Iranian Journal of Crystallography and Mineralogy
Year:2010 | Volume:18 | Issue:3|Papers Count:21

Rich area’s sub volcanic bodies in southwest of Birjand have intruded into upper cretaceous ophiolite mélange. These rocks are in diorite porphyry to monzonite porphyry range and their main texture is porphyry with microgranular groudmass. Plagioclase and green hornblende phenocrysts are made about 70% of these rocks. Plagioclases are andesine with albitic and carlsbad twining and distinct zoning which altered to calcium carbonate in center parts. Hornblende phenocrysts have altered partly to biotite so show a weakly potassic alteration. The average ratio of Ce/Yb in these rocks are 25.40 show they belong to an enrich magmatic arc. There is a negative anomaly in high field strength elements (HFSE) such as P, Nb and Ti in these rocks which is a geochemical character for continental margin magmatic arc. High ratio of LREE / HREE, Sr/Y (average is 38.14), and SiO2 amount with absent of Eu negative anomaly show these rocks are very similar to high SiO2 adakites. High ratio of Sr/Y can be interpreted of high depth melting in plagioclase unstability and garnet stability field. The source of this magma can be an eclogite or garnet amphibolites which derived of subducted metamorphosed oceanic plate in east of Iran. Dating with zircon uranium- lead show this magmatic event occurred 39.1±0.7 Ma (late Eocene).

In this research the magnetoelastic properties of Nd6Fe13-xCoxCu (x=0 and 1) compound are investigated. Analysis of X-ray diffraction patterns indicates that a single phase is formed approximately for x=0 and the x=1 sample is multi-phase. The lattice parameters were decreased, the Néel temperature of main phase and the Curie temperature of impurity phase was increased with Co content. Due to the presence of Nd2Fe17-yCoy ferromagnetic phase in the sample with x=1 the change of the anisotropy and increase of exchange effects was observed in the magnetic and magnetoelastic measurements. Thermal expansion, longitudinal (ll) and transverse (lt) magnetostriction were measured using the strain gauge method in the selected temperatures range of 80- 500 K under applied magnetic fields up to 1.5 T. Anomaly and Invar effect are observed in the linear thermal expansion and a (T) curves at the Néel temperature. The linear spontaneous magnetostriction decreases sharply by approaching the Néel temperature and also shows the short-range magnetic ordering effects when antiferromagnetic to paramagnetic transition occurs. In the low field region, the absolute values of anisotropic magnetostriction of Nd6Fe13Cu compound are small and then start to increase with applied magnetic field. Each isofield curve of the anisotropic magnetostriction passes through a minimum and then approaches to zero with increasing temperature. This magnetostriction compensation arises from the difference in the magnetoelastic coupling constants of the sublattices in this compound.

The structural of fresco pigments of period parti in kuh-e khwaja of Sistan were studied by XRD and Complementary EDX analysis showed that Artist pigments were used of inorganic mainly.

Shanderman eclogites are exposed at the west of Shanderman town, Talesh Mountains in the north of Iran. Protoliths of these rocks had basaltic composition. Geochemical studies indicate that most of the samples have tholeiitic feature. Mg# versus Cr and Ni show that they experienced olivine and clinopyroxene fractionation. Spider diagram shows more fractionation of olivine compared to clinopyroxene. The trace element versus major oxides diagrams show that major oxides had no significant (except Na and to some extent Fe) variation during alteration and subsequent metamorphism. Based on ∑REE, eclogite of the Shanderman can be divided into two groups. First group shows ∑REE= 31.1 ppm and (La/Lu)N=0.6. Second group have ∑REE= 139.2 ppm and (La/Lu)N=2.3. Chondrite REE normalized patterns show that they are comparable with N-MORB and E-MORB.  These patterns (N-E MORB) indicate that either Shanderman eclogite protolith magma source was not homogenous or it experienced different melting degrees, changing from LSS (Slow spreading ridge) to FSS (fast spreading ridge).

All samples of Shanderman eclogites contain amphibole, epidote group minerals and chlorite as retrograde phases. Amphiboles show zoning with high FeO and Al2O3 content at the rims and high MgO in the cores in some samples. In these samples, the amphibole compositions vary from tremolitic hornblende to tschermakite and edenitic hornblende from core to rim, respectively. Amphibole inclusions in zoisite have similar composition to matrix amphiboles and show tremolitic hornblende nature. Epidotes include both zoisite and clinozoisite existing in all samples. They show zoning and have high Al2O3 content in the core and high FeO content at the rims. Pistasite content in the core is 0.09% and at the rim is 0.17%. Plagioclase is enriched in Na and is almost pure albite endmember. Chlorites are MgO rich and are of Repidolite and Brunsvigite types. They show FeMg-1 and tschermakitic substitutions. Fe/Mg distribution coefficient among amphibole and chlorite for the cores of the minerals is around 0.5 and for the rims is 1. Thermobarometry of zoned amphiboles show that these minerals are grown from core to rim due to an increase in temperature and pressure. 

The iron-apatite deposits of the Bafq mining district contain elevated REE content and occur together with vast country-rock alterations which were formed due to widespread hydrothermal processes in Early Cambrian. Apatite and rare earth element geochemistry as well as radioactive isotope studies of Sm-Nd show that apatite formation might be due to hydrothermal activities and remobilization of coeval or older sedimentary phosphorites which are consequently deposited as apatite veins or veinlets associated with iron-oxide mineralization. This huge hydrothermal circulation was induced by intrusion of Early Cambrian igneous rocks such as granites and locally diorites, and is responsible to iron-apatite mineralization, locally associated with REE minerals, and extensive host rock alterations (sodic-potassic) due to vast fluid-rock interaction.

Microstructural, petrographical features and field relations, show that formation of the metapelitic rocks of Bolandparchin and Poshtuk in Northwestern Iran was poly-metamorphic. Mineral assemblages in the metapelites of two areas are different. The Bolandparchin schists are graphite-rich and have dark color. Peak metamorphic assemblage is garnet, biotite, staurolite, aluminosilicate minerals (andalusite/sillimanite), muscovite and quartz in these rocks, but Poshtuk metapelites are graphite-free and their mineral assemblages are garnet, staurolite, chloritoid, chlorite, muscovite and quartz, which usually take place by contact metamorphism, the isograds are not compatible with Barrovian type, but reflect the first appearance of chloritoid in the aluminous bulk compositions. This study shows that in spite of same protolith and geothermal gradient in the both areas, existence of different mineral assemblages is due to presence or absence of graphite and consequently different aH2O, so that Poshtuk rocks are graphite-free and have aH2O ~ (0.8-1.0) therefore, chloritoid is formed.  Bolandparchin rocks have aH2O ~ (0.5) and aluminosilicate minerals such as andalusite/kyanite/sillimanite are formed in these rocks

Neogene high silica adakitic domes of South of Quchan, have been outcropped in the northern part of the Quchan-Esfarayen Cenozoic magmatic arc (in the north of the Sabzevar ophiolitic and metamorphic belt). In this volcanic belt, magmatic activities has been started since Eocene (about 40 Ma ago) and continued to Plio-pleistocene (about 2 Ma ago). The ages of volcanic rocks range from Eocene to Plio-pleistocene from south (in adjacent to the Sabzevar ophiolitic belt) to north (in south of Quchan) respectively. Neogene northern part of this high silica adakitic arc composed of pyroclastic units and several domes contain trachyandesites, trachytes, dacites and rhyodacites (2-12 Ma ago) which usually overlain an olivine basaltic- basaltic basement of Eocene to lower Miocene(19-20 Ma ago). Existence of Eocene volcanic enclaves and gneissic, siltstonic, marlly and pellitic enclaves, appearance and disappearance of some mineral phases, corrosions and chemical disequilibriums of some phenocrysts and sieve textures are some evidences of magmatic contamination. 87Sr/86Sr ratios range from 0.7041 to 0.7057 confirms this contamination. A clear positive anomaly in LREE and LILE and a negative anomaly in HREE found in the rocks of Neogene domes. Negative anomalies in HFSE (e.g. P, Nb, Ti) which is the indicator of arc settings, also found in these rocks. Calc-alkaline nature, continental arc subduction setting, presence of an eclogitic or garnet-amphibolitic source rock (resulted from metamorphism of Sabzevar subducted oceanic crust as a source of magma generation), high silica adakitic nature of magmatism (HAS) and the role of fractional crystallization, assimilation and magmatic contamination in the genesis and evolution of magma in these domes, indicated by the geochemical evidences. These adakitic magmas were the latest melts resulted from partial melting of young and hot Sabzevar Neotethyan subducted oceanic crust and its overlaying mantle wedge, which have been emplaced and manifested in the form of subvolcanic adakitic domes.

The chromite deposits of Aland (Barajok and Kochak villages) and Gheshlagh area in the Khoy ophiolite occur as layered, lenticular or irregular masses, surrounded by dunitie and harzburgites. These chromites are compositionally similar to alpine-type chromites, characterized by nodular, massive, disseminated and banded textures. EMPA data show that they varies widely in term of Cr-number [100Cr/Cr+Al]. On average, Cr# of chromites in harzburgites is 45.13, in disseminate Gheshlagh and Barajok chromites are 40.58 and 58.12 respectively but in Barajok and Kochak Chromitites are 66.7 and 73.43 respectively. The chromite composition in terms of Cr#, Mg#, Cr2O3, Al2O3, Fe2O3, MgO and TiO2 contents and also regarding to correlation coefficients between different oxides is comparable to podiform chromitites. The compositions of chromitites from Aland area with Cr#>66% and Gheshlagh area with Cr# about 40 wt% fall within high-Cr and high-Al types respectively. According to TiO2, Cr2O3 and Al2O3 content of the samples, it seems that the Aland chromites were formed from boninitic magmas in a supra-subduction zone although the Gheshlagh chromites were formed from tholeiitic magma in a geotectonic setting similar to the MORB.

In the mafic-ultramafic suite of Tazehkand, Kalaybar-NW Iran, of Early-Cenozoic age, pyroxenitic core is surrounded by gabbro and total complex is rounded by Paleocene Majid Abad volcano clastic formation. The pyroxenite is composed chiefly of Cpx+Ol+Ore. The associated gabbro minerals consist of Pl + Cpx + Am + Phl. The pyroxene composition in the two rock types is diopside-rich and ranges between hedenbergite to Ca-tschermak. Plagioclase is anorthitic and opaque mineral is mostly hematite. Some results of this investigation on the relationship between major phases activity and mineral chemical composition in these rocks are: Ca-tschermak activity in the pyroxenes is controlled with Al-content in T-site, Tschemakite activity in amphiboles has direct relation with (IV) Al, but reverse relations with (IV) Si, (VI) Al and (A) Na. Using several thermobarometric methods, temperature of 900oC for pyroxenites and pressure of 7-9 kbar on the same temperature for gabbro crystallization, are estimated. The temperature of observed ilmenite lamellae exsolution from hematite matrix during sub-solidus phenomena is detected 470oC. Calculated Log fO2 for the source magma is -8 to -14. This quantity is higher for pyroxenites than gabbros

The Mashhad ophiolitic and metamorphic complex was intruded by Mashhad granitoids in three different episodes of magmatisms. Dehnow pluton with diorite-granodiorite composition was intruded in earliest stage of magmatism in late Triassic (Norian, 215±4My).This pluton is cut across by the NW-SE trending ductile shear zones which are dominated by an intense ductile deformation. The rocks of the Dehnow pluton along the shear zones are converted into protomylonite, mylonite and ultra-mylonite with steeply dipping mylonitic foliation and gently plunging stretch lineation on it. Kinematic analysis of shear sense indicators such as S-C fabrics, asymmetric folds, asymmetric porphyroclasts, mica fish and domino-type fragmented porphyroclasts reveal that the ductile deformation is related to right lateral reverse slip that may describe by a transpressional deformation regime. the minerals in the mylonitic rocks shows variable microstructures such as patchy to crosshatch undulose extinction, shear fracture, deformation lamellae, subgrains formation, bulging  dynamic recrystalization (BLG) and subgrain rotation recrystalization (SGR) in quartz grains, also subgrain formation , deformation twins, flame-shaped prethities , dynamic recrystalization (BLG) in feldspars , all indicated that the ductile deformation have occured in 300-500oC (upper green schist and lower amphibolites facies conditions). Age and cross cutting relations between various lithological units in the study area revealed that the ductile shear zones were formed during Cimmerian orogeny between Norian to Early Jurassic age.

The study of quantitative textural analysis and crystal size distribution on amphibole, plagioclase and quartz in the company of microprobe and thermobarometry investigations on amphibole phenocrysts, guide us to some information about magma process in magma chambers. Petrographic studies with microprobe and crystal size distribution investigations in Neogene igneous rocks of SW of Tehran, demonstrate that there are three populations of amphiboles related to different conditions of crystallization in different depths and point to existence of at least three magma chambers below the volcano in this area. The occurrences of plagioclase in lavas confirm that magma evolution take place at lower depth in a magma chamber near the surface of the earth and at the lower fugacity of water.

Nowadays, acid mine drainage (AMD) is one of the most important problems in coal mine contamination. The Karmozd coal mines in Mazandaran province are one of the largest and oldest in the coal extraction in Central Alborze Coal Basin. The sampling of coals, host rocks, mine drainages and secondary surface minerals have been carried out in summer season of 2005. On the basis of hydrogeochemistry studies of drainages mine in Karmozd, two types waters: 1) acid drainage of Mg-SO4 type (pH=4.59) and 2) alkali drainage of Na-HCO3-SO4 type has been recognized. The most important factor in acid drainage formation is non-evacuation of mine drainage in active tunnel Nummber13 and a long term contact of mine drainage with sulphidic minerals. As result, the concentration of SO42- contemporary with oxidation of pyrite is increased. The scatter diagrams indicate with increasing of  SO42-  which is caused the decreasing of pH value and HCO3 while heavy metals, alkali metals, earth alkali metal, (PO4)3-, electrical conductivity (EC) and total dissolved solid (TDS) increase in water. Hydrogeochemistry modeling indicates that minerals such as jarosite, alunite, iron oxide, oxyhydroxide, Al oxide and oxyhydroxide are mainly in over saturation state, while carbonates minerals like calcite, dolomite and aragonite are undersaturated. X-ray differaction (XRD) results have proved the existence of natrojarosite, pickeringite, halotrichite, gypsum and iron oxide and oxyhydroxide precipitated due to acid drainage. Gibbs diagram indicates that lithology is the most important factor in increasing the ionic concentration of mine drainage from acidic and neutral to alkali drained.

The dynamo-magmatic gneisses of Azna have a mylonitic texture characterized by large retortshape porphyroclasts or augen of feldspars, around which a more ductile, medium to fine-grained matrix of white-mica (phengitic muscovite), biotite, quartz and feldspar is deflected. The structure is named core-and-mantle structure.  Feldspars behave in both plastic and brittle fashion. Evidence of strain, such as deformation twins, bent or curved twins, undulatory extinction, deformation bands and kink bands occur characteristically in plagioclase and display dynamic deformation in Solid state. Deformation of quartz in dynamo-magmatic gneisses commonly results in the development of core-and-mantle structure and quartz ribbons of elongated, preferably oriented, newly recrystallized quartz aggregates suggesting a dynamic recrystallization. Most of the micas are completely aligned subparallel or parallel to the margins of quartz ribbons and define the foliation in the rock. The textures are introduction of dynamic deformation during the crystallization and after it

The study area is located within the shear zone of the north of Shahrekord. There are many small and medium granitoid plutons that have intruded in the metamorphic rocks in middle Jurassic. These rocks show sharp mylonitic foliation and lineation as the results of undergoing strong deformation.  Most of these granitoid plutons contain the assemblage quartz +K-feldspar + plagioclase + biotite + hornblende + allanite + titanite + magnetite + magmatic epidote + apatite + zircon ± garent in apparent textural equilibrium. Epidotes exhibit textural and compositional characteristics implying their magmatic origin. The granitoid plutons bearing magmatic epidote must have formed under moderately high pressures, corresponding to lower crustal depths. The Al-in-hornblende geobarometry yields pressures of 7.3-8.1 kbar (average 7.7 kbar) corresponding to a depth of about 28 Km. Also, amphibole-plagioclase geothermometry gives temperatures from 663 to 711oC. The geothermobarometry results are in agreement with the presence of magmatic epidote in the granitods.