Structure and physical properties of the garth＇s interior

The studies on the structure and physical properties of the Earth‘s interior done by Chinese geophysicists from 1999 to 2002 were reviewed in this paper. It includes several research areas: the structure of the Earth‘s interiors using seismic tomography, anisotropy of the upper mantle in China and its adjacent areas, quality factor Qβ for S waves, subduction zone, mantle discontinuities, physical properties of Earth‘s materials and others. The review concerns mainly the contents, the methods and the results of the studies. It can be seen that new progress in the study on the structure and physical properties of the Earth‘s interior has been made in the last 4 years in China. It is shown on three aspects: advancement made on some preexistent areas; pioneering on some new fields and new methods adopted.     

地球内部结构及物性研究的进展及问题

本文对近几年中国地球物理学家在地球内部结构和物质性质方面的研究工作进行总结.从地球内部结构的地震波速度成像,地幔介质的各向异性,地幔间断面及地幔介质物性进行了综述,指出在一些原有的研究领域,工作更加深入,方法更加先进,而且进行了广泛的国际合作,合作的范围也逐渐扩大,方式多样,并开拓了一些新的研究方向.在肯定我们近几年取得的一些新的进展的同时,也提出了地球内部结构研究中应进一步研究的问题.     

P.ecent progress in studies of experimental rock mechanics and tectonophysics in China

This paper reviews the recent progress in the studies of experimental rock mechanics and tectonophysics concern-ing seismology and physics of the Earth‘s interior in China. The progress is presented in the following aspects: a) A lot of results of experiment and numerical simulation enrich our knowledge of the brittle fracturing process under the condition with heterogeneity in material and structure; b) Some new results on frictional behavior of non-homogeneous faults reveal the complexity of faulting behavior; c) Some new results on the brittle-plastic tran-sition and plastic flow are obtained; especially the important progress is obtained on theological properties of rocks in the lower crust and the upper mantle; d) A lot of experimental results are obtained on rock physics at high tem-perature and pressure and have been used in study of material composition and state. These results provide useful information for understanding the physical properties and deformation mechanisms of material of the Earth‘s inte-rior and earthquake physics.     

Progress in studies on the structure and physical properties of the mantle in China

The studies on the structure and physical properties of the mantle by Chinese geophysicists from 2003 to 2007 are reviewed in this report. It mainly contains studies on the seismic velocity structure of the mantle,anisotropy of the mantle,mantle discontinuities,mantle convection and the physical properties of mantle. The review concerns mainly the contents,the methods used and the results of the studies. It can be found that new progress in the study on the structure and physical properties of mantle has been made in the last four years in China. In some preexis-tent areas much progress has been made,advanced methods have been adopted,extensive international co-operation has been conducted in many ways,and the scope of the co-operation has gradually expanded. More-over,some new fields appear as well.     

地幔内部间断面研究的进展

随着数字化地震台网的普及和利用以及计算机分析处理技术的提高，近几年利用地震波研究地幔内部间断面有了一定的进展。本文概述了近年来国内外有关学者对地幔内部间断面的认识，采用的研究方法及研究动态。     

地幔粘度结构的研究

地幔的流变性质已成为认识地球内部结构及动力学过程的核心问题之一。本文总结了近年来地幔粘度结构研究的方法,其中包括利用地球物理观测资料进行反演计算和实验室试验研究,重点讨论了利用冰期后回跳,板块运动速度和大地水准面异常资料反演地幔粘度结构２的方法和结果以及地幔矿物的实验结果,并对不同方法进行了比较总结。最后简单讨论了地幔粘度结构研究存在的问题和未来的研究方向。     

液核动力学扰动引起的地球形变

讨论了地球固体部分对液核动力学效应引发的核幔边界和内核边界上压力和引力扰动的形变响应．采用弹性-引力形变理论描述地幔和内核的形变，给出了内部负荷Love数的一般表达式．以初始参考地球模型为例，分别计算了在地球表面、核幔边界和内核边界上的内部负荷Love数．探讨了液核边界上压力和引力扰动导致的地球形变场的空间和频率分布特征．本文的结果可以为中短周期液核动力学理论模拟提供必要的边界条件．      

上地幔高导层与内生金属矿产及油气藏的关系

依据大地电磁测深所发现的上地幔高导层顶面深度可以给出大陆岩石圈-软流圈界面(LAB)的空间发育特征,为认识岩石圈结构及壳幔相互作用等提供重要信息.本文在1996年编制的中国大陆上地幔高导层顶面深度图的基础上,补充了1995—2010年大地电磁测深结果和大地热流数据,以1°×1°网度编制了新的中国大陆上地幔高导层顶面深度图.我国上地幔高导层顶面深度变化很大,具有南北分带,东西分块的特征,呈东浅、西深、北浅、南深的格局,从最浅的50~60km到最深的230km,平均深度为100~120km.据上地幔高导层顶面分布形态,全国共可划分出27个隆起区.通过与中国已知内生金属矿产和油气田的分布对比,发现我国大陆80%以上中生代内生金属矿床分布在上地幔高导层隆起带或其梯度带上方.中国大陆东部含油气盆地主体对应上地幔隆起区,油气田多位于隆起区上方或其边部的过渡带上;西部主体位于幔坳区,主要油气田对应盆地中心的幔坳向周边幔隆过渡的梯度带上;中部表现为仅盆地腹地对应幔坳,盆地周边对应规模较大的上地幔隆起带,主要油气田位于隆起带.总的来看内生金属矿床一般分布在上地幔隆起区靠近造山带一侧,而油气田一般分布在上地幔隆起区靠近盆地一侧.软流圈的不断上隆,造成岩石圈减薄、拉张,张性断裂的出现成为地球深部物质和热量向地壳上部运移的有利通道,为内生金属矿产的形成提供了成矿物质和能量保障,也为含油气盆地带来了生烃催化剂、热能和无机成因的石油与天然气.地球深部超临界流体的存在对上地幔高导层的形成、成矿物质运移可能发挥了重要作用.     

秦岭造山带与邻域华北克拉通和扬子克拉通的壳、幔精细速度结构与深层过程

秦岭造山带与其南北两侧华北克拉通和扬子克拉通属三大构造单元,不论其各构造单元体还是其界带构造均甚为复杂,并受到多期次构造运动的制约,形成了大陆内部特异的造山过程.尽管在这一地域曾做过大量的地表地质工作和一些相关的地球物理工作,但对其壳、幔精细结构、深层动力过程,特别是同步穿越华北克拉通、秦岭-大巴造山带和扬子克拉通系统的耦合研究甚少.为了研究和探索该地域的壳、幔精细速度结构和其形成的深层过程,专门布置了一条北起榆林,向南经咸阳、宁陕直抵涪陵长达1000 km的高精度地震宽角反射、折射波场探测剖面.通过剖面辖区高分辨率的数据采集,数据处理、反演和壳、幔层、块精细速度结构,发现剖面辖区深部壳、幔结构存在特异的速度和结构变化,并厘定了一系列的新认识.研究结果表明:(1)秦岭—大巴造山带具有同一基底,其形成乃为结晶基底隆升所致,即它的形成仅涉及到上地壳的受力变形和空间状态.造山带与其南、北两侧的前陆盆地为陆内造山过程中同一深层过程的产物,但其沉积速率和形态却不相同.华北克拉通与秦岭造山带之间前陆盆地B_fc拉张为该区Moho界面的局部隆升所致.(2)首次提出了沿1000 km长剖面连续的沉积建造、结晶基底、上地壳、下地壳和上地幔顶部的层、块速度结构和各界面的起伏变化与空间状态.基于地震波边界场响应厘定了华北克拉通、秦岭—大巴造山带和扬子克拉通的分区界带.论述了三大构造单元各自的内部结构和其相邻界域的速度变化特征.(3)该区大陆内部速度结构和不同类型断裂分布及层序在华北克拉通、秦岭—大巴造山带、扬子克拉通三大块体地域存在显著差异.不同规模、层次与产状的断裂分布反映出它们在变形行为和机制上及所受构造运动的制约上均存在明显的差异.     

Electrical Structure in Marine Tectonic Settings

This review paper presents recent research on electrical conductivity structure in various marine tectonic settings. In at least three areas, marine electromagnetic studies for structural exploration have increasingly progressed: (1) data accumulations, (2) technical advances both for hardware and software, and (3) interpretations based on multidisciplinary approaches. The mid-ocean ridge system is the best-studied tectonic setting. Recent works have revealed evidence of conductive zones of hydrothermal circulation and axial magma chambers in the crust and partial melt zones of the mid-ocean ridge basalt source in the mantle. The role of water or dissolved hydrogen and its redistribution at mid-ocean ridges is emphasized for the conductivity pattern of the oceanic lithosphere and asthenosphere. Regions of mantle upwelling (hotspot or plume) and downwelling (subducting slab) are attracting attention. Evidence of heterogeneity exists not only in the crust and the upper mantle, but also in the mantle transition zone. Electrical conductive zones frequently overlap seismic low-velocity zones, but discrepancies are also apparent. Some studies have compared conductivity models with the results of seismic and other studies to investigate the physical properties or processes. A new laboratory-based conductivity model for matured oceanic lithosphere and asthenosphere is proposed. It takes account of both the water distribution in the mantle as well as the thermal structure. It explains observed conductivity patterns in the depth range of 60–200 km.     

20世纪90年代我国对地壳上地幔结构的人工地震探测研究

介绍了20世纪90年代我国人工地震探测在研究大震区和潜在震源区深部细结构，发震构造的深部特征、介质物性，地壳和上地幔结构与地球动力学过程，火山深部结构，油气生成的深部构造环境等方面取得的成果，以及人工地震资料解释中P波和S波的联合应用，浅层地震反射法在地壳浅层细结构、深浅构造关系研究方面取得的进展。     

Lithospheric structure and evolution of the North China Craton:An integrated study of geophysical and xenolith data

Determination of the physical and chemical structures of the inaccessible continental lithosphere by comprehensive geophysical and geochemical studies can provide valuable information on its formation and evolution.Extensive studies from various disciplines have revealed complex lithospheric modification of the North China Craton(NCC),but less attention has been paid to an integrated study from different fields.Here we provide an integrated constraint on the lithospheric mantle structure of the NCC by comprehensive semiology,gravity and thermal studies with xenolith data involving depth(levels in the lithosphere),property(chemical and physical),and timing(formation and reworking ages).Our results suggest that the NCC has a relatively heterogeneous lithospheric mantle.Its margins and internal weak zones,especially in the eastern NCC,are generally underlain by the fertile,weakly metasomatized mantle with generally young formation ages.In contrast,its core tends to preserve the refractory,strongly metasomatized mantle with ages roughly coupled to the overlying Archean crust.Such a lithospheric structure shows the preferential modification of the lithospheric mantle in the eastern NCC and in the peripheral regions of the western NCC.The interior of the craton,especially most of the western NCC,remains stable and has been weakly modified.     

南海北部陆缘珠江口盆地岩石圈热结构

沉积盆地岩石圈热结构特征是岩石圈构造-热演化过程的综合反映和盆地热史恢复的约束条件,对盆地动力学研究和油气资源评价具有重要意义.由于海洋勘探难度大、勘探程度低,相对于大陆地区,边缘海盆地比较缺乏岩石圈热结构方面的研究.本文在收集整理珠江口盆地及邻区大地热流数据的基础上,补充收录了自2003年以来发表的新数据,绘制了研究区最新版的大地热流等值线图;基于中美合作双船地震剖面揭示的深部地壳结构计算了研究区的壳-幔热流、深部温度以及"热"岩石圈厚度.研究表明,珠江口盆地地壳热流介于18.7~28.6 mW·m^-2,地幔热流介于36.9~91.4 mW·m^-2,壳幔热流比值0.23~0.75;由陆架、陆坡至中央海盆,在地壳热流逐渐减小的情况下地表热流逐渐递增,说明地表热流分布主要受深部热作用控制;盆地"热"岩石圈厚度介于34.0~87.2 km,平均65.5 km,反映出显著拉张减薄的特征.     

南海深部地球动力学特征及其演化机制

利用地热学、流变学和重力学方法，计算了南海岩石层温度结构、流变特征及地幔对流格局.南海莫霍面温度在600-1000℃之间.岩石层底界面温度在1150-1300℃之间，有效粘滞系数为1020-1021Pa·s，与冰期回弹资料确定的地幔粘度吻合，表明南海深部具备产生地幔热对流的物理条件.研究认为地幔物质由北西向南东方向的运移以及印澳-欧亚板块的碰撞，导致南海北部大陆边缘向洋扩张、离散和断裂解体.在向洋离散过程中，陆-洋岩石层底部地幔局部对流使中央海盆扩张和北部陆缘发生差异性块断运动.     

Subduction tectonics vs.plume tectonics——Discussion on driving forces for plate motion

Plate tectonics describes the horizontal motions of lithospheric plates,the Earths outer shell,and interactions among them across the Earths surface.Since the establishment of the theory of plate tectonics about half a century ago,considerable debates have remained regarding the driving forces for plate motion.The early"Bottom up"view,i.e.,the convecting mantledriven mechanism,states that mantle plumes originating from the core-mantle boundary act at the base of plates,accelerating continental breakup and driving plate motion.Toward the present,however,the"Top down"idea is more widely accepted,according to which the negative buoyancy of oceanic plates is the dominant driving force for plate motion,and the subducting slabs control surface tectonics and mantle convection.In this regard,plate tectonics is also known as subduction tectonics."Top down"tectonics has received wide supports from numerous geological and geophysical observations.On the other hand,recent studies indicate that the acceleration/deceleration of individual plates over the million-year timescale may reflect the effects of mantle plumes.It is also suggested that surface uplift and subsidence within stable cratonic areas are correlated with plumerelated magmatic activities over the hundred-million-year timescale.On the global scale,the cyclical supercontinent assembly and breakup seem to be coupled with superplume activities during the past two billion years.These correlations over various spatial and temporal scales indicate the close relationship and intensive interactions between plate tectonics and plume tectonics throughout the history of the Earth and the considerable influence of plumes on plate motion.Indeed,we can acquire a comprehensive understanding of the driving forces for plate motion and operation mechanism of the Earth's dynamic system only through joint analyses and integrated studies on plate tectonics and plume tectonics.     

Global P-wave tomography: On the effect of various mantle and core phases

In this work, many global tomographic inversions and resolution tests are carried out to investigate the influence of various mantle and core phase data from the International Seismological Center (ISC) data set on the determination of 3D velocity structure of the Earth's interior. Our results show that, when only the direct P data are used, the resolution is good for most of the mantle except for the oceanic regions down to about 1000 km depth and for most of the D″ layer, and PP rays can provide a better constraint on the structure down to the middle mantle, in particular for the upper mantle under the oceans. PcP can enhance the ray sampling of the middle and lower mantle around the Pacific rim and Europe, while Pdiff can help improve the spatial resolution in the lowermost mantle. The outer core phases (PKP, PKiKP and PKKP) can improve the resolution in the lowermost mantle of the southern hemisphere and under oceanic regions. When finer blocks or grid nodes are adopted to determine a high-resolution model, pP data are very useful for improving the upper mantle structure. The resulting model inferred from all phases not only displays the general features contained in the previous global tomographic models, but also reveals some new features. For example, the image of the Hawaiian mantle plume is improved notably over the previous studies. It is imaged as a continuous low velocity anomaly beneath the Hawaiian hotspot from the core-mantle boundary (CMB) to the surface, implying that the Hawaiian mantle plume indeed originates from the CMB. Low-velocity anomalies along some mid-oceanic ridges extend down to about 600 km depth. Our results suggested that later seismic phases are of great importance in better understanding the structure and dynamics of the Earth's interior.     

Deep electrical conductivity features in the transition zone from the Pacific to Eurasia

Understanding the processes that occur in the transition from the Pacific Ocean to Eurasia is key to constructing the tectonic models of the Earth’s shells and the convection models of the upper mantle. The electromagnetic methods permit estimating the temperature and fluid content (and/or carbon (graphite) content) in the Earth’s interior. These estimates are independent of the traditionally used estimates based on seismic methods because the dependence of electrical conductivity on the physical properties of the rock is based on different principles than the behavior of the elastic waves. The region is characterized by a complicated geological structure with intense three-dimensional (3D) surface heterogeneities, which significantly aggravate the retrieval of the information about the deep horizons in the structure of the Earth’s mantle from the observed electromagnetic (EM) fields. The detailed analysis of the nature of the deep electrical conductivity and structural features of the transition from the Pacific to Eurasia included numerical modeling of the typical two- and three-dimensional models has been carried out. Based on this analysis, the approaches that increase the reliability of the interpretation of the results of the EM studies are suggested.     

On Earth’s Mantle Constitution and Structure from Joint Analysis of Geophysical and Laboratory-Based Data: An Example

Determining Earth’s structure is a fundamental goal of Earth science, and geophysical methods play a prominent role in investigating Earth’s interior. Geochemical, cosmochemical, and petrological analyses of terrestrial samples and meteoritic material provide equally important insights. Complementary information comes from high-pressure mineral physics and chemistry, i.e., use of sophisticated experimental techniques and numerical methods that are capable of attaining or simulating physical properties at very high pressures and temperatures, thereby allowing recovered samples from Earth’s crust and mantle to be analyzed in the laboratory or simulated computationally at the conditions that prevail in Earth’s mantle and core. This is particularly important given that the vast bulk of Earth’s interior is geochemically unsampled. This paper describes a quantitative approach that combines data and results from mineral physics, petrological analyses of mantle minerals, and geophysical inverse calculations, in order to map geophysical data directly for mantle composition (major element chemistry and water content) and thermal state. We illustrate the methodology by inverting a set of long-period electromagnetic response functions beneath six geomagnetic stations that cover a range of geological settings for major element chemistry, water content, and thermal state of the mantle. The results indicate that interior structure and constitution of the mantle can be well-retrieved given a specific set of measurements describing (1) the conductivity of mantle minerals, (2) the partitioning behavior of water between major upper mantle and transition-zone minerals, and (3) the ability of nominally anhydrous minerals to store water in their crystal structures. Specifically, upper mantle water contents determined here bracket the ranges obtained from analyses of natural samples, whereas transition-zone water concentration is an order-of-magnitude greater than that of the upper mantle and appears to vary laterally underneath the investigated locations.     

地震层析成像板块构造及地幔演化动力学

地震层析成像技术的飞速发展给人类提供了一个探测地球内部结构的强有力的工具，也给人类展示了一片新的天地，使人类更加清晰地在两个层次之上（地球的层圈构造和内部横向不均匀性）了解地球内部，特别是对幔内部非均匀结构，从全球和区域的尺度上揭示出地球内部特别是地壳和上地幔横向不均匀结构。呈现出全新的地球，特别是地幔结构的三维图像框架，很容易理解，这一基本框架正是地幔演化热动力学过程的现代表现，如此，我们可以利用该框架去追溯、探讨全球构造特别是地幔构造演化的历史，从而深化对于我们这个星球演化过程的理解。     

Redox state of amphibole-bearing mantle peridotite from Nüshan, Anhui Province in eastern China and its implications

Using secondary spinel standard method, we have measured precisely the compositions of spinels of amphibole-bearing mantle peridotite xenoliths from Nüshan in eastern China, and calculated the mantle oxygen fugacities recorded by the xenoliths. Results indicate that the mantle metasomatism for forming amphiboles in Nüshan region of Anhui has resulted in the decrease of mantle redox, which is in contrast with theoretical estimation and previous research results from other areas around the world. Combining with related studies on the mantle of eastern China, we give a reasonable explanation to the ‘new finding’ and further elucidate the compositions and nature of mantle fluids in eastern China.