Depositional environments and salt-thickness variations in Urmia Lake (NW Iran): Insight from sediment-core studies

Urmia Lake is a large-scale hypersaline lake that experienced a drastic water-level fall due to natural and anthropogenic forces during the last two decades. Construction of a causeway in the central part of the lake after 1989 has divided the lake into northern and southern parts and caused an extreme change of the lake hydrochemical system. Precipitation of evaporite minerals as crust on the lake floor was caused by the combination of lake level fall and increasing water salinity. However, some parameters controlling rates of salt deposition and dissolution and temporal and spatial variation in salt thickness in Lake Urmia are poorly understood. This study reviews 90 sediment cores from various parts of the lake to put forward a better understanding of the salt depositional system and salt thickness variations in the basin for the last 40 years (1977–2017). Our results indicate that the sedimentary system of Urmia Lake changed rapidly during the last two decades from a permanent hypersaline lake with predominantly fast terrigenous–biochemical sedimentation to a seasonally changing playa sedimentary environment with predominance of evaporite minerals. These changes are responsible for rapid salt deposition that generated a salt-crust with a maximum thickness of 2.95 m overlying Holocene terrigenous sediments. The salt-crust thickness and the water depth have a positive correlation for water depth greater than 1 meter, which means that salt-crust thickness increases where water depth increases. While the thickness of shallow deposits are affected by fresh-water dissolution. In addition, the average salt precipitation rate in the northern and the southern parts of the lake is 466 and 266 times higher, respectively, than the average (0.3 mm/y) sedimentation rate before the lake shrinkage. Similar to other large hypersaline lakes such as the Great Salt Lake (USA) and the Aral Sea (Central Asia), the manmade intervention at Urmia Lake (damming of the catchment, extension of agricultural fields, and causeway construction in the middle part of the lake) threatens its further hydrologic existence.

Modeling Water Droplet Freezing and Collision with a Solid Surface

Water droplets released from the sea surface represent one of the major causes of ice accretion on marine vessels. A one-dimensional model of the freezing of a spherical water droplet moving in cold air was developed. The crystallization model allows one to obtain an analytical solution if a uniform temperature distribution over the liquid’s core is assumed. The model was validated using STAR CCM+ Computational fluid dynamics (CFD) code. A collision of a partially frozen droplet with a solid wall assuming the plastic deformation of an ice crust was also considered. The ratio of the crust deformation to the crust thickness was evaluated. It was assumed that if this ratio were to exceed unity, the droplet would stick to the wall’s surface due to ice bridge formation caused by the water released from the droplet’s core.

Prospectivity Mapping for Magmatic-Related Seafloor Massive Sulfide on the Mid-Atlantic Ridge Applying Weights-of-Evidence Method Based on GIS

The Mid-Atlantic Ridge belongs to slow-spreading ridges. Hannington predicted that there were a large number of mineral resources on slow-spreading ridges; however, seafloor massive sulfide deposits usually develop thousands of meters below the seafloor, which make them extremely difficult to explore. Therefore, it is necessary to use mineral prospectivity mapping to narrow the exploration scope and improve exploration efficiency. Recently, Fang and Shao conducted mineral prospectivity mapping of seafloor massive sulfide on the northern Mid-Atlantic Ridge, but the mineral prospectivity mapping of magmatic-related seafloor massive sulfide on the whole Mid-Atlantic Ridge scale has not yet been carried out. In this study, 11 types of data on magmatic-related seafloor massive sulfide mineralization were collected on the Mid-Atlantic Ridge, namely water depth, slope, oceanic crust thickness, large faults, small faults, ridge, bedrock age, spreading rate, Bouguer gravity, and magnetic and seismic point density. Then, the favorable information was extracted from these data to establish 11 predictive maps and to create a mineral potential model. Finally, the weights-of-evidence method was applied to conduct mineral prospectivity mapping. Weight values indicate that oceanic crust thickness, large faults, and spreading rate are the most important prospecting criteria in the study area, which correspond with important ore-controlling factors of magmatic-related seafloor massive sulfide on slow-spreading ridges. This illustrates that the Mid-Atlantic Ridge is a typical slow-spreading ridge, and the mineral potential model presented in this study can also be used on other typical slow-spreading ridges. Seven zones with high posterior probabilities but without known hydrothermal fields were delineated as prospecting targets. The results are helpful for narrowing the exploration scope on the Mid-Atlantic Ridge and can guide the investigation of seafloor massive sulfide resources efficiently.

Incompressible analytical models for spinning-down pulsars

We study a class of Newtonian models for the deformations of non-magnetised neutron stars during their spin-down. All the models have an analytical solution which allows to easily grasp the dependence of the strain on the star’s main physical quantities, such as radius, mass, and crust thickness. We first use the model proposed by Franco, Link, and Epstein that depicts the star as made of a fluid core and an elastic crust with the same density, to compare the response to a decreasing centrifugal force on stars having different masses and equations of state. We find that the strain angle is peaked at the equator and its maximum value decreases as a function of the mass. Afterwards, we introduce a second, more refined, model in which the core and the crust have different densities, and the gravitational potential of the deformed body is self-consistently accounted for. The strain angle is still a decreasing function of the stellar mass, but now its maximum value is typically peaked at the poles and is larger (by a factor of four) than the corresponding value in the one-density model. Finally, within the present analytic approach, we evaluate the impact of the Cowling approximation: when the perturbations of the gravitational potential are neglected, we find an underestimation of the centrifugal effect on the star, since the strain angle is about 40% of the one obtained with the complete model.

The 102–103° E geodivider in the modern lithosphere structure of Сentral Asia

A quasi-linear zone of noticeable geological and geophysical changes, which coincides approximately with 102–103° E meridians, is termed by the authors as “geodivider”. Active submeridional faults are observed predominantly along the zone and coincide with its strike. Seismicity is most intensive in the central part of this zone, from the Lake Baikal to the Three Rivers Region at the Sino-Myanmar frontier. Transects with deep seismic sections and energy dissipation graphs show most sharply increasing seismic energy amounts and hypocenter depths in the western part of the geodivider which delimits (in the first approximation) the Central Asian and East Asian transitional zones between the North Eurasian, Indian and Pacific lithosphere plates. The transpression tectonic regime dominates west of the geodivider under the influence of the Hindustan Indentor pressure, and the transtension regime prevails east of it due to the Pacific subduction slab submergence and continuation. The regime change coincides with an abrupt increase in the crust thickness – from 35–40 km to 45–70 km – west of the geodivider, as reflected in the geophysical fields and metallogenic characteristics of the crust. The direction ofP- andS-waves anisotropy together with the GPS data show decoupling layers of the crust and mantle in the southern part of the geodivider. According to our investigations, the 102–103° E geodivider is a regional geological-geophysical border that may be compared with the Tornquist Line, and, by its scale, with the Uralian and Appalachian fronts and some others large structures.

COPRA Experiments on Melt Pool Behavior With Eutectic NaNO3-KNO3 Simulant

The COPRA experiments were performed to study the natural convection heat transfer behavior in a large-scale homogeneous melt pool inside the reactor pressure vessel lower plenum. The test section consists of a two-dimensional 1/4 circular slice with an inner radius of 2.2 m. A non-eutectic binary mixture 20%NaNO3-80%KNO3 was selected as melt simulant in the previous tests and the Rayleigh number of the melt pool reached up to 1016. In this paper, the working fluid was a eutectic binary mixture 50%NaNO3-50%KNO3. The melt pool temperature, heat flux distribution and crust thickness were obtained in the experiments with different heating powers. Results from the eutectic molten salt tests can be applied for posttest calculations and comparative analyses.