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Li X.,Changan University | Liu W.-T.,Changan University | Zhi Q.-Q.,Chinese Academy of Geosciences | Zhao W.,Changan University
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The traditional interpretation methods of nuclear magnetic resonance (NMR) usually use 1D inversion based on homogeneous half space or layered conductive earth model and the information of water amount in each layer will be derived. However, these methods usually ignore the influence of the inhomogeneous underground conductivity to the interpretation results. Meanwhile, these results are easily restricted to local water-bearing structures. For the purpose of avoiding the problems aforementioned, a novel joint interpretation method combining transient electromagnetic (TEM) and NMR data is proposed in this paper, which provides an effective and practical interpretation method for the detection of complex hydrogeological conditions. This paper proposes a novel joint interpretation method combining transient electromagnetic (TEM) and NMR data based on the forward modeling theory of NMR method in 3D conductive media. Firstly, a fast resistivity image is derived from floating plate interpretation results of TEM data. Afterwards, the resistivity imaging data will be used as the electrical model in 3D NMR inversion. The distribution of transmitting magnetic field is calculated by FE method directly. The transmitting current source is loaded by introducing a pseudo-delta source, and the influence of “weak solution” in three dimensional simulation of magnetic field is eliminated by a force introduction of divergence condition. In order to improve the illness of sensitivity matrix and eliminate the noise, a non-linear fitting objective function considering the penalty terms is proposed and the linearized inversion method is used in the inversion process. The results of homogenous half-space model show that solutions of excitation magnetic field are almost the same as FEM solutions and digital filtering solutions and the influence of “weak solution” is eliminated. Results of the distribution of the NMR kernel function in different conductive models show that: (1) The background conductive of a model affects the distribution of the kernel function, especially when it is a low conductive one, and the lower of the conductive, the smaller range of the influence of excitation at the same pulse moment will be; (2) Local low resistive bodies with reasonably scale also have a significant effect on the distribution of the kernel function, lower resistivity and shallower buried depth causing greater influence, vice versa; Several conclusions can be drawn from the inversion results: (1) smaller variation of the geo-electrical model from the real case will lead to more accurate inversion results; (2) The inversion result can deviate from reality when using a homogenous half-space as the electrical model directly while the low conductive body have a certain scale, and the accuracy of the inversion result will see a significant improvement with the introduction of the floating plate interpretation method based on TEM data; (3) Though the accuracy of the floating plate interpretation decreases with increased depth, the impact of low conductive bodies on the distribution of the kernel function also decreases with that. Therefore, the fast resistivity image result based on TEM data, in spite of being an approximate result, can still offer a reasonable electrical model for NMR inversion. This paper proposes a novel joint interpretation method combining transient electromagnetic (TEM) and NMR data based on the forward modeling theory of NMR method in 3D conductive media. Results of the 3D distribution of kernel function show that low resistive bodies have a significant effect on the distribution of the kernel function, and the media conductivity should be considered during the NMR inversion. The floating plate interpretation based on TEM data can provide a reasonable geo-electrical model, and the accuracy of the NMR inversion will be improved significantly after introducing joint interpretation method combining transient electromagnetic (TEM) and NMR data. ©, 2015, Science Press. All right reserved. Source

Bi E.,Water Resources University | Liu Y.,China National Petroleum Corporation | He J.,Water Resources University | Wang Z.,Chinese Academy of Geosciences | Liu F.,Water Resources University
Ground Water Monitoring and Remediation | Year: 2012

In order to collect baseline information on the environmental occurrence of volatile organic compounds (VOCs) in groundwater in East China, shallow groundwater samples were collected from five alluvial plains in East China in 2008 to 2009. All samples were analyzed for 54 VOCs representing a wide variety of uses and origins. Sampling sites were mainly selected in the areas to be susceptible to contamination from human activities in terms of previous hydrogeological survey. The data of all samples showed a variety of different hydrogeological systems with potential sources of VOCs, with 36 of the 54 VOCs being found. The most frequently detected compounds include naphthalene (56.9%), chloroform (16.9%), 1,2-dichloroethane (16.2%), 1,2-dichloropropane (13.1%), and 1,2,3-trichlorobenzene (12.3%). The concentrations of methylene chloride, 1,2-dichloroethane, carbon tetrachloride, trichloroethene, 1,2-dichloropropane, and tetrachloroethene exceeded the relating drinking water standards. Future work will be needed to identify those factors that are most important in determining the occurrence and concentrations of VOCs in groundwater in China. © 2011, National Ground Water Association. Source

Liu X.,CAS Institute of Tibetan Plateau Research | Hsu K.J.,CAS Institute of Geology and Geophysics | Ju Y.,China Metallurgical Geology Bureau | Li G.,Chinese Academy of Geosciences | And 4 more authors.
Journal of Asian Earth Sciences | Year: 2012

We present a new interpretation of tectonic evolution in southern Tibet that is drastically different from the existing models. A detailed tectono-sedimentary study crossing the Yarlung Zangpo ophiolite zone shows that many geological features are different from those commonly described in large subduction collision models. For example, no N-S oriented shear zones are found between the ophiolitic sequence and country flysch strata, whereas a conformable contact relationship is recognized between them. A tectonic window exists inside the ophiolite body in the Bailang region. Some intrusion-like mafic-ultramafic bodies occurred in the Renbu region, where the country strata are in sub-concordant contact with these bodies and show contact metamorphic aureole. Toward the west, the ophiolite zone was separated by flysch sequences into sub-parallel branches. In the Lhasa region, the sedimentary facies are similar on both sides of the Zangpo Valley, and have preserved an intact Mesozoic basin system. Instead of ophiolite rocks, volcaniclastic deposits occurred in the corresponding location of the ophiolite in the Zangpo Valley. Consequently, we conclude that the Zangpo ophiolite zone has a tectonic affinity of back-arc basin with its spasmodic growth of juvenile oceanic crust. The real tectonic suture, or the closure zone of the Neotethys, should be represented by the High Himalaya Central Gneiss Unit, which shows a large scale strong shearing in same orientation, high metamorphism and protracted re-mobilization. The oceanic crust subducted northward and split off the Himalaya continental front arc, created the Zangpo back-arc basin since Late Triassic. The collapse of the Zangpo back-arc basin by supra-subduction occurred since the Eocene. The final collision between India and the Himalayan arc took place since Late Eocene with a re-mobilized large shear system. The major mylonitic zones migrated progressively southward with bulk of shear slip absorbing the crust of north India and south Tibet. © 2012 Elsevier Ltd. Source

Shi G.-H.,China University of Geosciences | Shi G.-H.,CAS Institute of Geology and Geophysics | Zhu X.-K.,Chinese Academy of Geosciences | Deng J.,China University of Geosciences | And 3 more authors.
Geochimica et Cosmochimica Acta | Year: 2011

Here we report spherules in Myanmar jadeitite, a rock forming from jadeitic fluids within mantle-derived serpentinized rocks in subduction zones under high-pressure conditions (>1.0GPa) and rather low temperatures of about 250-370°C. The spherules have off-centre iron nuclei and dendritic wüstite cortexes, with tiny wüstite crystals perpendicular to the surface of iron core. Within the spherules are vesicles occupied by calcite, jadeite, albite? or mixtures of these phases, and the cortexes contain about 10wt.% SiO2+Al2O3+Na2O filling materials within wüstite. The spherules are in direct contact with jadeite crystals. Contrasting patterns of some individual spherules are obvious between a front area with a crowd of hill-like prominences and a rear zone with one or more rings on the surface. Such surface features and internal textures suggest that they experienced movement at high temperature and then rapid cooling. Chemical compositions of the nuclei are homogenous and consist of nearly pure iron with minor Cr (<0.05wt.%), Mn (<0.80wt.%), and Ni (0.142-0.23wt.%), and a trend of Ni decreasing and Cr increasing from core to cortex. Mn in the cortex (up to about 2.00wt.%) is far more enriched than the nucleus. The bulk ratios (average) of δ56Fe and δ57Fe in the core and cortex are 0.51and 0.78, respectively. Such features suggest that there is a very low possibility of origin associated with volcanic explosive eruption, impact ejecta, chemical reduction or oxidation of iron on seafloor. Since biological reduction processes are not significant under high P/T condition in subduction zones, this origin is excluded. Considering their low Ni contents, it is more likely that they belong to the minor type-I deep-sea cosmic spherules/dusts of low isotope fractionation. This discovery shows that such spherules could remain stable under low-temperature and high-pressure conditions during recycling processes, and therefore could be found in rocks related to slab-derived sediments within subduction zones. This also suggests that subducted oceanic slab sediments contribute to the formation of jadeitite, coupled with dehydration of sediments and altered oceanic crust. © 2011 Elsevier Ltd. Source

You Y.,China University of Geosciences | Tian M.,China University of Geosciences | Yang Y.,Chinese Academy of Geosciences | Gao L.,China Institute of Veterinary Drug Control
WIT Transactions on Ecology and the Environment | Year: 2014

The present study explored the interpretation system of Hexigten Global Geopark of China, which is the vital medium for geoheritage protection. Geoheritage is the most important natural heritage for tracing the past evolutionary history of the earth, understanding the present natural environment condition and predicting the harmonious future between the human-being and nature. The protection of the geoheritage is therefore our sacred obligation, and the establishment of geoparks is the best choice to reach this goal. Through field survey and indoor comparative analysis, the results showed that an interpretation system is an efficient medium to enhance tourists' awareness of protecting the geoheritage. Therefore, geoparks' interpretation system should be further supported for scientific popularization and geoheritage protection. © 2013 WIT Press. Source

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