نشریه علوم زمین خوارزمی
سال دوم شماره 1 (بهار و تابستان 1395)

Determination of porosity value and type is one of the most important parameters in reservoir quality assessments. In this study, using sequential digital images from 30 samples of a carbonate reservoir, the 3D porosity model has been reconstructed. A very thin layer of rock (200 micron) is picked up in any stage and a digital photo was prepared. As the main purpose is porosity network modeling, rock surface was saturated with a green colored paste for porosity separation. The excessive green paste then removed from the rock surface. Prepared images were analyzed with MATLAB software and green channel was extracted. Each value of this channel with its x, y and z coordination stored in a new matrix. By modeling of the matrix in RockWorks software and filtering based on mean ± standard deviation porosity distribution model was reconstructed and quantified. In addition of porosity volume and 3D network, other rock parameters such as reducible and irreducible water saturation, permeability and pore throat can be also determined using the proposed model.

There are small plagiogranite intrusions and veins in the ophiolitic complex of Northern Kamrod and Southern Dehshir containing feldsparꫦꮷ㾛誋抵±garnet minerals. The host rock of plagiogranites are granular and foliated metagabbro. Ragged boundary and partial replacement of pyroxene by amphibole in the massive metagabbros indicate a disequilibrium state and metamorphic origin of amphibole. In the foliated metagabbro unlike granular ones the relicts pyroxene is absent. Whole rocks geochemical evidences imply partial melting as the main process in generation of plagiogranites in a slow-spreading center of suprasubduction setting. Probably water infiltration through fractures of a spreading setting of back arc resulting of Neotethys subduction caused hydrothermal metamorphism and hydration of ophiolitic sequence gabbros, partial melting and creation of plagiogranitic melt. Alternatively it is possible that during injection of hot magmatic bodies, amphibole dehydration, partial melting and generation of plagiogranitic melt have been occurred as well. On the basis of chemical composition of clinopyroxene, crystallization temperature of gabbroic cumulate is determined between 959 to 977°C. Pressure and temperature conditions of hydrothermal stage estimated as less than 3 Kb and 750°C, owing to chemical composition of metamorphic amphibole. Based on whole rock geochemical signatures of the plagiogranites and their comparison with experimental results, the partial melting temperature is calculated as less than 850ºC. The latest stage of hydrothermal metamorphism was associated with prehnite formation under shallow conditions.

The study area is comprised of lavas and volcanoclastic rocks with basaltic andesite, andesite, trachy-andesite, trachyte-trachydacite, dacite and rhyolite-ignimbrite compositions which erupted in five episodes in an aqueous to sub-aerial environments. All the volcanic-sedimentary series intruded by younger acidic sub-volcanic massifs. The intermediate-acidic volcanic rocks recorded evidences of magma mixing and mingling. In discrimination magmatic diagrams, the lavas represent calc-alkaline, high-K calc-alkaline and shoshonitic characteristics. In spider diagrams, the basic-intermediate samples follow continental arc pattern. The spider diagrams of acidic samples follow the patterns of peraluminous rhyolite and upper crust. REE and spider patterns of the volcanic rocks, display enrichment of LREE, LILE relative to HREE, and clear depletion of HFSE (such as Nb, Ta and Ti), which signifies subduction zones. After collision of the Arabian and Iranian plates and shortening of the Alborz in Eocene, by subsequence lithospheric delamination, partial melting occurred in sub continental lithospheric mantle (SCLM). The resulted melt accumulated in the upper crust, and formed shallow magma chamber(s). Partial melting of the upper crust produced acidic magma. It seems that magma mixing and mingling had important role in generation of the basic-intermediate rocks.

The Posht-e-Badam ophiolite is situated in the 15 KM of the southwest of the Posht-e-Badam Robate village and in the northeast of Yazd province. The Posht-e-Badam ophiolite belongs to the Paleozoic and is a remnant of the Paleo-Tethys ocean. This ophiolite has passed three phases of metamorphism and consists of metaperidotite, metagabbro, amphibolite (ortho-amphibolite), rodingite and listwaenite. Metalherzolite is the most intact unites of the metaperidotite. Petrography study shows that metalherzolites consist of metamorphic minerals of olivine, tremolite, serpentine , chlorite, chromian magnetite and magnetite. The main textures of these rocks are nematoblastic, poikiloblastic, jack-straw and mesh texture. Mineral chemistry studies of metalherzolites indicate that olivines have Mg# (0.79-0.80), and are chrysolite in composition. Amphiboles are tremolite which present high values of Mg# (0.93-0.96). Chlorites are peninite in composition with Mg# (0.92-0.93). Spinels have Cr# 0.97, and are chromian magnetite in composition. Magnetite inclusions in metamorphic olivines reveals that the studied rocks were partly altered in greenschist facies. Tremolite with Jack-straw texture, as well as presence of Mg-chlorite and antigorite indicate progressive metamorphism in the amphibolite facies P-T conditions. Late-stage retrograde metamorphism led to formation of chlorite around of some of tremolites and partial serpentinization of metamorphic olivines. The phase relationships of metalherzolites of Posht-e-Badam ophiolite, in the CMASH (C = CaO, M = MgO, A= Al2O3, S = SiO2, H = H2O) model system, indicated that studied metalherzolites metamorphosed under lower amphibolite facies P-T conditions, followed by a retrograde metamorphism under greenschist facies conditions.

Metalliferous basinal brines, as the key factor, are commonly involved in the formation of structural-related F–Ba (±Pb–Zn) deposit, although in many instances, the sources of metals is often thought to be the underlying basement rocks. The Atash Kuh F–Ba±Sulfide vein-type deposit in the southwestern of the Markazi Province is an example of these deposits which is recognized by epigenetic characteristics, open space filling, breccia and vugy textures, occurred in lower to middle Jurassic carbonated-shale host rock. The vein-type mineralization is associated with ESE–WNW and NNE–SSW-oriented local fractures, dolomitization, silisification and argillic alterations. Minor amount of sulfide minerals such as galena, pyrite and chalcopyrite dispersed in the vein system. Evidences show that fluorite mineralization and accompanied minerals occurred at the three stages with three types of fluid inclusion including, 1) liquid-rich (L), 2) solid-bearing (L埤), and 3) CO2-bearing (L1⽯), in the fluorite, barite and quartz host minerals. The pressure-temperature estimation based on aqueous and CO2-bearing fluid inclusions isochore intersection, suggest P-T condition entrapment of 150 Mpa and 250°C in the early stage and 100 Mpa and 200°C in final stage of mineralization. Microthermometry and microchemical evidences of fluid inclusions at Atash Kuh area, suggested that the salt-rich basinal brines experienced an extensive fluid-rock interaction between Na-rich to Ca–Na±Mg–K end-members. Mg-metasomatism and dolomitization could be result of Ca/Na increase and fluorite mineralization. Evidences shows that the Atash Kuh F–Ba±sulfide veins probably occurred as heterothermal mixing of two end-member brines includes: primary Na–K±Ca–Mg brines (with Triassic-Jurassic evaporitic source) and secondary Ca-rich brines (due to fluid-rock interaction). Consequently, due to depressurization and wide migration of meteoric dilute recharge fluids in shallow depth occurred at the final stage of mineralization.

The Late Permian Dalan Formation in folded Zagros region, as well as the Persian Gulf, contains giant gas resources, so that this formation along with the Triassic Kangan Formation in the Persian Gulf contain about 50% of total gas reservoirs. Based on petrographic studies, the thickness of the Dalan Formation in the X well in the South Pars gas field is 370 meters with dominant dolomite, dolomitic limestone, limestone lithology and anhydrite interbeds. The identification of original composition of carbonates is difficult due to the effects of diagenetic processes, as over time aragonite and high magnesium calcite change into a low magnesium calcite and caused changes in further texture and original composition of the rock. Therefore elemental studies should be used as an integral to the petrographic studies. Concentration of the major and trace elements in carbonates are depend on their mineralogy composition and the mineralogy composition itself, changes by the influence of diagenetic processes. Study of major elements (Ca, Mg), trace elements (Mn, Fe, Na, Sr) and compare them with the published results by different researchers for aragonitic mineralogy, and considering petrographic evidence such as oomold porosity, high frequency of bivalves, selective dolomitization, spalled ooids, isopachous fibrous marine cement, implied that original mineralogical composition of Dalan Formation was dominantly aragonitic. Eighteen microfacies are determined for the Dalan Formation. Based on the identified microfacies, this carbonate succession was developed on a homoclinal carbonate ramp.

The Bazman batholith is located in the south of Lut block, southeastern Iran. The intrusive rocks include alkali granite, intermediate granitoid (quartz-monzonite, quartz-monzodiorite and granodiorite), gabbro and some leucocratic dykes (aplitic) which have been intruded into upper Paleozoic sedimentary rocks and causing a contact metamorphic aureole. In the granitoids, A/NK>1 and A/CNK