RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2008 | Volume:32 | Issue:3 (GEOLOGY)|Papers Count:13

Orbitolinids are among the most important group of foraminifera which are of high importance in sediment biostratigraphy of the Early-Mid Cretaceous sequences. Concerning the origin of orbitolinids, there are different ideas, the most important and newest of which has been introduced by Cherchi and Schroeder that shows 4 different phylogenetic lineages in this group. Six species belonging to the genera Mesorbitolina Schroeder and Praeorbitolina Schroeder were identified through the Dariyan Formation of the Dashtak area.Based on appearance and stratigraphic distributions of orbitolinids in the Dashtak stratigraphic section and comparison with Cherchi and Schroeder's evolutionary model, Praeorbitolina wienandsi- Mesorbitolina ovalis-periva phylogenetic lineage is herein suggested for the upper part of the Dariyan orbitolinids in the studied area comprising part of the Praeorbitolina cormyi - Mesorbitolina aperta Cherchi and Schroeder phylogeneticlineage. The most important changes in the phylogenetic lineage, reperesented herein are as follows: the change in the position of embryonic apparatus, the shape of protoconch and subembryonic zone, size increase in embryonic apparatus and protoconch, increase in number of subembryonicand deuteroconch partitions.

The area of study is in the North of khur and North-East of Arusan-e-kur-e-Gaz, which in geology divisions is in Central Iran. In petrographic study intrusive body, aplitic dikes and enclaves are alkali granite. Minerals of alkali granites are K-feldspar (orthoclase and microcline), plagioclase (albite and oligoclase), quartz with undoluse straight extinction, biotite, muscovite, zircon and apatite. Chlorite is created by biotite alteration. Intrusive body has foliation in many parts that look like auegen gneiss in the first view. But investigations show that this intrusive mass is mylonitized.Geochemical investigation shows the nature of calc alkalin, peraluminous and S-type nature of understudy granitoids. Thus samples of studying area located in syncollision region. The temperature given by two feldspars thermometry, that is lower than temperature of igneous environment, present the sub-solidus changes of feldspars composition. Ti in biotite thermometry result 632-661oC for biotites of intrusive body, aplitic dikes and enclaves. The obtained temperatures reveal the igneous temperatures of biotite crystallization. In addition, chlorites of alkali granites display a temperature around 188oC. This temperature indicates the biotite alteration temperature.

Tirgan Formation (Barremian-Aptian) in the Kopet-Dagh basin mainly consists of oolitic and orbitolina limestones that conformably overlies and underlies the Shurijeh and Sarcheshmeh Formations, respectively. Two stratigraphic sections in south west of Jozak (315 m) and Chaman Bid (242 m) area were measured and sampled. Petrographical studies indicate that these sediments may have been deposited on a shallow carbonate platform ramp type and consist of 4 carbonate lithofacies (12 subfacies). These lithofacies indicate that they may have been deposited in open marine, shoal, lagoon and tidal flat environmental conditions. Sequence stratigraphy analysis led to identification of 4 third order depositional sequences, bounded by type 2 sequence boundaries. Comparison of interpreted sea level change of study area and three measured sections in the eastern Part of the basin indicate that the depth of basin decrease toward east and south east.

The study of planktonic foraminifera of the Gurpi Formation at Lar area (Kuh-e-Gach) led to recognition of 8 genera and 16 species of the planktonic foraminifera.Four biozones were determined in the Gurpi Formation including: Globotruncana ventricosa zone (Middle Campanian), Globotruncanita ca1caratazone (upper part of Middle Campanian), Globotruncanita stuarti zone (lower part of Upper Campanian), Gansserina gansseri zone (upper part of Upper Campanian-Middle Maastrichtian). Study of the morphotype groups of planktonic foraminifera represents a relatively deep marine condition for deposition of the Gurpi Formation at the study area.

Hired gold mineralization area is located at 160 Km to the south of Birjand (air distance) and 80 Km to the north of Nehbandan in south Khorasan province. Mineralization in the Hired prospecting area is observed in 4 targets named target 1 to 4. Intrusive rocks associated with mineralization are illmenite-type granite, granodiorite and monzonite with low magnetic susceptibility and are post Eocene. Mineralization type at Hired is reduced intrusion-related gold system because of reduced source rocks and mineral assemblages such as pyrrhotite & arsenopyrite. Detailed mineralogical studies indicate that sulfide mineralization along with gold have pyrrhotite only in the eastern part of target 1. Mineralogical studies, magnetic susceptibility measurements on drilled cores and ground magnetic data confirm the presence of pyrrhotite on the eastern part of target 1. Based on detailed drilled core studies, there is relatively good correlation between the increase of pyrrhotite (to 6%) and the amount of gold (to 5 ppm) in the eastern part of target 1. Total Magnetic Intensity (TMI) of the surveyed profiles and contour map from this part of the mineralization reveal obvious anomalies in the eastern part of target 1that the causative sources of them are pyrrhotite along with mineralization. Mineralogical studies, magnetic susceptibility measurements from bore holes and ground magnetic survey on the western part of target 1 and target 3 indicate no pyrrhotite along with mineralization. The amount of gold on these areas is much less than the eastern part of target 1. Based on the presence of pyrrhotite along with gold mineralization on the eastern part of target 1, magnetic method is used as a useful geophysical method for the determination of drilling location and consequently access to gold mineralization in the eastern part of target 1.

Two types of rodingitization (static and dynamic) are observed in the rodingites of the ophiolite in the North Of Nain. Two stages have occurred in the formation of static rodingites. In the initial stage, epidote, prehnite and hydrogrossular have crystallized respectively, at the expense of plagioclase, with the increase of calcium content rodingite forming fluid. In the advanced stage, xonotlite in the expense of plagioclase, and Mg chlorite, tremolite and secondary diopside, at the expense of pyroxene, have been formed simultaneously with an increase of Si content of rodingite forming fluid. During rodingitization, the Ca and OR content, have increased, whereas the amounts of K, Al and Na are reduced. Mn, Fe and Mg values are slightly reduced but Si remains constant.

Pillow lavas, massive lava flows, basaltic and diabasic dikes, meta basalts, andesites, meta-andesites, gabbros, pegmatite gabbros, dacitic dikes along with epiclastites, hyaloclastites and cold breccias are the main constituents of the crustal unit of the Siyah-Cheshmeh ophiolite. The various rock units of the Siyahcheshmeh ophiolite are petrographically and geochemically different and based on the trace elements and tectonomagmatic diagrams; they are considered to form in different environments. Some of pillow lavas, basaltic flows, meta-basalts, basaltic ftagments in epiclastites and basaltic dikes display alkaline characteristics. They are marked by enrichment in LREE, Nb and Ta. These geochemical behaviors resemble exclusively both to oceanic island basalts (OIB) and to E-MORB-OIB basalts. On the other hand, some rock units including lava flows, pillow lavas, diabasic dikes, andesitic-dacitic dikes, lapilli tuffs, pegmatite gabbros and gabbroic dikes are characterised by high LREE/HREE ratio and depletion in Ti, Nb, Ta and therefore show either IAT or calk-alkaline affinity.It is clear that the formation of OIB-E-MORB basalts are related to the interaction between mantle plumes and an oceanic spreading center. Otherwise, petrogenesis of calk-alkaline and IAT rocks is thought to be related to supra-subduction zone.

Eocene volcanic rocks with andesite, andesibasalt to dacite composition in north of the Anarak area are exposed as small and scattered masses. Exposures of these rocks mainly follow the faults direction.Geothermometry studies of even equilibrated amphibole-plagioclase phenocrysts indicate that crystallization temperature of these phenocrysts ranges between 835oC to 925oC. Results of amphiboles barometry on the base of Al content shows that amphibole phenocrysts in these volcanic rocks had been crystallized in pressure of about 6.19-8.62 Kbar. On the basis of calculated pressure, magma chamber of these rocks have occured about 30km in depth. The geochemistry trends in the Harker and spider diagrams for rare earth elements, Eocene volcanism in north of Anarak area is specified with two distinctive magmatic series. In terms of magmatic series segregation diagrams, these two series have transitional characteristics and tend to be shoshonitic type. Enrichment and depletion in some elements such as Ta, Th, Ce and K is related to the contamination and magma mixing in Eocene volcanism in the north of Anarak area.

he surk huge dome is a part of Plio-Quaternary Uromieh-Dokhtar Magmatic Belt lying in the west of Yazd province. The studied dome is exposed as an high elevated morphology. It consists of volcanic and pyroclastic rocks. Thermal metamorphism of Neogene conglomerate by the dome proved that the dome belongs to the Plio-Quaternary period. The lithology of the Surk dome is mainly dacite and rhyolite. The studied pyroclastic rocks have dark and rounded enclaves. The presence of rounded, dusty, absorbed and sieved plagioclases with abruptly zoning, new feldspar growth around the sieved plagioclase and rounded quartz in these rocks can be taken as evidences of magma mingling event. Opacitization of biotite and hornblende show that PH20 and 102 during rock formation were high. Based on geochemical data, the parent magma is mainly acidic, calc-alkaline and metaluminous in nature.

Measurement of the acidity of precipitations in the years 2005 and 2006 indicates occurrence of acid rain in the region adjacent to the Sar Cheshmeh Copper Smelter at 155 km southwest of Kerman. This paper deals with the mobility, leaching and chemical change of three nutrient elements namely, Ca, Mg and Cu, by acid rains, from entisols and inceptisols of the Sar Cheshmeh region. Laboratory experiments were performed on 12 undisturbed soil core samples (50 cm tall, 6.1 cm in diameter) with acid solutions of pH=3.1 (eas prediction of acute condition), pH=4.1 (acid rain of studied area) and pH=5.6 (as natural rain). The sprinkling lasted 31 days, simulating a rainfall of 370mm, and the drainages were analyzed. Soil properties and forms of Ca, Mg and Cu in 0-15cm, 15-50cm and 30-50cm depths were determined before and after simulation.The investigations show that acid rain could mobilize and leach out some elements from soils of the studied area. Acid rain causes a decrease in the exchangeable form of calcium and magnesium, while soluble form of these nutrient elements increases. Furthermore, acid rain causes an increase in the available form of Cu.These changes could have negative and/or positive environmental effects on the Sar Cheshmeh area.

Lamprophyric stocks and pillow lavas are situated in the southeast of Anarak (Isfahan Province), adjacent to the Turkmeni-Ordib fault. Rock-forming minerals are amphibole (kaersutite), plagioclase (oligoclase and albite), K-feldspar (sanidine), Cr-Ti spinel, ilmenite, apatite with low amount magnetite, chlorite, pumpellyite, epidote, sphene, leucoxene and calcite.Textures of pillow lavas are microlitic and variolitic, and textures of stocks are porphyritic and intersertal. The cavities are filled by calcite. These rocks are enciched in alkalis, Ti02 and LREE, and the Si02 content ranges from 40 to 52 weight percent. In classification of lamprophyres, these rocks are alkaline lamprophyres and tectonically are formed in intracontinental plate setting.

In the southern Caspian Sea ophiolite complex, in the structural zone of Gorgan-Rasht, some gabbroic bodies have penetrated the southern Caspian Sea ophiolite rocks that have upper cretaceous age. These ophiolite rocks have tholeiitic nature but these gabbros fall in alkaline rocks field (Si02: 45.5-48.5; Al2O3: 14.8-18.45; MgO: 3.2-4.27; Fe2O3 (t): l0.45-13.3; CaO: 8.2-9.41; TiO2: 2.79-3.82; (Na2O+K2O): 5.2-6 and Ti/v: 83-l03). In spite of the relationship and Accompaniment of alkaline gabbros andophiolitic rocks complex, it seems after formation of tholeiitic units, alkaline gabbrospenetrated into that but since any effect of alkaline gabbros is not found in younger Cenozoic units, it is suggested that these rocks are not very younger of their hostedrocks. The mineral chemistry of alkali gabbros of the Southern Caspian Sea ophiolite (SCO) is consistent with crystal-liquid.Fractionation of primitive basalts at low pressures.The presence of low magnesian clinopyroxene, presence of zoning in clinopyroxene together with the presence of plagioclase (with low An%), indicate low pressure crystal fractionation of primitive basaltic melts.Mineralogical and geochemical data suggest that the alkali gabbros are formed and enriched MORE source.