فهرست مطالب

Earth Sciences - Volume:8 Issue: 1, Apr 2016

Iranian Journal of Earth Sciences
Volume:8 Issue: 1, Apr 2016

  • تاریخ انتشار: 1395/05/29
  • تعداد عناوین: 7
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  • Saeed Saadat*, Charles R. Stern Pages 1-24
    The Lut block in eastern Iran is a micro-continental block within the convergent orogen between the Arabian, Eurasian and Indian plates. Large areas of the north-central, eastern, and western Lut block are covered by volcanic rocks of Paleogene, Neogene and Quaternary age. Peak volcanic activity took place in the north-central part of the Lut block during the Eocene, and then dramatically decreased, becoming more restricted to the eastern and western margins of the block during the late Miocene and Quaternary. There is also significant variation in chemistry between the Paleogene igneous rocks from the north-central part compared to the Neogene and Quaternary volcanic rocks from the western and eastern margins of the Lut block. The Neogene and Quaternary olivine basalts, which were erupted along both margins of the Lut block, are similar in trace element chemistry to the average composition of oceanic island basalt. In contrast, the Paleogene volcanic units of the north-central Lut block, which include basalts through rhyolites, follow both calc-alkaline and alkaline trends. Low TiO2 and high Ba/Nb and La/Nb ratios for both Paleogene basalts and andesitic samples from the north-central Lut block suggest affinities, at least for some of these samples, with convergent plate boundary arc magmas. LILE/HFSE ratios, interpreted as an indication of subduction signature, increase to the south-southwest of the central Lut block, where Neotethys oceanic crust was subducted beneath Iran in a northeastern direction from approximately Late Triassic to Late Oligocene time. We suggest that components derived from low angle subduction of this crust during the Mesozoic and early Tertiary were stored in the mantle lithosphere below the north-central Lut block until the Paleogene, when changing subduction geometry, associated with the collision of Arabia with Iran and the closing of Neotethys, caused hot asthenosphere to well up under the Lut block. This created the Eocene peak in volcanic activity, generating basalts from asthenospheric mixed with lithospheric melts, with both alkaline and calc-alkaline affinities. After this volcanism waned, becoming restricted during the Neogene to OIB-type alkaline basalts erupted through deep lithospheric structures along both the western and eastern margins of the Lut block.
    Keywords: Eastern Iran, Lut block, volcanism, basalts, subduction
  • Gholamreza Ahmadzadeh*, Reza Zamani Pages 25-35
    Clinopyroxene phenocrysts and microphenocrysts in potassic and sodic Eosen alkaline volcanic rocks from the northern Lahrud (NW Iran) record various stages in the crystallization and evolution history of the alkaline melt as well as its origin. The rock series hosting the clinopyroxene phenocrysts is phonolitic tephrite and tephritic phonolite composition. Theses rocks generally show porphyritic texture and have a variable phenocryst-rich nature (25–50%), with phenocryst assemblages characterized by Cpx ± An ± Pl. The studied clinopyroxenes have relatively high Mg-numbers (0.66-0.90), variable Al2O3 (3.77-7.31 wt%), low TiO2 (
    Keywords: alkaline volcanic, clinopyroxene, sodic, potassic, magma mixing, NW Iran
  • Jamal Tarrah* Pages 36-44
    Specific elements (Cr, Al, Ca, and Si) and loss on ignition (LOI) were used for semi-quantitative determination of the normative mineralogical composition of naturally occurring chromium ores in ophiolite complexes. By far the occurring ore minerals are complex both from the mineralogical and chemical viewpoints. The secondary minerals serpentine and Cr-containing chlorite (kaemmererite) form next to the spinel, the most abundant mineral in the ores. As a secondary formed mineral, Cr-containing garnet (uvarovite) is very rare. Among the primary minerals olivine occurs most often. Diopside plays a subordinate role. The amounts calculated for mineral associations of chromium ores occurring in south-eastern Iran are sufficiently accurate. The sum of calculated mineral contents varies from 83 to 108 wt. %. In the application of the normative procedure, Mg, Fe, Mn and Ni were not used for the calculation. Therefore, tests could be performed by comparing the measured Mg, Fe, Mn and Ni contents with the amounts of these elements deriving from normative calculation. The results are satisfactory, considering of the general problems of quantitative phase analysis of mineral associations.
    Keywords: Normative calculation, Cr ores, Ophiolite complexes, SE Iran
  • Habib Allah Torshizian* Pages 45-51
    The study area is located in the northeast of Iran. Miankuhi Formation is 500m thick and comprises homogeneous shales, brown granular sandstone and siltstone. In this study, 45 samples were taken from Miankuhi shales and sandstones in order to determine their tectonic origin by using a polarizing microscope. Samples were analysed by X-Ray Fluorescence (XRF) method to determine their chemical compositions and tectonic origin. Twelve shale and siltstone samples were also analysed by the X-Ray Diffraction method with the aim of identifying their mineral composition. According to the investigations conducted, the type of sandstone is greywackes. Based on XRD results, quartz, albite, orthoclase, calcite, kaolinite, and illite have existed in shales and siltstones. Chemical analysis of the rocks indicated the source of these clastic rocks as oceanic arc areas and active peripheries of a landmass. The corrosive rocks of this formation are believed to originate from intermediate felsic igneous rocks and to a lesser extent from clastic quartz-containing rocks in the region.
    Keywords: Clastic rocks, Kopet, Dagh, Tectonic origin, Triassic
  • Fatemeh Hadavi, Marziyeh Notghi Moghaddam*, Lida Khodadadi Pages 52-68
    Calcareous nannofossil assemblages recovered from a long, continuous section have been described from the Sarayan region in Lut Block in east Iran. The marine Upper Cretaceous sediments of this section yield medium diverse and well-preserved calcareous nannofossil assemblages. A structural analysis of Upper Cretaceous calcareous nannofloras has revealed 30 nannofossil species. A revised zonation for the Cretaceous is used to subdivide the Cretaceous deposits in this section into five zones (CC21-CC25). Finally, the paleoecological applications of Upper Cretaceous nannofossils are considered in this section. Surface water temperature, productivity, and fertility are believed to have been the principal factors controlling species distribution. Warm water indicators such as Uniplanarius sissinghii, Uniplanarius trifidus, and Micula murus suggest warm surface water conditions in the studied thickness. In the Sarayan section, based on Lithraphidites carniolensis and Watznaueria barnesae, lower fertility conditions with low productivity at the Campanian to Maastrichtian were suggested for this region.
    Keywords: Biostratigraphy, Paleoecology, Cretaceous, Calcareous nannofossil, Sarayan, Iran
  • Yousef Vasigh* Pages 69-77
    The Razei region in the northwest of Ardabil is considered a part of West Alborz-Azerbaijan. Rocks in this area were created by Eocene volcanic activities. These rocks range from andesite to olivine basalt. The common texture of these rocks is Porphyritic with microlithic matrix. The phenocrysts of these rocks are often clinopyroxene, plagioclase, and olivine. The texture is made of microlithic plagioclase and fine crystals of pyroxene. The studied rocks have clear desire to alkali basalts in terms of chemical nomenclature. Disequilibrium factors between liquid and crystal show the processes of magmatic evolution in an open thermodynamic system. The mixed climate in this region has probably contributed the most to changing the chemical composition of these rocks. In the spider diagrams, enrichments often include some LIL elements and depletions usually include some HFS elements. Enrichment of LILE is probably accompanied with the contamination of the basic magma with materials from continental lithosphere. The volcanic rocks in Razei have mainly geochemical characteristics of back arc basin, and the magmas that created the rocks in this region have an origin of lithospheric mantle.
    Keywords: Petrogenesis, Eocene, Volcanic rocks, Razei, Ardabil
  • Vahab Sarfarazi *, Hadi Haeri Pages 78-87
    In this paper, a compression-to-tensile load converter device is developed to determine the anisotropic tensile strength of brittle material. A cubic sample with an internal pore was used as the test specimen, and a series of finite element analysis and DDM simulations were performed thereafter to analyse the effect of pore dimensions on the stress concentration, as well as to render a suitable criterion for determining the anisotropic tensile strength of concrete. The results obtained by this device show that the tensile strength of concrete is similar in different directions because of the homogeneity of bonding between the materials.
    Keywords: compression to tensile load, anisotropic tensile strength of concrete