最新刊期
卷 61 ， 期 1 ， 2022
- 摘要：Rare metal pegmatites in the Chinese Altay have shown characteristics of multi-period, multi-type and mainly formed in the late Paleozoic to early Mesozoic. A world-class large-superlarge scale rare metal pegmatite metallogenic belt represented by the Keketuohai rare metal No.3 pegmatite is the most prominent feature of Altay orogeny, with a peak forming age in the Triassic (250-202 Ma). There are only a few Mesozoic rare metal pegmatites related to synchronous high fractionated granitic melts (such as Askaerte Be-Nb-Mo pegmatite). The Keketuohai rare metal No.3 pegmatite has nearly the same zircon U-Pb ages (220-211 Ma) as the Ala'er granites, but they are not related in genesis because of the distance between them excessing 10 km and the different εHf(t) values. The Mesozoic pegmatites are widely distributed but the synchronous granites are relatively less. Most rare metal pegmatites display temporal decoupling(large gap of forming age) and different sources (εHf(t), Nb/Ta, Zr/Hf, and K/Rb ratios) with their surrounding granites, indicating that pegmatites in the Chinese Altay were not derived from differentiated granitic melts. A reasonable genetic model for the Mesozoic Altay rare metal pegmatite is that they were generated by lower degree (<10%) dehydration partial melting of a mixed juvenile with metapelite source, i.e., anatectic pegmatite—the Altay-type rare metal pegmatite.关键词：Chinese Altay;rare metal pegmatite;Mesozoic;anatectic pegmatite
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发布时间：2023-11-01
Invited review
- 摘要：The 1918 Mw7.5 Nan’ao earthquake is one of the few events which are associated with a tsunami in the coastal region of South China. Historical records provide clear evidence of tsunami phenomena along the coasts of Guangdong and Fujian. Based on the constraint of historical records， post-earthquake survey， and the most updated geophysical data， we propose several synthetic earthquake scenarios with different fault geometries and investigate the corresponding tsunami hydrodynamics in detail. Our numerical modelling results suggest that the tsunami generated by this event may have affected a large portion of coastline ranging from Macau to Quanzhou in South China.The most impacted region is the southern and eastern coast of Nan’ao island with the maximum tsunami wave height of 3- 4 m in Qing’ao Bay. Followed by the coast of Dongshan County in Fujian （2-3 m）， and Shantou in Guangdong （~1 m）. The first positive tsunami wave arrives in Nan’ao and Shantou in half an hour and reaches Quanzhou， Hong Kong， and Macau in 3 hours， 4 hours and 5 hours， respectively. Based on the tsunami propagation process， distributions of tsunami wave height， and the analysis of tsunami waveforms in representative locations， we point out that the tsunami generated by earthquakes along the littoral fault possesses two unique features which may cause substantial damage in the future： 1） the long tsunami duration （longer than 48 hours） due to shelf resonance and edge wave trapped in the very broad continental shelf of northern South China Sea； 2） strong tsunami currents induced by rapid change of sea level will pose a significant threat to coastal infrastructures， e.g. ports， wharves， and aquaculture farms in southern China. Our sensitivity tests on earthquake parameters suggest that the tsunamigenic capacity is strongly affected by the source mechanism and fault geometries. Detailed marine geophysical surveys are required to better understand the geometrical characteristics and seismogenic behavior of the littoral fault. Such geophysical data provides the scientific basis for the potential earthquake and tsunami hazard assessment in the coastal region of South China.关键词：submarine earthquake;tsunami;shelf resonance;littoral fault zone
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发布时间：2023-11-01 - 摘要：Deep-sea gravity flow deposition is an important sedimentary process for sediments to be transported along the shelf and slope to the deep-sea basin under the drive of gravity. It plays an important role in the “source-sink” study and is closely related to the formation of oil-gas and gas hydrate. Based on the newly acquired two-dimensional multichannel seismic data， the sequence stratigraphy of the Zhongsha Trough is studied， the seismic facies characteristics and temporal and spatial distribution characteristics of gravity flow deposits are analyzed， and the genetic mechanism of gravity flow deposits is discussed in conjunction with the regional tectonic and sedimentary background. It shows that the sedimentary strata of Zhongsha Trough can be divided into 6 seismic sequences， included Sq1 （Paleogene）， Sq2 （Lower Miocene）， Sq3 （Middle Miocene）， Sq4 （Upper Miocene）， Sq5 （Pliocene）， and Sq6 （Quaternary）. The temporal development of gravity flow deposits is different for the south and north parts. In the southern part， they were mainly developed from the Late Miocene to the present and developed extensively in the Late Miocene and the Pliocene； moreover， multiple phases of mass transport deposits （MTD1-8） have been identified in the Pliocene and Quaternary. While in the northern part， gravity flow deposits were mostly developed during the Early Miocene and the Middle Miocene； from the Late Miocene to the present， due to the retreat of the northern part of the Zhongsha Platform， only contour deposits developed. The factors affecting gravity flow deposits in the Zhongsha Trough include sediment sources， relative sea-level changes， high carbonate productivity， and magmatic activity. The results of this study contribute to the understanding of the gravity flow deposition around the carbonate platform in the deep-water area and provide references for oil-gas exploration and geological hazard assessment in the region.关键词：gravity flow deposits;developmental characteristics;genetic mechanisms;carbonate platform;Zhongsha Trough
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发布时间：2023-11-01 - 摘要：The littoral fault zone （LFZ） in the northern South China Sea， is an important boundary fault between South China sub-plate and South China Sea sub-plate， is the seismogenic structure in the northern continental margin， and acts as a basin-controlling fault in the Pearl River Mouth Basin. Studies on the deeper crustal structures， structural evolution， and the latest activities of the LFZ have great significance in understanding the structural architecture and geodynamic processes， and in seismic hazard assessment. We review the deep structure exploration， tectonic attributes， activities， and seismogenic structure of the LFZ. Based on these， we propose that the LFZ is segmented concerning the deeper crustal structures and active characteristics； moreover， it has the potential of strong earthquakes when all three components of the LFZ， a NW-striking fault， and a low-velocity layer meet together. Finally， we highlight the problems to be solved in the future about the LFS， including the coupling of the deep and shallow structures， the relationship with the intersected NW-striking faults， the latest activities， and the assessment of earthquake-tsunami disasters.关键词：northern South China Sea;littoral fault zone;geophysics exploration;latest activity;seismogenic structure
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发布时间：2023-11-01 - 摘要：Based on newly acquired seismic data and previous published seismic data， we defined tectonic division and petroleum reservoirs of distal rifting basins in the southern South China Sea （SCS）. Considering the differences between proximal and distal rifting basins， we propose that distal rifting basins， including Nanan， Zengmu， and Liyue basins， are mainly controlled by a extensional fault system of NE-SW striking. The hydrocarbon system in this region includes an isolated carbonate platform， deep-water turbidity systems， and shelf-margin delta systems. The distal rifting basin locating between the central basin of the South China Sea （SCS） and Paleo-SCS has been far away from continent and in deep-water as early as Eocene， where sediments are composed of a massive set of carbonates accompanying by deep-water terrigenous debris depositions. The hydrocarbon system in the southern SCS， especially a combination of shelf-margin delta deposition with the isolated carbonate-platform system， is different from that in the northern SCS. The results enrich petroleum theory and would help to identify new exploration targets.关键词：South China Sea;distal rifting basin;tectonic division;petroleum system;reservoir
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发布时间：2023-11-01 - 摘要：The seabed and base of the deep-sea basin area of the South China Sea are rugged and have complex underground geological structures. These factors make a large number of complex multiple-waves and diffraction waves of seismic data develop. Meanwhile， caused by ghost waves， the low-frequency signal loss of deep reflection seismic profile is severe， which brings great challenges to the imaging of middle and deep targets. Concerning the problems of weak energy of deep low-frequency signal， the development of complex multiples and serious interference of diffraction waves in the 2D seismic data of the South China Sea， three key processing techniques， namely adaptive ghost wave removal， complex multiple wave combination suppression method and multi-attribute constrained complex diffraction attenuation， are adopted. The actual seismic data processing results show that： the deep 5-13 Hz low-frequency signal energy has been significantly enhanced， the signal-to-noise ratio has been increased from 5 to 10， and the suspected Moho imaging has improved significantly， which provides reliable basic data for subsequent comprehensive geological research.关键词：deep seismic reflection;adaptive ghost suppression;combined multiple attenuation;complex diffraction wave attenuation
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发布时间：2023-11-01 - 摘要：The East China Sea （ECS） is becoming attractive for marine scientific research owing to its special tectonic location， being recognized as an ideal site for sea-land geological comparison and deep crustal structure research. A deep seismic survey line has been deployed along the NW-SE direction in the ECS shelf to study the deep crustal structure. Abundant seismic phases， such as Ps， PsP， Pg， PcP， and PmP， are identified by analyzing the obtained 13 stations based on wide-angle reflection and refraction theory. The model shows that the burial depth of the Mesozoic and Cenozoic sedimentary is deeper in the east than in the west： in the west segment， it is about 1.5-3.5 km， with the velocity of 1.7-3.6 km/s， while in the east segment， it is about 3.5-9.0 km with the velocity of 1.7-5.4 km/s. The crust is divided into two layers： the upper crust， which has the velocity of 5.6-6.2 km/s， the bottom boundary in the depth of 13.0-14.5 km with a little undulation， and the lower crust， which has the velocity of 6.3-6.9 km/s， the bottom boundary in the depth of 26.5-28.5 km with some undulation. The bottom of the lower crust has no obvious velocity disturbance， implying that there are no large-scale magma activities or mantle upwelling. The crustal thickness is 17.5-27.0 km， presenting a thinned continental crust， and more thinning in the east. The stretching factor is estimated to be 1.2 for the west segment and 1.3-1.8 for the east segment， indicating that the east part of the ECS shelf has experienced more intense crustal stretching and thinning activities than the west part.关键词：East China Sea shelf;ocean bottom seismometer（OBS）;seismic phase;crustal structure
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发布时间：2023-11-01 - 摘要：Three-dimensional modeling provides a spatial perspective of geological objects that helps the understanding of underground structures. In metro engineering， it is difficult to obtain the complex spatial patterns of geological blocks， because generally there are limited data available while many are locally distributed. It becomes a bottleneck in reconstructing large-scale 3D geological models with high precision. In this study， we proposed a multi-scale 3D reconstruction method of geological structures integrating the idea of hierarchical modeling based on the Extended GOSIM algorithm of multiple-point statistics （MPS） method， using 2D geological cross-sections as input data， and taking an objective function with spatial pattern similarity. As an example， the reconstruction of the 3D geological model of a metro station of Line 11 of Guangzhou Rail Transit illustrated that the hierarchical modeling successfully reconstructed the spatial structures of different lithology with faults. As the relationships among geological objectives are fully considered， the proposed method can reproduce the 3D spatial pattern of geological blocks with high precision using limited data. It can further be utilized for metro design and construction.关键词：multiple-point statistics;hierarchy modeling;3D geological modeling;metro engineering
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发布时间：2023-11-01 - 摘要：The geological conditions in karst areas are complex and diverse.Cross-hole seismic wave CT can be used to detect the development of karst for engineering construction. To investigate the characteristics of detection errors and factors influencing these errors， we carried out field tests in Baiyun District， Guangzhou， to detect multiple CT profiles using the same bridge pile with different borehole distances， and analyzed the relationship between the error of cross-hole seismic wave CT detection and the transmission-reception distance of boreholes.The results show that： 1） the detection error increases almost exponentially with the increase of the borehole distance， 2） the average error increases from 0.2 m to 0.7 m while the borehole distance increases from 10 m to 21 m， and 3） when the borehole distance is over 20 m， the detection of CT profile may be not reliable. Under reasonable technical parameters and test schemes， the seismic wave cross-hole CT method can accurately identify geological anomalies with a size of 1 m or more. Using currently available equipment， the appropriate CT borehole distance should be 5 to 20 m for the area of medium to slightly weathered limestone.关键词：cross-hole CT;cross-hole seismic;karst investigation;error analysis;resolution
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发布时间：2023-11-01 - 摘要：There is a great argue about the ages of the late Pleistocene sediments in the Pearl River delta. The significant uncertainties，the transgression initiated during MIS3（Marine Oxygen Isotope Stage 3） or MIS5，restrained discussing the corresponding pattern of the sea level to global change and evolution history of the delta. In this article， the core GZ-2（22°42.339′N， 113°30.831′E） near the Lingdingyang estuary， located on the Wanqingsha area of the delta， were selected to reconstruct the geomagnetic records based on the study of the sediments magnetic properties. The rock magnetic experiments illustrate that the fine magnetite contributes the main changes of the nature remanent magnetization of the sediments. The reliable inclination and relative paleointensity （RPI） of the geomagnetic field can be reconstructed from the samples.Comparing the relative intensity curve （PRI=NRM（20-40）mT/ARM（20-40）mT） constrained by the AMS 14C and Optically Stimulated Luminescence （OSL） ages， with the standard high-resolution intensity proxies from the GLOPIS-75 and the north Atlantic ocean， the chronology the sediments can be recovered. The results show the age of the fine sediments is younger than ~43 ka， and the transgression initiate at the MIS3 stage. The marine sediments during the MIS3 stage in the Pearl River delta as well as in the southeast coastal areas of China may be raised from the tectonic subsidence dominated the relative sea level rising， which intrude along the river valley and formed the marine sediments.关键词：Pearl River Delta;Late Pleistocene transgression;chronology of the stratigraphy;geomagnetic field variation
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发布时间：2023-11-01 - 摘要：The computation resources required by elastic wave simulations are related to the number of grid points. The grid spacing for the conventional uniform grid is determined by the lowest velocity in the complex model， and thus the high-velocity zones are unnecessarily discretized to a too-small grid spacing. Adaptive Mesh Refinement（AMR） can flexibly deal with different irregular structures， using fine grids only for lower velocity zones， thus with high efficiency. We combine AMR with the finite-difference method to simulate the two-dimensional elastic wave for models with complex structures. The governing equation is the velocity-stress elastic wave equation in the first-order partial differential equation form. We calculate the spatial derivatives using high-order collocated-grid central difference schemes with an explicit filtering operator and implement the time integration with the Runge-Kutta method. We build up our implementation on an existing AMR framework to fulfill the data structure management， mesh generation， and load balance of the AMR. The results of the numerical experiments reveal that our scheme can be used for seismic wave simulations in complex velocity models. The results obtained by the proposed scheme fit well with those obtained by using a uniform grid with both phase and amplitude errors of ~10%. The proposed AMR scheme increases the computational efficiency by two folds： reducing the number of grid points and enlarging the time step as the grid spacing is increased in high-velocity regions.关键词：elastic wave numerical simulation;finite-difference method;adaptive mesh refinement;load balance
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发布时间：2023-11-01 - 摘要：The surface sediments in northern South China Sea shelf （SCSS） carry the information of provenances of heavy metal elements and their environmental effects， potential ecological risks and their relationships with human activities. Thirty surface sedimentary samples were collected from the 27 sites in the northern SCSS during the 2016 summer survey. These samples are characterized by sand， silt， silty clay and clay with particles in size ranging from 0.77Φ to 6.28 Φ （average value of 3.43Φ）. The heavy metal elements of Cu，Zn，As，Cd，Pb and V are higher than those in the upper crust and show the significant enrichment along the coastal areas of the Moyang River-Eastern Hainan and the Han River estuary. Zn，V，Cr，Ni，Pb，Cu and Cd contents increase with the amount of Al， Sc and the values of particle size， indicating their similar continental provenance of the weathering materials. Such a pattern is mainly controlled by both transportations from the Pearl River， Han River and Moyang River and coastwise current in the northern SCSS， with rare human interference. However， element As shows poor correlation with the particle size of the surface sediments， suggesting significant human interference and potential environmental pollution.关键词：heavy metal elemental contents;surface sediments;input of continental provenance;the northern South China Sea shelf
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发布时间：2023-11-01 - 摘要：Based on AMS14C dating results of five samples of drilling core GMD06， the sedimentary framework of the age-depth of Chizhou， Anhui Province， was established. The pollen analysis data reveal the vegetation succession history in this Yangtze River basin since the late MIS3. During the late MIS3 period （~30 540 - 25 330 cal a BP）， the vegetation type of the study area was evergreen deciduous broad-leaved mixed forest； the dominant species were Cyclobalanopsis and Pinus， while the Quercus-deciduous and Castanea/Castanopsis were relatively less； and the climate was warm-cool and humid. During the MIS2 period （25 330 - 9 640 cal a BP）， the vegetation was mainly characterized by deciduous broad-leaved forest； the climate gradually changed from cold and dry to cool and wet during the last glacial maximum. During the early and middle Holocene （9 640 - 5 180 cal a BP）， the vegetation began to flourish， particularly， the tree pollen reached the peak； the climate was warm and humid. During the late Holocene （~5 180 cal a BP）， the Poaceae （> 40 μm） pollen increase significantly which probably indicates the increased rice agricultural activities； coupled with the sharp decreasing of tree pollen， it suggests the intensified disturbance of natural vegetation by human activities.关键词：the Yangtze river basin;MIS3;pollen analysis;Paleoenvironment
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发布时间：2023-11-01
Research articles
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