RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2007 | Volume:27 | Issue:1|Papers Count:13

Northern parts of Isfahan province are included into well known Cenozoic Magmatic Belt of Central Iran. There are extensive Eocene volcanic events. Field observation indicated that, the late intrusion bodies which are belonged to Oligo – Miocene are caused some dispersed hydrothermal alteration in area. On the base of XRD, XRF and SEM data mineralogy and chemical composition of fresh and altered volcanics are determined. Volcanic rocks with chemical composition andesite to trachy- andesite have more extensive in this area. Kaolinite, alunite and jarosite are major minerals in altered pyroclastic rocks. Mineral assemblages of these alterations are characteristic of acid – sulfate or advanced argilic type alterations. With attention to the geochemistry of major and trace element the kaolinite - alunite association are likely from hypogene source in Kesheh area.

The aim of this study was the reconstruction of hydrocarbon production potential of the Pabdeh Formation (Paleogene in age).The Pabdeh Formation comprises the alternation of thin to thick limestone’s and dark to light gray shale beds, enriched in planktonic foraminifera. These lightfaces are known as pelagic facies in Zagros Basin. The coal seams in the upper unit of Pabdeh Formation are composed of Vitrinite rich humic coals which are heterogeneous with respect to maceral content and chemical composition. Based on the petrographic study, these samples are composed of three maceral groups (Vitrinite, Inertinite and Liptinite), of which Vitrinite is more abundant. They contain up to 76.8% TOC, 445 (mg Hc/org C) HI, 0.65% Ro and 448°C Tmax. Based on the average of Tmax (441.3°C) and Ro (0.6%), these samples are at the mature stage and occur on the top of oil window containing a mixed type of II/III kerogens. Based on the organic geochemical study done on bituminous facies of the Pabdeh Formation, more than 65% of samples are in mature stage and occur on the top of oil window. These samples contain a mixed type of I/II/III kerogens.

Eocene volcanic rocks present good exposure in south of Ardestan area. A low percent of these volcanic rocks belong to shoshonitic magma series with composition of absarokite and shoshonite. Minerals of shoshonites are clinopyroxene (augite), analcime, plagioclase (labradorite), sanidine, chloritized olivine, apatite, celadonite, prehnite, pumpellyite, calcite, epidote, ilmenite and magnetite. Analcimes are secondary mineral and produced by metasomatism of leucite.Mineralogical studies demonstrate that shoshoniticmagma passed a loss and gain during ascending through the thick continental crust. During these ion exchanges, shoshoniticmagma losses K2O and gains SiO2, Na2O and H2O.

The study area is a part of Cretaceous volcanic rocks lying in the border of the north of Sanandaj-Sirjan zone in Saquez area. On the basis of petrography and geochemistry studies. These rocks could be divided into two groups. The first group includes basalt. andesitic basalt and andesite. The second include andesite trachy-andesite and decide rocks. The geochemistry of rare earth dements shows that these rocks are calc-alkaline and transitional in nature that have been generated in active continental margin. Various major and rare earth elements diagrams show some magmatic differentiation. In addition. Nb and Ti negative and Th. P. U positive anomalies in comparison with MORB and chondrite point to the mantle metasomatism. Also the low ratios of Ce/pb, Nb/U, Th/pb.

The pervasive metasomatism in the margin of the Delmo intrusive body has generated different variety of tommalinization in the host pelitic rock; 1) Stratiform tourmalinites in pelitic hornfelses; 2) Pegmatitic vein in arenitic sediments; and 3) Qumiz-tourmalinethin veins that cover the surface of pegmatitic veins. The Fe/(Fe+Mg) ratio for tourmaline in stratiform tourmalinites, pegmatites and veins are in the range of 0.484-0.553, 0.375-0.509 and 0.357-0.509, respectively. These tourmalines are schorl-dravite solid solution. The chemical zonation in these minerals reflects the fluctuating conditions expected from fluid mixing in open systems. The fractionated REE patterns in stratiform tourmalines in spider diagram show sedimentary origin of these minerals. This pattern in pegmatite and vein tommalines is flatted indicating the mobility of LREE as a result of alteration of host arenitic sediments that caused the increased HREE/LREE in these two types of tourmalines.

The Gosh Kamar Bauxite deposit is located in the north east of the Eshghabad City, 49 kilometers from the Dastgerdan district near Tabas Town. This bauxite occurred as a regular geosynclines striking north- south with two limbs toward the east and west. The bauxite deposit unconformability overlying on the Bahram limestone Formation as lenses, layers and small karst in which the thickness some times reaches up to 15 meters. The color of bauxite on the field varies from light red to dark red. The Bauxite deposit shows sharp contact with overlay and under lay rocks. The purpose of this study is to understand and the mineralogy and geotectonic of bauxite deposit. To do this, we have used the thin sections for the study of the texture and XRD for mineralogy. Gosh Kamar bauxite shows a pelitomorphic, micro granular texture with several secondary textural elements. Where the bauxitization is proceeding, concentric pisolites have been formed. Based on X-ray analysis, Goshkamer bauxite deposit is Gibsite type accompanied with some amounts of bohemite. The other major minerals along with these minerals are Kaolinites, Hematite and Anatase associated with Goethite and Rutile as a minor amount. From classification point of view, this bauxite is classified as clayey bauxite and-Ferrous Kaolin. The geochemical data and oxide minerals indicate that this bauxite has been deposited in the active continental margin.

Based on the field observations as well as aerographical study, the plagiogranites of the ophilitic sequence of Anarak, Ashin- Zavar and Nain show that these rocks have identical brecciated granular, granophyric and graphic texture. From the mineralogy point of view. quartz, plagioclase and amphibole are the main minerals while sphene, apatite and zircon are the accessories. The Anarak plagiogranites are metamorphosed and show some foliation while the plagiogranites of Ashin- Zavar have two generations.The first generation is old and metamorphosed occurrs crushed fragments. The second generation is the youngest rocks in the study area crosscutting by pillow lavas. The Nain's plagiogranites are intersected by sheeted dikes mainly rhyolitic to dacitic in nature. The analysis of acidic rocks of these ophiolites sequences show that the trace and major elements contents display limited variations with quartzdiorite to quartzolite. Composition of the plagioclase varies from albite to oligoclase.

One of the major petroliferous basins covering a larg part of Turkumenstan, Afghanistan and northeast Iran is the Kopet-Dagh intracontiental basin. The Aitamir Formation is deposited during Albian- Cenomanian in this Basin. This Formation is composed of Glauconitic sandstone, mudstone and limestone which rests comformably on the Sanganeh and overlies the Abderaz Formations. Surface and subsurface studies show that the Aitamir Formation was deposited in lagoon to shallow open marine environments. Transgressive system tract (TST), high stand system tract (HST) and low stand system tract (LST) in these sections have been interpreted based on lateral and vertical lightfaces variations as well as abundance of glaucony and bioclastic grains. Identified depositional sequences in the studied area range from 2 (Shurijeh section) to 6 (Khangiran well numbers 35, 40). Sequence boundaries in all studied sections (except the upper boundary of last depositional sequence) are type 2 (SB2). Interpreted sea-level curve at the fall of sea-level during the Cenomanian Time can be relatively correlated with the global sea-level curve.

In north of Chah Zard farm, Jandaq metamorphic complex contains schising and marble underlay the amphibolites. Amphibolites are metamorphosed basalts of Jandaq ophiolite. and Jandaq metamorphic rocks are metasedimentary cover of Jandaq metaophiolite. Ampbibolites contain hornblende, plagioclase, garnet, alkali feldspar (orthoclase), magnetite. biotite. muscovite, sphene and quartz. These rocks present very good lineation and foliation. By metamorphic differentiation. mafic and felsic minerals are seperated in some locations. Mineralogical studies. Hornblende barometry, and hornblende - plagioclase thermometry, conclude the metamorphism of these rocks under upper part of amphibolite facies (7.10 to 9.91 Kbars and 619 to 650°C). Presence of actinolite, epidote and calcite in amphibolites demonstrates a retrograde metamorphism under green schist facies.

Tarbur Formation, Campanian-Maestrichtianin age, is a lithostratigraphic unit, deposited in the Zagros Basin. Two stratigraphic sections (in Semirom and Borujen areas) were sampled and studied to determine their microfacies and sedimentary environment. Based on field observations, facies analysis and petrographic studies, 11 microfiches of the open marine, shelf margin. Shelf lagoon and tidal flat sub environments are recognised. These sediments were dopesited in a carbonatre ramp. At the section in Borujen, a thick bedded rudistic limestone which formed a biostrome. is exposed. The rudistic biostrom was formed in a warm relatively high salinity and low energy shallow marine environment. Presence of rudists indicted a photozoan assemblage.

Late Devonian sequence of Shams-Abad vicinity, northwest of Kerman (SE Iran) is investigated by means of conodonts. The fauna including shallow water forms of I.criodus alternatus alternatus, I. cornutus, I. iowaensis iowaensis, I. iowaensis ancylus. Polygnathus semicostatus. P. communis and Pelekysgnathus serradentatus confirms an age range from the Middle triangularis to the Late crepida zones time interval. This finding can be an early Famennian occurrence for Polygnathus alatus in the Shams-Abad beds as it was previously found in the contemporaneous beds of the Hutk section.

Surk skarns are located in NW of Yazd province and are included in Cenozoic Magmatic Belt of Central Iran. There is Surk ophiolite assemblage in vicinity of these skarns. Granodiorite intrusions are hosted by Eocene volcanics and pyroclastics. so these iron skarns are developed in them. In the first stage diopside skarns are formed due to peack thermal contact metamorphism. In the second stage the andradite garnets are taken place mainly as replacement bodies (T = 520°C ´ CO2 = 0.6 and P = 0.5 Kb). In the life time of garnet genesis. pressure reduction of hydrothermal system caused an abrupt change in garnet composition as revealed by zoning.