Iranian Journal of Crystallography and Mineralogy
Year:2008 | Volume:16 | Issue:2|Papers Count:13

The calcareous rocks in the Takht-e-Soleyman area (NW Iran) crop out in association with a variety of metamorphic rocks including amphibolites, granitic gneisses, pelitic schists and meta-ultramafic rocks. Retrogressive metamorphism of these rocks occurred during decompressional cooling during exhumation. Cummingtonite-bearing rocks resulted from retrogression of the calc-silicates in the area. Their dominant mineral assemblage is plagioclase+garnet+calcic–amphibole+ferromagnesian–amphibole+quartz+calcite±titanite±epidote. Calcic-and ferromagnesian-amphiboles were determined by petrographical observations and EMPA analysis. Hornblende and cummingtonite compositions dominate the analysed amphiboles. Formation of Ca-poor cummingtonite coexisting with calcite and calcic-hornblende in the retrograde calc-silicates of the Takht-e-Soleyman area is a rare petrological occurrence. Thermometric estimates using mineral compositions of cummingtonite co-existing with hornblende is in the range of 550-600oC. Al in hornblende barometry yields a pressure of 6.5±0.6 kbar, corresponding to medium pressure amphibolite facies.

Incheh granitoid intrusive body is located in east of Heris, East-Azarbaidjan. It intruded the older rock units including the Sonajil sub-volcanic stock (upper Eocene-lower Oligocene) of micro-diorite porphyry composition. The Incheh intrusive ranges in composition from diorite through syeno-diorite to quartz-diorite. The major constituent minerals include plagioclase, hornblende, and pyroxene accompanied by minor amounts of biotite, alkali-feldspars, quartz, olivine, epidote, and tourmaline. These rocks feature dominantly porphyritic texture, however, granular, trachytoid, and ophitic textures are also sporadically present. The Incheh intrusive has been evolved by the influence of magmatic differentiation, fractional crystallization, assimilation, and crustal contamination. Chemical analyses show that the rocks of Incheh intrusive are chiefly metaluminous, and belong to high-K calc-alkaline to shoshonitic magma series. From the viewpoint of tectonic environment, the Incheh body was emplaced in a post-collision volcanic arc and an active continental margin setting.

This area is located in Derenjal Mountains, 60Km northwest of Tabas in central Iranian structural zone. The igneous rocks occur as plutonic with composition of olivine-gabbro, gabbro, diorite and monzodiorite in Kalshaneh Formation with Middle Cambrian age and as the extrusive rocks with composition of olivine basaltic lavas in lower part of Niur Formation with Silurian age. Petrographical and geochemical evidences show a genetic relationship between the plutonic and volcanic rocks and generation of them from a common magma. Unlike the magmatic differentiation process, the role of magmatic contamination was weak and olivine mechanical separation was the main process in their magmatic evolution. Different diagrams and documents have been shown that these rocks have transitional to alkaline nature and produced in a within plate continental setting by 12-17 percent partial melting of an enriched garnet-pridotite mantle source during the early Silurian. This tectonic setting is agree with an extensional setting (intercontinental rifting) in Central Iran during Lower Paleozoic and specially with Silurian magmatism during Paleo-Tethyan rifting in this part of Central Iran.

Strontium titanate polycrystalline thin films were prepared by sequent deposition of three TiO2/SrO/TiO2 layers using spray pyrolysis technique. Deposition parameters such as: precursor solution, deposition temperature, flow rate of solution and annealing conditions were optimized to obtain homogeneous transparent films. Prepared thin films have granular microstructure. The optical transmittance and absorption spectra show that the films are absorber of the ultraviolet and transparent against visible lights. The transparency and grain size of the prepared samples increase by annealing process. The calculated optical band gap (3.38 eV) is in good agreement with the existing data.

Despite that, in the Alvand complex, the mafic-intermediate rocks (gabbros, diorites and tonalites) are mostly older than felsic rocks (granodiorites and monzogranites), and mineralogical and geochemical discontinuity is seen between them, there are evidence that indicate they have sometimes been co-existed. With the studies on field relationship of rocks, xenocrysts assemblages, synplutonic dykes and their related enclaves I affirm synchroneous occurrence of mafic and felsic magmas, in some periods, and I present evidence of magma mingling/mixing between them. Gabbro-dioritic magmas of mantle origin from one side and crustal, anatectic magmas from another side were intruded the area repeatedly and sometimes synchroneously, and produced a range of crustal (anatectic), mantle and hybrid rocks. Granitic rocks of crustal origin mostly contain restitic (surmicaceous) enclaves, sillimanite, andalusite, cordierite and garnet xenocrysts and their common mafic mineral is biotite (without any hornblende). Migmatitic rocks containing porphyroblast assemblages resemble the xenocryst minerals of granites occuring near to granites. Mantle type rocks (gabbro-diorite-tonalites) commonly have pyroxene and hornblende as common mafic minerals and surmicaceous enclaves and xenocrysts are not common in them. Hybrid rocks have a set of geological characteristics between crustal and mantle type rocks. Geochemical properties of mentioned rock types are seperatable from each other and confirm deductions outlined above.

Acidic and basic volcanic and intrusive rocks of Harzandat-Divan Daghy as individual masses, are located in North and Northwest of Marand (Harzandat) and South of Jolfa (Ghareh Gose-Divan Daghy) trending NW-SE. These rocks are located under Permian progressive deposits, which are covered by an igneous sole unconformity. Lithological composition of the acidic volcanic rocks ranges from dacite, rhyodacite to rhyolite, and basic volcanic rocks range from basalt to basaltic-andesite, where as plutonic rocks are of quartz-syenite. Major minerals of the acidic volcanic rocks and acidic intrusive bodies are quartz, plagioclase and K-feldspar and of the basic volcanic rocks are plagioclase, pyroxene and olivine. Minor minerals of these rocks are biotite, amphibole, sodic pyroxene, apatite, titanite and zircon. Emplacement of intrusions was in shallow depths as dyke, sill and small stocks and are of A-type. Studies show that acidic volcanic rocks are cognate to intrusive bodies and these rocks are A1 type. Basic volcanic rocks plot in two field on the discriminant diagrams for basalts: oceanic basalts and within plate basalts, therefore two possibilities may reinforced:1) either these basalts are the remanents of early Paleo-Tethys oceanic-crust or 2) these basalts were erupted in post collision and within plate environments perior to acidic eruptions and intruding of acidic masses. With respect to shoshonitic characteristics of these basalts which have been determined on the basis of immobile elements, and considering absence of shoshonitic rocks in oceanic environments the latter idea seems to be more acceptable.

The study area is located about 110 Km south of Shahrood in north of Central Iran structural zone. There are many cumulate enclaves with ferroanpargasite gabbroic composition within the Middle Eocene basic volcanic rocks in the study area. Amphiboles are one of the most important minerals in gabbroic cumulates and host basaltic rocks. Based on results of electron microprobe analyses, amphibole minerals present in these cumulates, according to leake et al. classification are calcic and show ferropargasite compositions. Plagioclase shows a notably CaO-rich composition and has normal zoning from anorthite in the core to bytownite at the rim. Clinopyroxene composition range between calcic augite and diopsite. According to the amphibole geobarometer of Schmidt, amphiboles in these gabbroic cumulates are crystallized at ~7.5 Kbar corresponding to a depth of ~26 Km. Geothermometry of amphiboles of these rocks also were calculated with different thermometer and range from 830 to 860oC. The low contents of HREE and La/Yb and Dy/Yb ratios of gabbroic cumulstes suggest that their parental magma was probably formed by relatively high degree of partial melting (16 to 18%) of the mantle.

The study area is situated within the Lut Block 50 Km northeast of Ferdows. The oldest exposed rocks are Cretaceous limestone. Kerman conglomerate cover the limestone. Dacite-rhyodacite lava and pyroclastic rocks erupted over Kerman conglomerate. Volcanic activities took place at different time in Tertiary. The composition ranges between trachyandesite, andesite, andesite-basalt and rhyolitic tuff. Sub-volcanic diorite, monzodiorite, monzonite, quartz monzonite and granite porphyry intruded the volcanic rocks during Oligo-Miocene time. Both volcanic and intrusive rocks are K-rich calc-alkaline to shoshonitic. Intrusive rocks (except granite porphyry) are I-type granite and belong to magnetite series. The pattern of spider diagrams both volcanic and intrusive rocks are similar. In comparison with mantle, They are enriched in Cs, K, Rb, La and Zr and depleted in Ba, P and Ti. Two groups of alteration zones are recognized: 1- silicified assemblages (silica-sericite-propylitic, silica-propylitic & silica-sericite). This group is related to granitic magma. 2- propylitic-sericitic-argillic group which are associated with monzonite, quartz monzonite-diorite intrusive rocks. Mineralization associated with granite porphyry show Mo, Ag, Pb and Zn anomalies. Mineralization associated with monzonite, quartz monzonite-diorite show signs of porphyry copper. They have Cu, Au, Pb and Zn geochemical anomalies.

Pillow lavas are one of the important rock units of Nain ophiolite. Rock forming minerals of Nain ophiolite pillow lavas are chloritized olivine, plagioclase, clinopyroxene (augite), Cr-spinel, magnetite, amphibole, chlorite, pumpellyite, epidote, prehnite and calcite. Whole rock geochemical analyses and composition of clinopyroxenes and chromian spinels of these rocks indicate that they are similar to mid-ocean ridge basalts. These lavas are basalt to andesite in composition and produced by high degree of partial melting of a depleted mantle lherzolite. According to their field studies, petrography, mineral and whole rock geochemistry, they have undergone sub-sea floor metamorphism and changed to spilite. Application of clinopyroxene thermometry shows that they have formed at 1058 to 1170oC.

Detailed studies are done in order to investigate the ore body in Sangan mine. Analyses results showed very low amount of gold in mineralized zone, (max 32 ppb). It is indicated that there is a positive relation between Au, S and As whereas there was no special relation between Au and Cu. Therefore Au can not be found along with Cu sulfides such as chalcopyrite. The LREE elements are higher than HREE in the ore body. Pyrrhotite has two generations which are distinguishable under the microscope: It might be formed either with or after magnetite formation. Careful XRD studies indicate that these two generations have different amounts of Fe and S.

The Plio-Quaternary volcanic eruptions have made basaltic lavas in NW Iran and Azerbaijan. Basaltic lavas with prismatic structure cover the Plio-Pliostocene volcano-sedimentary or Quaternary alluviums. The studied regions are situated in Azerbaijan provinces in areas of Monnavar, Herris, Ahar, Kaleibar, Mahabad, Salmas, Maku, Marand, Sarab and Zunuz. The studied sample rocks are olivine basalt, trachy basalt and basaltic andesite. These rocks have microlithic porphyritic vesicular, hyallo microlithic vesicular porphery and doleritic textures in thin sections. On the basis of chemical analysis, magma that has formed the rocks had alkaline nature with a Na2O/K2O>1 ratio. The tectonic environment for the samples in discriminate diagrams is post collisional volcanic arc setting. The study of Rare earth elements patterns in diagrams show that, common dip of variations have descending trend and indicate basaltic rocks enriched in LREE and depleted in HREE. Other features of the diagrams are small negative anomaly for Eu, Ta, Nb and distinct positive anomaly for U, Th, La, Rb, Ba, and Cs. The study of rare earth elements patterns display that magma originated from an enriched asthenospheric mantle with garnet in source.

Aghadjari bauxite deposit is located in ~15km south of Shahindezh, West-Azarbaidjan province. This deposit was developed as stratiform lenses along the contact of Rutheh and Elika carbonate formations. Bauxitization processes led to the formation of boehmite, diaspore, kaolinite, pyrophyllite, illite, hematite, goethite, anatase, rutile, and quartz. Ferrugenization and deferrugenization mechanisms are two important factors controlling distribution of elements in this deposit. Mafic igneous rocks are the potential protolith. Obtained data show that elements such as Al, Ti, Fe, Zr, Hf, REE, and Nb moved down from the upper horizons to the lower parts of residual system by organic complexes during kaolinization processes. The carbonate bedrocks played dual roles in distribution of elements in this deposit. These rocks neutralized the acidic weathering solutions causing an increase in deposition of iron oxides and hydroxides which in turn due to their adsorption capacity caused considerable concentration of Cr, Co, and LREE in lower parts of the bauxite horizon. On the other hand, the carbonates by forming stable ionic complexes with HREEs caused these elements to drain out of the residual system.