RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2008 | Volume:29 | Issue:3 (GEOLOGY)|Papers Count:15

By intrusion of gabbros in mantle peridotites of the Central Iran ophiolites, a chemical potential gradient established and new metasomatic rocks are formed in contact zone. These rocks produced by this special type of contact metamorphism, are clinopyroxenite, olivine clinopyroxenite wehrlite, lherzolite plagioclase peridotite and troctolite, from mantle peridotite side to the gabbro side. The studied rocks are formed at the expense of peridotitic part of the contact zone. The occurrence of these types of reactions in ophiolitic associations are required a careful sampling and attention should be focused on the interpretation of gabbroic, peridotitic and pyroxenitic rocks data.

The Torab clay deposit is located in the Bikheirkhong plain in 70km south of Abarkouh. This plain is located in the north of the Sanandaj-Sirjan metamorphic zone and it is a part of clay-rich province of the south Abarkouh. This plain is in continuation of the well known Shahreza-Abade-Hambast’s clay belt. The stratigraphical age of the clay layers is attributed to Permian (Artinskian). This age is within the time of the global evidence of clay genesis in Permo-Triassic tome. In this study, the Torab clay deposit is chosen as a typical example of the region clay deposits. For mineralogical and geochemical studies, we used XRD, XRF, ICPMS and soil mechanical methods. The sediments of the Torab clay deposits are a kind of highly weathered Paleosols. These sediments have diverse resources which can be the sedimentary reworked cycles or they can be the erosion products of some felsic and mafic rocks. The results of studies on stratigraphy, mineralogy, geochemical properties, sedimentary basin condition and geological and geographic position show a correlation between these clay sediments and the global evidence of clay genesis in Permo-Triassic period. Autogenic transformations had a great effect on improvement of soils industrial properties. This soil has proper range of harmful and useful industrial elements and soitabi mineralogical and mechanical properties to be used in pottery and brick making. This soil is also suitable for pharmacological uses.

P-T trends represent the single reliable source for thermal and dynamic record of metamorphic and igneous complexes and may serve as a basis for geodynamic models that simulate exhumation of such complexes from mantle. This study demonstrates that, knowledge of P-T trend configuration in combination with isotopic geochronology makes it possible not only to ascertain the nature of polymetamorphism but also to define a mechanism of rock exhumation. Analysis of P-T trends has shown that, the Precambrian granulite complex of Limpopo (South Africa) is repeatedly exhumed. First, this complex was accommodated within the crust and remained for long period of time (up to few hundred million years) and then, these rocks which were in a metastable state in the Earth’s gravity field were reactivated by the fluid and heat flow from the mantle plume which caused the reduction in viscosity and upward movement toward the surface.

The Zayandehrud river total flow is composed of two main components, i.e. total base flow and direct runoff. The former component includes secondary components resulted from groundwater discharge, overland flow produced by slow melting of snow and delayed interflow. The later component (the direct runoff), consists of secondary components of surface runoff from precipitation, overland flow produced by prompt snow melting and rapid interflow. The separation of main components of total stream flow has been performed by "HYSEP" model on the basis of daily stream flow data. This software employs three methods (fixed interval, sliding interval and local minimum) to compute values of above-mentioned main components. Since the flood intensity related to maximum value of direct runoff and drought intensity related to minimum value of total base flow, both can be analyzed for different return period using Zayandehrud stream flow long term data. On the basis of obtained results, a flood with total stream flow equal or exceed to 161.05 cms and direct runoff equal or exceed to 96.28 cms arise every 196 years. On the other hand, a drought with total stream flow less than or equal to 16.09 cms and total base flow less than or equal to 13.83 cms occur every 16 years.

The mylonitic granite of Varzaneh in the north east of Golpayegan, located within the Sanandaj-Sirjan Zone. The changes in the geochemical diagrams for major elements Versus SiO2 and also the triangular diagrams were used simultaneously to show the changes of two or three elements and to determine the trends of comagmatic complexes and phases of major element and to evaluate the origin and evolution of mylonitic granite in the north of Varzaneh. The diagrams of compatible and incompatible major-trace elements were used to show the simultaneous changes of these elements and also to study the independent or non independent behavior of differentiation processes. The diagrams of normalized trace elements like spider diagrams(related to normalized granitoids, primitive mantle, upper and lower crust, continental crust and ocean ridge granite) were used to interpret the evolution steps of differentiation processes or even the origin of mylonitic granite in the north of Varzaneh. By using experimental evidences, it could be concluded that, the chemical changes within intrusive masses in the north of Varzaneh were apparently preliminarily by differentiating crystallization calcic plagioclase (changes diagram of FeO and MgO versus SiO2), K-feldspar (triangular diagram CaO-Na2O-K2O), biotite (changes diagram of FeO and MgO versus SiO2), and etc. About the origin of mylonitic granites, the results indicate that, although there are some evidences about the assimilation of host rocks, but negative anomalies of Nb in normalized multielement diagrams (spider diagrams) in mylonitic granite of Varzaneh is one of the suitable indexes to determine the origin of continental rocks, which could show the contribution of crust in magmatic processes. The concentration of other trace elements within the mylonitic granite of Varzaneh was controlled by specific minerals including: Zr by zirconium, P by apatite, Sr by plagioclase, Ti and Nb by ilmenite and rutile, Rb, Cs, Ba and Na by feldspars, and also the Cr, Co, Ti, Fe and Mg contents were controlled by ferromagnesian minerals such as biotite.

The shemshak Formation includes a widespread area in the Alborz Basin. Its thickness is greater than 2000 meter in the study area and consists of sandstone, shale, siltstone and conglomerate. Based on lithology, this formation can be subdivided into three members.Plant macrofossils mainly occur as leaves in the sediments of the lower parts of Shemshak Formation, in the Tilabad area. In this study, 7 macrofossil species were identified, including: Dictyophyllum cf. acutilobum, Baiera muensteriana, Podozamites distans, Nilssonia harrisi, Pterophyllum schenki, Pterophyllum bavieri, Scytophyllum persicum.Based on stratigraphical distributions of the encounted macrofossils Late Triassic age is suggested for the lower unit of the Shemshak Formation. The collected flora suggests a subtropical conditions at the time of deposition of the Shemshak Formation.

The amphibolites and amphibolitic dikes are among the metamorphic rocks found in Nain and Ashin-Zavar ophiolitic mélanges. These rocks are produced by the regional metamorphism of basic rocks existing in these ophiolites including pillow lavas, basalts and djabasic dikes. Field studies in these two areas show that the foliated amphibolites and amphibolitic dikes are in contact with mantle peridotites, so these rocks seem to be a part of the Nain ophiolitic melange, and not exotic blocks carried by tectonic processes. In addition, a pertographic similarity is observed in amphibolites and amphibolites dikes of Nain and Ashin-Zavar. The common minerals in these rocks are amphibole, plagioclase, quartz, sphene, chlorite, calcite, prehnite and magnetite. The only difference is the presence of garnet and clinopyroxene, in the amphibolites and amphibolitic dikes. The chemical analyses indicate rock forming-minerals in both areas are extremely similar in composition. According to the geothermobarometry the temperature and pressure gained for the Ashin-Zavar amphibolites and amphibolitic dikes are about 676Co and 2.9 to 6.8 Kbars. In addition, the temperature for the Nain amphibolitic dikes is about 770Co while the pressure range is between 6.4 to 6.8 Kbars. Application of ICP-MS and NAA methods for whole rock analyses demonstrate a tholeiitic composition for the studied rocks. Which could be formed in a mid-ocean ridge setting.

The Chadormalu Iron Ore deposit is located in 80 Km north of Bafq. Its age is Upper Proterozoic. The tectonic process is intensive and geological structure is complex in this area. Igneous rocks are associated with metamorphic and sedimentry rocks. The country rocks of ore minerals are igneous rocks. Based on mineralogical studies some of the needle shape apatites are observed in plagioclases. This assemblage is associated with magnetite. Magnetite and apatite are magmatic in origin. The d18O in magnetite and hematite is determined between -0.64 to 2.19 per mil. Therefore, these minerals have magmatic origin and magnetite is subsequently converted to hematite. Furthermore, the d34S in pyrite is +6.1 per mil, showing this mineral has crustal origin and is formed in the late stages of mineralization process. The isotopic evidences indicate that magnetite in association with plagioclase could be formed at temperatures between 500-800oC. Also, fluid inclusion study in apatite shows temperature of about 600oC for the formation of these minerals. In addition, the LREE (light rare earth element) enrichment pattern enrichment in ore deposit and the country rocks is similar indicating a common magmatic origin for both.

The studied section is located in Central Iran, in 35km southeast of Shahreza in Ramsheh area. The Ramsheh area structurally belongs to the southwest Central Iran including the Shahreza- Abadeh- Hambast belt, which is separated by faults from the Gavkhoni- Abarquh depression to the northeast and from the Yazdekhast-Dehbid metamorphism belt to the southeast.The Carboniferous deposits with 620m thickness including Shishtu2 and sardar Formations, the former (Shishtu2 Fm), mainly consists of 315m dark to gray limestones with dolomites and alternation of thin to medium bedded platy shales. According to Conodont funa the following Conodozones are recognized: 1-? expansa-sulcata zone 2-duplicate zone 3-typicus zone 4-ancuralis-latus zone The upper part (Sradar Fm.) with 298m thickness consists of carbonate-terrigenous deposits including limestones, sandy limestones conglomerate and oolitic limestones with conodont funa. The following conodozones are recognized from this part: 1-muricatus zone 2-noduliferous zone 3-sinutus-minutus zone 4- sinusus-delicatus zone 5-?elongatus zone The section checked with regard to Conodont biostratigraphy and depositional environment. According to the above mentioned Conodozones, the Carboniferous deposits in Asadabad section dated from Tournasian to Moscovion in age.The topmost of the section with the Vajnan Formation have parallel disconformity and the lower boundary is covered. The upper located among rocks of late Carboniferous is probably related to global variation of sea level due to glacial epoch (Late Carboniferous) in vast area of Gondwanan Supercontinent.

This paper is devoted to application of integrated geophysical methods in the investigation of Nazloo dam site, located in 27 km NW of Orumieh city. In this study, a combination of shallow seismic refraction profiling and resistivity sounding and dipole-dipole profiling methods were applied. The goals of study were the determination of alluvium properties such as thickness and grain-size, preparation of iso-depth map of the bed rock, iso-thickness map of alluvium in the dam foundation and rock mass quality in the dam embankments. The results lead to identify three layers in the alluvium with resistivity of 100, 300, and 1000 W m and P-wave velocities of 2000, 1000, and 500 m/sec from depth to surface respectively. Maximum thickness of the alluvium was found to be about 70 meter below the dam axis.

In order to determine the microfacies and sedimentary environment of the Tarbur Formation, one stratigraphic section in 15 Km SW of Semirom was sampled and studied.In the studied area the Tarbur Formation with 804 m thickness, composed of carbonate and terrigenous rocks, which deposited during Maastrichtian. The lower boundary with Amiran Formation is conformable and the upper boundary with Kashkan Formation is marked by an erosional surface.According to the lithological and petrographic characteristics of the Tarbur Formation five lithofacies units were recognized in Semirom area.Field studies and obtained data from microscopic thin sections led to recognition of 7 carbonate facies attributed to lagoon (L1, L2, L3), bar (B1, B2) and open marine (O1, O2) subenvironments and 4 terrigenous facies interpreted as shallow (Lsh) to deep marine (Osh) setting and meandring river (Fss, Fsh) system.The Tarbur Formation was formed in a carbonate platform (epicontinental sea) in a homoclinal ramp. presence of rudist debris indicates a photozone assemblage and suggests a tropical condition for deposition of the carbonate sediments.

The Emaft Fluorite mine is located in 20km southeast of Pole- sefid area in Mazandaran Province. The host of the ore is Tizkouh Formation with lower Cretaceous age, which is fractured by the NE-SW trending fault. Its lithology includes biomicrite, micrite and mudstone altered to dolomite by hydrothermal fluids. The oxygen isotope values of the most altered carbonate (dolomites) surrounding the fluorite deposits show that these deposits subjected to low temperature hydrothermal fluids. There is a trend of decreasing lighter carbon and particularly oxygen isotope values towards the orebody. The lightest oxygen isotope values are close to the orebody. The oxygen and carbon isotope values in altered carbonate (dolomite) are significantly lighter than those least- altered dolomite away from mineralized area. The alteration percentage in oxygen and carbon isotopes is maximum close to the orebody. Thus, the alteration percentage of oxygen is %88 close to orebody but its minimum identified some about %19 far from orebody.These characteristics can be used as a key to explore the unknown orebody.The results of this study is similar to the tin ore deposits of Renison mine, Tasmania in Australia and Pb-Zn ore deposit of kouh-e-Sorme of Iran.Due to the similarity in pattern of fluorite and host rock, it can be concluded that remobilization of REE and F occurred.The dissimilarity in normalized patterns of igneous rock, shale,sandstone and fluorite suggest that these rocks cannot considered as the source rocks for F. The negative Eu anomaly and positive Ce anomaly, indicate a reduction environment for ore formation.

The studied area is located in 200 Km north east of Isfahan, near the Jehagh and Zanjanbar village. The rocks of the area are composed of three units of sedimentary, igneous and metamorphic rocks. The predominant sedimentary rocks are dolomites of Shotori Formation with Triassic age. The igneous rocks comprise intrusive rocks of Oligocene-Miocene with composition of quartz-monzonite, monzodiorite, quartz-diorite, gabbro and volcanic rocks of Eocene. Skarn and marble are formed the metamorphic rocks of the area. The skarns of the area are magnesian and replaced-calcic skarns.The phlogopite bearing skarn is the most widespread skarns in the area.These skarns have formed during three stages of magmatic, post magmatic and post skarnification. In the post magmatic stage phlogopitization process takes place synchronously with the replacement of magnesian skarn by calcic skarn.The study of rare earth elements of phlogopite, spinel, garnet, vesuvianite and epidote shows the considerable enrichment of these elements, because the endogenic hydrothermal fluids is considered as the source of rare earth elements in the magnesian skarn and the replaced-calcic skarns.