VLBI of supernovae and gamma-ray bursts

Supernovae and gamma-ray bursts (GRBs) are among the brightest events in the universe. Excluding Type Ia supernovae and short GRBs, they are the result of the core collapse of a massive star with material being ejectedwith speeds of several 1000 km/s to nearly the speed of light, and with a neutron star or a black hole left over as the compact remnant of the explosion. Synchrotron radiation in the radio is generated in a shell when the ejecta interact with the surrounding medium and possibly also in the central region near the compact remnant itself. VLBI has allowed resolving some of these sources and monitoring their expansion in detail, thereby revealing characteristics of the dying star, the explosion, the expanding shock front, and the expected compact remnant. We report on updates of some of the most interesting results that have been obtained with VLBI so far. Movies of supernovae are available from our website. They show the evolution from shortly after the explosion to decades thereafter, in one case revealing an emerging compact central source, which may be associated with shock interaction near the explosion center or with the stellar corpse itself, a neutron star or a black hole.     

Palaeoecology of well-preserved coral communities in a siliciclastic environment from the Late Pleistocene (MIS 7), Kish Island, Persian Gulf (Iran): the development of low-relief reef frameworks (biostromes) in increasingly restricted environments

Major changes in community structure and depositional relief of high-latitude coral communities in the southern Persian Gulf between marine isotope stage (MIS) 7 and the present day suggest that the area has become increasingly restricted. Corals and bivalves from outcrops on Kish Island, Iran, were identified in order to interpret the Late Pleistocene palaeoenvironmental setting. U/Th disequilibrium dating was used to constrain the ages of the stratigraphic units. During MIS 7, two coral-bearing sequences were deposited on what is now Kish Island. The lower sequence is dated as MIS 7.5 and changes laterally from an assemblage dominated by Cyphastrea sp. and Platygyra daedalea in the west to one characterized by branching Montipora in the east. By contrast, the upper sequence, dated as MIS 7.1, transitions from an assemblage dominated by platy Montipora in the west to a diverse assemblage of Platygyra and other faviids in the east. The assemblages of both sequences are within a marl matrix and bounded by thin lithified mollusc-rich layers. Corals and bivalves indicate that the sequences were deposited on gentle slopes in sheltered environments less than 20 m deep. The MIS 7 deposits may be classified as coral carpets or biostromes that developed a low-relief framework. During MIS 5, coral communities were no longer framework building and are now limited to an Acropora-rich layer of coral rubble that covers large parts of the island, and two small incipient reefs with sparse faviids. Similarities between the MIS 5 and modern nearshore coral communities suggest that the environmental conditions during MIS 5 were comparable to those of today. The late Pleistocene coral carpets and non-framework coral communities of the southern Persian Gulf may serve as models for coral biostromes in the fossil record, which formed under restricted environmental conditions such as elevated terrigenous input, high turbidity, and strong seasonal changes in temperature and/or salinity.     

Spatial prediction of soil erosion susceptibility: an evaluation of the maximum entropy model

Soil erosion is considered as the most widespread form of soil degradation which causes serious environmental problems. This study investigates the performance of the maximum entropy (ME) in mapping rill erosion susceptibility in the Golgol watershed, Ilam province, Iran. To this end, ten rill erosion conditioning factors were selected to be employed in the modelling process based on an investigation of the literature. These layers are: elevation, slope percent, aspect, stream power index, topographic wetness index, distance from streams, plan curvature, lithology, land use, and soil. Then, a training dataset of rill erosion locations was used for modelling this phenomenon. The area under receiver operating characteristics curve was used for evaluating the performance of the ME model. In addition, Modified Pacific South-West Inter Agency Committee (MPSIAC) framework was applied and sediment yield was determined for different hydrological units in the study area. At last, Jackknife test was implemented to show the contribution of the factors in the modelling process. The results depicted that area under ROC curve for training and validation datasets were 0.867, and 0.794, respectively. Therefore, this conclusion can be achieved that ME worked well and could be a good tool for generating rill erosion susceptibility maps and its output could be employed for soil conservation in similar areas.     

Assessment of groundwater suitability for irrigation in a gold mine surrounding area,NE Iran

The Kouh-e Zar mining area with iron oxide-rich types of Cu–Au (IOCG)-type gold mineralization is located in a fractured zone between two main “Darouneh” and “Taknar” faults in 35 km northwest of Torbat-e Heydarieh. In this study, the hydrogeochemistry and water quality of groundwater were examined for irrigation uses. Totally, 11 groundwater samples were collected in semi-arid area surrounding the mine. According to the irrigation water quality indices such as sodium absorption ratio, sodium percentage, residual sodium carbonate, residual sodium bicarbonate, potential salinity, salinity index, salinity hazard, permeability index and magnesium hazard, the water resources were appraised suitable to unsuitable. Na⁺ was a dominant cation and HCO₃^? was a dominant anion in the water samples. Fortunately, SO₄^2? content is low (<?250 mg/L) in the water samples because of low-sulfide content mineralization in this mine. Water–rock interaction was defined as the controlling process on groundwater chemistry based on the Gibbs diagram. Calculated saturation indices revealed that the anion and cations in groundwater originated from dissolution of minerals and evaporation process. In the case of dominant Ca²⁺ and Mg²⁺, they were originated by dissolution of carbonate minerals such as calcite, dolomite and aragonite. Na⁺ was likely originated by plagioclase weathering in the brecciated volcanic rocks. Though the sulfidic mineralization is not so high in the Kouh-e Zar area, however, considering the existence of metalogenic mineralization in the Kouh-e Zar area, there is also a risk potential of release of toxic elements into the groundwater on which further deep investigation is ongoing in the area.     

Evidence for Accelerating Glacier Ice Loss in the Takht＇ e Solaiman Mountains of Iran from 1955 to 2010

This study reports on the clean ice area and surface elevation changes of the Khersan and Merjikesh glaciers in the north of Iran between 1955 and 2010 based on several high to medium spatial resolution remote sensing data.The object-oriented classification technique has been applied to nine remote sensing images to estimate the debris-free areas.The satellite-based analysis revealed that the clean ice areas of Khersan and Merjikesh glaciers shrank since 2010 with an overall area decrease of about 45% and 60% respectively.It means that the dramatic proportions of 1955 glaciers surface area are covered with debris during the last five decades.Although the general trend is a clean ice area decrease,some advancement is observed over the period of 1997-2004.During 1987-1991 the maximum decrease in the clean ice area was observed.However,the clean ice area had steadily increased between 1997 and 2010.To quantify the elevation changes besides the debris-free change analysis,several Digital Elevation Models(DEMs) were extracted from aerial photo(1955),topographic map(1997),ASTER image(2002) and Worldview-2 image(2010) and after it a 3-D Coregistration and a linear relationship adjustments techniques were used to remove the systematic shifts and elevation dependent biases.Unlike the sinusoidal variation of our case studies which was inferred from planimetric analysis,the elevation change results revealed that the glacier surface lowering has occurred during 1955-2010 continuously without any thickening with the mean annual thinning of about 0.4 ± 0.04 m per year and 0.3 ± 0.026 m per year for Khersan and Merjikesh glaciers,respectively.The maximum thinning rate has been observed during 1997-2002(about 1.1 ± 0.09 per year and 0.96 ± 0.01 mper year,respectively),which was compatible partially with debris-free change analysis.The present result demonstrates that although in debris-covered glaciers clean ice area change analysis can illustrate the direction of changes(retreat or advance),due to the high uncertainty in glacier area delineation in such glaciers,it cannot reveal the actual glacier changes.Thus,both planimetric and volumetric change analyses are very critical to obtain accurate glacier variation results.     

Metamorphism and deformation of golpayegan metapelitic rocks, Sanandaj-Sirjan Zone, Iran

The metapelitic schists of the Golpayegan region can be divided into four groups based on their mineral assemblages: (1) garnet-chloritoid schists, (2) garnet schists, (3) garnet-staurolite schists, and (4) staurolite-kyanite schists. Paleozoic pelagic shales experienced progressive metamorphism and polymetamorphism from greenschist to amphibolite facies along the kyanite geotherm. Mylonitic granites are concentrated in the central part of the region more than in other areas, and formed during the dynamic metamorphic phase by activity on the NW-SE striking Varzaneh and Sfajerd faults. The presence of chloritoid in the metapelites demonstrates low-grade metamorphism in the greenschist facies. The textural and chemical zoning of garnets shows three stages of growth and syntectonic formation. With ongoing metamorphism, staurolite appeared, and the rocks reached amphibolite facies, but the degree of metamorphism did not increase past the kyanite zone. Thus, metamorphism of the pelitic sediments occurred at greenschist to lower amphibolite facies. Thermodynamic studies of these rocks indicate that the metapelites in the north Golpayegan region formed at 511?C618°C and 0.24?C4.1 kbar.     

Textural relations,P-T path,polymetamorphism and also geodynamic significance of metamorphic rocks of the Aligudarz-Khonsar region,Sanandaj-Sirjan zone,Iran

The metamorphic rocks of the Aligudarz-Khonsar region can be divided into nine groups: slate, phyllite, sericite schist, biotite-muscovite schist, garnet schist, garnet-staurolite schist, staurolite schist, mylonitic granite, and marble. In this metamorphic region, four phases of metamorphism can be identified (dynamothermal, thermal, dynamic and retrograde metamorphism) and there are three deformation phases (D1, D2 and D3). Paleozoic pelagic shales experienced prograde metamorphism and polymetamorphism from the greenschist to amphibolite facies along the kyanite geotherm. The metapelites show prograde dynamothermal metamorphism from the greenschist to amphibolite facies. Maximum degree of dynamothermal metamorphism is seen in the Nughan bridge area. Also development of the mylonitic granites in the Nughan bridge area shows that dynamic metamorphism in this area was more intense than in other parts of the AligudarzKhonsar metapelitic zone. The chemical zoning of garnets shows three stages of growth and syn-tectonic formation. With ongoing metamorphism, staurolite appeared, and the rocks reached amphibolite facies, but the degree of metamorphism did not increase past the kyanite zone. Thus, metamorphism of the pelitic sediments occurred at the greenschist to amphibolite facies (kyanite zone). Thermodynamic studies of these rocks indicate that the metapelites in the Aligudarz-Khonsar region formed at 490–550°C and 0.47–5.6 kbar.     

Arsenic in soil and vegetation of a contaminated area

Plant and soil samples were collected from one uncontaminated and four contaminated sites (in the Dashkasan mining area western Iran). Total and water-soluble arsenic in the soil ranged from 7 to 795 and from 0.007 to 2.32 mg/kg, respectively. The highest arsenic concentration in soil was found at the ore dressing area (up to 1,180 mg/kg) and lowest at an uncontaminated area (up to 11 mg/kg). A total of 49 plant species belonging to 15 families were collected from four sampling sites. A significant positive correlation was detected between the concentrations of arsenic in plant dry matter and those in soils. The highest arsenic concentrations were found in Hyoscyamus kurdicus Bornm. (up to 205 mg/kg) and Helichrysum oligocephalum DC. (up to 162 mg/kg). These two accumulator species could have potential for soil clean-up by phytoextraction. The data have been compared with those for the Zarshuran mining area (north-western Iran) obtained in a former study.