including gabbro, dunite, marble and diabase. Tectonically, the Dalampar ophiolite is severely mingled and the boundary of different units in this complex is indistinguishable. The amphibolites show a discontinuous outcrops as pods and lenses. Sometimes have lineation and foliation. Amphibole and plagioclase are main mineral constituents in the rocks. Study of whole rock chemistry of the amphibolites indicates that they are originated from an a igneous protolith with basaltic (or gabbroic) and tholoitic to calk-alkaline nature. Chondrite normalized-REE diagram show LREE enrichment relative to HREE. Primitive mantle- normalized trace elements diagram show depletion of HFSE and HREE. According to the discrimination diagrams of tectonomagmatic setting, the protolith of investigated metabasites has been islands arc and somewhat mid ocean ridge.
