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Zheng D.,China University of Geosciences | Zheng D.,Beijing University of Technology | Li H.,China University of Geosciences | Li H.,Beijing University of Technology | And 4 more authors.
Geophysical Journal International | Year: 2016

The crustal and upper mantle velocity structure in the northeastern Tibetan Plateau is obtained from joint analysis of receiver functions and Rayleigh wave dispersions. The resulting velocity model reveals a close correlation between the thick (>60 km) crust and the presence of an intracrustal low-velocity zone beneath the Qiangtang and Songpan-Ganzi terranes as well as the northwestern Qilian orogen. However, the high Vp/Vs ratio of the crust is found only beneath the Qiangtang and Songpan-Ganzi terranes. The crustal low velocity zone does not appear in the west Qinling and southeastern Qilian orogens, which have a relatively thin (~50 km) crust, indicating that crustal channel flow is not the primary mechanism by which the northeastern Tibetan Plateau grows. A continuous low velocity zone from the mid-to-lower crust down to 160 km beneath the eastern Kunlun fault suggests an induced local mantle upwelling after partial detachment of the lithosphere. © The Authors 2015.


Pan F.-B.,Zhejiang University | Zhang H.-F.,Wuhan University | Xu W.-C.,Wuhan University | Guo L.,Wuhan University | And 2 more authors.
Lithos | Year: 2015

Mafic intrusive rocks are widely exposed in the Motuo tectono-magmatic belt, southeast Lhasa terrane. LA-ICP-MS U-Pb zircon dating shows that they have magma crystallization ages of 69 and ca. 50Ma. These mafic intrusive rocks are characterized by variable SiO2 (44.60-57.60wt.%), high Al2O3 (17.19-20.86wt.%), and low MgO (1.85-5.38wt.%) with Mg# of 31-55. Their chemical composition is comparable with low-MgO high-Al basalts to basaltic andesites. They are enriched in LILEs (Rb, Ba, K) and LREE and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), with weakly evolved Sr-Nd-Hf compositions (whole-rock (87Sr/86Sr)0 =0.7064 to 0.7086, ε Nd(t)=-3.41 to +1.22, and zircon ε Hf(t)=-3.8 to +6.4). The mafic rocks were derived from partial melting of metasomatized lithospheric mantle. Geochemical and Sr-Nd-Hf isotopic data show that they were insignificantly modified during magma emplacement. We provide a different secular evolution of the lithospheric mantle beneath the eastern part relative to the central part of the southern Lhasa terrane. Sr-Nd isotopic composition of the Motuo Late Cretaceous-Eocene mafic rocks argues that they were derived from partial melting of a relatively homogeneous and depleted lithospheric mantle. We propose that the Late Cretaceous delamination resulted in the replacement of ancient lithospheric mantle by the juvenile homogeneous lithospheric mantle in the eastern Lhasa terrane. The foundered ancient materials may subsequently re-fertilize the lithospheric mantle not only in the eastern Lhasa terrane but also in the surrounding areas. © 2015 Elsevier B.V.


Pan F.-B.,Wuhan University | Pan F.-B.,Zhejiang University | Zhang H.-F.,Wuhan University | Xu W.-C.,Wuhan University | And 3 more authors.
Lithos | Year: 2016

Mafic intrusive rocks are widely exposed in the Motuo tectono-magmatic belt, southeast Lhasa terrane. LA-ICP-MS U-Pb zircon dating shows that they have magma crystallization ages of 69 and ca. 50 Ma. These mafic intrusive rocks are characterized by variable SiO2 (44.60-57.60 wt.%), high Al2O3 (17.19-20.86 wt.%), and low MgO (1.85-5.38 wt.%) with Mg# of 31-55. Their chemical composition is comparable with low-MgO high-Al basalts to basaltic andesites. They are enriched in LILEs (Rb, Ba, K) and LREE and depleted in HFSEs (Nb, Ta, Zr, Hf, Ti), with weakly evolved Sr-Nd-Hf compositions (whole-rock (87Sr/86Sr)0 = 0.7064 to 0.7086, εNd(t) = -3.41 to +1.22, and zircon εHf(t) = -3.8 to +6.4). The mafic rocks were derived from partial melting of metasomatized lithospheric mantle. Geochemical and Sr-Nd-Hf isotopic data show that they were insignificantly modified during magma emplacement. We provide a different secular evolution of the lithospheric mantle beneath the eastern part relative to the central part of the southern Lhasa terrane. Sr-Nd isotopic composition of the Motuo Late Cretaceous-Eocene mafic rocks argues that they were derived from partial melting of a relatively homogeneous and depleted lithospheric mantle. We propose that the Late Cretaceous delamination resulted in the replacement of ancient lithospheric mantle by the juvenile homogeneous lithospheric mantle in the eastern Lhasa terrane. The foundered ancient materials may subsequently re-fertilize the lithospheric mantle not only in the eastern Lhasa terrane but also in the surrounding areas. © 2015 Elsevier B.V.


Lan X.-Y.,Geological Exploration Technologies Institute of Anhui Province | Du J.-G.,Anhui Geological Survey | Yan J.-Y.,Chinese Academy of Geological Sciences | An M.,Geological Exploration Technologies Institute of Anhui Province | And 7 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

Three-dimensional geological modeling is an important way to realize the breakthrough of deep mineral exploration. This method is based on the three-dimensional modeling of ore-controlling geological bodies, which can directly describe the spatial, genetic and evolutionary relationship between the ore controlling factors. At present, the 3D modeling mainly uses geological data; while in the absence of drilling and other known information, it is difficult to construct a reliable 3D geological model. In order to overcome the disadvantages of poor accuracy and low reliability of conventional 3D geological modeling, we propose an effective method based on the prior information. In this approach, a series of sections obtained by the 2.5D interactive inversion, combined with the sections of 3D physical property inversion, are employed to correct the process of building a 3D geological model. Using this method, the 3D geological model of the Tongling ore concentration area is successfully established, that objectively describes the 3D spatial characteristics of strata, fractures and rock mass. Through the interactive analysis of the 3D model, we draw the following conclusions. 1) The important ore-controlling formations (C-P-T2) of the Tongling area are mainly distributed in the syncline and volcanic-covered area with intense deep magmatic activity, which will greatly expand the prospecting space in the Tongling area. 2)The traditional five orefield intrusive rocks are characterized by having a composite rock, especially with the pyroxene diorite symbiosis mineral iron copper-based, and the gold mines is closely related to the intermediate-acid intrusive rocks. This inference, if established, will have a significant impact on selection of the Tongling area prospecting target. 3) Nappe structure is well developed in the Tongling area, the early Paleozoic basement in the Muzhen sag region and the Daigongshan anticline in the NW edge of the Nanling basin are the product of a regional nappe structure. 3D physical property inversion reveals that the Tongling area intrusive rocks have deep-middle-shallow triple structure, which provides some evidence for the thrusting cause of the Tongling terrane, and also we can look for another “Tongling” outside the Tongling area. © 2015, Science Press. All right reserved.


Pan F.-B.,Zhejiang University | Zhang H.-F.,Wuhan University | Xu W.-C.,Wuhan University | Guo L.,Wuhan University | And 2 more authors.
Tectonophysics | Year: 2015

Early Paleogene granitoids in Southern Lhasa subterrane have been widely investigated and many petrogenesis and geodynamic models have been proposed in the past few years. However, contemporaneous granitoids in the Motuo tectono-magmatic belt, southeast Lhasa terrane, are still limitedly studied. Here we present the petrology, zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotope data of the Damu and 52K quartz-monzonite in the Motuo area. LA-ICP-MS U-Pb zircon dating shows that they have magma crystallization ages of 49 and 69Ma, respectively. The Damu quartz-monzonite (SiO2 =63.76-68.33wt.%) is high-K calc-alkaline (K2O=2.54-4.02wt.% with K2O/Na2O=0.59-1.09) and metaluminous to weakly peraluminous (A/CNK=0.99-1.07). The 52K quartz-monzonite (SiO2 =61.12-66.12wt.%) shows slightly higher K2O contents (3.80-5.28wt.% with K2O/Na2O=1.03-1.45) and metaluminous series (A/CNK=0.96-1.00). The analyzed samples are characterized by high Ba (850-2573ppm), Sr (534-986ppm) contents, and fractionated REE patterns ((La/Yb)N =22-72 and (Sm/Yb)N =4.55-8.24). These geochemical features are comparable with those of high Ba-Sr granite. They display weakly evolved Sr-Nd-Hf compositions (whole-rock (87Sr/86Sr)0 =0.7068 to 0.7086, ε Nd(t)=-4.20 to -3.41, and zircon ε Hf(t)=-5.2 to -0.9). Geochemical and Sr-Nd-Hf isotopic data reflect that the Damu and 52K quartz-monzonite represent residual magma from AFC processes of lithospheric mantle-derived mafic melts. The over-thickened lower crust in the eastern Lhasa terrane had been delaminated during ca. 83-70Ma, which led to the replacement of ancient lithospheric mantle by the juvenile lithospheric mantle. The juvenile mantle wedge in the study area was suspected to be metasomatized by melts that were derived from the foundering arc root, rather than the subducted sediments. Thus, the early Paleogene high Ba-Sr magmas from the SE Lhasa terrane may provide evidence for recycling of continental lithosphere by density destruction. © 2015.


Xu Y.,Beijing University of Technology | Xu Y.,Chinese Academy of Geological Sciences | Lu Q.-T.,Chinese Academy of Geological Sciences | Zhang G.-B.,Beijing University of Technology | And 4 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2015

The Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) is one of the most important metallogenic belts in China and plenty of researches have done in this belt. In this paper, we determined a 3-D S-wave velocity structure of the mantle down to 600 km depth beneath the MLYRMB by using 5524 S-wave relative travel times collected from 163 teleseismic events recorded by 73 static seismic stations located within this belt and its adjacent areas. The tomography method used in our study is the TOMOG3D, which has been widely used in a lot of tomography studies and gained a lot of achievements. In the data processing, we chose the data with high signal to noise ratio according to 3 criteria and used an automatic method called MMCC to pick up the relative travel times precisely. Besides that, we have also applied the crust correction method to reduce the effect caused by the crustal inhomogeneity, in order to make the final result more accurate. Our result shows: (1) there exist a low velocity anomaly in the upper mantle and the trend of the anomaly is consist with MLYRMB, which maybe the upwelling of asthenosphere; (2) there exist a high velocity anomaly in the mantle transition zone and the bottom of upper mantle which maybe the subduction of paleo-Pacific plate and the delaminated lithosphere; (3) the low velocity anomaly beneath the belt has a trend that is gradually shallower from the south to the north, which means the up welling of asthenosphere start from south to north. Combining a lot of studies about geophysics, geochemistry, geology and so on, we assumed that the formation of the MLYRMB in Mesozoic was mainly caused by the delamination of lithosphere. © 2015, Science Press. All right reserved.


Wang H.-Q.,Geological Exploration Technologies Institute of Anhui Province
Wutan Huatan Jisuan Jishu | Year: 2013

In fact, not all of the wavelets are suitable for separation of Gravity and magnetic field by using multi-resolution wavelet analysis. In this paper, we choose the symmetry, compactly supported Daubechies wavelet for multi-resolution Wavelet analysis of the gravity field, and extract regional gravity field based on geological significance, and calculate residual gravity field. The proposed method is verified by one numerical example and results show that the approach is effectiveness.


Zhang Z.,Zhejiang University | Wu L.,Zhejiang University | Wang R.,Kunming Institute of Exploration | Zhang J.,Geological Exploration Technologies institute of Anhui Province
Zhongnan Daxue Xuebao (Ziran Kexue Ban)/Journal of Central South University (Science and Technology) | Year: 2013

The first kind of Fredholm integral equation in the downward continuation was solved by adopting conjugate gradient method with the assumption that the coefficient matrix is positive definite. The theoretical model test shows that downward continuation has a very fast convergence rate but suggests poor ability to compress the noise.compared with integral iteration method, conjugate gradient method indicates a faster convergence rate, as well as divergence rate, and is not so applicable. In order to acquire stable solutions the regularization of the operator of the ill-posed problem was carried out and the problem was transformed to solve the minimum value of the least squares estimations. After using the conjugate gradient method to solve the least squares problem, a method was implemented for downward continuation based on CGNR method that has a better ability to suppress noise. Model test demonstrates that this method has strong ability in restraining noise. This method convergence fast and has obvious computation advantage by a comparison with least square steepest descent method.


Wang Q.,Geological Exploration Technologies Institute of Anhui Province
Scientia Geologica Sinica | Year: 2014

On the shallow covered area of Bengbu-Fengyang, we explained the geological construction using the gravity and magnetic anomalies, and ascertained the tectonic system. We deemed that the Bengbu anticlinorium is outstanding southward. The trend identical with the Bengbu upwarping tectonic line is NEE direction on the west area. The trend is near E-W direction in the Fengyang County, which is in the middle of the area. On the east area, the trend is NE-trending. The left-lateral tractive effects of Tanlu fault zone is the main reason of the axis changing. We determined the hidden boundary of the Bengbu rock mass and the range of the Fengyang-Zongpu tectonic magmatic hydrothermal zone, and drew the map of the Bengbu-Fengyang area geophysics deducing bedrock tectonic outline. It is suggested that the intrusive contact zone of the Bengbu rock mass, the tectonic magmatic hydrothermal activity and the intersections of the important fault zones are the favorable prospecting zone. The prospecting direction is put forward.


Zhou J.-J.,Central South University | Qiang J.-K.,Central South University | Tang J.-T.,Central South University | Wang H.-Q.,Geological Exploration Technologies Institute of Anhui Province
Dizhen Dizhi | Year: 2010

In the application of CSAMT, the sounding curve is often distorted with the impact of electric dipole source, which produces confusions in data inversion and interpretation. Based on the 1-D layered earth conventional least-square inversion for CSAMT data, this paper introduces an optimized technique to get better result by discussing the forward modeling calculation, mechanism of inversion, selection of initial model, and iteration model controlling. Formulas of electromagnetic field components, E x and H y, given as integrations which contain Bessel functions of first kind of order 0 and 1, can be obtained using numerical method. During the calculation, the kernel functions of integrations are changed respectively in order to get better convergence properties. Taking the short transmitter-receiver distance into account, the relatively long grounded linear wire source should be assumed as an accumulation of dipoles, thus the theoretical apparent resistivity can be calculated by the field responses of dipóle series. The forward calculation of CSAMT needs configuration parameters such as source location, measuring point position, current amplitude and so on,which are different from MT modeling. A primary objective of inversion is to recover a geologically interpretable model that can reproduce the set of observations. Based on the least square inversion theory, the method iteratively updates the vector of model parameters to get the minimum of the vector of relative mean square errors, where the Jacobi matrix can be obtained by difference method. Singular value decomposition method is adopted in equations solving,and we replace small singular value with zero. To get rid of falling into local minimum point during the iteration, it is necessary to control the model parameter excess when the model becomes abnormal. Actually the action will destroy the convergence, but it also increases the chance to find out the global minimum point. Numerical experiments show that the inversion result is better than the conventional one. The selection of initial model has an impact on the inversion results. Based on the theoretical similarity of CSAMT far-field data and MT data, the semi-quantificational Bostick resistivity-depth curve can be used as the base of initial model. Then, by decreasing the layers number according to the resistivity trend with apparent depth,and abandoning the deformed thin layers produced in layer cutting if necessary, the appropriate initial model is created. Some synthetic studies and a case of field data are followed to validate the inversion mechanism, and their resultant response fits the observed data well with acceptable inversion precision and computing time. In conclusion,it is available to adopt semi-quantificational Bostick resistivity-depth curve as the base of initial model for the CSAMT 1 -D inversion. The multiplicity of solutions can be suppressed by the number of inversion parameters cut down using the Bostick curve optimization techniques. Appropriate initial models and iteration controlling are introduced to help enhance the capability of algorithm to find the global minimum, which satisfies the geophysical exploration requirements.

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