Search

We present here a combined EMPA and EBSD study of the late Proterozoic massive magnetiteepidote-amphibole ore of Takab (NW Iran). Magnetite (Mt) forms large (≤1 mm) oscillatory dark and light grey zoned grains (BSE images). Bright Mt needles and bands crosscut or are aligned along cleavages and fracturing planes. Some bands contain relict hematite (Hem), and show, then, abundant porosity. EBSD inverse pole figure maps reveal inter-grain orientation changes in grey Mt. Moreover, intra-grain misorientations, similar to undulose extinction in other minerals, indicate dislocations in the crystal lattice formed through deformation. Relict Hem and bright Mt show the coincidence of the orientations of the planes {0001} Hem //{111} Mt and{11-20} Hem //{110} Mt , which is a good evidence for a direct transformation process. Grey Mt show low and variable Fe content (68.5-71.5 wt.%) with high Si (1 wt.%), Mg and Al (1500-4000 ppm) and Ca (2100-3300 ppm), these elements being likely trapped on the lattices of Mt during crystallization. Bright Mt has higher Fe content (~72 wt.%) and < 1000 ppm of the other elements. Both grey and bright Mt have low Ti and V contents (

The Middle Eocene Climatic Optimum (MECO), a ∼500 kyr episode of global warming that initiated at ∼ 40.5 Ma, is postulated to be driven by a net increase in volcanic carbon input, but a direct source has not been identified. Here we show, based on new and previously published radiometric ages of volcanic rocks, that the interval spanning the MECO corresponds to a massive increase in continental arc volcanism in Iran and Azerbaijan. Ages of Eocene igneous rocks in all volcanic provinces of Iran cluster around 40 Ma, very close to the peak warming phase of the MECO. Based on the spatial extent and volume of the volcanic rocks as well as the carbonaceous lithology in which they are emplaced, we estimate the total amount of CO2 that could have been released at this time corresponds to between 1052 and 12 565 Pg carbon. This is compatible with the estimated carbon release during the MECO. Although the uncertainty in both individual ages, and the spread in the compilation of ages, is larger than the duration of the MECO, a flare-up in Neotethys subduction zone volcanism represents a plausible excess carbon source responsible for MECO warming.

International audience; The siliceous iron ore deposits in the NW part of Iran (Takab region) are hosted within para-metamorphic rocks, and are attributed to Late Proterozoic age. They comprise massive, banded, nodular and disseminated ore types, which are mainly composed of magnetite. Magnetite contains traces of Al. It is variously hematitized. Hematite show higher Al, Si and Ca contents than the magnetite. The iron oxides contain inclusions of zircons, apatite, uraninite, Mn-carbonate and euhedral monazite. Later hydrothermal solutions precipitated goethite surrounding the magnetite-hematite-maghemite grains and replacing hematite. Barite occurs in fractures of iron oxides, Mn-Ba-Pb oxi-hydroxides and scheelite occur interstitial to iron oxides. The ∂ 56 Fe values observed for magnetite decrease from disseminated to nodular iron ore (averages: +1.3, +0.4 and-0.4 ‰ (± 0.2 ‰), respectively). Iron isotopes of hematite in disseminated & layered ore show higher ∂ 56 Fe values than those of magnetite, in the range of +2 to +4 ‰ (± 0.2 ‰).

International audience; The siliceous iron ore deposits in the NW part of Iran (Takab region) are hosted within para-metamorphic rocks, and are attributed to Late Proterozoic age. They comprise massive, banded, nodular and disseminated ore types, which are mainly composed of magnetite. Magnetite contains traces of Al. It is variously hematitized. Hematite show higher Al, Si and Ca contents than the magnetite. The iron oxides contain inclusions of zircons, apatite, uraninite, Mn-carbonate and euhedral monazite. Later hydrothermal solutions precipitated goethite surrounding the magnetitehematite-maghemite grains and replacing hematite. Barite occurs in fractures of iron oxides, Mn-Ba-Pb oxi-hydroxides and scheelite occur interstitial to iron oxides. The ∂ 56 Fe values observed for magnetite decrease from disseminated to nodular iron ore (averages: +1.3, +0.4 and-0.4 ‰ (± 0.2 ‰), respectively). Iron isotopes of hematite in disseminated & layered ore show higher ∂ 56 Fe values than those of magnetite, in the range of +2 to +4 ‰ (± 0.2 ‰).

International audience; Siliceous banded and nodular iron ores intercalated in mica schists and marbles of Precambrian age, were studied from the NW part of Iran (Takab region). The iron ore is composed of magnetite, which was partly transformed into maghemite and hematite along fractures and cleavages during a major oxidizing deformation event. Quartz shows undulose extinction. Both quartz and iron oxides partly form 120° triple junctions, but essentially grain boundary migrations. In the nodular ore, grain boundary migration is more pronounced leading also to grain isolation quartz is partially annealed. Iron oxides are agglomerated, elongated and disrupted. These finding indicate a longer recrystallization episode in the nodular ore. The iron oxide grains contain inclusions of euhedral, zoned and corroded zircons and euhedral monazite. Magnetite contains traces of Al. Hematite and goethite show higher Al, Si and Ca contents. Later hydrothermal solutions precipitated goethite surrounding the magnetite-hematite-maghemite grains and replacing hematite. Barite and uraninite occur in fractures of iron oxides, Mn-Ba-Pb oxi-hydroxides and scheelite occur interstitial to iron oxides.

Regarding to the fast growth of computer, internet, and virtual learning in our country (Iran) and need computer-based learning systems and multimedia tools as an essential part of such education, designing and implementing such systems would help teach different field such as science. This paper describes the basic principle of multimedia. At the end, with a description of learning science to the infant students, the method of this system will be explained., {"references":["Nigel and Jenny Chapman, \"Digital Multimedia\" 1st Edition, John Wiley\n& Sons, March 2000","Multimedia Computer Assisted Learning - Phillip Barker, Kogan","Tay Vaughan , \"Multimedia: Making it Work\" , McGraw Hill 005.75","http://www.sei.cmu.edu/ Carnegie Mellon University, Software\nEngineering Institute, Retrieved, September 2005.","http://metric.ma.ic.ac.uk/worlds/ Mathematical Microworlds , Retrieved,\nAugust 2005.","http://www.riven.com/online/myst/mystHome","Jonanssen, D. H., & Carr, C. S. (2000). Mindtools: a.ording multiple\nknowledge representations for learnings. In S. P. Lajoie (Ed.),\nComputers as cognitive tools. No more walls. Hillsdale, NJ: Lawrence\nErlbaum Associates, Inc.","Papert, S. (2000). Does easy do it? Children, games. and learning html,\nRetrieved, September 2004.","http://www.cybersoftware.co.uk/educational_software_drill_and_practis\ne.html"]}