2017年 28卷 第4期
Water is the most important component in Earth system evolution. Here, I review the current understanding of the fate of water in the mantle dynamics system based on high-pressure and temperature experiments, geochemical analyses, seismological and geomagnetic observations, and numerical modeling of both regional-and global-scale mantle dynamics. In addition, as a numerical example, I show that the water solubility of the deep mantle is strongly sensitive to global-scale water circulation in the mantle. In a numerical example shown here, water solubility maps as functions of temperature and pressure are extremely important for revealing the hydrous structures in both the mantle transition zone and the deep mantle. Particularly, the water solubility limit of lower mantle minerals should be not so large as ~100 ppm for the mantle transition zone to get the largest hydrous reservoir in the global-scale mantle dynamics system. This result is consistent with the current view of mantle water circulation provided by mineral physics, which is also found as a hydrous basaltic crust in the deep mantle and the water enhancement of the mantle transition zone simultaneously. In this paper, I also discuss some unresolved issues associated with mantle water circulation, its influence on the onset and stability of plate motion, and the requirements for developing Earth system evolution in mantle dynamics simulations.
Recycled oceanic crust (ROC) has long been suggested to be a candidate introducing enriched geochemical signatures into the mantle source of intraplate basalts. The different parts of oceanic crust are characterized by variable oxygen isotope compositions (δ18O=3.7‰ to 13.6‰). To trace the signatures of ROC in the mantle source of intraplate basalts, we measured the δ18O values of clinopyroxene (cpx) phenocrysts in the Cenozoic basalts from the Shuangliao volcanic field, NE China using secondary ion mass spectrometer (SIMS). The δ18O values of the Shuangliao cpx phenocrysts in four basalts ranging from 4.10‰ to 6.73‰ (with average values 5.93‰±0.36‰, 5.95‰±0.30‰, 5.58‰±0.66‰, and 4.55‰± 0.38‰, respectively) apparently exceed those of normal mantle-derived cpx (5.6‰±0.2‰) and fall in the typical oxygen isotope range of altered oceanic crust. The δ18O values display the negative correlations with the Eu, Sr anomalies of whole rocks and erupted ages, demonstrating that (1) the ROC is the main enriched component in the mantle source of the Shuangliao basalts and (2) the contributions of ROC varied with time. The basalt with the lowest δ18O value is characterized by a significant K positive anomaly, highest H2O/Ce and Ba/Th ratios, suggesting that the mantle source of basalts with low δ18O can also include a water-rich sediment component that may be the trigger for partial melting. Considering the continuous subduction of the Pacific slab, the temporal heterogeneity of the source components is likely to be caused by the Pacific slab subduction.
Measuring the relative importance and assigning weights to conditioning factors of landslides occurrence are significant for landslide prevention and/or mitigation. In this contribution, a fractal method is introduced for measuring the spatial relationships between landslides and conditioning factors (such as faults, rivers, geological boundaries, and roads), and for assigning weights to conditioning factors for mapping of landslide susceptibility. This method can be expressed as ρ=Cε–d, where d is the fractal dimension, and C is a constant. This relationship indicates a fractal relation between landslide density (ρ) and distances to conditioning factors (ε). The case of d > 0 suggests a significant spatial correlation between landslides and conditioning factors. The larger the d ( > 0) value, the stronger the spatial correlation is between landslides and a specific conditioning factor. Two case studies in South China were examined to demonstrate the usefulness of this novel method.
Conodonts and ammonoids have played significant roles in the Permian-Triassic timescale. In order to uncover the nature of the Permian-Triassic mass extinction and subsequent recovery, we studied conodont and ammonoid biostratigraphies around the Permian-Triassic boundary from Jianzishan of Hubei, South China. A total of four conodont zones and two ammonoid beds are recognized. In ascending order, the conodont zones are Late Changhsingian Clarkina changxingensis Zone, Clarkina yini Zone and Griesbachian Hindeodus parvus Zone, Hindeodus postparvus Zone; the ammonoid beds are Late Griesbachian Ophiceras beds and Early Dienerian Ussuridiscus varaha beds. At Jianzishan, Ophiceras beds are stratigraphically younger than Hindeodus parvus Zone, but it is likely to be the same level with Hindeodus postparvus Zone. The Lower Dienerian in Bed 8 in this section is characterized by ammonoid Ussuridiscus varaha beds, which is associated with many Late Griesbachian conodonts including Hindeodus postparvus, Hindeodus praeparvus, Hindeodus typicalis, Hindeodus pisai, Hindeodus latidentatus, Hindeodus parvus, Hindeodus anterodentatus and Isarcicella turgida, indicating these conodont species could pass through the Griesbachian-Dienerian boundary and occurred in the Early Dienerian oceans.
Previously undescribed Ediacaran macrofossils are documented in and close to a quarry southwest of Zigui in Shunyang Valley, near Sixi Village, Yangtze Three Gorges region, Hubei Province, China. Discoidal impressions, vendotaenids, and a new branching form occur in bedded carbonates through the entire 235 m thickness of the Dengying Formation. The quarry and nearby outcrops in the stream valley have significant potential for further discoveries of Ediacaran macrofossils.
Xitaijinair (XT) Salt Lake, located in the western Qaidam Basin, is significant for reconstructing the evolution of inland drying climate. However, the chronological and mineralogical records from this lake are rare. This study investigated the chronology (accelerator mass spectrometry (AMS) 14C ages and optically stimulated luminescence (OSL) ages) and mineral compositions of sediment in the 240-cm-deep XT Section of the Xitaijinair Salt Lake region. The conclusions are drawn as follows: (1) Nine AMS 14C ages, ranging between 33 and 40 cal ka BP, are obviously younger than the two OSL ages (57.9 and 69.1 ka). The 14C ages probably reflect contamination with modern carbon. (2) Both 14C and OSL ages indicate that the surface of Xitaijinair Salt Lake region has suffered erosion. (3) The sediments of XT Section are composed of silicates (quartz, muscovite, clinochlore and albite), carbonates (calcite, dolomite, and ankertie), halite and gypsum.
The sedimentary environment, formation conditions, sedimentary characteristics and the basin evolution model of high-frequency oscillatory lake in arid climatic background of the Lower Eocene in the Dongying depression were studied through the analysis of drilling cores, sporepollen, geochemistry and geophysics data. During the sedimentary period of the Eocene Ek1-Es4x formations, because of the frequent alternation between dry and wet climates in the arid climatic background and the gentle paleogeomorphology, the lake level and salinity of the Early Eocene Dongying depression frequently and rapidly increased and decreased, which is referred to as a high-frequency oscillatory lake. The sedimentation and distribution of sediments in this high-frequency oscillatory lake basin were controlled by the frequently alternating dry-wet climates. During periods with relatively wet climate, the seasonal floods and unstable rivers led to the formation of over-flooding lake deltas in the gentle slope belt, and fine-grained clastic sediments, with minor thin layers of gypsum-salt rocks in the sag belt. During the relatively arid climatic periods, sedimentation occurred mainly in the limited area of the sag belt with thick gypsum-salt rocks. Because of the impact of the salinity stratification of the lake water, these gypsum-salt rocks exhibit annular structural features. A sedimentary cycle of the oscillatory lake began with isochronous flood channels and ended with relatively thick gypsum rocks and salt rocks. The thickness of one oscillatory cycle is generally 4-20 m. The superposition of multiple sedimentary cycles of the oscillatory lake constitutes the overall vertical filling sequence of the high-frequency oscillatory lake basin.
The Huadian Basin is an oil shale-bearing basin located in northeastern China. Thirteen oil shale layers deposited in this basin, and the characteristics of oil shale are different among these oil shale layers. Based on the core observation and microscope identification, using the organic and inorganic data from borehole HD3 and outcrops, the formation conditions of different grade oil shale have been evaluated. Based on measuring oil yield (OY in short) of an oil shale to determine its grade, this paper classifies the oil shale as high grade (OY≥10%), medium grade (10% > OY≥5%) and low grade (5% > OY≥3.5%). The high grade oil shale is mainly in brown or dark brown, and the bulk density ranges from 1.59to 1.81 g/cm3. The results of X-ray diffraction indicate the content of carbonate minerals is 28.0%. The HI (hydrogen index)-Tmax, HI-OI (oxygen index) and S2-TOC (total organic carbon) diagrams indicate the kerogen types are Ⅰ and Ⅱ1. The high grade oil shale generally formed in the relatively arid paleoclimate, deposited in the brackish water, dysoxic environment, when the bioprodctivity is extremely high, and the information is mainly from the inorganic parameters diagrams of chemical index of alteration (CIA), Sr/Ba and V/(V+Ni). The medium grade oil shale mainly shows grey-black or black-brown color and the bulk density ranges from 1.87to 2.08 g/cm3. The average content of carbonate minerals is 16.4%, far less than high grade oil shale and the kerogen type is mainly Ⅱ1. The inorganic parameters diagrams reflect the medium grade oil shale generally formed in the less humid paleoclimate, deposited in the brackish water, dysoxic to anoxic environment, when the bioproductivity is medium. The color of low grade oil shale is major in grey-black or dark grey and the bulk density ranges from 2.00to 2.15 g/cm3. The average content of carbonate minerals is sharply decreased and the kerogen type is mainly Ⅱ1. The inorganic parameters diagrams indicate the low grade oil shale generally formed in the relatively humid paleoclimate, deposited in the freshwater to brackish water, anoxic environment, when the bioproductivity is relatively low. Comprehensive study suggest the increasing precipitation caused by a relatively humid paleoclimate resulted in decreasing oxygen concentration and salinity in the bottom water, restrained the salinity stratification, and tended to form the low grade oil shale. The strong evaporation leading to relatively arid paleoclimate resulted in increasing oxygen concentration and salinity in the bottom water, and promoted the salinity stratification. The area with well preservation conditions caused by the relative high sedimentary rate and salinity stratification are favorable to high grade oil shale deposit. In summary, the bioproductivity and the paleoclimate are the main factors controlling the oil shale grade in the Huadian Basin, when the bioproductivity is relatively high and the paleoclimate is relatively arid, it is prone to form the high grade oil shale. However the low grade oil shale developed in the low bioproductivity and relatively humid paleoclimate.
Hydrocarbon micro-seepage can cause oxidation reduction reactions and produce altered minerals in surface sediments and soil. The typical altered minerals mapping by their diagnostic spectral features on hyper-spectral images is an important tool for the petroleum exploration industry. In this study, the airborne hyper-spectral data were used to investigate the altered minerals induced by hydrocarbon micro-seepages by spectral feature fitting (SFF) in the loess coverage area of Xifeng Oilﬁeld. The results reveal that the distribution region of the altered minerals induced by hydrocarbon micro-seepage is larger than the known oilfield exploration area. The potential hydrocarbon micro-seepage region was also revealed by the distribution of altered minerals besides the known hydrocarbon area. A fast index was proposed by the absorption depths of clay and carbonate minerals for assessment of hydrocarbon micro-seepage. And it gave much clearer boundaries for the hydrocarbon micro-seepage in the loess coverage area than those by the altered mineral mapping. In addition, some field samples were analyzed by X-ray diffraction (XRD) and atomic absorption spectrophotometer to validate the results. Within the extents of hydrocarbon micro-seepage, there are lower contents of ferric iron and higher contents of carbonate minerals in these samples. Therefore, it is satisfactory to have the airborne hyper-spectral data to outline the extents of hydrocarbon micro-seepage for further hydrocarbon exploration in the loess coverage area.
Remnant ocean basin is a key to understand the plate suturing and subsequent uplift and erosion of orogen. The Bay of Bengal Basin (BOBB) provides a typical example to analyze the remnant ocean basin structures, evolution, and relationships between depositional filling and uplifting of the Himalayan Orogen. Thirty-nine seismic profiles as well as interval velocities of well BODC3 were used to compile isopach maps of the basin. Among the seismic data, 26 seismic profiles were applied to establish 8 cross sections. The cross sections suggest the basin is asymmetric, bounded to the west by the eastern continental margin of India (ECMI) with graben-horst and to the east by the Sunda convergence margin dominated by trench-arc system. The BOBB is characterized by a prominent down flexure structures caused by huge amount of Bengal fan turbidite sediments accumulation. Our isopach maps and chronology data collected from adjacent regions reveal the initial development and fast southward growth of the Bengal fan were related to the early and major stage uplift and erosion of the Himalayan Orogen, respectively. The BOBB has experienced a critical transition from an ocean basin to a remnant ocean basin at Late Oligocene. Such basin structures and evolution features indicate the BOBB provides whole records of oblique convergence of the India and Asia plates, and the early and major stage evolution of the Himalayan Orogen.
We address the role of the concave and convex arcs (as observed from the subducting plate) on the deformation occurring along the Myanmar-Andaman-Sumatra margin. We categorize the pre-and post-seismic deformations of the lithosphere using earthquake database occurring either prior to 26th December 2004 Mw 9.3 off-Sumatra mega-event or after the incidence. Analysis under pre-seismic domain shows that area near Sumatra records highest seismicity, which largely drops in the area past the North Andaman, and further increases towards north. Shallowest depth and minimum dip of the subducting lithosphere is recorded at the central segment where the arc transformed into concave shape. The annual moment energy release during earthquake decreases to more than two orders of magnitude past the North Andaman towards north under post-seismic deformation phase. Higher depths of continuity of events are presumably associated with more dipping Benioff zones in both the Indo-Myanmar and Andaman-Nicobar convex arcs. These observations obviously account for tectonic subdivision of the margin near concave shape arc around the central part. Absence of volcanism, presence of splay faults in the back-arc, sharp reduction in seismicity near central segment are interpreted to be caused by major tectonic impact of the NNE-ward converging buoyant Ninety-east Ridge against the Asian Plate. Shallowest dip, small elastic thickness, weak converging Indian lithosphere, and evidences of series of en-echelon blocks off the eastern side of the broken northern Ninety-east Ridge might be incapable of generating great earthquake in this area.
Elastic migration has been widely paid attention by employing the vector processing of multicomponent seismic data. Ray based elastic Kirchhoff migration has such properties as high flexibility and high efficiency. However, it has failed to solve many problems caused by multipath. On the other hand, elastic reverse-time migration (RTM) based on the two-way wave equation is known to be capable of dealing with these problems, but it is extremely expensive when applied in 3D cases and velocity model building. Based on the elastic Kirchhoff-Helmholtz integral, we calculate decoupled backward-continued wavefields by introducing elastic Green functions for P-and S-waves, which is expressed by a summation of elastodynamic Gaussian beams. The PP and polarity-corrected PS images are obtained by calculating the correlation between downward and decoupled backward-continued vector wavefields, where polarity correction is performed by analyzing the relation between the polarization direction of converted PS waves and incident angle on the interface. To a large extent, our method combines the high efficiency of ray-based migration with the high accuracy of wave-equation based reverse-time migration. Application of this method to multicomponent synthetic datasets from the fault model and Marmousi 2 model demonstrates the validity, flexibility and accuracy of the new method.
Using seismic attributes as features for classification in feature space, in various aims such as seismic facies analysis, is conventional for the purpose of seismic interpretation. But sometimes seismic data may have no attributes or it is hard to define a small and relevant set of attributes in some applications. Therefore, employing techniques that perform facies modeling without using attributes is necessary. In this paper we present a new method for facies modeling of seismic data with missing attributes that called dissimilarity based classification. In this method, classification is bas ed on dissimilarities and facies modeling will be done in dissimilarity space. In this space dissimilarities consider as new features instead of real features. A support vector machine as a powerful classifier was employed in both feature space (feature-based) and dissimilarity space (feature-less) for facies analysis. The proposed feature-less and feature-based classification is applied on a real seismic data from an Iranian oil field. Facies modeling using seismic attributes provide better results, but the feature-less classification outcome is also satisfactory and the facies correlation is acceptable. Indeed, the power of attributes to discriminate different facies causes to that facies analysis using attributes provide more reliable results comparing to feature-less facies analysis.
In order to interpret the vertical electrical sounding data more reliably and effectively in the case of lacking proper priori information, two inverse schemes are proposed to invert combined resistivity and induced polarization data by using particle swarm optimization technique. Based on the computational formula of induced polarization, the inversion for chargeability/polarizability data can be transformed into inverting equivalent resistivity data. Then, the inversion for combined data can be decomposed into two procedures: inverting resistivity data and inverting equivalent resistivity data. A sequential inversion scheme is presented to run the two procedures sequentially. Contrast to the sequential scheme, a simultaneous one is proposed to invert resistivity and induced polarization data simultaneously. Both the sequential and simultaneous schemes are performed via centered-progressive particle swarm optimization algorithm for more exploratory purpose. Numerical experiments show that both the designed inversion algorithms can invert resistivity and induced polarization data successfully with fast convergence and high accuracy, even performed in a large search space. The inverse results are comparable to the results from generalized linear method. As an approximate importance sampler, the particle swarm optimization based algorithm can provide posterior analysis conveniently. We employ the posterior probability distributions of inverted model parameters to evaluate the performance and uncertainty of inversion. The posterior analysis and further field data testing show that the proposed inversion algorithms perform good sampling of the equivalence region and make sure that the global optimum can locate in the high probability areas.
Combined with tectonic evolution, a multi-isotopic method (δD, δ18O, 87Sr/86Sr and 14C) and hydrochemistry data have been used to study the origin and classification of geothermal water in the Guanzhong Basin. The study shows that geothermal water of Xianli terrace primarily came from northwest direction when accepting recharge. A small amount supply source of geothermal water in Xi'an City is from Qinling Mountain and the principal supply source comes from the west direction, but geothermal water of Chang'an District mainly accepts supply from Qinling Mountain. Based on geothermal environment is open or not, the degree of water-rock interaction, and the origin of geothermal water, geothermal water of the study area can be divided into four types: A, geothermal water of Gushi depression, perfect closed thermal environment and significant water-rock interaction, belonged to residual sedimentary water origin; B, geothermal water of Xianyang City, good closed environment and relatively significant water-rock interaction, belonged to residual sedimentary water origin mixed with fossil leaching water; C, geothermal water of Xi'an City, half closed environment and some water-rock interaction, belonged to fossil leaching water origin; D, geothermal water of Chang'an District, open environment and mixed with modern precipitation, belonged to fossil leaching water origin.
The Ångström turbidity coefficient (β) and Linke turbidity factor (TL) are used to study the atmospheric conditions in Wuhan, Central China, using measured direct solar radiation during 2010–2011 in this study. The results show that annual mean β values generally increase from 0.28 in the morning to 0.35 at noon, and then decrease to 0.1 in the late afternoon during the day; annual mean TL generally varies from 3 to 7 in Central China. Both turbidity coefficients have maximum values in spring and summer, while minimum values are observed in winter months. It also reveals that β values show preponderance (52.8%) between 0.15 and 0.35, 78.1% of TL values are between 3.3 and 7.7, which can be compared with other sites around the world. Relationship between turbidity coefficients and main meteorological parameters (humidity, temperature and wind direction) have been further investigated, it is discovered that the local aerosol concentrations, dust events in northern China and Southwest Monsoon from the Indian Ocean influences the β values in the study area.