RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2008 | Volume:30 | Issue:1 (GEOLOGY)|Papers Count:12

A total 191 samples of the sediments of the Qom Formation in northwest part of Siahkuh were investigated. The Qom Formation, in the examined section with a thickness of 359m., mainly consists of argillaceous limestone, limestone, marl and gypsy marl and disconformably overlies the Lower Red Formation and underlies the sediments of the Upper Red Formation. A study of foraminifera was led to identifying 50 genera and 79 species from benthonic and plankthonic foraminifera. Based on the occurrence of the index foraminiferal species and their stratigraphic distribution, the age of the Qom Formation in the studied section is Early Miocene (Aquitanian to Burdigalian). Study of assemblage, abundance, and species diversity of foraminifera in the examined samples shows noticeable changes in the paleoenvironmental conditions, and species diversity of foraminifera is decreased and increased through the studied section. The maximum diversity is nineteen species. On the basis of species diversity, the mentioned section is classified to seven assemblages A to G. The abundance of foraminifera in each assemblage indicates that species the sediments of the Qom Formation belongs to marine and shelf (lagoon to outer shelf) environments.

The Sorkhshad area is located in the northwest of Anarak (Central Iran). In this area the hydrothermal alteration is affected as a progressive model. Many types of alteration can be observed in the area. Protilites often have andesitic extrusive body. Field study and electron microprobe, NAA, analysis characterized type of alteration and member of minerals. Alteration of the area according to tectonic consists of two major types. 1- Propylitic, Sericitic, Silicification, 2- Argillic zone consists of intermediate and advanced argillic alteration. Alunitic and acid sulfate are subset of advanced argillic alteration. The major types of mineral in these alterations are hematite, limonite, epidote, quartz. Acid sulphate soils are the nastiest soils in the world. High concentrations of heavy metals are toxic. Different hazards are posed by different kinds of acid sulphate soil.

The studied area is located in 110 Km north-east of Ardestan in Isfahan province and, in Iran's geological classification, it lies in the central Iran zone. This collection consists of intermittent of lava flows (mainly basaltic andesite, andesite, dacite, rhyodacite and rhyolite) and pyroclastics (tuff, ignimbrite and agglomerate). These lavas are composed essentially of quartz, plagioclase, kfeldspar, amphibole, biotite, clinopyroxene and olivine, set in a matrix of the same minerals associated with apatite, zircon and opaque mineral. The study of volcanic rocks shows a selective enrichment of large ion lithophile elements (eg., K, Rb, Ba) and a depletion in elements having high field strength (HFSE) as Nb, Ti, Ta compared to chondrites and primitive mantle. Based on the geochemical data, trace and REE element diagrams, these rocks are high potassium calc-alkaline and shoshonite. Trace element patterns show similarities with volcanic arc magma. Therefore, volcanic rocks of north-east of Ardesten are products of volcanism of metasomatized mantle.

The studied section is located in Central Iran, 135 km southeast of Isfahan in Ramsheh area (latitude N 31o 46' 65", longitude E 52o 8' 63") GPS-WGS84 coordinates. The Ramsheh area structurally belongs to the Southwest-Central Iran and is checked regarding to microfacial and paleoinvironmental points of view as well as to biostratigraphical evidences. Carboniferous depositions (including Shishtu II sub Formation and Sardar Formation) are formed from limestones, dolomylimestones, shales, sandylimestone, sandstones and oolitich limestones. Based on detailed petrographical investigations and field studies, 15 mircofacies have been identified: 13 of them belong to carbonate microfacies that form in four sub-sedimentary environments, including Open marine, Barrier, Lagoon and Tidal flat and the other 2 microfacies show clastic material presence. The facies sequences observed in the carbonate platform sedimentation are the result of changes in environment through time and by natural processes operating within the environment or by fluctuations in the external factors controlling sedimentation such as tectonic activities and change in a sea-level. A characteristic of carbonate platform is its continuation without any breakage into the deepwater sedimentation.

Tabas coalfield is one of the most important coalfields in Central Iran. Mazino is the biggest thermal coal deposit in Tabas coalfield. The aims of the present paper are to explain coal quality and coal composition in the Mazino coal deposit. Coal-bearing strata in Tabas coalfield (as well as Mazino deposit) are within the Middle Jurassic of Nayband and Hojadk formations. This sedimentation has been developed in alluvial plain and coastal environment in Tabas coalfield. The coal-bearing sediments in the Mazino area are called Mazino (Hojadk) Formation (central Middle Jurassic). The Mazino Formation mainly consists of sandstone, shale, and siltstone and carbonates rocks. Several coal seams with different thickness are interbeded with these sediments. The Hojadk (Mazino) Formation is underline by the upper Middle Jurassic oolitic limestones (Badamu Formation). It is also overlain by the lower Middle Jurassic sandy oolitic limestones (Tabas or Parvadeh Formation). Petrographic observations have shown that the coal beds of the Mazino deposit are mainly anthracite to semi-anthracite and dominated by macerals of the vitrinite group and the amounts of inertinite macerals are relatively very low. The dominant mineral phases of these coals are pyrite, siderite, calcite, gypsum, barite, illite and other clays. The clays are argillite, kaolinite and montmorilinite.

Jandaq ophiolite suites are covered by metamorphic rocks that are marbles and schists. This old ophiolitic association has passed different phases of serpentinization and metamorphism. In this rock association, gabbroic dikes cross cut the serpentinized mantle peridotites. Joints and cracks of brittle gabbroic dikes are filled by veins that are light in color. These veins are formed after metamorphism and serpentinization. These coarse grain rocks are free from deformation and foliation, and are formed by calcite, prehnite, epidote, clinopyroxene and chlorite. The most important mineralogical characteristic of these veins is existence and considerable amount of calcite, that is the evidence of high f CO2 in minerals bearing fluid. Vein enclosing gabbros, are metamorphosed in amphibolite facies (2.7 to 9 kbar pressure and 630 to 750 of C temperature), and then pass through a retrograde metamorphism in green schist facies.

Sulphate deposits are one of the important constituents of oilfields and usually form the cap rock of hydrocarbon reservoirs. In the present study, sulphate sediments of the Agha Jari oilfield's cap rock are investigated. In this field, member 1 of Gachsaran Formation with 50 m mean thickness of anhydrite, marl, limestone and bituminous shale is considered as the cap rock. In the present study, the following methods are used: Gamma ray & Sonic well logs, Microscopic thin sections, Scanning Electron Microscope with elemental analyzer (SEM-EDS) and Carbon Isotope. With consideration of lithostratigraphic column of the field, 7-8 separate anhydrite units with different levels of thickness are recognized. Anhydrite sediments show various textures and fabrics such as nodular, lath, decussate, enterolithic and blocky some of which are used to determine the depositional environment and their alteration during burial. Anhydritization, cementation, recrytalization, compaction and replacement are the most important diagenetic processes of sulphate deposits in the Agha Jari oilfield. Carbon Isotopic (d13C) studies of associated carbonate layers in anhydrites, show the value of %0 -20.4. All of lithological, petrographical and isotopic data indicate intermediate depositional environment (lagoon or sabkha).

The Qorveh Plutonic Complex (QPC) is in Sanandaj-Sirjan Zone (SSZ), that is located in south of Qorveh about 80 km in NW Hamadan, between 47o 42’ and 48o E-longitude and between 34o 50’ and 35o 10’ N-latitude. Due to post-emplacement tectonism QPC is a multi-pulse structure, containing a large variety of rocks. Three main units have been identified within the QPC based on field observations and mineralogical and geochemical characteristics. Mafic intrusions consist of gabbro-diorites, followed by felsic units that include granitoids and aplites. The QPC lies within the SSZ and emplaced during Eocene-Oligocene times. Microgranular mafic enclaves (MME) and amphibole-rich clots (ARC) are in the QPC. It is composed mainly of metaluminous with I-type affinity and had occurred in volcanic arc to an active continental margin setting. Harker variation diagrams show compositional gap between 59 to 68 wt% SiO2 contents and different units derived from a different sources. The combinations of field, petrographic and geochemical data show mafic units derived from mantle source that were enriched by Nb, Rb, Sr, Ba by hyrous fluids and/or malts through crustal contamination.

Kuh-e Dom granodiorite intrusion, located at the Northeastern of Ardestan, includes abundant of rounded and rarely ellipsoid microgranular enclaves composed of quartz diorite, monzodiorite and quartz monzodiorite. The diameters of the enclaves range from a few millimeters to 30 centimeters. These enclaves are very fine-grained and show chilled margin so that the size of their crystal gradually decreases from center to the margin. The chilled margin is an evidence of rapid magma cooling once the enclaves were surrounded by host felsic magma. The occurrence of mafic microgranular enclaves within the felsic rocks accompany with the disequilibrium textures including: 1) poikilitic and Antirapakivi texture at K-feldspar megacrysts, 2) ocelli quartz rimmed by a zone of fine-grained aggregates of early formed minerals, 3) rounded and corroded plagioclase, 4) mafic clots, 5) acicular apatite, 6) small lath-shaped plagioclase in large plagioclase, and 7) crenated and cuspate contact in enclave-host rock which all indicate the mingling of two magmas. Based on microprobe data, the plagioclase crystals show a variable composition from oligoclase to andesine in granodiorite and from andesine to labradorite in enclaves. They have essentially normal zoning and occasionally indicate oscillatory zoning. The enclaves and their host rocks, geochemically, are different from each other and based on the fact that the first one is Na-rich whilst the other is K-rich. In addition, the enclaves display LREE and LILE depletion accompany with the HREE and Ti enrichment compared to their host granodiorites. Therefore, it seems that the enclaves and granodiorites might have been originated from two various magmas which were located adjacent to each other by magma mingling process.

The abundance of peridotite rocks in Naein ophiolite is about of 70 percent of melange. The studied rocks are mantle peridotites of an oceanic lithosphere that have been emplaced in north of Naein in Late Cretaceous to Early Tertiary time. The petrographic and field studies, with mineralogical comparison of lherzolite, harzburgite and dunite, show transitional changes of lithology and mineralogy. The applied geothermoeters and barometers show that olivine-spinel equilibrium temperature in lherzolite is 730 and in harzburgite 778oC, but in contrast two pyroxene crystallization temperatures obtain 1092oC for lherzolite and 1219oC for harzburgite. Field and petrographical studies and difference between obtained temperatures by applied geothermometers and increasing trend of olivine-spinel geothermometry from lherzolite to dunite, reveal the melt/mantle reaction. Moreover, chemical analysis of spinels and olivine show that Cr# of spinels increase from lherzolite to dunite, but the Mg# of coexisting olivines decreases. This negative correlation in mentioned factor has been formed by increasing of the replacive olivines during melt/mantle reaction and incongruent melting of orthopyroxenes. Consequently, studied rocks are tectonites that have been affected by melt/mantle interaction.