Comparison of recent crustal movements with quaternary movements in japan and its plate-tectonic implication

Recent crustal movements may be classified into two categories: one being associated with major earthquakes and the other being creep deformations without a direct association with any major earthquake. The spatial distribution of the rate of creep deformation during the last 70 years as detected by the precise re-leveling, shows a similar configuration on a map to the distribution of amount of Quaternary vertical movements, throughout the Japanese Islands with the exception of Hokkaido.Comparison of the rate of recent movement with the total amount of Quaternary movement suggests the following two interpretations, which have the advantage of simplicity compared with other possibilities:

1. (1) The rate of the recent movements is four times larger than the average rate for the Quaternary.

2. (2) If the rate of crustal movements is almost uniform as most of creep deformations can be shown to be, then the Quaternary movements must have started about 0.5 million years ago.

Nevertheless, the author suggested in 1967, that the active period of Quaternary tectonic movements might have begun about one million years ago. This suggestion was based upon the measurement of the total amount of movement compared with the rate of movement as detected from the deformation of late Quaternary terraces. These tectonic movements, naturally include the crustal movements associated with major earthquakes.

It is highly probable that the movements associated with major earthquakes and the creep deformations not directly associated with major earthquakes became active at the same time. If so, a third interpretation could be advanced:

3. (3) The rate of the recent creep deformations is about twice the average, and the crustal movements in the Japanese Islands commenced their active period about one million years ago.

On the basis of a bend in the hot-spot trace along the Hawaiian volcanic chain, the Pacific plate seems to have changed the position of its rotation axis and its angular velocity about one million years ago. The agreement of both of these dates with the increasing rates of activity suggests that the Quaternary tectonic movement in Japan was activated by the change in the pole of rotation of the Pacific plate which took place at about one million years ago and in doing so caused the bend in the eastern end of the Hawaiian island chain.     

开合构造在不同时空尺度下的地学表现

开合构造是研究地球开合运动及其构造特征,分析开合构造体系的形成机制,探索地球成因和演化的一种新假说。不同时空尺度的开合构造在地学上存在不同的表现,需要从不同角度开展研究。以亚欧非邻区巨型开合构造区、地中海大型开合构造区、东大别中型开合构造区为例,研究了开合构造理论在大地构造分区、地震活动以及现代大地测量结果解释等方面的应用。研究表明:(1)依据开合构造观点可将亚欧非邻区巨型开合构造划分为俄罗斯构造集群、非洲构造集群、北亚构造集群、中亚构造集群、南亚构造集群及东亚构造集群;(2)亚欧非邻区的强地震活动与构造集群间的新生代开合构造转换带关系密切;(3)地中海大型开合构造区内的地震剖面及震源机制揭示了地中海—土耳其—伊朗—阿富汗构造转换带现今构造运动主要以合为主;(4)东大别中型开合构造周边的狮子山、黄梅、麻城等台站的地倾斜和地应变、周边GNSS和流动重力观测结果揭示了该区周边存在时间尺度较短、量级较弱的由“合”向“开”的趋势转变,开合运动是近期诸多观测数据趋势出现准同步性变化的共同机理。     

天山与阴山─燕山造山带的深部结构和地震

天山与阴山-燕山是中国北部两个重要山系,它们几乎位于同一纬度。天山造山带是一个著名的地震活动带,而阴山-燕山断隆带历史上不但没有大地震发生,小地震也不多见,是一个地震空白区。这两个造山带地震活动性的差异与它们在时、空域中的构造环境相联系：中国的西部处于强烈的挤压环境,而东部为一伸展与走滑环境。天山造山带是中、新生代造山带,目前构造活动水平较高;而阴山-燕山造山带新生代以来已经成为东北稳定块体的一部分,其构造活动的鼎盛期已经过去,目前构造活动水平较低。地震的孕育、发生与深部构造环境密切相关。天山地震带的地壳内部,发育壳内高导层与低速层,地壳结构复杂;阴山-燕山造山带下面没有发现壳内高导层与低速层,整个地壳结构比较简单。壳内低速层、高导层的存在表明地质构造活动强烈,是地震带的重要标志之一,也是地震孕育、发生的深部动力学条件。     

天山与阴山─燕山造山带的深部结构和地震

天山与阴山-燕山是中国北部两个重要山系,它们几乎位于同一纬度。天山造山带是一个著名的地震活动带,而阴山-燕山断隆带历史上不但没有大地震发生,小地震也不多见,是一个地震空白区。这两个造山带地震活动性的差异与它们在时、空域中的构造环境相联系：中国的西部处于强烈的挤压环境,而东部为一伸展与走滑环境。天山造山带是中、新生代造山带,目前构造活动水平较高;而阴山-燕山造山带新生代以来已经成为东北稳定块体的一部分,其构造活动的鼎盛期已经过去,目前构造活动水平较低。地震的孕育、发生与深部构造环境密切相关。天山地震带的地壳内部,发育壳内高导层与低速层,地壳结构复杂;阴山-燕山造山带下面没有发现壳内高导层与低速层,整个地壳结构比较简单。壳内低速层、高导层的存在表明地质构造活动强烈,是地震带的重要标志之一,也是地震孕育、发生的深部动力学条件。     

Crustal Composition of China Continent Constrained from Heat Flow Data and Helium Isotope Ratio of Underground Fluid

Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58–1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K2O in China crust are in ranges of 0.83–1.76 μg/g, 3.16–6.69 μg/g, and 1.0%–2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China’s continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986), and Wedepohl (1995) overestimate the abundance of incompatible elements such as U, Th and K of continental crust.     

Crustal density structure from 3D gravity modeling beneath Himalaya and Lhasa blocks,Tibet

The Himalaya and Lhasa blocks act as the main belt of convergence and collision between the Indian and Eurasian plates. Their crustal structures can be used to understand the dynamic process of continent–continent collision. Herein, we present a 3D crustal density model beneath these two tectonic blocks constrained by a review of all available active seismic and passive seismological results on the velocity structure of crust and lower lithosphere. From our final crustal density model, we infer that the present subduction-angle of the Indian plate is small, but presents some variations along the west–east extension of the orogenic belt: The dip angle of the Moho interface is about 8–9° in the eastern and western part of the orogenic belt, and about 16° in the central part. Integrating crustal P-wave velocity distribution from wide-angle seismic profiling, geothermal data and our crustal density model, we infer a crustal composition model, which is composed of an upper crust with granite–granodiorite and granite gneiss beneath the Lhasa block; biotite gneiss and phyllite beneath the Himalaya, a middle crust with granulite facies and possible pelitic gneisses, and a lower crust with gabbro–norite–troctolite and mafic granulite beneath the Lhasa block. Our density structure (<3.2 g/cm³) and composition (no fitting to eclogite) in the lower crust do not be favor to the speculation of ecologitized lower crust beneath Himalaya and the southern of Lhasa block.     

中国新生代准造山运动

新生代地质时期如同前期地质时期一样,同样发生过造山运动,由于地质历史时期的短暂或运动正在发展过程之中,其强烈程度显示较差,往往不被人们所注意。但是,只要中研究中国大小山川构造地貌发展过程,不难看出新徨代时期,特别是第四纪地质时期是造成璀构造地貌形态的主要时期,或者是说最新造山运动时期。本文主要涉及陆内区的准造山运动。     

Division of tectonic–strata superregions in China

The continent of China is grouped into Pan–Cathaysian blocks, Laurasia and Gondwana Continental margins and relics of three oceans-Paleoasian, Tethys, and Pacific as a whole. In detail, the continent of China grew up by coalescence of three blocks or platforms (North China, Tarim and Yangtze) and eight orogenic belts (Altay–Inner Mongolia–Daxinganling, Tianshan–Junggar–Beishan, Qinling–Qilian– Kunlun, Qiangtang–Sanjiang, Gangdisê, Himalaya, Cathaysia, Eastern Taiwan) during the processes of oceanic crust disappearance and acceretionary-collision of continental crusts. In the orogenic belts, six convergent crustal consumption zones (Ertix–Xar Moron, South Tianshan, Kuanping–Foziling, Bangong co–Shuanghu–Nujiang–Changning–Menglian, Yarlung–Tsangpo, Jiangshao–Chenzhou–Qinfang) have been distinguished. Correspondingly, the strata of the continent of China are subdivided into 17 tectonic-strata superregions, which tectonically belong to three blocks or platforms, six convergent crustal consumption zones and eight orogenic series, respectively. This division is based mainly on differences of tectonic environment and tectonic evolution among blocks, zones and belts, including the timing of when the oceanic crusts transferred into continental crusts, the paleobiogeographic features, and the types of strata.     

Origin and formational history of some Pb-Zn deposits from Alborz and Central Iran: Pb isotope constraints

Several Pb-Zn deposits and occurrences within Iran are hosted by Mesozoic–Tertiary-aged sedimentary and igneous rocks. This study reports new Pb isotope analyses for galena from 14 Pb-Zn deposits in the Alborz and Central Iran structural zones. In general, Pb isotope ratios are extremely variable with data plotting between the upper crustal and orogenic curves in a plumbotectonic diagram. The latter may be attributed to Pb inputs from crustal and mantle end-members. Most of the galena samples are characterized by high ²⁰⁷Pb/²⁰⁴Pb ratios, suggesting significant input of Pb from old continental crust or pelagic sediment. Pb isotope data also indicate that some of the deposits, which are hosted by sedimentary rocks in Central Iran and Alborz, have similar Pb isotopic compositions and hence suggest similar source regions. Most of the galenas yield Pb model ‘ages’ that vary between ~140 and ~250 Ma, indicating that mineralization resulted from the extraction of ore-bearing fluids from Upper Triassic–Lower Jurassic sequences. The similarity in Pb isotope ratios for the Pb-Zn deposits located within these zones suggests analogous crustal evolution histories. Our preferred interpretation is that Pb-Zn mineralization within the sedimentary and igneous rocks of the Central Iran and Alborz tectonic regions occurred following a Late Cretaceous–Tertiary accretionary stage of crustal thickening in Iran.     

Seismic Velocity Structure and Composition of the Continental Crust of Eastern China

On the basis of a one-by-one latitude-longitude grid three-dimensional seismic velocity model, the crustal P-wave velocity structure in eastern China (105-125°E and 18-41°N) is obtained, and a set of geotherms for each grid is established for P-T correction on P-wave velocities. The average depths of sub-crustal layers and their average P-wave velocities of 18 tectonic units in eastern China are exhibited. Our result presents a 32-34 km thick crust beneath eastern China, which is thinner than previous studies, with an average velocity of 6.54 km/s, corresponding to a 5 kg/m3 variation in crustal mean density. The thicker upper but thinner middle and lower crust results in a lower average seismic velocity of eastern China. An intermediate crustal composition with a SiO2 content of 59.7 wt% has been estimated. However, there exists a significant lateral variation in the crustal structures among the tectonic units of eastern China. The structure and composition features of some regions in eastern China in     

探测壳内低速层的深地震测深方法及应用

中国及全球大陆不同构造域广泛存在壳内低速层。壳内低速层不仅与地壳表层金属、非金属矿床、油气资源及地壳变形密切相关, 而且也是一些重大地震和活动断裂的发育场所。一般认为,地壳低速层反映了地壳物质的含水、热状态和部分熔融等信息, 其研究对探讨地壳结构及其动力学演化有重要意义。本文总结了利用深地震测深资料的震相走时、振幅、相位信息识别壳内低速层的5种典型方法: 1)Pg震相走时中断;2)低速层顶、底界面反射波走时曲线近似平行;3)30°~60°入射角范围内低速层顶界面反射转换波强于反射纵波;4)低速层底界面反射波强于顶界面;5)低速层顶界面反射波极性反转等。研究实例表明, 以上方法为利用深地震测深资料揭示壳内低速层提供了有效途径。     

多旋回的板块构造运动与南海新生代构造

<正> 黄汲清教授(1979)在研究板块构造演化模式时曾经强调指出:板块构造是长期的、多阶段发展的,也就是说是多旋回发展的。它包括多旋回构造运动(板块俯冲、褶皱造山),多旋回沉积建造,多旋回岩浆活动(花岗岩、火山岩等)以及多旋回找矿作用。南海及其周缘的地质构造就是板块构造多旋回发展的一个实例。本文试图根据南海及周缘地区的地质地球物理调查成果,对其新生代(包括晚白垩世)的多旋回构造作一简要概述。     

苏鲁造山带区域地壳山根结构特征

本利用苏鲁大别造山带及其邻区的三维P波速度资料，详细对比研究了苏鲁与大别超高压变质带莫霍面深度和深部P波速度结构分布特征。结果表明，尽管苏鲁、大别超高压变质带都具有上地壳明显高速且上凸；中地壳增厚；下地壳埋藏较深且下凹等共同的P波速度结构特征，与大别地区相比较，苏鲁超高压变质带还存在着独特的区域性特征。从地貌上看，苏鲁地区山脉已经基本消失。苏鲁超高压变质带的地壳厚度为32～33公里，深于其周围地区2～3公里，但是莫霍面下凹程度远不如大别地区，造山带地壳山根已逐步趋向消失。苏鲁地区上地壳P波速度高于大别，比其周围地区约快1～1．2km/s，有可能显示了该区有更多高速、高密度的超高压变质岩折返到上地壳与地表的岩石物性效果。大别造山带山脉依然存在，莫霍面下凹更明显，沿NWW向串状残留地壳山根最深为37～38公里，深于其周围地区3～4公里。对比研究结果表明，由于区域构造运动的作用，苏鲁大别造山带中的不同地段，在其造山、演化过程中也存在着差别。苏鲁的造山运动起始虽略晚于大别，但结束的更快，比大别更早进入了造山运动的后期。分析促使苏鲁造山运动进程加速的主要构造原因可能有两点，郯庐断裂带的左旋走滑运动以及通过中国华北区域的大范围NW-SE向扩张应力场的影响。大区域构造背景加速了苏鲁造山带地表高山侵蚀过程的同时，随着山根浮力的不断减弱，地壳深部山根逐渐趋向消失。地壳速度结构特征有可能反映了苏鲁造山带的地壳山根随着地表山脉的侵蚀而减弱，趋向消失的过程。     

用综合方法研究中国东部深部构造

<正> 近年来在我国获得大量的地质、地球物理和地球化学等资料的基础上,特别是将地表地质构造的研究与深部地质构造和新构造运动的研究结合起来,更加深和丰富了对大地构造的认识。 1957年,地质部航测大队首次在我国东部发现了郯城—庐江深大断裂带。同时,大量的地球物理工作,为我国早期油田的勘探与开发提供了地质构造的依据。六十至七十年代,利用人工地震研究地壳和上地幔的结构,提出了部分地区的详细地壳模型和地壳厚度。在我国某些地区开始了古地磁学的研究。     

内蒙古大青山印支运动厘定

根据中下侏罗统五当沟组与下伏地层之间角度不整合接触关系，结合同位素年代与岩浆活动特征和各种构造要素之间叠加改造关系，证实了大青山地区存在强烈印支运动。构造样式和构造要素组合特点表明大青山印支运动是一次强烈逆冲推覆、褶皱造山运动，形成了东西向展布的大型逆冲推覆构造和褶皱构造，构成了大青山地区中生代造山带主体构造格架。在地壳构造变形过程中伴随有强烈岩浆活动，形成了一系列的岩株和岩墙。大青山地区印支构造运动的确定对研究阴山—燕山板内造山带形成演化历史和地球动力学机制具有重要意义。     

Thermomechanical evolution of the high‐grade core in the nappe zone of Variscan Sardinia,Italy: the role of shear deformation and granite emplacement

In the nappe zone of the Sardinian Variscan chain, the deformation and metamorphic grade increase throughout the tectonic nappe stack from lower greenschist to upper amphibolite facies conditions in the deepest nappe, the Monte Grighini Unit. A synthesis of petrological, structural and radiometric data is presented that allows us to constrain the thermal and mechanical evolution of this unit. Carboniferous subduction under a low geothermal gradient (~490–570 °C GPa^?1) was followed by exhumation accompanied by heating and Late Carboniferous magma emplacement at a high apparent geothermal gradient (~1200–1450 °C GPa^?1). Exhumation coeval with nappe stacking was closely followed by activity on a ductile strike‐slip shear zone that accommodated magma intrusion and enabled the final exhumation of the Monte Grighini Unit to upper crustal levels. The reconstructed thermo‐mechanical evolution allows a more complete understanding of the Variscan orogenic wedge in central Sardinia. As a result we are able to confirm a diachronous evolution of metamorphic and tectonic events from the inner axial zone to the outer nappe zone, with the Late Variscan low‐P/high‐T metamorphism and crustal anatexis as a common feature across the Sardinian portion of the Variscan orogen.     

Intraplate seismotectonic features of North China

Intraplate earthquakes in North China are characterized by shallow depth, large magnitude and high frequency. Obviously, the zonal distribution of earthquakes is closely related to recent active faults and Cenozoic graben and rift systems.The active faults are mainly oriented NNE with right-lateral movements, and partially oriented NW with left-lateral movements.The Hetao-Yinchuan graben, Fenhe-Weihe graben and North China Plain rift systems often reflect crustal thinning and mantle uplift.According to the data concerning crustal deformation, particularly the movement patterns of faulting, crustal taphrogenesis and earthquake surface rupture, it is suggested that a shearing-extension mechanism could be considered as a cause of the formation of seismotectonic structures in North China since the Early Cenozoic Era.Graben and rift systems also developed in Northeast and South China. They formed earlier than the graben and rift systems in North China, however, and their activity has decreased during the Quaternary period. It is reasonable that the seismicity in Northeast and South China is not as strong as that in North China.     

Tectono-Metamorphic Impact of a Subduction-Transform Transition and Implications for Interpretation of Orogenic Belts

Subduction-transform tectonic transitions were common in the geologic past, yet their impact on the evolution of orogenic belts is seldom considered. Evaluation of the tectonic transition in the Coast Ranges of California is used as an example to predict some characteristics of exhumed regions that experienced similar histories worldwide.

Elevated thermal gradients accompanied the transition from subduction to transform tectonics in coastal California. Along the axis of the Coast Ranges, peak pressure-temperature (P/T) conditions of 700 to 1000° C at a pressure of ～7 kbar, corresponding to granulite-facies metamorphism, and cooling to 500° C, or amphibolite facies, within 15 million years, are indicated by thermal gradients estimated from the depth to the base of crustal seismicity. Greenschist-facies conditions may occur at depths of 10 km or less. These P/T estimates are consistent with the petrology of crustal xenoliths and thermal models. Preservation of earlier subduction-related metamorphism is possible at depth in the Coast Ranges. Such rocks may record a greenschist or higher-grade overprint over blueschist assemblages, and late growth of metamorphic minerals may reflect dextral shear along the plate margin, with development of orogen-parallel stretching lineations.

Thermal overprints of early-formed high-P (HP), low-T (LT) assemblages, in association with orogen-parallel stretching lineations, occur in many orogenic belts of the world, and have been attributed to subduction followed by collision. Alternatively, a subduction-transform transition may have caused the overprints and lineations in some of these orogenic belts. Possible examples are the Sanbagawa belt of Japan and the Haast schists of New Zealand. P/T conditions of inferred granulite-grade metamorphism in the Coast Ranges, and predicted cooling of these rocks through lower thermal gradients, resemble the P/T evolution of many granulite belts, suggesting that some granulite belts may have formed as a result of a subduction-transform transition. Arclike belts of plutons also can form as a consequence of subduction-transform transition.     

Neotectonics and seismicity in southern Patagonia

Research for evaluation of geologic hazards involving earthquakes and volcanic eruptions in southern Argentina seems to have historically received little attention. Nevertheless, the relatively small work done indicates a Neogene tectonic architecture in the area with capability of generating potential hazardous earthquakes in a growing population region. Seismicity and some morphotectonic evidences of Quaternary activity of the Magallanes–Fagnano left‐lateral fault system in the transform boundary between South America and Scotia plates, are analysed in this paper. This fault system is considered to be an important seismogenic source, responsible for large earthquakes that have occurred in southern Argentina. Some examples from the South and Austral Andean Volcanic Zones are also examined in order to show recent volcanic activity which also generated crustal seismicity. Preliminary hazard estimation clearly shows the presence of both potentially active volcanic centres in southern Patagonia that may also trigger seismicity and the high probability for large crustal earthquake generation. Copyright © 2015 John Wiley & Sons, Ltd.     

中国大陆第四纪地壳运动时程

本文从中国大陆有代表性的青藏高原、黄土高原、三峡地区着手,进行了新构造运动剖析。并结合全国火山活动期次,总结出中国大陆第四纪地壳运动的时程变化。从而为进一步探讨新构造运动特点和规律,为国民经济建设及人类生存环境提供了一定的地质背景资料。