PETROLOGY
Year:2015 | Volume:5 | Issue:20|Papers Count:9

In the central part of Dehaj-Sarduieh volcano-plutonic belt in Kerman province, there are some special doleritic dykes containing plagioclase megacrysts. This area is located 70 km south of Kerman city, and represents a part of Urumieh-Dokhtar volcanic belt. The most abundant rocks in the area include pyroclastic rocks and basaltic to andesitic lava flows with Eocene in age and are considered as the host rocks for the studied dykes. The thickness of the dykes reach up to 7 meters in the field, in which plagioclases are the only minerals can be recognized. Plagioclase crystals show a clear flow differentiation and generally, tend to concentrate in the central parts of the dykes. Under the microscope, the studied dykes contain plagioclase megacrysts and olivine phenocrysts set in a fine-grained and microlithic matrix. Different types of non-equilibrium textures such as mesh, dusty and zoning are found in the plagioclases. These evidences suggest some processes such as replenishment of magma chamber and decompression due to rapid ascent of magma. Geochemically, these rocks belong to the calc-alkaline magmatic series with some tendency toward the tholeiitic ones. Depletion of Nb, P, Ta and Ti elements suggest that the parent magmas relate to the subduction zone setting and affected by crustal contamination. According to the petrogenetic studies, the dykes formed in an active continental margin environment. Trace element concentrations revealed that the parent magmas probably, produced by partial melting of mantle sources. The source may have been metasomatized by slab-derived fluids and variations in Th/Yb and Ta/Yb ratios indicate that the resulted magmas have been affected by crustal contamination en route to the surface.

We present new whole rock geochemical data for the Sahand dacite and rhyolite rocks lying in the south of Tabriz, and formed during the Oligo-Miocene period, when the collision between the Arabian and the Eurasian plates occurred following the subduction of Neo-Tethys ocean during the Cenozoic. The investigated rocks were emplaced into the late Cretaceous and Eocene sedimentary, volcano-clastic and volcanic rocks. The dacite and rhyolite rocks are characterized by low Y and high Sr concentrations and highly fractionated LREE/HREE patterns, the common characteristics of slab melt-derived adakites. Geochemical studies indicate that lava flows belong to calc-alkaline magmatic series and their parent magmas have not been subjected to extensive fractionated. The highly enrichment of LREE compared to HREE, high contents of LILE relative to HFSE and significant anomalies of Nb, P and Ti suggest a subduction-related volcanism. In the trace and major elements correlation diagrams, the Sahand samples are plotted in the field of high-Si adakite. Also, the Sahand adakites show higher MgO and Mg# contents. Which is interpreted as reflecting interactions between the ascending adakitic magma and the overlying mantle wedge. These rocks belong to the post-collisional arcs. In this tectonic setting, magma ascent is controlled by strike-slip faulting and associated pull-apart extensional tectonic.

The Ghalilan granitoid pluton is located in SW- of Qorveh and in the Sanandaj-Sirjan zone. Based on petrographic studies, the body includes three rock units, composing of granitoid, porphyritic granite and diorite. These rocks are mainly composed of plagioclase, alkali-feldspar, quartz and amphibole. The composition of the studied plagioclase is An 14-50 (the minimum value in granite) to An 41.4-58 (the maximum value in diorite) and some samples display normal zoning and rapakivi texture. The results of electron microprobe analysis (EMPA) indicate the amphiboles studied are magnesio hornblende in composition implying I-type nature of magma. Application of different barometers and thermometers (e.g. Al-in-Hornblende, Plagioclase-Amphibole) exhibits a pressure of ~ 1 to 3.3 kbar and temperatures of 690-804oC for the intrusion. The reaction of these variations is reflected by the growth of minerals such as large zoned plagioclase crystals in the porphyrtic granites. In addition, the presence of the zoned plagioclase implies the PH2O variations at the time of crystallization and emplacement of the magma in the depth of ~8 km. The composition of hornblendes suggests their formation in high oxygen fugacity condition, which is in accordance with their mineralogical characteristics and tectonic setting of Ghalilan body (subduction in active continental margin).

The Misho Mafic magmatic massif (in NW of Iran) with complex and un-clear paleotectonic is situated in the Soltaniye- Misho zone, in SW of Marand city between the north and the south of the Misho faults. This mafic massif intruded into the PreCamberian Kahar sedimentary rocks and is covered by Permian sedimentary rocks. The lithological units of this massif are gabbro, norite, anorthosite, pyroxenite, olivine gabbro and troctolite. Diabasic dykes with gabbroic composition cut the mafic massif. The main mineral in these leucocratic rocks with cumulate texture is plagioclase which is mainly bitownite and labradorite in composition. Anorthosites are not distinguishable from gabbros on different discrimination diagrams. Anorthosites and gabbros are related to tholeiitic to calc-alkaline magmatic series indicating similar source for both rock types. Gabbros and anorthosites are meta-aluminous and show MORB affinity. Dating of anorthosites by zircon U-Pb method and considering this age for the Misho mafic massif helps us to identify the Misho paleotectonic. Dating results show that the emplacement time for gabbros and anorthosites is early Carboniferous (356.7±3.4 Ma), which is also confirmed by stratigraphy relation (between Kahar Cambrian sediments and Permian sedements). We suggest that Misho mafic massif is formed by an extension event related to plume- type magmatism in early Carboniferous. This is the reason for initiation of spreading of Paleotethys oceanic crust in NW Iran.

The study area is located in NW of Piranshahr town, Western Azerbaijan province. Based on the petrography, mineralogy and textural relations, the peridotites studied are classified into two groups: serpentinized peridotites and serpentinites. The second type, on the base of serpentine polymorphs and texture can be classified into three subgroups in turn: a) hydrated serpentinites which are characterized by low temperature serpentine polymorphs (chrysotile and lizardite), b) antigorite (high temperature serpentine polymorph) bearing serpentinites which formed at relatively high T and P conditions having interpenetrative texture and c) listwanitic serpentinites with brecciated texture containing of minerals as serpentine, chlorite and high amounts of carbonates. Distinguishing of serpentine polymorphs in the investigated rocks has been done using Raman spectroscopy and microprobe analysis. Formation of low-T serpentine polymorphs in the hydrated serpentinites are most likely related to the in-situ alteration of oceanic crust whereas antigorite in the metamorphic serpentinites is formed due to regional metamorphism during subduction and/or subsequent closure of ocean. Tremolite, clinochlore/picnochlore and Fe-rich spinel are coexisting minerals with antigorite. Temperature and pressure of the antigorite bearing serpentinites are obtained on the basis of equilibria reactions using THERMOCALC, as 550oC and 7 kbar, respectively. On the base of olivine and pyroxene norm, the protolith composition of the Piranshahr metaperidotites is determined as harzburgite and less lherzolite. The high MgO and relatively low CaO and Al2O3 contents of the investigated rocks indicate ophiolitic characteristics of the Piranshahr metaperidotites. Considering the location of the Piranshahr ophiolites at the end of the northwestern part of the Zagros ophiolitic belt, it can be concluded that hydrated serpentinites and antigorite-bearing serpentinites are formed in relation with static oceanic floor alteration and subsequent dynamic metamorphism during subduction and/or closure of the Neotethys ocean, respectively.

The Tarom Olia quartz monzonitic intrusive is one of the plutons cropped out in Alborz-Azarbaijan zone which is elongated in NW-SE direction. The pluton, lithologically comprises monzodiorite, monzonite, quartz monzonite and monzogranite. Field and petrological studies as well as geochemical considerations revealed that this pluton crystallized from an I-type metaluminous magma with shoshonitic affinity. The magma has originated by melting of a metasomatized lithospheric mantle then affected by processes by which modified composition of the primary magma to produce the intermediate and felsic rocks.

The Khut copper skarn deposit is located 50 km northwest of Taft city in Yazd province. Intrusion of granodiorite apophyses of Oligocene-Miocene age into upper Triassic carbonate units of the Nayband formation has led to the formation of skarn occurrences and sulfide marbles resulting in systematic depletions of 13C and 18O values in the calcite types. Based on the calculated models, isotopic depletion of calcites from less altered limestones to skarn zones can be attributed to the magmatic fluid infiltration. Skarn calcites show the most depletion compared to the other zones. These skarn calcites have been formed by magmatic fluids (d18O=11.0‰) that reacted/interacted with unaltered limestone rocks at temperatures of less than 600oC with X (CO2) =0.02 and water/rock ratio of 20 to 50%. The d34S values of chalcopyrite separates from skarns and marbles from the Khut deposit indicate that there can be a dominant contribution of magmatic fluid that contains primitive mantle-dominated sulfur, such that d34S values (d34S of 1.4 to 5.2‰) in this deposit are similar to those of many notable porphyry Cu deposits and related Cu and Cu-Au skarns. Based on the microthermometric studies, salinity and temperature associated with formation of the Khut deposit, have been estimated 16.3 wt.% NaCl equivalent and 400oC, respectively.

The Ghohroud intrusion is a part of the Orumieh-Dokhtar magmatic belt. This pluton with probably Oligo-Miocene age, occurred due to intensive volcanic activity during the Alpine orogenic which is composed of granodiorite to tonalite rocks. The pluton is mainly composed of felsic minerals, such as quartz, plagioclase and alkali feldspar. Ferromagnesian minerals are biotite, amphibole and clinopyroxene. Dioritic enclaves are common in the pluton which vary extensively in diameters. Mineral chemistry of the pyroxenes from the diorite enclaves indicate augite- diopside composition that locally have undergone oralitic alteration. Chemical composition of the clinopyroxenes confirmed a subduction geological setting, the pressure of 6-15 kbars and the temperature of 1250-1300 °C as well as the presence of high percent water content in the magma. High oxygen fugacity and water content increment during magmatic evolution could represent that the clinopyroxenes were crystallized during magma ascent and within different pressures.

In the northeast of Kerman toward Ravar around Hour village, a series of rocks in the form of dike have been penetrated into the Lower-Middle Paleozoic Formations. The color of these rocks is dark with non-equigranular texture resulted from large phenocrysts of brown amphibole and pyroxene set in a fine grain groundmass. The existing phenocrysts, according to their abundance, are consist of calcic amphiboles, clinopyroxene and pseudomorphosed olivines. The main characteristics of lamprophyric rocks are non equigranular texture as well as mafic minerals. The normativre results indicate the occurrence of leucite and nepheline and the lack of quartz. According to mineralogical and geochemicai studies, these rocks are classified as alkaline Lamprophyres and are probably comptonite. The average contents of Al2O3, K2O, MgO, Na2O, SiO2 and TiO2 are (12.92, 2.64, 9.98, 1.29, 39.35 and 3.44) Wt% respectively, in all samples the amount of K2O is over that of Na2O and the K2O/Na2O ratio is more than one which indicating the potassic nature of these rocks. All samples show enrichment in lithophile elements in spider diagrams and are plotted in intracontinental extension environment in tectonic discriminate diagrams. As the spider diagrams show the lamprophyres studied are enriched in HFSE and volatiles. Generally, these lamprophyres are derived from enriched garnet lherzolite mantle under low degree (%2 to %5) of partial melting.