PETROLOGY
Year:2017 | Volume:8 | Issue:29 |Papers Count:9

The Irankuh mining district is located 20 km southwest of Isfahan and is geologically situated in Sanandaj - Sirjan zone and the lower Cretaceous sequence of Isfahan-Malayer ore mineralization area. The ore minerals are emplaced in the faulted contact of Jurassic shale and Cretaceous carbonates and include pyrite, galena, sphalerite, calcite, barite, dolomite, quartz as well as minor marcasite, smithsonite, cerussite, gypsum, malachite, hematite and goethite. The mineralization is mainly occurred as hydrothermal veins and veinlets associated with fractures and faults, suggesting the deposit is likely to be of epigenetic type. A comparison between geothermometric results obtained from calcite twins and fluid inclusions showed a similar temperature range for the mineralization (less than 170ºc). Fluid inclusion studies indicate the temperature, salinity and density ranges of 80-166ºc, 5.39-20.94 wt.% NaCl and 0.95-1.12, respectively. The obtained data share many similarities with those of the MVT deposits.

The investigated granite intrusion is located at the north of Ayghalesi village, east of Takab The Ayghalesi granite has been intruded the Eocene sandstone and conglomerate rocks and low grade metamorphic hornfels have been metamorphosed host rocks. The main constituent minerals are K-feldspar, plagioclase, quartz and muscovite. and minor garnet. The main texture is granular but pegmatitic, myrmektitic, graphic and perthitic occur as minor textures. Chemically, the rocks are granite on the various classification diagrams. The Ayghalesi intrusion body is classified as S-type, peraluminous composition, calc-alkaline nature and is calcic-alkali to alkali-calcic on the base of modified alkali lime index (MALI). The investigated body, on the tectonic discrimination diagrams, fall on syn-collisional tectonic setting domain, suggesting that it was originated during collision of Central Iranian and Arabian plates.

The study area is located in the Central Alborz (northeast of Baladeh). The Permian magmatism in this area occurs as a basaltic unit between Ruteh-Nessen Formation. Petrographically, the rocks are plagioclase phyric and geochemically, display alkaline sodic nature. Chondrite- normalized rare earth element (REE) patterns are extremely LREE- enriched similar to those of oceanic island basalts (OIB) with (La/Sm) N, (Sm/Yb) N and (La/Yb) N in the ranges of 1.95- 4.62, 4.23- 5.45 and 8.30- 20.52, respectively. Furthermore, primitive mantle normalized multi element diagrams represent OIB characteristics. Modeling based on trace element values and the content of some major elements reveal low degree partial melting (<10%) of a deep (~110 km) garnet-bearing mantle source. In addition, variation of some trace element ratios such as Nb/Rb, K/La, La/Nb, Ba/Nb, Th/Nb and K/Nb suggests a HIMU mantle origin. As the samples geochemically show intra-plate tectonomagmatic setting without subduction zone signatures. Thus, during the Permian (and earlier times), Alborz has been as a passive continental margin in the southern border of Paleo-Tethys and its magmatism was more probably affected by extensional tectonism or mantle plume activity related to earlier stages of Neo-Tethys ocean development.

In aplites of Khaku area, located in the east of the Alvand body, tourmaline nodules with spherical and dendritic shapes are dispersed. Some of these nodules have light halo that is actually a transition zone between the core of nodules and the host aplites. Geometrically, these nodules are fractal shapes. In these nodules fractal dimension vary from 1.46 in dendritic nodules to 1.92 in spherical nodules. In three-dimensional reconstructions of the studied nodule, the average volume for the core is 34% and 66% for its margin. Based on evidences such as lack of veins between nodules, tourmalines with anhedral forms, presence of a leucocratic halo in the aureole of some nodules, their spherical shape, their linear and flow dispersion in the host rock these nodules have been crystallized in magmatic condition. In the final stages of magma crystallization and the B content increment followed by beginning of unmixing in the melt, distinct spherical bubbles have been developed which gave rise to nodules formation. Magmatic system acts as chaotic systems and the presence of rotational and limited closed areas in the vicinity of areas with disturbed paths has led to the formation of rounded and dendritic nodules beside each other.

Joveinan marbles and skarns are located 5 km NE of Ghohrood and 140 km NW of Isfahan in the *central part of Urumieh- Dokhtar magmatic arc. Intrusion of Ghohrood granitoid into the Cretaceous carbonate rocks caused the contact metamorphism and formation of skarn mineral paragenesis wollastonite, clinopyroxene, garnet, actinolite, epidote, chlorite, calcite, quartz, magnetite and sulfides (iron and copper). Mineralogical studies and paragenetic mineral relations confirm that the Joveinan skarn is polygenetic in origin and evolved in two major stages, metamorphism and metasomatism (progressive and retrogressive). In metamorphism stage that occurred immediately after the granitoid magma emplacement within carbonate rocks, Joveinan marbles were formed. Metasomatic stage occurred with generation of anhydrous calc-silicates minerals such as wollastonite, diopsidic-hedenbergitic pyroxene and ugrandite garnets. The main stage of retrograde metasomatic, alteration of primary calc-silicate minerals of skarn (pyroxene-garnet), caused the formation of epidote, actinolite and chlorite. The association of wollastonite, magnetite and andradite represents that skarn crystallized in over 550oC temperature range and low partial pressure of CO2. Joveinan skarn is a calcic skarn that has been formed at shallow depth by oxidative hydrothermal fluids and evolved in different stages.

Zafarghand granitoid pluton with compositional range from gabbro to granite and early to middle Miocene age cropped out about 35 km of SE Ardestan. This pluton intruded the Eocene volcanic and volcanosedimentary rocks of the Urumieh - Dokhtar structural zone. In this research, for the first time, the emplacement mechanism of Zafarghand granitoidic pluton method has been investigated using of anisotropy of magnetic susceptibility (AMS). Based on field observations, as well as petrography and interpretations of magnetic parameters, Zafarghand pluton divided into 5 domains (1A, 1B, 2, 3, 4 and 5). Domain 1, in turn, is divided into 1A and 1B. Domains 2 and 4 are lithologically, gabbro to quartzdiorite and have been emplaced first. They have played as feeder zones. Domains 1A, 1B, 3, and 5 are dominantly granodioritic to granitic composition and have been emplaced as a big and low dip magmatic flow (or possibly as a sill). The occurrence of gabbro to quartzdiorite as well as grandiorite, granite and tonalite in the margin borders of the body, are all indication of magma mixing. It is should be noted that during emplacement of the pluton studied, fractional crystallization, magma mixing and crustal contamination contributed to its generation and the evolution as well.

The Some-Ahani and Ferezneh prospect areas are two of the eastern anomalies of Khaf’s Sangan iron mine in Khorasan Razavi province. Biotite monzonite porphyry and biotite syenogranite Tertiary plutons occurred in the area of study. Due to the severe alteration of biotite monzonite porphyry intrusion, geochemical studies have been focused on the biotite syenogranite. It is chemically peraluminous, moderate to high potassic and magnesian and its tectonic setting is of post orogenic. In both A-type granites and in differentiated peralkaline I-type granitic rocks: negative Eu anomaly, mild enrichment of LREE, positive, relatively flat HREE pattern, negative anomalies of Ba, Sr, La, Ce, Ti, and large amount of Ga (16- 24 ppm) are the same. On the basis of major oxide values and SiO2 vs. FeOt/MgO ratio, the prospect area samples fall in the range of I-type granites. Variations in the minor and trace elements in all samples indicate fractional crystallization in separation of plagioclase, alkali feldspar and biotite, generated by fractional crystallization from an I-type granitic magma poor in P. Increase in HFS elements such as Ga and Nb is associated with the differentiation of these granites. Comparison of the intrusions studied with Bermani and Sarkhar rocks in southeast Sangan shows that variations in the major, minor and rare earth elements are similar to each other and to those of I-type granites, which can be differentiated by various degrees of partial melting of andesite and dacite protolith or are produced by a two-stage process of remelting intermediate rocks.

Basic dykes, trending NE-SW and cross cutting the middle Jurassic granodioritic rocks exposed in the Boroujerd area. They are dark green and fine to medium–grained rocks and are characterized by ophitic to subophitic texture. These rocks are dominated by major minerals including amphibole and plagioclase as well as minor biotite, apatite, sphene and prehnite. Amphibole is calcic, with magnesia-hornblende to actinolitehornblende composition. T=600-700ºC and P=3.5-5.2 kbar were calculated for crystallization of these minerals. The composition of plagioclases ranges from albite to oligoclase. The basic dykes studied are undeformed and the youngest magmatic activity in the area.. The collision of Arabian and Central Iranian plates, gave rise to the pressure in the Central Iranian plate, which expanded the extension fractures in the direction of the plate movement. As a result, the dykes in discussion formed in direction of plate movement. Thus, development of basic dykes in the Northeast-Southwest direction with respect to the convergence zone is justified. The basic dykes, on the discrimination tectonic diagrams, are classified as alkaline series and plotted on within plate environment field, which originated from partial melting of an enriched mantle source.

Green tuffs of middle Eocene age in Hesarbon area, south west of Firoozkuh (East of Central Alborz) consist of a thick sequence of lithic-, crystal-, vitric-and calcareous-tuffs. Microscopic and x-ray diffraction studies show plagioclase (albite and oligoclase), alkali feldspar (sanidine), quartz, cristobalite, biotite and hornblende are the major minerals in the rocks studied. Secondary minerals such as analcime, chlorite, prehnite and clay minerals are mainly present in the groundmass of the rocks. Extensive tectonic activities have created a variety of structural features including numerous folds and faults and therefore, have caused the green tuffs to be crushed and converted to breccia tuffs in many parts. Veins and cavities are filled by considerable amounts of zeolitic minerals including heulandite group, clinoptilolite and natrolite along with calcite and secondary quartz. Based on geochemical data, they lie on the dacite and rhyodacite field showing a calc-alkaline nature in the corresponding diagrams. According to the chondrite and primitive mantle normalized diagrams of trace elements, negative anomalies of Eu, Nb, Ti, P and depletion of HFSE together with their position in the petrogenesis discrimination diagrams, it is most likely that these rocks are formed in the active continental margin of a subduction zone. The existence of analcime and prehnite in the groundmass demonstrate that these rocks have undergone some degrees of low-grade metamorphism due to the overburden of the layers in the temperature range 200-300 °C. The present study shows that zeolite minerals filling the fractures and cavities of tuffs are precipitated by hydrothermal fluids with a neutral pH to acidic.