The assemblage diaspore+quartz in metamorphic rocks: a petrological, experimental and thermodynamic study   总被引：1，自引：0，他引：1  

T. THEYE  C. CHOPIN  K.-D. GREVEL  & E. OCKENGA 《Journal of Metamorphic Geology》1997,15(1):17-28

The upper pressure limit of pyrophyllite is given by the equilibria (i) pyrophyllite=diaspore+quartz and (ii) pyrophyllite=diaspore+coesite. High- P experimental investigations carried out to locate equilibrium (i) yield brackets between 497 °C/24.8  kbar and 535 °C/25.1  kbar, and between 500 °C/23  kbar and 540 °C/23  kbar. Equilibrium (ii) was bracketed at 550 °C between 26.0 and 28.3  kbar. In the experimental P–T  range, equilibria (i) and (ii) are metastable with respect to kyanite. A stable P–T  grid is calculated using thermodynamic data derived under consideration of the present experimental results. According to these data, the lower pressure limit of the assemblage diaspore+quartz according to equilibrium (i) range from about 12  kbar/300 °C to 20  kbar/430 °C (in the presence of pure water). The upper stability of diaspore+quartz is limited by the reaction diaspore+quartz=kyanite+H₂O at about 450 °C (nearly independent of pressure) and, to higher pressure, by the quartz=coesite transition. Equilibrium (ii) is metastable over the whole P–T  range.
Natural occurrences600.S of the diaspore–quartz assemblage in metamorphic rocks in Sulawesi, New Caledonia, Amorgos and the Vanoise are characterized by minerals indicative of high- P such as ferro-magnesiocarpholite, glaucophane, sodic pyroxene and lawsonite. The metamorphic P–T  conditions of these rocks are estimated to be in the range 300–400 °C, >8  kbar. These data are compatible with the derived P–T  stability field of the diaspore+quartz assemblage. We conclude that, in metamorphic rocks, diaspore+quartz is, as ferrocarpholite, an indicator for unusual low- T  /very high- P settings.  相似文献   

五台山早前寒武纪碰撞造山带中的韧性剪切带及其大地构造意义     

刘志宏  王安建  李晓峰 《吉林大学学报(地球科学版)》1997,(3)

在五台山早前寒武纪碰撞造山带中存在两种类型韧性剪切带，即逆冲型和伸展型剪切带。除变质程度不同外，南部和北部构造片体中的角闪岩相逆冲型韧性剪切带与中部构造片体中的绿片岩相逆冲型韧性剪切带具有相同的变形特征，它们形成于同一变形过程中，是造山作用早期地壳拼合阶段的产物。伸展型韧性剪切带在整个造山带都有分布，与造山作用晚期显著增厚的地壳发生大规模纵向伸展作用相联系  相似文献   

Continental rifting and drainage reversal: The clarence river of Eastern Australia     

R. J. Haworth  C. D. Ollier 《地球表面变化过程与地形》1992,17(4):387-397

The Clarence River on Australia's east coast has an anomalous drainage pattern. Its right-bank tributaries are markedly barbed, suggesting reversal, whereas Tertiary volcanism has disrupted its left-bank drainage. The southeast-flowing Clarence is closely aligned with the northwest-flowing Condamine River just across the Continental Divide. The Condamine-Clarence alignment is continued by a large southern tributary, the Orara River, which flows northwest, away from the sea, to meet the southeast-flowing Clarence. A broad river with a quite different character flows east from near the Orara-Clarence junction to the sea. This is essentially an overflow channel. This series of aligned streams, the Condamine-Clarence-Orara, represents the remains of an earlier northwest-flowing stream that extended the full length of the Clarence-Moreton Basin, an eastern extension of the Great Artesian Basin. During the Jurassic, the Clarence-Moreton Basin was filled with sediments from the surrounding highlands, including those to the east of the present coastline. Continental rifting from Late Cretaceous times onwards led to the opening of the Tasman Sea, causing the reversal and beheading of the original northwest-flowing streams and the formation of the Great Escarpment. The evolution of the Clarence River does not fit into most conventional geomorphic paradigms such as cycles, climatic geomorphology or steady-state landforms. It is the result of a succession of unique events on a very long timescale, and as such is a classic example of evolutionary geomorphology.  相似文献   

安比拉事件在中国存在的证据   总被引：2，自引：1，他引：2  

葛同明  樊利民 《地质学报》1992,66(4):381-389

黄土地层、珠江口盆地第四纪地层以及雷州半岛英利火山岩的古地磁学研究表明,布容极性时出现有反极性地磁场。英利火山岩的K—Ar同位素年代测定值为0.58±0.13Ma。据气候地层学和生物地层学资料确定,黄土地层和珠江口盆地第四纪地层的反极性层段的年代分别为0.45Ma和0.47—0.48Ma。这些反极性层段的年代相当于安比拉事件的年代。从中国不同地区、不同地层揭示的这一事件证实了安比拉事件为全球性极性倒转,并非极性漂移。安比拉事件的确定将为中、晚更新世地层的划分提供磁极性的依据。  相似文献   

The time reversal effect of the impulse response of crust     

郑文衡  王乘  陈湘鹏 《地震学报(英文版)》2001,14(4):394-403

IntroductionTime reversal effect is a kind of reversed dynamic process in a limited space or time interval, which can be realized artificially by resetting the boundary and loading conditions. In this case the time seems to be reversed and such effect therefore is called time reversal effect, which was first proposed in and applied to the field of ultrasonic. Although the focusing of ultrasonic wave has powerful effect, it is difficult to focus in an anisotropic or homogeneous medium. Fink (19…  相似文献   

Dynamic instability of clays: an energy approach   总被引：1，自引：0，他引：1  

Eugene A. Voznesensky  Steinar Nordal 《Soil Dynamics and Earthquake Engineering》1999,18(2):601

The dynamic instability of any soil is based on the ability to accumulate from cycle to cycle a part of the energy to be dissipated. Using the general thermodynamic approach in combination with high resolution experiments it is possible to analyze the transformations of energy in soil under dynamic loading. Undisturbed specimens of two Norwegian clays, sufficiently different in their engineering properties, were used in a number of undrained cyclic triaxial tests to study the influence of confining stress, coefficient of earth pressure at rest (K₀), dynamic stress amplitude and frequency of loading in the development of instability in the clays. This paper discusses the unit dissipated energy and the unit activation energy as possible energy criteria for evaluation of dynamic instability in soils.  相似文献   

中生代地球系统与核—幔边界动力学研究进展   总被引：3，自引：1，他引：2  

邵济安  韩庆军 《地质论评》1998,44(4):382-388

本文介绍了９０年以来地球物理学在地球磁场方面的研究成果,揭示了２００－１００Ｍａ全球低的地球磁场古强度;１２４－８３Ｍａ低的极性反转频率以及１７０－１１０Ｍａ近乎停滞的真极移。  相似文献   

Trends in Cretaceous and Tertiary geomagnetic reversals     

R.A. Reyment 《Cretaceous Research》1980,1(1):27-48

The statistical theory of modulated renewal processes is used to analyze the polarity reversal scales of Larson & Hilde (1975) and LaBreque, Kent & Cande (1977). The results suggest that the trending effect in these data may be modelled by a rate parameter with an exponential quadratic trend. Short times in one polarity state tend to be followed by short times in the other state. The graphical analysis points to the possibility of an undulating pattern in reversal rates. The empirical distributions of the normal and reversed polarities show slight differences in comparison with each other in most of the statistical tests, but a moving-window analysis indicates possible serial effects for the normal times. As a rough approximation, a statistical two-state model for reversals might be realistic, for example, an alternating renewal process under relaxed assumptions. There has been a gradual stepping-up of the minimum reversal rate from the Oligocene to the present, but little change in the observed range of the reversal rates. With the long quiet (Mercanton) interval removed from the data, the average time spent in the reversed polarity state is slightly greater than for the normal state. A change in statistical properties for the entire set of data considered as a single sample occurs around the Eocene-Oligocene transition (Middle Eocene on earlier time scales). The analyses of the statistical second-order properties of the entire sequence of 271 observations, and the subsets of normal and reversed between-times, reject a renewal hypothesis if theoretical statistical considerations are strictly applied to the results (although this hypothesis is not rejected for the Oligocene to Recent observations); this result is at variance with some geophysical models. A short appendix on the theory of point processes is provided to aid the general reader in following the arguments used in this paper.  相似文献   

新疆吐鲁番桃树园二叠-三叠系古地磁初步研究     

李永安  李锦玲  程政武  孙东江  刘俊  郑洁 《新疆地质》2004,22(2):136-142

通过对吐鲁番桃树园二叠—三叠系古地磁特征初步研究,建立了二叠—三叠系界线磁性层柱,将其界线置于锅底坑组中下部,即37—36层(采点66～65).对二叠、三叠系古地磁研究表明,其古纬度为北纬26°～35°,属热带—北温带古气候环境,与古生物资料和沉积相相一致,推断古生物灭绝与新生,可能与地磁的转化密切相关。  相似文献   

青藏高原末次快速隆升与“亚澳”陨击事件   总被引：11，自引：3，他引：11       下载免费PDF全文

葛肖虹  任收麦  刘永江  吴光大  袁四化 《第四纪研究》2004,24(1):67-73

黄土、山前磨拉石年代学最新研究成果表明青藏高原及其相邻山脉最晚一期,也是最强烈的隆升事件发生在早更新世晚期(0.9～0.8MaB.P.)。这是一次由于印度板块脉冲式陆内俯冲(A型)引起的“挤压隆升”,而不是重力均衡引起的“伸展隆升”。它对中亚及我国西部广袤区域盆-岭地貌的形成、盆地中-新生界构造变形和大范围的干旱与沙漠化起了决定性的影响。0.9～0.8MaB.P.期间发生在印度洋洋中脊三联点附近(67°E,20°S)的“亚澳”陨击事件,很可能是引起印度洋快速扩张、导致印度板块在锡瓦利克带强烈俯冲(A型),并引起了青藏高原0.9～0.8MaB.P.快速隆升的大陆动力学背景。其影响不止于印度洋周边,而且还涉及西南太平洋。0.9MaB.P.前后引起全球气候变化的“中更新世革命”(MPR)、“西太平洋暖池”的形成以及0.78MaB.P.布容期与松山期地磁极性倒转(BM界限)的发生都可能与此有关。  相似文献