Geochemistry of dissolved and particulate elements in the major rivers of China (The Huanghe,Changjiang, and Zhunjiang rivers)

The relationship between the geochemistry of dissolved and particulate materials and geographic conditions was investigated. Samples of water and suspended particulate matter were collected from five locations in three of the major rivers of China (the Huanghe, Changjiang, and Zhunjiang rivers). Because these rivers generally flow parallel to latitudes and flow through diverse geologic and climate zones, they provide excellent opportunities for comparisons of solute transport. The geochemistry of these rivers is influenced strongly by climate. The low discharge of the Huanghe River influences the character of the major ionic materials (Cl^?+SO₄ ^2? and Na⁺+K⁺) as well as the high degree of mineralization within the system. Dissolved concentrations of both major ions and trace elements are lower in the southern reaches of the rivers. The highly mobile ions, such as, Na⁺ and Ca²⁺, are depleted from the suspended particulate material in the southern regions, while the relatively immobile ions of Al, Fe, Ti, Mn, and trace metals are concentrated within the suspended mateiral. The relative mobility of some elements as measured by the Dissolved Transport Index (DTI) changes with climate. The geology of the area drained by the rivers has a major influence on the geochemistry in areas of similar climate. Lowest leaching rates in the southern climates occur in areas dominated by granite, which is resistant to weathering. The composition of both cations and anions among the three tributaries of the Zhujiang River are dependent on the rocks that dominate each eregion. Some particulate forms of the rare earth elements are present in the highest concentrations in regions dominated by granite. The DTI calculated for the major rivers in China are much smaller than those computed for other major rivers of the world. The low concentration of heavy metals in the particulate material suggests that pollution in the rivers of China is less serious than in rivers of other industrialized countries.     

Metamorphism of ultrahigh‐pressure eclogites from the Kebuerte Valley,South Tianshan,NW China: phase equilibria and P–T path

Eclogites from the Kebuerte Valley, Chinese South Tianshan, consist of garnet, omphacite, phengite, paragonite, glaucophane, hornblendic amphibole, epidote, quartz and accessory rutile, titanite, apatite and carbonate minerals with occasional presence of coesite or quartz pseudomorphs after coesite. The eclogites are grouped into two: type I contains porphyroblastic garnet, epidote, paragonite and glaucophane in a matrix dominated by omphacite where the proportion of omphacite and garnet is >50 vol.%; and type II contains porphyroblastic epidote in a matrix consisting mainly of fine‐grained garnet, omphacite and glaucophane where the proportion of omphacite and garnet is <50 vol.%. Garnet in both types of eclogites mostly exhibits core–rim zoning with increasing grossular (X_gr) and pyrope (X_py) contents, but a few porphyroblastic garnet grains in type I eclogite shows core–mantle zoning with increasing X_py and a slight decrease in X_gr, and mantle–rim zoning with increases in both X_gr and X_py. Garnet rims in type I eclogite have higher X_py than in type II. Petrographic observations and phase equilibria modelling with pseudosections calculated using thermocalc in the NCKMnFMASHO system for three representative samples suggest that the eclogites have experienced four stages of metamorphism: stage I is the pre‐peak temperature prograde heating to the pressure peak (P_max) which was recognized by the garnet core–mantle zoning with increasing X_py and decreasing X_gr. The P–T conditions at P_max constrained from garnet mantle or core compositions with minimum X_gr content are 29–30 kbar at 526–540 °C for type I and 28.2 kbar at 518 °C for type II, suggesting an apparent thermal gradient of ～5.5 °C km^?1. Stage II is the post‐P_max decompression and heating to the temperature peak (T_max), which was modelled from the garnet zoning with increasing X_gr and X_py contents. The P–T conditions at T_max, defined using the garnet rim compositions with maximum X_py content and the Si content in phengite, are 24–27 kbar at 590 °C for type I and 22 kbar at 540 °C for type II. Stage III is the post‐T_max isothermal decompression characterized by the decomposition of lawsonite, which may have resulted in the release of a large amount of fluid bound in the rocks, leading to the formation of epidote, paragonite and glaucophane porphyroblasts. Stage IV is the late retrograde evolution characterized by the overprint of hornblendic amphibole in eclogite and the occurrence of epidote–amphibole facies mineral assemblages in the margins or in the strongly foliated domains of eclogite blocks due to fluid infiltration. The P–T estimates obtained from conventional garnet–clinopyroxene–phengite thermobarometry for the Tianshan eclogites are roughly consistent with the P–T conditions of stage II at T_max, but with large uncertainties in temperature. On the basis of these metamorphic stages or P–T paths, we reinterpreted that the recently reported zircon U–Pb ages for eclogite may date the T_max stage or the later decompression stage, and the widely distributed (rutile‐bearing) quartz veins in the eclogite terrane may have originated from the lawsonite decomposition during the decompression stage rather than from the transition from blueschist to eclogite as previously proposed.     

Modeling three‐dimensional hydraulic fracture propagation using virtual multidimensional internal bonds

Propagation of fractures, especially those emanating from wellbores and closed natural fractures, often involves Mode I and Mode II, and at times Mode III, posing significant challenges to its numerical simulation. When an embedded inclined fracture is subjected to compression, the fracture edge is constrained by the surrounding materials so that its true propagation pattern cannot be simulated by 2D models. In this article, a virtual multidimensional internal bond (VMIB) model is presented to simulate three‐dimensional (3D) fracture propagation. The VMIB model bridges the processes of macro fracture and micro bond rupture. The macro 3D constitutive relation in VMIB is derived from the 1D bond in the micro scale and is implemented in a 3D finite element method. To represent the contact and friction between fracture surfaces, a 3D element partition method is employed. The model is applied to simulate fracture propagation and coalescence in typical laboratory experiments and is used to analyze the propagation of an embedded fracture. Simulation results for single and multiple fractures illustrate 3D features of the tensile and compressive fracture propagation, especially the propagation of a Mode III fracture. The results match well with the experimental observation, suggesting that the presented method can capture the main features of 3D fracture propagation and coalescence. Moreover, by developing an algorithm for applying pressure on the fracture surfaces, propagation of a natural fracture is also simulated. The result illustrates an interesting and important phenomenon of Mode III fracture propagation, namely the fracture front segmentation. Copyright © 2012 John Wiley & Sons, Ltd.     

Deformation characteristics of inherently anisotropic granular media under repeated traffic loading: a DEM study

Acta Geotechnica - The cardioid-shaped loading path induced by moving traffic has been reproduced in the virtual element test of granular media using the discrete element method (DEM). The DEM...     

A simplified analysis approach for the effect of the installation of adjacent XCC pile on the existing single XCC pile in undrained clay

Acta Geotechnica - In this paper, a simplified two-stage analysis method is introduced to predict the lateral response of the existing X-section Cast-in-place Concrete (XCC) pile caused by adjacent...     

Modeling of the Correlation Between Mineral Size and Shale Pore Structure at Meso- and Macroscales

Mathematical Geosciences - Inorganic pore structures are critical to understand the oil and gas transport and storage properties of unconventional reservoirs. However, it can be difficult to...     

Holocene tectono-geomorphic evolution of Haryana plains,Western Ganga plain,India

Haryana plain is the drainage divide between the Ganga plain in the east and the Indus plain in the west. Being a part of the Himalayan foreland, its geomorphology, sedimentation processes, and tectonism are broadly controlled by the Himalayan tectonics. Soil and geomorphological mapping in Haryana plain bring out geomorphic features such as paleochannels, various active drainage patterns, and landforms such as old fluvial plains, floodplains, piedmonts, pediments, terminal fans, and eolian plains. Based on the degree of soil development, and Optical stimulated luminescence (OSL) ages, the soil-geomorphic units were grouped into six members (QIMS-I to VI) (Quaternary Indus Morphostratigraphic Sequence) of a morphostratigraphic sequence: QIMS-VI 9.86–5.38 Ka, QIMS-V 5.38–4.45 Ka, QIMS-IV 4.45–3.60 Ka, QIMS-III 3.60–2.91 Ka, QIMS-II <?2.91–1.52 Ka, and QIMS-I <?1.52 Ka. OSL chronology of different geomorphic features suggests six episodes of tectono-geomorphic evolution in the region since 10 Ka. Neotectonic features such as nine faults, two lineaments, and five fault-bounded tectonic blocks have been identified. Independent tilting and sagging of the blocks in response to neotectonics have resulted in modification of landforms, depositional processes, and hydro-geomorphology of the region. Major rivers like the Yamuna, the Ghaggar, and the Sutlej show different episodes of shifting of their courses. Lineament controlled few extinct channels have been recorded between 20 and 25 m depth below the surface in the ground-penetrating radar (GPR) profiles. These buried channels are aligned along the paleo-course of the Lost Saraswati River interpreted from the existing literature and hence are considered as the course of the lost river. Seven terminal fans have been formed on the downthrown blocks of the associated faults. The Markanda Terminal Fan, the first of such features described, is indeed a splay terminal fan and was formed by a splay distributary system of the Markanda River. Association of three terminal fans of different ages with the Karnal fault indicates the segment-wise development of the fault from west to east. Also, comparison with other such studies in the Ganga plain to further east suggests that the terminal fans formed by streams with distributary drainage pattern occur only in semiarid regions as in the present area and thus are indicators of semiarid climate/paleoclimate. Though the whole region is tectonically active, the region between the Rohtak fault and Hisar fault is most active at present signified by the concentration of earthquake epicenters.     

Application of instantaneous amplitude gradient for ground penetrating radar signal analyses

Ground penetrating radar (GPR) is an effective geophysical method for environmental and engineering exploration. However, significant background interference occurs around most work sites, which increases the difficulty of analyzing and interpreting GPR profiles. For time-distance profile analyses, more accurate results can be obtained using the instantaneous parameters of the analytic signals. In this study, these instantaneous parameters are extracted and compared using 1D model waveform and 2D model strong interference profiles. The results show that the instantaneous amplitude gradient effectively reflects the model information, even under strong interference. The instantaneous amplitude gradient is applied to GPR survey data from a study site, and the results indicate that the technique reflects the underground structure information of the survey area. Drilling verification further confirms that the instantaneous amplitude gradient accurately reflects the underground structure information.