RESEARCH JOURNAL OF UNIVERSITY OF ISFAHAN "SCIENCE"
Year:2004 | Volume:20 | Issue:2|Papers Count:14

lower Cretaceous succession at Soh area dominantly comprises limestone and shale deposits. In order to determine the microfacies and sedimentary environment of the succession, one stratigraphic column in the south of Kashan (Soh area) was sampled and studied. Facies analysis and petrographic studies resulted in recognition of 9 carbonate microfacies of the open marine, shoal, barrier, lagoon and tidal flat subenvironments. Three clastic facies are also recognized. Considering the characteristics of the carbonate microfacies and their comparison with the standard facies of carbonate platforms it can be concluded that the lower Cretaceous sediments in the study area deposited in a homoclinal ramp. The bioclastic and non-bioclastic (ooids and peloids) components in this area indicate a photozoan assemblage, formed under a tropical condition.

Due to the considerable presence of Tertiary andesitic components around Birjand and their role in active geodynamic regims, their study is of crucial importance. Accordingly, Andesitic Tertiary volcanic rocks in Birjand region and their geochemical and petrogenetic parameters have been studied with regard to the index of andesitic complexes. Based on the results, continuity and absence of gap in goechemical diagrams and relation between different kinds of elements suggest that these rocks have been crystalized from differentiation of an initial parent magma. Petrogenetic parameters show that these rocks belong to the active continental margin orogenic andesites. The results also show that Calcoalkaline magma is mixed with relatively thick crust materials, and this mixing has influenced the main and trace elements of parent magma. In addition, there is some evidence concerning magma mixing idea.

Metamorphic rocks in the Khoy region are restricted by obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic to the northeast. The Qom Formation (Oligocene-Miocene) with basal conglomerate transgressively overlies all these rocks. The metamorphic rocks consist of both metasediments and metabasits. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta arkose, marble and quartzite, where metabasits are greenschist and amphibolite with basalt and gabbroic protolith and their origin of tholeitic and calc-alkaline magma type. Geotermobarometry based on equivalence of minerals stability and their paragenises in these rocks and microprobe analysis by several different ways indicate that metamorphism occurred in temperature (450oc to 680oc) with 5.5 - 7.5 kb pressure. In the margin of the minerals, pressures decrease considerably (<2kb) where temperature decrease is insignificant. The PTt path in these metamorphics was normal. The MFG line passes over the triple junction of Al2SiO5 polymorphs and the average geothermal gradient during metamorphism was between 27oc to 30oc per kilometer which is more concordant with collision zones. It is concluded that the thickening of the crust produced metamorphism in this area when the Arabian plate collided with Azarbayjan plate during post Cretaceous (probably Eocene).

Goldaragh nepheline syenite ore deposit (located in eastern Azarbayjan) consists of alkaline nepheline syenite with an intermediate composition between miascitic to agpaitic. There are five principal types of ore deposit: type A (foyaite), type B (sodalite alkali nepheline syenite), type C (nepheline monzonite), type D (nepheline diorite to nepheline gabbro), and type E (altered rocks). The most important minerals are orthoclase, microcline, nepheline, cancrinite, sodalite, plagioclase, analcime, aegirine, aegirine augite, as well as amphibole (arfvedsonite), garnet (melanite), biotite (lepidomelane), sphene, magnetite, hematite, loparite and scolecite. Rocks of northern area of ore deposit ( type B) due to the high content of nepheline, sodalite, cancrinite and low content of mafic minerals have low iron (1.65%) and high alkalies (total 13.2%), and compared to the south area with high content of mafic minerals and conclusively high iron content (3.97%) and low alkalies (10.76%), are more suitable for glass and tile production.

Gorgan Metamorphic complex which passes like a band from east to west bound from 5 km south of Gorgan city in the north of Iran, generally contains low grade melamorphic rocks such as slate, phyllite and slate-schists. Along with these series there are both intrusive and extrusive igneous rocks and some grain and pach of earlier formation in the low grade metamorphism"s ourscraps, which show olistostorome form in Gorgan metamorphic region. Some complete remain forms of palynomorphs are obtained from low grade metamorphism system which contain fungale spores, Gymnosperm pollens and Angyosperm pollens. Based on the results of the study, the age of Gorgan metamorphic complex seems to be "Tertiary" .

In north of Anarak city, the ultramafic rocks of Anarak Ophiolite are in contact with the lower member of Chah Gorbeh metamorphic group of Anarak metamorphics (Sebarz schists). Field studies show that the lower part of Sebarz schists is an Olistostrome with exotic blocks of Anarak ophiolite. Due to strong deformations of ultramafic and metamorphic rocks, their contacts are highly tectonized and faulted. Large amount of talc schists and schists rich in talc exist in the lower parts of the Sebarz schists. Ophiolitic olistoliths, banded metacherts close to the contact of ultramaphics, subparallel foliation in the ultramafics and schists indicate that these two rock units had relations during the sedimentation, later deformations and metamorphism events. Foliation in schists anastomose around ophiolitic olistoliths. It is concluded that ultramafics are the oldest rock units in Anarak area and belong to Late Proterozoic.

There is a high diversity of Mesozoic plants, such as Cycadophyta, Pterophyta, Coniferophyta, Ginkyophyta in the Upper Trias-Lias of Iran. Lithostratigraphycally deposites of studied area (Shemshak Formation) can be divided into there parts. The first part contains plant fossils which can be used for age determination and interpration of climatic history of the past. On the basis of systematic studies, some of the most important fossils are: Cladophlebis cf. australis, Pterophyllum bavieri, Zamites sp.1, Elatocladus conferta, and Scytophyllum persicum. Most of the studied speciemen are long range flora, but the presence of Scytophyllum persicum in part 1 indicates the age of Upper Trias (Rhaetian) for this part of the Formation. Collected flora suggest a subtropical condition in the time of deposition of the Shemshak Formation.

Ardestan, behind the magmatic arc (Bazman-Uroomieh trend). Thick sequence (465 meters) of sediments equivalent to Qom formation overlain the Eocene volcanic rocks (andesite, trachyandesite and andesitbasalt). Lithologicaly the Qom formation comprises six members and four submembers. The thickness of the Qom Fromation is most increased around the city of Qom. The sediments in the study area (west Ardestan) are not dividable into members. In this study numbers of corals are gathered, identified and introduced. Corals are from 150 meters above the base of the section and are used for paleoecology and paleobiogeo graphical considerations. The corals are mixtures of Indopacific and Mediteranian corals. Scattered solitary corals in some horizons reflect turbulence within environment and faviides and porites corals in some other horizons also confirm turbulence in Oligo-Miocene time in the study area. As a result, deposition of the above mentioned sediments took place under strong high energy, turbulent and shallow water depth of deposition.