GEOSCIENCES
Year:2004 | Volume:11 | Issue:51-52|Papers Count:14

Dezful embayment located in southwest Iran is bounded to Bala-Rud flexure towards northwest, Dezful embayment fault towards northeast, Mountain front fault towards north, and Zagros foredeep fault towards southwest. The embayment consists of thick sedimentary sequences of Mesozoic and Cenozoic time. The whole region is charecterised by intense structural depression. Structural analysis of five anticline reservoirs in Dezful embayment based on interpretation of seismic reflection profiles, and depth sections indicates: Based on dip isogons analysis, and relative competence of the layers, the (competent) reservoir horizons such as Asmari, Sarvak, and Dariyan are of class IB, while source and cap rock (incompetent) layers such as Pabdeh, Gurpi, and Garu are of class IA and IC. egarding fault-fold relationship, there are fault-propagation folds and fault-bend folds. The Haftkel structure is interpreted as antiformal stack; the Naft sefid structure is fault-bend fold; the Parsi field is fault-propagation fold, and Mamatain and Karanj structures are possibly detachment folds.

Surface and internal characteristics of tongue-shaped rock glacier have been studied at the north slope of Haram summit on interior Sabalan Mountain. The formation of surface depressions indicates the existence of a solid ice core, and its origin also is determined by using RILA concept. It is probable that a normal glacier has been buried beneath a cover debris. The vertical section of this rock glacier shows three layers from bottom to top, and based on the dynamic criterion, the rock glacier is an active one.

Field and microscopic studies and geochemical analyses suggest that granitoid rocks may be subdivided into three main groups. The first group of granitoid rocks is S-type syn-tectonic granitic gneiss sheets, the second group is I-type volcanic arc granite and granodiorite and the third group is S-type post-collision alkali-granite.The rocks of Soresat metamorphic complex are different kinds of schist. Andalusite, staurolite, garnet, sillimanite (fibrolite) are the main metamorphic porphyroblasts in these rocks. The protolith of Soresat metamorphic complex are a sequence including shale, siltstone and graywacke with carbonate, arkosic sandstone and pyroclastic intercalations.A prominent, regionally penetrative foliation (S2) is distinguished in studied area. S2 is generally parallel to meta-sedimentary bedding plane. Thin section studies reveal two discrete deformational events. The first deformational event (D1) is preserved as straight inclusion trails in Pre -S2 Post – S1 andalusite, staurolite porphyroblasts. The S2 is generated by the second deformational event. The retrograde metamorphic event follows the second deformational event. The proposed P-T-t path shows a clock-wise path for Soresat metamorphic complex (Pmax=3.7Kbar, Tmax=600°C).

Ekhtiarabad sinkhole which is located 14 km NW of Kerman, near a homonymus Village, appeared suddenly in July the first, 1998. Mechamism of formation of the cave system which created the hole is of great importance for detecting suspected subterranean caves in the region .In this regard, several ideas have been put forward, namely, dissolution of evaporites, dissolution of limestone, and mechanical wash-out of fine sands (piping). To resolve this problem, geologic and hydrogeologic conditions of the region were analysed, and a hydrogeochemical approach, based upon evaporite dissolution index, was proved to be efficient .The index is over 40 in the vicinity of the hole, but decreases abruptly away from it to less than 5, indicating dissolution of evaporites , which seem to be gypsum. Some other clues ,such as electrical conductivity of groundwaters, evaporitic facies of Neogen sediments, and a nearby gypsum mine all increase this possibility .Several mechanisms; as decline in groundwater level, trrafics , and enhanced disssolution induced by pumping groundwaters are suspected as collapsed triggers.

Basal part of the Shemshak group in Galandrud area, in north Alborz about 16km south of Ruian city (Alam- Deh) was investigated palynologicaly. The studied section attains a thickness of 590 meters and, consists of limestone, shale, sandstone and siltstone beds. A total of 29 samples were selected and treated in the palynological laboratory of the geological survey of Iran. Eighty one palynomorph taxa were encountered. The recorded dinoflagellate species were arranged in four local bioassemblage biozones and a superbiozone (Rhaetogonyaulax).Biozone I; Heibergella asymmertrica, occurs in a thickness of 60 m, suggesting an Early Norian age.Biozone II; Heibergella aculeata, occurs within 50m, representing a Middle Norian age.Biozone III; Hebecysta balmei, which occurs in a thickness of 40 m, indicating the Middle to Late Norian age.Biozone IV; Rhaetogonyaulax rhaetica, occurs in a thickness of 330 m, indicating a Late Norian to Rhaetianage.Statistical studies on the recorded palynomorph assemblages show that lower parts of the section have been deposited in an open marine environment. In Late Norian a regression of the sea caused sediment of the Rhaetian to be deposited in a deltaic environment. The Early Kimmerian and the following orogenic phases have had the least effccted on the sedimentation processes during Late Triassic age in this area and the carbonaceous Elika Formation turned into Shemshak group gradually and without any disruption.

The upper part of the Shemshak Formation at Tazareh area consists of sandstone, siltstone, and shale beds with marine fossils.Based on systematic study of the ichnofossils in these sediments, 9 ichnogenera, in two assemblages have been identified. The first assemblage with low ichnodiversity (Skolithos, Arenicolites, Diplocraterion) occurs in the siltstone and sandstonebeds. This assemblage ofichnofauna represents the skolithos ichnofacies which formed in a relatively high energy condition. The second assemblage with higher ichnodiversity (Planolites, Palaeophycus, Neonerites, Cochlichnus, Rhizocorallium,Chondrites) is very common in the shale beds. This assemblage represents the cruziana ichnofacies which formedin a relatively lower energy condition.

Sikhoran Ultramafic-Mafic Complex, in southeastern Iran, has intruded into the Palaeozoic metamorphic rocks and is overlainby Mesozoic colored melanges with fault boundary. The age of the complex and other similar complexes have Stratigraphically been supposed to be Palaeozoic. Detailed field and laboratory studies particularly, isotope geochemistry, not only revealed the age of different parts of the complex, but more significantly also showed its polygenetic nature.Radiometric age determinations by K-Ar method on minerals and whole rocks of different parts of the complex show 305±7 Ma for biotite of host Palaeozoic gneiss, 330±8 Ma for muscovite of anatectic granite intrusions in host Palaeozoic gneiss, 325±17Ma for amphibole of host Palaeozoic amphibolites (Middle-Late Carboniferous), 250-280 Ma for amphibole of gabbro-pegmatoid dykes cutting the ultramafic-mafic cumulates (Permian), 184-220 Ma for amphibole and plagioclase of some gabbro-pegmatoid dykes and basic migmatites resulted form amphibolite anatexis in the contact of isotropic gabbros with Paleozoic metamorphic rocks of host amphibolites (Middle-Late Triassic, the age of isotropic gabbro emplacement),81. 160 Ma for whole rock samples of diabaslc dykes (Middle Jurassic-Upper Cretaceous) and finally 8l±2 Ma for phengitic muscovite of Ashin colored melange mica schists.

The Bozghoosh mountain is located on the east of Orumieh lake. The structure is characterised by the normal faults trending ENE-WSW and reverse faults trending ESE-WNW. These faults transversally cut a number of the stream channels.The vertical movements of the faults has caused the dislocation of river terraces and has controlled the distribution and migration of the alluvial fans on the northern piedmonts of Bozghoosh mountains. These aggradational landforms have been studied as evidences of morphotectonic and morphoneotectonic, in the review of the quaternary evolution. Finally; based on morphometery and morphological analysis it has been revealed that the tectonic is important, the geomorphologic evolution.

The Preset study is on alluvial sediments with variable origin of the Karhkeh river, in order to recognize their heavy minerals dominant pattern distributions. The distribution data analyzed by monovariable. Variance and covariance cofficient statistical analyses. 100 samples which are collected from recent and old traces river sediments are considered fof studies on 30 heavy minerals which are seperated by heavy liquid method (Bromoform). Although, the net volum of heavy minerals in the study area is negiigible but the variation and local concentration of minerals is so high and considerable. The highest measured volume of heavy minerals after concentration of 5000 c.c is still negligible. 5 samples were analyzed using XRD method to recognize other minerals and also confirme microscopic mineralogy observations. Also 7 samples were analyzed by NAA method to present correlation patterns of elements in high potential area.According to variance analyses and mineralogical studies most of the heavy minerals in the Karkheh sediments originate from 3 lithological units which are. dominantly located in the upper parts of the basin and the Sanandaj- Sirjan Zone. Due to observation of bright and dark heavy minerals, total percent of bright heavy minerals(zircon- rutill- garnet and turmaline) in the Karkheh sediments is more than 5% (63285.86 gr/t) and total percent of dark heavy minerals (ilmenite – hematite-chromite - ch romite - mangnetite) is more than 6% (7474.84 gr/t). Based on the procedure suggested by Rose & webb (1979) several high potential area pionts were selected for garnet, zircon, ilmenite and rutile explorations. Covariance coefficient shows close positive carrelation for zircon and rutile mineral in all samples and anomaly areas have similar quantites of these minerals. The quantity of ilmenite in all samples is consider ably high and several remarkable anomalous points are present. Garnet present with magnetite which is the most abundant mineral in alluvium, and shows a constant distribution along the field sampling.

Miduk in one of the largest copper ore reserves in Iran that is situated in the north west of Kerman province. It consititues approximately 157 million tons of ore with an average grade of 85%. One of the most important elements of the open pit planning is the determination of the final pit limits. The simulation method (positive floating cone) is a commonly used method for this purpose in which the users design by grade blocks. In this presentation, geostatistic methods have been described and their application in open pit mine planning discussed. Furthermore, computer programs of CSMINE and VARIOC have then been explained and parameters required for the application of the software programs obtained. Finally, The optimum design of the pit is determined by using two sets of real data and applying the above computer programs. The recommended pit will produce appropriate ore for the ore dressing plant with maximum average and the highest amount of economic gain mind.

Binalud Mountain is geographically the continuation of Alborz Mountain but because of some facies similarities and the effects of folding, it is considered to be the transition zone between Central Iran and Alborz. In this study, eight plant macrofossil species are identified from Shemshak Formation in Golmakan, Binalud. They are Coniopteris hymenophylloides, Klukia westi, Sphenobaiera longifolia, Sphenobaiera cf. pulchella, Czekanowskia rigida, Nilssonia macrophylla, Nilssonia acuminata and Nilssonia feriziensis. According to their stratigraphical distribution, Late Liassic - Early Dogger age canbe inferreded for this assemblage.

Approximately 50 chromite outcrops are observed in the Esfandagheh Paleozoic ophiolite complex, of which few are economically important. Rock types in Abdasht area are mostly dunite and harzburgite and the chromite deposits occur as lens- shaped bodies in dunite. Texture of the bodies is nodular, disseminated and massive which occasionally all these textures can be seen together in one orebody.These deposits are rich in chromium and poor in aluminum. Moreover, there is no mineral concentration of elements such as Ni, Co and PGE in the chromite ore and host rocks. The chromite deposits in Abdasht region are of Alpine type (podiform).