Geochemical constraints on the genesis of the volcanic rocks in the southeast of Isfahan area, Iran

Late Miocene–Pliocene to Quaternary calc-alkaline lava flows and domes are exposed in southeast of Isfahan in the Urumieh Dokhtar magmatic belt in the Central Iran structural zone. These volcanic rocks have compositions ranging from basaltic andesites, andesites to dacites. Geochemical studies show these rocks are a medium to high K calc-alkaline suite and meta-aluminous. Major element variations are typical for calc-alkaline rocks. The volcanic rocks have SiO₂ contents ranging between 53.8% and 65.3%. Harker diagrams clearly show that the dacitic rocks did not form from the basaltic andesites by normal differentiation processes. They show large ion lithophile elements- and light rare earth elements (LREE)-enriched normalized multielement patterns and negative Nb, Ti, Ta, and P. Condrite-normalized REE patterns display a steep decrease from LREE to light rare earth elements without any Eu anomaly. These characteristics are consistent with ratios obtained from subduction-related volcanic rocks and in collision setting. The melting of a heterogeneous source is possible mechanism for their magma genesis, which was enriched in incompatible elements situated at the upper continental lithospheric mantle or lower crust. The geochemical characteristics of these volcanic rocks suggested that these volcanic rocks evolved by contamination of a parental magma derived from metasomatized upper lithospheric mantle and crustal melts.     

A study on the effects of soil moisture,air humidity,and air temperature on wind speed threshold for dust emissions in the Taklimakan Desert

Natural Hazards - Soil and the atmospheric conditions are important factors that affect wind speed threshold of surface dust emissions. Based on the observed data of surface dust emissions in the...     

Identification and evaluation of the hydrogeochemical processes of the lower part of Wadi Siham catchment area, Tihama plain, Yemen

One hundred forty-eight groundwater samples were collected from the lower part of Wadi Siham catchment area for hydrogeochemical investigations to understand the hydrogeochemical processes affecting groundwater chemistry and their relation with groundwater quality. Groundwater in the study area is abstracted from different aquifers. The study area is characterized by arid climate and extremely high relative humidity. The results indicate that groundwater in the study area is fresh to brackish in nature. The abundance of the major ions is as follows: Na⁺¹?>?Ca⁺²?>?Mg⁺²?≥?K⁺¹ and Cl^?1?>?HCO ₃ ^?1 ?>?SO ₄ ^?2 ?>?NO ₃ ^?1 . Various graphical and ionic ration plots, statistical analyses, and saturation indices calculations have been carried out using chemical data to deduce a hydrochemical evaluation of the study area. The prevailing hydrogeochemical processes operating in the study area are dissolution, mixing, evaporation, ion exchange, and weathering of silicate minerals in the eastern part (recharge areas). The reverse ion exchange and seawater intrusion control the groundwater chemistry along the Red Sea coast areas and few parts of the study area. Deterioration in groundwater quality from anthropogenic activities has resulted from saltwater intrusion along the coastal areas due to groundwater overpumping and extensive use of fertilizers and infiltration of sewage water. Salinity and nitrate contamination are the two major problems in the area, which is alarming considering the use of this water for drinking.     

Behavior of Shallow Strip Footing on Twin Voids

This paper numerically examines the bearing capacity and failure mechanism of a shallow strip foundation constructed above twin voids. The voids may refer to caves, caverns, underground aqueduct or tunnels due to water seepage, chemical reaction or deliberately excavated in soil deposit. The ability of numerical model to accurately predict the system behavior is evaluated by performing verification analyses on existing researches. Subsequently, a parametric study carried out to reveal the influence of size of footing/voids and their location (i.e. depth, spacing, eccentricity) on the bearing capacity of footing. To clarify the failure mechanism, the distribution of shear strain in the soil for different scenarios is assessed. The parametric study provided a new framework to determine the bearing capacity and the mode of failure for footings on voids. Based on the results, a criterion can be issued to avoid collapse of footing/voids regarding the shape, location and size of voids. The results can also be used to design construction of a footing on existing voids while the acquired failure mechanisms can be appointed to develop analytical solutions for this problem. Results demonstrated that a critical depth for voids and a critical distance between them exist where the influence on the ultimate bearing capacity of footing disappears.     

<Emphasis Type="Italic">H-M</Emphasis> bearing capacity of a modified suction caisson determined by using load-/displacement-controlled methods

This paper presents a series of monotonically combined lateral loading tests to investigate the bearing capacity of the MSCs (modified suction caissons) in the saturated marine fine sand. The lateral loads were applied under load- and displacement-controlled methods at the loading eccentricity ratios of 1.5, 2.0 and 2.5. Results show that, in the displacement-controlled test, the deflection-softening behavior of load-deflection curves for MSCs was observed, and the softening degree of the load-deflection response increased with the increasing external skirt length or the decreasing loading eccentricity. It was also found that the rotation center of the MSC at failure determined by the load-controlled method is slightly lower than that by the displacement-controlled method. The calculated MSC capacity based on the rotation center position in serviceability limit state is relatively conservative, compared with the calculated capacity based on the rotation center position in the ultimate limit state. In the limit state, the passive earth pressures opposite the loading direction under load- and displacement-controlled methods decrease by 46% and 74% corresponding to peak values, respectively; however, the passive earth pressures in the loading direction at failure only decrease by approximately 3% and 7%, compared with their peak values.     

The effect of the electron sound speed on wave propagation in the ionospheric plasma

In this study, the effect of the electron sound speed on the extraordinary wave propagation is calculated without an approximation for either collisional or collisionless cases in the ionospheric plasma by using the real geometry of the Earth’s magnetic field for the Northern Hemisphere. It is observed that there is no remarkable effect on the propagation of the extraordinary wave, especially at reflection altitudes. But it is also observed that the magnitudes of k ² (the square of the wave number) have changed every season, and the phase velocity of wave in warm ionospheric plasma has increased.     

Investigation on mantle peridotites from Neyriz ophiolite, south of Iran: geodynamic signals

Neyriz ophiolite in Abadeh Tashk area appears as four major separated massifs in an area with 125 km², south of Iran. Peridotites including harzburgite, dunite, and lesser low-Cpx lherzolite are the major constituents of the ophiolite with very minor mafic rocks. Usual gabbros of ophiolite complexes are virtually absent from the study area. Mineral modality associated with bulk rock and mineral chemistry of the peridotites show a progression from fertile to ultra-refractory character, reflected by a progressive decrease in modal pyroxenes and in Al₂O₃, CaO, SiO₂, Sc, Ta, V, and Ga values of the studied rocks by approaching chromite deposits. The Neyriz peridotites vary from low-Cpx lherzolite (MgO, 41.97–43.1 wt.%; Al₂O₃, 0.8–1.3 wt.%) with low content of Cr# spinel (36.7–37.6) and Fo olivine (90.79–91.5) to harzburgite (MgO, 44.31–45.25 wt.%;Al₂O₃, 0.29–0.45 wt.%; Cr# spinel, 58.2–73.45; Fo olivine, 91.23–91.56), and then to dunite (MgO, 45.9–49.2 wt.%; Al₂O₃, 0.18–0.48 wt.%) with higher content of Cr# spinel (74.34–79.36) and Fo olivine (91.75–94.68). Compared to modern oceanic settings, mineral and rock composition of low-Cpx lherzolite plot within the field of mid-ocean-ridge environment, whereas those of harzburgite and dunite fall in the field of fore-arc peridotites. As a result of the studies on minerals and whole rock chemistry along with rock interrelationships, we contend that the peridotites were subsequently affected by percolating hydrous boninitic melt from which the high-Cr–Mg, low-Ti chromitites were formed within mantle wedge above the supra-subduction zone in a fore-arc setting.     

Using uncertainty and sensitivity analysis for finding the best rainfall-runoff model in mountainous watersheds(Case study: the Navrood watershed in Iran)

In watersheds that have not sufficient meteorological and hydrometric data for simulating rainfall-runoff events, using geomorphologic and geomorphoclimatic characteristics of watershed is a conventional method for the simulation. A number of rainfall-runoff models utilize these characteristics such as Nash-IUH, Clark-IUH, Geomorphologic Instantaneous Unit Hydrograph(GIUH), Geomorphoclimatic Instantaneous Unit Hydrograph(GcIUH), GIUH-based Nash(GIUH-Nash) and GcIUH-based Clark(GcIUH-Clark). But all these models are not appropriate for mountainous watersheds. Therefore, the objective of this study is to select the best of them for the simulation. The procedure of this study is: a) selecting appropriate rainfall-runoff events for calibration and validation of six hybrid models, b) distinguishing the best model based on different performance criteria(Percentage Error in Volume(PEV); Percentage Error in Peak(PEP); Percentage Error in Time to Peak(PETP); Root Mean Square Error(RMSE) and Nash-Sutcliffe model efficiency coefficient(ENS)), c) Sensitivity analysis for determination of the most effective parameter at each model, d) Uncertainty determination of different parameters in each model and confirmation of the obtained results by application of the performance criteria. For application of this procedure, the Navrood watershed in the north of Iran as a mountainous watershed has been considered. The results showed that the ClarkIUH and GcIUH-Clark are suitable models for simulation of flood hydrographs, while other models cannot simulate flood hydrographs appropriately. The sensitivity analysis shows that the most sensitive parameters are the infiltration constant rate and time of concentration in the Clark-IUH model. Also, the most sensitive parameters include the infiltration constant rate and storage coefficient in the GcIUHClark model. The Clark-IUH and GcIUH-Clark models are more sensitive to their parameters. The Latin Hypercube Sampling(LHS) on Monte Carlo(MC) simulation method was used for evaluation of uncertainty of data in rainfall-runoff models. In this method 500 sets of data values are produced and then the peak discharge of flood hydrographs for each produced data set is simulated with rainfall-runoff models. The uncertainty of data changes the value of simulated peak discharge of flood hydrograph. The uncertainty analysis shows that the observed peak discharges of different rainfall-runoff events are within the range of values of simulated by the six hybrid rainfall-runoff models and IUH that inputs of these models were the produced data sets. The range of the produced peak discharge of flood hydrographs by the Clark-IUH and GcIUH-Clark models is wider than those of other models.     

Development of an efficient surrogate model based on aquifer dimensions to prevent seawater intrusion in anisotropic coastal aquifers,case study: the Qom aquifer in Iran

Coastal aquifers are usually exposed to saltwater intrusion. Therefore, groundwater extracted from these aquifers should be regulated considering their dimensions and effective parameters. In this paper, optimum discharge from a large number of exploitation wells is evaluated according to variations of width, length, and anisotropy coefficient in the Qom aquifer near the salt lake in central Iran. First, the wells are divided into clusters to decrease the number of decision variables. Then, the location and discharge from each cluster is obtained using SEAWAT and charged system search (CSS) simulation–optimization model with the assumption of three-dimensional variable density flow. The maximum discharge considering various anisotropy rates is computed based on different values of lengths and widths of the aquifer. Finally, an M5-tree model is trained using the obtained samples to derive a linear relationship between input and output data. Based on the results, for various ranges of width and length of an aquifer with impermeable boundaries, different linear equations for optimum discharge are obtained. Also, it was found that for an aquifer with a small width, the critical discharge is a function of the length while the effect of the boundaries is negligible. Sensitivity analysis of the anisotropy coefficient reveals that with increasing the anisotropy rate, thickness and slope of the transition zone decrease and as the maximum discharge increases consequently. However, the sensitivity of the discharge to anisotropy rate is not remarkable. A comparison between the results of this study with those of the analytical method based on sharp interface assumption is carried out. For the critical condition, the best agreement between analytical equation (\(\overline {L} =0.87\overline {W} +0.62\)) and proposed method (\(\overline {L} =0.83\overline {W} - 1.41\)) is achieved for the anisotropic aquifer when the 50% isochlor is assumed as the measure of salt water intrusion.