南海南部边缘沉积盆地构造-热演化历史

南海南部边缘发育众多含油气盆地,具有可观的油气资源潜力.本文采用基于多期有限拉张模型的应变速率方法对南海南部边缘沉积盆地进行了构造-热演化模拟,并与南海北部边缘沉积盆地的构造-热演化历史进行了对比分析.南海南部边缘晚新生代具有明显碰撞挤压、走滑改造的痕迹,而同时期北部边缘以小规模的张性断裂活动为主,由于构造活动背景的不同,造成了南、北边缘沉积盆地构造-热演化历史的差异.     

Numerical modeling of block structure dynamics: dependence of a synthetic earthquake flow on the structure separateness and boundary movements

A seismically active region is modelled as a system of absolutely rigid blocks separated by infinitely thin plane faults. The interaction of the blocks along the fault planes and with the underlying medium is viscous-elastic. The system of blocks moves as a consequence of prescribed motion of the boundary blocks and of the underlying medium. When for some part of a fault plane the ratio of the stress to the pressure exceeds a certain strength level a stress-drop (a failure) occurs (in accordance with the dry friction model), and it can cause a failure in other parts of the fault planes. In the model the failures represent earthquakes. As a result of the numerical simulation a synthetic earthquake catalog is produced. The numerical modelling was carried out for three types of structures with increasing of the structure separateness inside of each type and for two types of boundary movements. A synthetic earthquake flow is characterised by several features including the frequency-magnitude relation (the Gutenberg-Richter curve). When the structure separateness increases the slope of the curve changes monotonously in the same direction for all considered types of structures if the boundary movement is the same. The directions of changing of the slope are opposite for two considered boundary movements.     

Rifting process and thermal evolution of the continental margin of Eastern Canada determined from subsidence curves

The subsidence history of the Nova Scotia and Labrador shelves, determined from deep exploratory well data, indicates that these regions underwent extension during rifting in the Early Jurassic and Late Cretaceous, respectively, and have since subsided passively due to conductive cooling of the lithosphere. The timing of the extension process is consistent with the ages of oldest sea floor adjacent to these margins. Extension parameters determined from the subsidence history of the Nova Scotian margin indicate both crustal and subcrustal material extended by approximately the same amount. For Labrador, the extension parameters indicate that the mantle lithosphere was extended considerably more than the crust. The magnitudes of extension on both margins are in good agreement with observed crustal thickness determined from seismic refraction data. Profiles depicting the sedimentary stratigraphies and depth to basement were constructed across each margin. The temperature distribution within the sediments was calculated from the extension parameters using a two-dimensional model with sediment units of varying thickness, radioactive heat production, and conductivity. The calculated temperature distribution across the margins is in good agreement with bottom hole temperatures measured in deep exploratory wells, and with surface heat flow measurements where they are available. Similar plots of temperature paleotemperature within the sediments suggest that thermal conditions have been favorable for hydrocarbon generation in some of the older strata.     

Comparison of gravimetric and seismic constraints on the structure of the Aegean lithosphere in the forearc of the Hellenic subduction zone in the area of Crete

The island of Crete is located in the forearc of the Hellenic subduction zone, where the African lithospheric plate is subducting beneath the Eurasian one. The depth of the plate contact as well as the internal structure of the Aegean plate in the area of Crete have been a matter of debate. In this study, seismic constrains obtained by wide-angle seismic, receiver function and surface wave studies are discussed and compared to a 3D density model of the region.The interface between the Aegean continental lithosphere and the African one is located at a depth of about 50 km below Crete. According to seismic studies, the Aegean lithosphere in the area of Crete is characterised by strong lateral, arc–parallel heterogeneity. An about 30 km thick Aegean crust is found in central Crete with a density of about 2850 kg/m³ for the lower Aegean continental crust and a density of about 3300 kg/m³ for the mantle wedge between the Aegean crust and the African lithosphere. For the deeper crust in the area of western Crete two alternative models have been proposed by seismic studies. One with an about 35 km thick crust and another one with crustal velocities down to the plate contact. A grid search is performed to test the consistency of these models with gravimetric constraints. For western Crete a model with a thick lower Aegean crust and a density of about 2950 kg/m³ is favoured. The inferred density of the lower Aegean crust in the area of Crete correlates well with S-wave velocities obtained by surface wave studies.Based on the 3D density model, the weight of the Aegean lithosphere is estimated along an E–W oriented profile in the area of Crete. Low weights are found for the region of western Crete.     

Comparison of gravimetric and seismic constraints on the structure of the Aegean lithosphere in the forearc of the Hellenic subduction zone in the area of Crete

The island of Crete is located in the forearc of the Hellenic subduction zone, where the African lithospheric plate is subducting beneath the Eurasian one. The depth of the plate contact as well as the internal structure of the Aegean plate in the area of Crete have been a matter of debate. In this study, seismic constrains obtained by wide-angle seismic, receiver function and surface wave studies are discussed and compared to a 3D density model of the region.The interface between the Aegean continental lithosphere and the African one is located at a depth of about 50 km below Crete. According to seismic studies, the Aegean lithosphere in the area of Crete is characterised by strong lateral, arc–parallel heterogeneity. An about 30 km thick Aegean crust is found in central Crete with a density of about 2850 kg/m³ for the lower Aegean continental crust and a density of about 3300 kg/m³ for the mantle wedge between the Aegean crust and the African lithosphere. For the deeper crust in the area of western Crete two alternative models have been proposed by seismic studies. One with an about 35 km thick crust and another one with crustal velocities down to the plate contact. A grid search is performed to test the consistency of these models with gravimetric constraints. For western Crete a model with a thick lower Aegean crust and a density of about 2950 kg/m³ is favoured. The inferred density of the lower Aegean crust in the area of Crete correlates well with S-wave velocities obtained by surface wave studies.Based on the 3D density model, the weight of the Aegean lithosphere is estimated along an E–W oriented profile in the area of Crete. Low weights are found for the region of western Crete.     

南海西南海盆壳幔结构重力反演与热模拟分析

壳幔结构及扩张期后的岩浆活动是研究南海西南海盆形成演化的关键.本文针对NH973-1剖面开展壳幔密度结构重力反演,并依据重力反演的壳幔模型,定量模拟海底扩张期后的壳幔热结构与热演化过程.重力反演表明:西南海盆中央残余扩张脊之下存在一个较深的凹陷带,其下Moho面比两侧略深,呈现扩张期后的热沉降特点.热模拟发现:海盆扩张终止后,壳幔并非均衡一致降温,而是以"地壳增温-地幔降温"方式进入热沉降阶段.海底扩张终结后,地壳继续增温约7 Ma之后才与地幔一同缓慢降温,同步进入后期热沉降.沿NH973-1剖面南、中、北段的地壳增温特点不同,在海盆扩张中心北侧约70 km之下7~9 km深度处,在9.6~4.6 Ma期间温度增幅一直保持在200℃以上,将该处地壳温度抬升至1100℃以上,具备了产生扩张期后岩浆熔融的温度条件.P-T图解分析也支持此期间如果地壳具备局部构造断裂形成的含水条件和减压条件,就可能因部分熔融产生岩浆活动.     

Numerical modeling of the penetration area of reversed submerged jet by the methods of finite elements and finite volumes

Water jet flow has many usages in the field of management and water resource operation that can be applied in mixing, dilution and aerification. The current study has calculated the flow velocity, length and height of jet penetration area (jet and main flow are of opposite directions) by the use of methods of finite element (FEM) and finite volume (FVM) and k–ε model. In order to evaluate and verify this turbulent model, the results of the numerical model have been compared with the experimental results. This model has been studied for consideration of various jet flow velocities and thicknesses. The conclusions have indicated that the length and the height of the penetration area have linear relationship with jet flow velocity; therefore, as the jet flow velocity increases, the length of jet penetration increases as well. The comparison of the results of numerical method with the experimental data have demonstrated that the FVM holds less convergence time and better results compared with FEM.     

南海西北部沉积盆地晚新生代沉降、沉积特征:对深部异常过程的响应

南海西北部雷琼区域出露大量晚新生代碱性玄武岩,且地震层析成像结果显示其地幔存在类似地幔热柱特征的低速异常体.为了揭示该异常体的活动信息及其对表层地质过程的影响,本文选择位于雷琼区域的北部湾盆地和珠三坳陷为研究对象,系统分析了它们早中新世以来的构造沉降、与基底隆升有关的剥蚀面和岩浆活动特征.结果显示,研究区晚中新世构造沉降速率表现为低速异常;晚中新世以来,研究区发育了2个因基底隆升形成的局部剥蚀面,剥蚀范围大致以雷琼火山区为中心呈环状分布,中心区域剥蚀量较大,累积厚度100~200 m;中中新世后研究区部分区域因岩浆活动导致上覆地层隆起和沉积环境变化.分析表明雷琼地区深部低速异常体对表层升降影响有限,推测该深部异常体规模较小,可能是深部更大规模异常体的一个分支.

     

Dynamics of thinning and destruction of the continental cratonic lithosphere: Numerical modeling

Thinning of the cratonic lithosphere is common in nature, but its destruction is not. In either case, the mechanisms for both thinning and destruction are still widely under debate. In this study, we have made a review on the processes and mechanisms of thinning and destruction of cratonic lithosphere according to previous studies of geological/geophysical observations and numerical simulations, with specific application to the North China Craton (NCC). Two main models are suggested for the thinning and destruction of the NCC, both of which are related to subduction of the oceanic lithosphere. One is the “bottom-up” model, in which the deeply subducting slab perturbs and induces upwelling from the hydrous mantle transition zone (MTZ). The upwelling produces mantle convection and erodes the bottom of the overriding lithosphere by the fluid-melt-peridotite reaction. Mineral compositions and rheological properties of the overriding lithospheric mantle are changed, allowing downward dripping of lithospheric components into the asthenosphere. Consequently, lithospheric thinning or even destruction occurs. The other is the “top-down” model, characterized by the flat subduction of oceanic slab beneath the overriding cratonic lithosphere. Dehydration reactions from the subducting slab would significantly hydrate the lithospheric mantle and decrease its rheological strength. Then the subduction angle may be changed from shallow to steep, inducing lateral upwelling of the asthenosphere. This upwelling would heat and weaken the overriding lithospheric mantle, which led to the weakened lithospheric mantle dripping into the asthenosphere. These two models have some similarities, in that both take the subducting oceanic slab and relevant fluid migration as the major driving mechanism for thinning or destruction of the overriding cratonic lithosphere. The key difference between the two models is the effective depth of the subducting oceanic slab. One is stagnation and flattening in the MTZ, whereas the other is flat subduction at the bottom of the cratonic lithosphere. In the NCC, the eastern lithosphere was likely affected by subduction of the Izanagi slab during the Mesozoic, which would have perturbed the asthenosphere and the MTZ, and induced fluid migration beneath the NCC lithosphere. The upwelling fluid may largely have controlled the reworking of the NCC lithosphere. In order to discuss and analyze these two models further, it is crucial to understand the role of fluids in the subduction zone and the MTZ. Here, we systematically discuss phase transformations of hydrous minerals and the transport processes of water in the subduction system. Furthermore, we analyze possible modes of fluid activity and the problems to explore the applied feasibility of each model. In order to achieve a comprehensive understanding of the mechanisms for thinning and destruction of cratonic lithosphere, we also consider four additional possible dynamic models: extension-induced lithospheric thinning, compression-induced lithospheric thickening and delamination, large-scale mantle convection and thermal erosion, and mantle plume erosion. Compared to the subduction-related models presented here, these four models are primarily controlled by the relatively simple and single process and mechanism (extension, compression, convection, and mantle plume, respectively), which could be the secondary driving mechanisms for the thinning and destruction of lithosphere.     

青藏高原东南缘大凉山新生代隆升建造过程——多封闭系统低温热年代学与热模型限制

长波长、低起伏度大凉山构造带新生代隆升剥露与建造过程是解译青藏高原东向扩展过程的关键核心地区之一.本文基于大凉山构造带喜德剖面和沐川剖面9件样品的多封闭系统低温热年代学年龄(即磷灰石(U-Th)/He(AHe)、磷灰石裂变径迹(AFT)和锆石(U-Th)/He(ZHe))定年,揭示出多封闭系统热年代学年龄与古岩性柱深度具有明显的正相关性,即伴随古岩性柱深度增大,多封闭系统热年代学年龄明显减小.喜徳剖面多封闭系统低温热年代学AHe、AFT和ZHe年龄值分别为7-9 Ma、14-22 Ma和25-38 Ma;沐川剖面多封闭系统低温热年代学AHe和AFT年龄值分别为10-26 Ma、23-85 Ma, ZHe年龄值为未完全退火年龄.多封闭系统热年代学和QTQt热史模拟揭示,大凉山构造带喜徳和沐川剖面岩性柱所有样品都经历大致相似的三阶段热演化过程,尤其是晚新生代快速隆升剥露阶段(30-20 Ma以来),其平均剥露速率分别为~0.15 mm·a-1和~0.20 mm·a-1,抬升剥露量分别为~3.0 km和~1.5 km.结合区域低温热年代学特征的大凉山构造带地表隆升动力学模型,揭示出重力均衡作用下地壳缩短与剥露作用(即构造隆升剥露机制)控制形成了现今大凉山造山带长波长、低起伏和高海拔地貌建造过程.     

Crustal and upper mantle structure of the Mediterranean area derived from surface-wave data

A summary of results based mainly on the inversion of available surface-wave dispersion data is given for the Mediterranean area both for crustal and upper mantle structure. The results are presented on maps outlining the regionalization of the crust and the lithosphere-asthenosphere system in the area. It is possible to distinguish several types of crust with average S-wave velocities in the range 2.8–3.8 km s⁻¹ and thickness varying from a minimum of about 10–16 km, in the Western Mediterranean, to a maximum of about 50 km (including a possible transitional layer) beneath the Ionian Sea. The average properties of the crust and of the lithospheric part of the mantle indicate a possible continuous structure extending from North Africa through the Ionian Sea to the Adriatic Sea, characterized by the presence of a transitional layer at the crust-mantle boundary. Strong lateral variations are present in the lithosphere-asthenosphere system both in thickness, from 30 km in the Western Mediterranean, to about 130 km, under the Alps, and in S-wave velocity, from 4.1–4.2 km s⁻¹ up to 4.7 km s⁻¹. The relatively high position of low resistivity material that seems to characterize the Mediterranean area agrees fairly well with the shallower average top of the asthenosphere found in this area from the study of the elastic properties. The usefulness of combining seismological and electromagnetic studies is stressed.     

基于区域重磁解释的南黄海及邻区地质结构构造

通过对南黄海及邻区已有高精度区域重磁资料整理,形成32°-38°N、118°-127°E的1/100万基础数据,结合已有钻井和地震剖面成果进行重磁综合反演与解释,给出了南黄海及邻区主要三级构造区划、断裂发育、古生界地层深度和厚度,以及主要盆地范围及次级凹陷分布,为南黄海前第三系油气前景评价提供了参考依据。     

江西相山火山盆地地质结构研究:来自大地电磁测深及三维地质建模的证据

江西省相山火山盆地是我国第一大、世界第三大火山岩型铀矿田,其西部牛头山一带铀矿勘探中发现深部有大垂幅的Pb-Zn-Ag矿化.60多年来,以该矿田为对象开展的研究取得了一系列丰硕成果,但对火山机构的认识仍不确定.我们采集了涵盖该火山盆地主要地质体的1386块钻孔岩芯标本和243块地表岩石标本,开展了电阻率、磁化率、密度等物性参数测量,并在火山盆地中施测了19条MT剖面（2条骨干剖面和17条精细剖面）,对3000 m以浅主要地层、岩体和断裂带等目标地质体的三维展布特征进行了解译和三维建模.研究结果表明：（1）相山火山盆地具有变质岩-花岗岩双基底.基底变质岩系顶界面表现为南北分带（三隆间两凹）和东西分块（两垒夹一堑）的三维地质格局;南西部有加里东期花岗岩侵入,具有似层状的空间展布特征;盆地基底变质岩系与上覆火山-沉积岩盖层之间呈连续的水平低阻异常带,不整合界面清晰.（2）打鼓顶组火山岩呈似层状产出,主要分布于盆地西部;在河元背-船坑-杏树下一带识别出近东西走向厚层的流纹英安岩凹槽,相山铀矿田西部探明的主要铀矿床分布在该凹槽内或其边缘.鹅湖岭组火山岩总体形态呈蘑菇状,在盆地中部厚度较大.在相山主峰半径约2 km的范围内,发现自下而上贯通式的低阻异常,推测是鹅湖岭组碎斑熔岩喷发的通道相（火山颈相）,其火山颈呈陡立管状,深部向南东倾伏,浅部向南东撒开.后期花岗斑岩呈岩墙-岩床组合状,总体构成一个向西开口的环形岩体.打鼓顶期主要岩浆通道位于相山顶-巴山之间,次岩浆通道位于河元背;鹅湖岭期火山活动主岩浆通道也位于相山顶-巴山之间,次岩浆通道位于河元背、阳家山（芙蓉山）、严坑和柏昌.（3）火山盆地中断裂构造发育,MT测量结果显示存在7条北东向、4条北西向和1条南北向格架性断裂构造（其中一条新发现的北东向断裂隐伏于白垩纪红盆之下）,盆地北部发育1条弧形火山塌陷构造,表现为大规模延续的低阻异常带.

     

山东齐河—禹城地区深部地质构造特征——来自大地电磁的证据

近年来,山东齐河—禹城地区矽卡岩型铁矿找矿工作取得重大进展,有望成为山东省内重要的富铁矿基地.但该地区覆盖层厚,深部异常信息难以获取,因此对控矿岩体的研究仍然相对薄弱.为此在该区布设了4条大地电磁剖面,采用夜间12 h采样时长、G-B阻抗张量分解法、二维非线性共轭梯度反演技术措施,并与航重、航磁、钻孔资料,联合反演获得了各剖面厚覆盖层之下侵入岩体的顶界面、岩体的侵入边界、地层结构及断层位置.依据所推断的岩体边界和断层位置处磁异常Tilt梯度特征,重新圈定了研究区内岩体的边界和断层位置,共圈定隐伏岩体5个,断层9条.断层间相互关系表明在岩体侵入之后,本区地质构造运动仍然比较显著,要重视后期构造作用对区内铁矿体的改造,区内构造活动剧烈部位是今后重点研究对象.通过研究发现,在厚覆盖区,利用大地电磁、航重、航磁、钻探资料综合反演解释,进行隐伏地质构造研究,是一种有效的方法组合.     

Numerical modeling of thermal evolution in the contact aureole of a 0.9 m thick dolerite dike in the Jurassic siltstone section from Isle of Skye,Scotland

In this study, we present a heat-transfer-model analysis of thermal evolution in the contact aureole of a 0.9 m thick dolerite dike in the Jurassic siltstone section from Isle of Skye, Scotland based on the constraints from the two types of vitrinite-reflectance geothermometers as well as geochemistry and burial history of host rocks. The predictions from the heat conduction models assuming the finite-time magma intrusion mechanism and pore-water volatilization can match well with both measured vitrinite reflectances and geological conditions of the host rocks. In the region where pore water volatilized and vitrinite reflectance rises with decreasing distance to the dike contact, the bomb geothermometer is consistent with the EASY%Ro model in validating the thermal evolution history of the host rocks, whereas it loses the function of temperature indicator out of the volatilization region. Possibly, the pore-water volatilization influenced the reliability of the bomb geothermometer. The computed total organic carbon contents based on the reconstructed thermal evolution history and the EASY%Ro model present the general agreement with the measured values, demonstrating the availability of the EASY%Ro model in indicating organic-matter transformation ratios at contact metamorphic conditions.     

城市冠层结构热力效应对城市热岛形成及强度影响的模拟研究

本文在城市边界层预报模式中耦合了一个单层冠层模式,此模式能够体现城市冠层结构和人为热源对城市热岛的共同作用.通过传统平板模式和城市冠层模式的模拟结果与自动气象站观测资料对比发现,耦合了城市冠层模式的模拟结果与观测资料更为吻合,尤其能够较好地模拟出城市地区夜间地面的气温变化情况.对北京城市区域的模拟结果进行分析,白家庄地区冠层建筑物使得城市地区气温白天下降,夜晚上升,不考虑人为热源作用时,城市冠层使得白家庄站地面气温白天最低下降2.5℃,夜间气温最大升高为4.7℃.针对模拟区域较小的理想算例模拟结果分析表明,城市冠层模式能够很好地模拟城市地区地表能量平衡关系,体现城市冠层对长短波辐射的封截以及热量存储能力,全天平均净辐射通量由传统模式的43.38 W/m2变为84.19 W/m2,热存储通量白天最大值为278.04 W/m2,夜晚最大释放热存储通量为160.35 W/m2.冠层建筑物和人为热源对夜间城市热岛强度的贡献分别为70.65％和29.35％.城市冠层建筑物对夜间城市热岛的形成起决定性作用.     

Hydrology and water quality in two mountain basins of the northeastern US: assessing baseline conditions and effects of ski area development

Mountain regions throughout the world face intense development pressures associated with recreational and tourism uses. Despite these pressures, much of the research on bio‐geophysical impacts of humans in mountain regions has focused on the effects of natural resource extraction. This paper describes findings from the first 3 years of a study examining high elevation watershed processes in a region undergoing alpine resort development. Our study is designed as a paired‐watershed experiment. The Ranch Brook watershed (9·6 km²) is a relatively pristine, forested watershed and serves as the undeveloped ‘control’ basin. West Branch (11·7 km²) encompasses an existing alpine ski resort, with approximately 17% of the basin occupied by ski trails and impervious surfaces, and an additional 7% slated for clearing and development. Here, we report results for water years 2001–2003 of streamflow and water quality dynamics for these watersheds. Precipitation increases significantly with elevation in the watersheds, and winter precipitation represents 36–46% of annual precipitation. Artificial snowmaking from water within West Branch watershed currently augments annual precipitation by only 3–4%. Water yield in the developed basin exceeded that in the control by 18–36%. Suspended sediment yield was more than two and a half times greater and fluxes of all major solutes were higher in the developed basin. Our study is the first to document the effects of existing ski area development on hydrology and water quality in the northeastern US and will serve as an important baseline for evaluating the effects of planned resort expansion activities in this area. Published in 2007 by John Wiley & Sons, Ltd.     

Three-dimensional structure of inclined sheet swarms: Implications for crustal thickening and subsidence in the volcanic rift zones of Iceland

Inward-dipping (cone) sheet swarms and an associated central volcano are well-exposed in the deeply-eroded Tertiary crust of Vatnsdalur, Skagi Peninsula region, northern Iceland. Spatially registered orientations of 389 mafic sheets, mapped in three distinct sheet swarms define both the overall shape and magmatic source of each swarm. The Vatnsdalur sheet swarms consist of planar inward-dipping sheets that collectively define a conical shape rather than a bowl- or trumpet-shape as have been found in swarms in other locations. In the best exposed swarm, three-dimensional projection of mafic sheets into the subsurface defines two distinct foci, which are interpreted as the magmatic sources of two temporally distinct sub-swarms. These results help to establish the influence of inclined sheet intrusion on crustal accretion at central volcanoes. The geometry of the swarm constrains the thickness of material that was added to the crust during sheet intrusion. When combined with estimates of surface relief, we calculate that 2.2 to 4.1 km of subsidence were required beneath the central volcano in order to accommodate the intrusion of the sheet swarm. Similar processes of crustal thickening and subsidence likely occur in a wide variety of both continental rift and mid-ocean ridge systems where magmatic activity is focused at central volcanoes.     

Turbulence structure in the upper ocean: a comparative study of observations and modeling

Observations of turbulent dissipation rates measured by two independent instruments are compared with numerical model runs to investigate the injection of turbulence generated by sea surface gravity waves. The near-surface observations are made by a moored autonomous instrument, fixed at approximately 8 m below the sea surface. The instrument is equipped with shear probes, a high-resolution pressure sensor, and an inertial motion package to measure time series of dissipation rate and nondirectional surface wave energy spectrum. A free-falling profiler is used additionally to collect vertical microstructure profiles in the upper ocean. For the model simulations, we use a one-dimensional mixed layer model based on a k–ε type second moment turbulence closure, which is modified to include the effects of wave breaking and Langmuir cells. The dissipation rates obtained using the modified k–ε model are elevated near the sea surface and in the upper water column, consistent with the measurements, mainly as a result of wave breaking at the surface, and energy drawn from wave field to the mean flow by Stokes drift. The agreement between observed and simulated turbulent quantities is fairly good, especially when the Stokes production is taken into account.