用宽频带远震体波波形研究中国及邻近地区地壳构造及地质意义初探

The theory and approach of the broadband teleseismic body waveform inversion are expatiated in this paper, and the defining the crust structure's methods are developed. Based on the teleseismic P-wave data, the theoretic image of the P-wave radical component is calculated via the convolution of the teleseismic P-wave vertical component and the transform function, and thereby a P-wavefrom inversion method is built. The applied results show the approach effective, stable and its resolution high. The exact and reliable teleseismic P waveforms recorded by CDSN and IRIS and its geodynamics are utilized to obtain China and its vicinage lithospheric transfer functions, this region ithospheric structure is inverted through the inversion of reliable transfer functions, the new knowledge about the deep structure of China and its vicinage is obtained, and the reliable seismological evidence is provided to reveal the geodynamic evolution processes and set up the continental collisional theory. The major studies are as follows: Two important methods to study crustal and upper mantle structure -- body wave travel-time inversion and waveform modeling are reviewed systematically. Based on ray theory, travel-time inversion is characterized by simplicity, crustal and upper mantle velocity model can be obtained by using 1-D travel-time inversion preliminary, which introduces the reference model for studying focal location, focal mechanism, and fine structure of crustal and upper mantle. The large-scale lateral inhomogeneity of crustal and upper mantle can be obtained by three-dimensional t ravel-time seismic tomography. Based on elastic dynamics, through the fitting between theoretical seismogram and observed seismogram, waveform modeling can interpret the detail waveform and further uncover one-dimensional fine structure and lateral variation of crustal and upper mantle, especially the media characteristics of singular zones of ray. Whatever travel-time inversion and waveform modeling is supposed under certain approximate conditions, with respective advantages and disadvantages, and provide convincing structure information for elucidating physical and chemical features and geodynamic processes of crustal and upper mantle. Because the direct wave, surface wave, and refraction wave have lower resolution in investigating seismic velocity transitional zone, which is inadequate to study seismic discontinuities. On the contrary, both the converse and reflected wave, which sample the discontinuities directly, must be carefully picked up from seismogram to constrain the velocity transitional zones. Not only can the converse wave and reflected wave study the crustal structure, but also investigate the upper mantle discontinuities. There are a number of global and regional seismic discontinuities in the crustal and upper mantle, which plays a significant role in understanding physical and chemical properties and geodynamic processes of crustal and upper mantle. The broadband teleseismic P waveform inversion is studied particularly. The teleseismic P waveforms contain a lot of information related to source time function, near-source structure, propagation effect through the mantle, receiver structure, and instrument response, receiver function is isolated form teleseismic P waveform through the vector rotation of horizontal components into ray direction and the deconvolution of vertical component from the radial and tangential components of ground motion, the resulting time series is dominated by local receiver structure effect, and is hardly irrelevant to source and deep mantle effects. Receiver function is horizontal response, which eliminate multiple P wave reflection and retain direct wave and P-S converted waves, and is sensitive to the vertical variation of S wave velocity. Velocity structure beneath a seismic station has different response to radial and vertical component of an accident teleseismic P wave. To avoid the limits caused by a simplified assumption on the vertical response, the receiver function method is mended. In the frequency domain, the transfer function is showed by the ratio of radical response and vertical response of the media to P wave. In the time domain, the radial synthetic waveform can be obtained by the convolution of the transfer function with the vertical wave. In order to overcome the numerical instability, generalized reflection and transmission coefficient matrix method is applied to calculate the synthetic waveform so that all multi-reflection and phase conversion response can be included. A new inversion method, VFSA-LM method, is used in this study, which successfully combines very fast simulated annealing method (VFSA) with damped least square inversion method (LM). Synthetic waveform inversion test confirms its effectiveness and efficiency. Broadband teleseismic P waveform inversion is applied in lithospheric velocity study of China and its vicinage. According to the data of high quality CDSN and IRIS, we obtained an outline map showing the distribution of Asian continental crustal thickness. Based on these results gained, the features of distribution of the crustal thickness and outline of crustal structure under the Asian continent have been analyzed and studied. Finally, this paper advances the principal characteristics of the Asian continental crust. There exist four vast areas of relatively minor variations in the crustal thickness, namely, northern, eastern southern and central areas of Asian crust. As a byproduct, the earthquake location is discussed, Which is a basic issue in seismology. Because of the strong trade-off between the assumed initial time and focal depth and the nonlinear of the inversion problems, this issue is not settled at all. Aimed at the problem, a new earthquake location method named SAMS method is presented, In which, the objective function is the absolute value of the remnants of travel times together with the arrival times and use the Fast Simulated Annealing method is used to inverse. Applied in the Chi-Chi event relocation of Taiwan occurred on Sep 21, 2000, the results show that the SAMS method not only can reduce the effects of the trade-off between the initial time and focal depth, but can get better stability and resolving power. At the end of the paper, the inverse Q filtering method for compensating attenuation and frequency dispersion used in the seismic section of depth domain is discussed. According to the forward and inverse results of synthesized seismic records, our Q filtrating operator of the depth domain is consistent with the seismic laws in the absorbing media, which not only considers the effect of the media absorbing of the waves, but also fits the deformation laws, namely the frequency dispersion of the body wave. Two post stacked profiles about 60KM, a neritic area of China processed, the result shows that after the forward Q filtering of the depth domain, the wide of the wavelet of the middle and deep layers is compressed, the resolution and signal noise ratio are enhanced, and the primary sharp and energy distribution of the profile are retained.

青藏高原东部电性结构特征及地球动力学意义

As the largest and highest plateau on the Earth, the Tibetan Plateau has been a key location for understanding the processes of mountain building and plateau formation during India-Asia continent-continent collision. As the front-end of the collision, the geological structure of eastern Tibetan Plateau is very complex. It is ideal as a natural laboratory for investigating the formation and evolution of the Tibetan Plateau. Institute of Geophysics, Chinese Academy of Sciences (CAS) carried out MT survey from XiaZayii to Qingshuihe in the east part of the plateau in 1998. After error analysis and distortion analysis, the Non-linear Conjugate Gradient inversion(NLCG), Rapid Relaxation Inversin (RRI) and 2D OCCAM Inversion algorithms were used to invert the data. The three models obtained from 3 algorithms provided similar electrical structure and the NLCG model fit the observed data better than the other two models. According to the analysis of skin depth, the exploration depth of MT in Tibet is much more shallow than in stable continent. For example, the Schmucker depth at period 100s is less than 50km in Tibet, but more than 100km in Canadian Shield. There is a high conductivity layer at the depth of several kilometers beneath middle Qiangtang terrane, and almost 30 kilometers beneath northern Qiangtang terrane. The sensitivity analysis of the data predicates that the depth and resistivity of the crustal high conductivity layer are reliable. The MT results provide a high conductivity layer at 20~40km depth, where the seismic data show a low velocity zone. The experiments show that the rock will dehydrate and partially melt in the relative temperature and pressure. Fluids originated from dehydration and partial melting will seriously change rheological characteristics of rock. Therefore, This layer with low velocity and high conductivity layer in the crust is a weak layer. There is a low velocity path at the depth of 90-110 km beneath southeastern Tibetan Plateau and adjacent areas from seismology results. The analysis on the temperature and rheological property of the lithosphere show that the low velocity path is also weak. GPS measurements and the numerical simulation of the crust-mantle deformation show that the movement rate is different for different terranes. The regional strike derived from decomposition analysis for different frequency band and seismic anisotropy indicate that the crust and upper mantle move separately instead of as a whole. There are material flow in the eastern and southeastern Tibetan Plateau. Therefore, the faults, the crustal and upper mantle weak layers are three different boundaries for relatively movement. Those results support the "two layer wedge plates" geodynamic model on Tibetan formation and evolution.

安多地区早中侏罗世岩浆岩岩石地球化学和同位素年代学研究及其对构造演化的制约

Anduo area is located in the Central Tibet, the middle segment of the Bangonghu-Nujiang suture. Anduo Block is the northern part of Lhasa terrane. The relationships among the different geological bodies were determined during the 1: 250000 regional geological surveying. Petrography, petrologic geochemistry, isotopic geochemistry and geochronology of igneous rocks from the suture and granitoids from Anduo Block were analyzed systematically as a whole for the first time. Then, their tectonic setting and history are discussed.Anduo ophiolitic melange consists of metamorphic peridotites, cumulates, plagiogranites, sheeted dykes swarm, pillow lava and radiolarian cherts. The concentration of Cr and Ni in the metamorphic peridotites is very high, with Mg# about 0.94 ~ 0.97, higher 87Sr/86Sr and Pb isotopic ratios, and lower 143Nd/i44Nd ratio. LREE is enriched relative to HREE and positive Eu anomaly is very clear. The REE distribution curve is U shape. Nb and Ta anomalies from cumulate gabbro and sheeted dyke swarm are not clear, while that are slightly negative from pillow lava. Plagiogranite belongs to strong calc-alkaline series with high Si, middle Al, low Fe, Mg and low K contents. Eu anomaly (~ 1.23) from plagiogranites is slightly positive. The character of all components of ophiolite is similar to that of the MORB, while to some extent the ophiolite was influenced by crustal material. Anduo ophiolite formed in a mature back-arc basin. Additionally, intermediate acidity volcanic rocks within Anduo phiolite melange are island arc calc-alkline rocks related to ocean subduction.The early-middle Jurassic plutonic rocks are tonalite, granodiorite bearing-phenocryst, magaporphyritic hornblende monzogranite, magaporphyritic monzogranite, monzogranite bearing-phenocryst and syenogranite in turn. They belong to calc-alkaline series which developed from middle K to high K series temporally. REE distribution curves of all plutonic rocks are similar and parallel to each other. SREE and negative Eu anomaly values decrease. In the multi-element spider diagram, the curves of different plutons are similar to each other, but troughs of Nb, Sr, P and Ti from young plutons become more evident. This suggests that thereare some closely petrogenetic affinities among plutonic rocks which make up amagma plutonism cycle of the early-middle Jurassic. Magma source is mainly crustal,but abundant mafic microgranular enclaves within granitoids indicate that crastalmagma should be mixed with mantle-derived magma and the mantle-derived magmadecreased subsequently. Tonalite has features of I-type granite, magaporphyriticmonzogranite is transition type, and monzogranite bearing-phenocryst is S-typegranite. The characteristic of granitoids from Anduo Block suggest that the formingtectonic setting is active continental margin.Reliable zircon U-Pb SHRIMP ages are obtained in the study area firstly. Plagiogranite from the Anduo ophiolite of the Bangonghu-Nujiang suture is 175.1 Ma, and granitoids from Anduo Block is 172.6-185.4 Ma. Additionally, plagioclase from the plagiogranite dates a 40Ar/39Ar age of 144 Ma, while biotite and hornblend from granitoids of Anduo Block give a 163-165 Ma.Similar cooling ages of plagiogranite from the Anduo ophiolitic melange and granitoids from Anduo Block and the spatial distribution of the ophiolitic rocks between Anduo, Naqu, and Shainzha area suggest that bilateral subduction of the Bangonghu-Nujiang oceanic basin took place in the early-middle Jurassic. During this subduction, Anduo ophiolitic rocks were related to north subduction of the Bangonghu-Nujiang oceanic basin and Anduo back-arc basin spreading, while granitoids from Anduo Block were related to south subduction.

地震反射界面形态与介质各向异性属性联立成像：地震反射波旅行时与偏振信息综合反演

It has been a difficult problem faced by seismologists for long time that how exactly to reconstruct the earth's geometric structure and distribution of physical attributes according to seismic wave's kinematical and dynamic characteristics, obtained in seismological observation. The jointing imaging of seismic reflector and anisotropy attributes in the earth interior is becoming the research hot spot. The limitation of shoot and observation system makes that the obtained seismic data are too scarce to exactly reconstruct the geological objects. It is popular that utilizing only seismic reflection traveltimes or polarizations information make inversion of the earth's velocity distribution by fixing seismic reflector configuration (vice versa), these will lead to the serious non-uniqueness reconstruction due to short of effective data, the non-uniqueness problem of reconstructing anisotropy attributes will be more serious than in isotropy media. Obviously it is not enough to restrict the media structure only by information of seismic reflection traveltimes or polarizations, which even sometimes will lead to distorted images and misinterpretation of subsurface structure. So we try to rebuild seismic reflection structure (geometry) and media anisotropic structure (physics) in the earth interior by jointing data of seismic wave kinematics and dynamics characteristics, we carry out the new experiment step by step, and the research mainly comprises of two parts: one is the reconstruction of P-wave vertical velocity and anisotropic structure(Thomsen parameter s and 8) in the transversely isotropic media with vertical symmetrical axis(VTI) by fixing geometrical structure, and the other is the simultaneous inversion of the reflector surface conformation and seismic anisotropic structure by jointing seismic reflection traveltimes and polarizations data. Simulated annealing method is used to the first research part, linear inversion based on BG theory and Simulated annealing are applied to the second one. All the research methods are checked by model experiments, then applied to the real data of the wide-angle seismic profile from Tunxi, Anhui Province, to Wenzhou, Zhejiang Province. The results are as following The inversion results based on jointing seismic PP-wave or PSV-wavereflection traveltimes and polarizations data are more close to real model than themodels based simply on one of the two data respectively. It is shown that the methodwe present here can effectively reconstruct the anisotropy attributes in the earth'sinterior when seismic reflector structure is fixed.The layer thickness, P-wave vertical velocity and Thomsen anisotropicparameters {s and 8) could be resolved simultaneously by jointing inversion ofseismic reflection traveltimes and polarizations with the linear inversion methodbased on BG theory.The image of the reflector structure, P-wave vertical velocity and theanisotropy parameters in the crust could be obtained from the wide-angle seismicprofile from Tunxi (in Anhui Province), to Wenzhou (in Zhejiang Province). Theresults reveal the difference of the reflector geometrical structure and physicalattributes in the crust between Yangtze block and Cathaysia block, and attempt tounderstand the characteristics of the crustal stress field in the areas.

大别（超）包产到户铁岩和阜新火山岩铂族元素斌存规律研究

The platinum-group elements (PGE), including Os, Ir, Ru, Rh, Pt and Pd, axe strongly siderophile and chalcophile. On the basis of melting temperature, the PGE may be divided into two groups: the Ir group (IPGE, >2000°C) consisting of Os, Ir and Ru, and the Pd group (PPGE, <20GO°C) consisting of Rh, Pt and Pd. Because of their unique geochemical properties, PGE provide critical information on global-scale differentiation processes, such as core-mantle segregation, late accretionary history, and core-mantle exchange. In addition, they may be used to identify magma source regions and unravel complex petrogenetic processes including partial melting, melt percolation and metasomatism in the mantle, magma mixing and crustal contamination in magma chambers and melt crystallization.Compared with other rocks, (ultra)mafic rocks have lower REE content but higher PGE content, so PGE have advantages in studying the petrogeneses and evolution of them. In this study, we selected (ultra)mafic rocks collected in Dabie Orogen and volcanic rocks from Fuxin Region. Based on the distribution and behaviour of platinum-group elements, combined with other elements, we speculate the magma evolution and source mantle of these (ultra)mafic rocks and volcanic rocks.Many (ultra)mafic rocks are widely distributed in Dabie Region. According to their deformation and metamorphism, we classed them into three types. One is intrusive (ultra)mafic rocks, which are generally undeformed and show no or little sign of metamorphism, such as (ultra)mafic intrusions in Shacun, zhujiapu, Banzhufan, qingshan, Xiaohekou, Jiaoziyan, Renjiawan and Daoshichong. The other one is ultrahigh pressure metamorphic (ultra)mafic rocks, some of them appeared as eelogites, such as complex in Bixiling and adjacent Maowu. Another one is intense deformed and metamorphic, termed as tectonic slice, alpine-type (ultra)mafic rocks. The most representative is Raobazhai and Dahuapin. However, there are many controversies about the formation of those (ultra)mafic rocks. Here, we select typical rocks of the three types. The PGE were determined by inductively coupled plasma mass spectrometry (ICP-MS) ater NiS fire-assay and tellurium co-precipitation.The PGE tracing shows that three components are needed in the source of the cretaceous (uitra)mafic intrusions. They could be old enriched sub-continental lithospheric mantle, lower crust and depleted asthenospheric mantle. The pattern of PGE also shows the primitive magma of these intrusions underwent S saturation. According to palladium, we can conclude that the mantle enrich in PGE. Distribution of PGE in Bixiiing and Maowu (ultra)mafic rocks display they are products of magmas fractional crystallization. The (ultra)mafic rocks in Bixiiing and Maowu are controlled by various magmatic processes and the source mantle is depleted in PGE. Of interest is that the mantle produced UHP (ultra)mafic rocks are PGE-depleted, whereas the mantle of cretaceous (ultra)mafic intrusions are enrich in PGE. This couldindicate that the mantle change from PGE-enriched to PGE-depleted during120-OOMa, which in accord with the time of tectonic system change in the East China. At the same time, (ultra)mafic intrusions in cretaceous took information of deep mantle, which means the processes in deep mantle arose structural movement in the crust The character of PGE in alpine-type (ultra)mafic rocks declared that the rocks had experienced two types of metasomatic processes - hydrous melt derived from slab and silicate melt. In addition, we analyze the platinum-group elements in volcanic rocks on the northern margin of the North China Craton, Fuxin. The volcanic rocks characterized by negative anomalies of platinum. This indicates that platinum alloys, which may host some Pt resided in the mantle. The PGE patterns also show that Jianguo alkali basalts derived from asthenospheric mantle source, but wulahada high-Mg andesites derived from lithospheric mantle.

利用宽频带台阵资料研究华北地区地壳及上地幔间断面结构

Intense tectonic renovation has occurred in the eastern continent of china since Mesozoic, as evidenced by the high heat flow, widespread magma extrusion and volcanic activities, and development of large sedimentary basins. To explain the cause and mechanism for the tectonic process in this period, some researchers have put forward various models, such as mantle plume, subduction of the Pacific slab, Yangtze Block-North China Block collision, etc. Their seismological evidence, however, is still scarce..During the period from 2000 to 2003, large temporary seismic arrays were established in North China by the Institute of the Geology and Geophysics, Chinese Academy of Sciences. Total 129 portable seismic stations were linearly emplaced across the western and eastern boundaries of the Bohai Bay Basin, and accumulated a large amount of high-quality data. Moreover, abundant data were also collected at the capital digital seismic network established in the ninth five-year period of national economic and social development. These provide an unprecedented opportunity for us to study the deep structure and associated geodynamic mechanism of lithospheric processes in North China using seismological techniques.Seismology is a kind of observation-based science. The development of seismic observations greatly promotes the improvement of seismologic theory and methodology. At the beginning of this thesis, I review the history of seismic observation progress, and present some routine processing techniques used in the array seismology. I also introduce two popular seismic imaging methods (receiver function method and seismic tomography).Receiver function method has been widely used to study the crustal and upper mantle structures, and many relevant research results have been published. In this thesis I elaborate the theory of this method, including the basic concept of receiver functions and the methodology for data pre-processing, stacking and migration. I also address some problems often encountered in practical applications of receiver function imaging.By using the teleseismic data collected at the temporary seismic arrays in North China, in particular, the traveltime information of P-to-S conversion and multiple reverberations of the Moho discontinuity, I obtain the distributions of the crustal thickness and the poisson ratio at the northwest boundary area of the Bohai Bay Basin and discuss the geological implications of the results.Through detailed intestigations on the crustal structural feature around the middle part of the Tanlu fault, considerable disparity in poisson ratios is found in the western and eastern sides of the Tanlu fault. Moreover, an obvious Moho offset is coincidently observed at the same surface location. A reasonable density model for the Tanlu fault area is also derived by simulating the observed gravity variations. Both receiver function study and gravity anomaly modeling suggest that the crustal difference between the western and eastern sides of the Tanlu fault is mainly resulted from their different compositions.With common conversion point imaging of receiver functions, I estimate the depths of the upper and lower boundaries of the mantle transition zone, i.e., the 410 and 660 km discontinuities, beneath most part of the North China continent The thickness of the transition zone (TTZ) in the study area is calculated by subtracting the depth of .410 km discontinuity from that of the 660km discontinuity. The resultant TTZ is 10-15 km larger in the east than in the west of the study area. Phase transitions at the 410 km and the 660 km discontinuities are known to have different Clapeyron slopes. Therefore, the TTZ is sensitive to the temperature changes in the transition zone. Previous studies have shown that the TTZ would be smaller in the mantle plume areas and become larger when the remnants of subducted slabs are present The hypothesis of mantle plume cannot give a reasonable interpretation to the observed TTZ beneath North China, Instead, the receiver function imaging results favor a dynamic model that correlates the thermal structure of the mantle transition zone and associated upper mantle dynamics of North China to the Pacific plate subduction process.

地幔对流理论及其在解释地球物理观测的应用

With the improving of mantle convection theory, the developing of computing method and increasing of the measurement data, we can numerically simulate more clearly about the effects on some geophysical observed phenomenons such as the global heat flow and global lithospheric stress field in the Earth's surface caused by mantle convection, which is the primary mechanism for the transport of heat from the Earth's deep interior to its surface and the underlying force mechanism of dynamics in the Earth.Chapter 1 reviews the historical background and present research state of mantle convection theory.In Chapter 2, the basic conception of thermal convection and the basic theory about mantle flow.The effects on generation and distribution of global lithospheric stres s field induced by mantle flow are the subject of Chapter 3. Mantle convection causes normal stress and tangential stresses at the bottom of the lithosphere, and then the sublithospheric stress field induces the lithospheric deformation as sixrface force and results in the stress field within the lithosphere. The simulation shows that the agreement between predictions and observations is good in most regions. Most of subduction zones and continental collisions are under compressive. While ocean ridges, such as the east Pacific ridge, the Atlantic ridge and the east African rift valley, are under tensile. And most of the hotspots preferentially occur in regions where calculated stress is tensile. The calculated directions of the most compressive principal horizontal stress are largely in accord with that of the observation except for some regions such as the NW-Pacifie subduction zone and Qinghai-Tibet Plateau, in which the directions of the most compressive principal horizontal stress are different. It shows that the mantel flow plays an important role in causing or affecting the large-scale stress field within the lithosphere.The global heat flow simulation based on a kinematic model of mantle convection is given in Chapter 4. Mantle convection velocities are calculated based on the internal loading theory at first, the velocity field is used as the input to solve the thermal problem. Results show that calculated depth derivatives of the near surface temperature are closely correlated to the observed surface heat flow pattern. Higher heat flow values around midocean ridge systems can be reproduced very well. The predicted average temperature as a function of function of depth reveals that there are two thermal boundary layers, one is close to the surface and another is close to the core-mantle boundary, the rest of the mantle is nearly isothermal. Although, in most of the mantle, advection dominates the heat transfer, the conductive heat transfer is still locally important in the boundary layers and plays an important role for the surface heat flow pattern. The existence of surface plates is responsible for the long wavelength surface heat flow pattern.In Chapter 5, the effects on present-day crustal movement in the China Mainland resulted from the mantle convection are introduced. Using a dynamic method, we present a quantitative model for the present-day crustal movement in China. We consider not only the effect of the India-Eurasia collision, the gravitational potential energy difference of the Tibet Plateau, but also the contribution of the shear traction on the bottom of the lithosphere induced by the global mantle convection. The comparison between our results and the velocity field obtained from the GPS observation shows that our model satisfactorily reproduces the general picture of crustal deformation in China. Numerical modeling results reveal that the stress field on the base of the lithosphere induced by the mantle flow is probably a considerable factor that causes the movement and deformation of the lithosphere in continental China with its eflfcet focuing on the Eastern China A numerical research on the small-scale convection with variable viscosity in the upper mantle is introduced in Chapter 6. Based on a two-dimensional model, small-scale convection in the mantle-lithosphere system with variable viscosity is researched by using of finite element method. Variation of viscosity in exponential form with temperature is considered in this paper The results show that if viscosity is strongly temperature-dependent, the upper part of the system does not take a share in the convection and a stagnant lid, which is identified as lithosphere, is formed on the top of system because of low temperature and high viscosity. The calculated surface heat flow, topography and gravity anomaly are associated well with the convection pattern, namely, the regions with high heat flow and uplift correspond to the upwelling flow, and vice versa.In Chapter 7, we give a brief of future research subject: The inversion of lateral density heterogeneity in the mantle by minimizing the viscous dissipation.

Isotope geochronology of Dapingzhang spilite-keratophyre formation in Yunnan Province and its geological significance

On the basis of the geological field investigations and isotope geochronological studies the Sm-Nd isochron age (513 Ma?0 Ma), Rb-Sr isochron age (511 Ma? Ma) and K-Ar age (312-317 Ma) of the Dapingzhang spilite-keratophyre formation in Yunnan Province are presented. From these geochronological data it is evidenced that this suite of volcanic rocks was formed in the Cambrian and the parent magma was derived from a depleted mantle, which was influenced by crustal contamination and/or seawater hydrothermal

Mantle-derived gaseous components in ore-forming fluids of the Xiangshan uranium

The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)22− and UO2 (CO3) 34− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids b0.2 ppm.

扬子地台晚震旦至早寒武世沉积碳同位素研究

震旦-寒武交变期是地史上一个重大转折期，从隐生宙向显生宙过渡，海、陆、空发生了显著不同的变化，是一个具有特殊意义的过渡时期。中国扬子地区广泛发育的海相沉积层序有效地记录了震旦一寒武交变期重要的地质事件，因此为研究该时期大气圈、生物圈、岩石圈和水圈的相互联系提供了独一无二的场所。在前寒武纪一寒武纪地质研究中，由于缺少标志性生物化石，行之有效的生物地层学方法在上前寒武系的划分和对比中受到很大限制，沉积有机，质干酪根和相应碳酸盐的稳定碳同位素分析已经成为全球对比和划分的一个极为重要的的研究方法。尽管一些学者对扬子地台进行了多年的地球化学研究，使用碳酸盐和与之共生的有机质碳同位素组成对广泛的扬子地台变化的沉积环境进行研究还很欠缺、对分析和探讨该时期的生命演化过程和环境变化的关系研究方面还不足。本研究是以中国扬子地区为研究范围，用沉积碳酸盐和与之共生的有机质碳同位素组成对广泛的扬子地台变化的沉积环境（台地相、盆地相、过渡地带）进行分析，初步建立了一个地球化学模型，用于解释震旦一寒武交变期沉积地球化学记录，分析和探讨区域扬子地台碳循环和环境变化与地质事件之间的内在和外在联系：（1）南沱期：有机碳同位素组成（瓮安剖面平均值在-35.0‰左右）表现为较强负异常。地球被称为雪球（Snow-ball）或部分冰雪覆盖球体（Slush-ball），水体滞留和水动力不强，原始产率较低，物源以深源为主；生物不发育，主要是细菌和低等的真核细胞生物；空气和海水的气体通过冰裂缝进行交换，促进了碳酸盐的溶解；有机碳循环主要通过厌氧过程，比如细菌硫酸盐还原作用进行。（2）陡山沱期和灯影期：南沱晚期一陡山沱早期，海水的碳酸盐碳同位素组成短期仍然较负（瓮安剖面的δl3Ccarb-avg为-2.8‰ 松桃剖面1、2的δ13Ccarb-avg分别是-3.5％0和-8.6％。）；有机质的碳同位素组成总体呈现正漂移（瓮安护3Corg－avg：-26.3‰；南明剖面的δ13Corg-avg高达-26.7‰），这正是全球分布的“帽”碳酸盐出现的时期：接近地表的火山去气作用释放出较之现代350倍的CO2，导致地球迅速变暖，冰雪融化，大陆风化作用加强，海平面上升，“雪球，，转化为“温室，大气中大量的CO2快速转化为碳酸钙沉入海水中。全球可能处于一个异常高的海洋沉积速率时期。随后陡山沱组的护3Ccarb值显著上升，暗示了这一时期生物作用加强，有机碳埋藏速率明显提高，有机碳和还原硫埋藏的增加，导致上层海水345的富集，硫同位素组成较高。热液作用和上升洋流作用促成了瓮安磷矿的形成和瓮安生物群的繁盛。在南沱冰期后的陡山沱期和灯影期，高的别3c的出现主要是由于进行光合作用的海洋植物群体产率的迅速增加、海洋沉积速率的升高、海洋深部水柱中缺氧层的存在、热液活动、上升洋流作用、海水分层结构引起的，而短期同位素组成的负漂移和生物产率的变化则可能是区域事件所造成。明显的碳同位素组成负漂移出现在前寒武／寒武界线附近，这反映了碳短期变化的翻覆，与震旦纪末生物绝灭、环境变化的地质事件相符合。（3）牛蹄塘期：本研究结果发现，在牛蹄塘组／郭家坝组底部黑色岩系中，有机碳、无机碳、有机硫、黄铁矿硫同位素组成值相对较低，有机碳和黄铁矿含量相对较高。δ3Corg-avg和δ3Ccarb-avg分别是-33.9士0.7‰和-2.5＝0.4‰；TOC＞0.5；黄铁矿平均含量为0.96％间变化；黄铁矿（δ4ScRs）和有机硫同位素组成（δ34SOBS）平均值分别为0.3士7.5‰和3.4土7.1‰。由于牛蹄塘初期的环境变化频繁和不稳定，扬子区处于一段特殊的时期，碳、硫同位素组成延续上震旦统的负漂移现象，海侵事件、还原环境、缺氧事件、裂谷作用火山喷发、、气液喷溢、热水作用等造成海水相刘较深，有机碳埋藏量增大，多金属富集成矿。在牛蹄塘中晚期碳同位素组成趋于稳定，碳同位素组成重化，有机碳和黄铁矿含量降低：碳酸盐和有机质的碳同位素组成平均值分别是0.31±1.0‰和-31．41．3％。（沙滩），呈现稳定的正漂移；TOC平均值是0.8％；沙滩剖面郭家坝组中上部样品的黄铁矿平均含量0.5％；δ34SCRS-avg和δ34SOBS-avg为17.8士2.0‰和16.9±1.8‰。在牛蹄塘中期，随着大气圈和水圈中CO2含量降低、环境稳定，促使寒武纪生物繁盛，可能与增加的寒武系生物产量和微生物作用有关。对牛蹄塘期的环境情况有如下分析：随着全球变暖、海平面迅速上升，上升洋流活跃，由于分层海水的存在，海水在氧化带附近及其上部具有较高的有机物生成率，使寒武纪初期成为形成植物繁衍和带壳动物爆发的重要时期。碳同位素组成由震旦一寒武交变期的不稳定负漂移变化到稳定正漂移，这与世界其它地区的变化相一致。下寒武统富有机碳和黄铁矿的黑色页岩沉积，暗示了早寒武世缺氧环境的存在。（4）凯里期：早中寒武世交变期有机碳和无机碳同位素组成规律的变化，出现在扬子地台台江剖面上。有机质埋藏的变化，与生物从下寒武到中寒武统的变化相联系。碳酸盐和有机碳同位素组成的变化规律，反映了震旦一寒武交变期沉积环境的多变和震旦一寒武交变期碳循环的波动，这与变化的古环境背景、环境条件和生物演化的变化相互联系。碳酸盐碳同位素组成反映了海水最初的同位素信息；海底热液作用和上升一洋流作用可能成为影响碳同位素组成的重要因素。然而，各一地区在同一时期存在相似性，也有很大的不同，所以针对区域和局部事件，还需要进一步研究和探讨。

山东地区中生代岩浆作用与地壳拉张-兼论煌斑岩与金成矿的关系

燕山期（205～65Ma）山东地区地壳活动强烈，构造体系已由古亚洲构造域完全转化为滨太平洋构造域，构造活动导源于太平洋板块对欧亚板块的俯冲。由于太平洋板块对欧亚板块的俯冲（NW向），鲁东地区岩石圈发生了快速拆沉减薄作用．同时鲁东地区也可能会出现地l漫柱的活动；另外，在太平洋板块俯冲作用影响下，炎区庐断裂（山东称沂沐断裂）带发生了大型左行走滑剪切和拉张活动。以上构造因素加上早白至世末一晚白至世期间燕山造山带的垮塌，都可能为山东地区中生代地壳拉张提供了动力条件。山东地区中生代（燕山期）基性脉岩特别发育，这些慢源基性岩脉充填张性裂隙，是大陆地壳拉张的标志；另外，山东地区也存在大量拉张背景下的燕山期火山岩和碱性岩。但关于它们的年代学和系统的地球化学研究还比较薄弱，且对其成因和形成的构造环境，仍存在着争议。本论文主要从同位素年代学、岩石化学、地球化学和Sr-Nd-Pb同位素方面对山东地区燕山期基性脉岩、火山岩和碱性超基性脉岩进行了系统研究。同时，考虑到鲁东地区煌斑岩中金含量普遍较高，且燕山期又是山东金矿的主成矿期，论文中对煌斑岩与金成矿之间的关系也作了一定的研究。通过研究，得出以下主要认识：1、火山岩为一套以钙碱性安山岩为主，含少量拉斑玄武岩和英安岩。成因上为富集地慢部分熔融作用的结果，但在成岩过程中也可能存在单斜辉石、斜长石、橄榄石和Ti-Fe氧化物等矿物的分离结晶作用。碱性超基性脉岩岩性上为单一的橄榄辉石岩，为富集地慢源低度（3.4％）部分熔融作用的产物，岩浆演化过程经历了以橄榄石为主的分馏作用。基性脉岩主要包括辉长岩、辉绿岩（主要分布在鲁西地区）和煌斑岩（以斜闪煌斑岩为主，同时含部分拉辉煌斑岩和角闪煌斑岩）（主要分布在鲁东地区），都为富集岩石圈地慢部分熔融的产物。三类岩石在侵位结晶过程都不存在明显的地壳混染。2、火山岩、碱性超基性脉岩和基性脉岩（除少数外）都形成于大陆板内拉张环境。3、富集地慢源区（EMI）的产生是俯冲并熔融的扬子下地壳物质进入华北岩石圈地慢并与之相互交代作用形成的。4、研究区中生代基性脉岩K-Ar年龄分布范围为72.2±1.70Ma～204.2±5.4Ma，且基本上在90～140Ma之间变化。综合碱性超基性脉岩和已知的青山组的火山岩、基性脉岩年龄数据，认为山东地区中生代地壳拉张至少存在四次：即约80Ma、100Ma、120Ma和 140Ma。但鲁东地区在地壳拉张方面可能存在着与鲁西地区不同的制约因素：即鲁东地区存在拆沉作用和可能存在地慢柱的影响，而鲁西地区可能受到了郊庐断裂的左行走滑剪切和拉张活动的影响。5、胶北地区煌斑岩为钙碱性系列，且金含量普遍较高（平均28ppb），该研究对胶北地区的找矿勘探工作具有一定意义。