Rare earth element-thorium correlations in sedimentary rocks,and the composition of the continental crust

There is a correlation between thorium and the light rare earth elements, indicated by La/Th ratios in fine grained sedimentary rocks of various ages from Australia and Greenland. The correlation between Th and the heavy rare earth elements (Th/Yb) is much less significant. Archean sedimentary rocks have a higher La/Th (3.6 ± 0.4) than post-Archean sedimentary rocks (La/Th = 2.7 ± 0.2).The cause of this correlation can be attributed to the coherent behaviour of these elements during most sedimentary processes (weathering, transport, diagenesis, etc.). Since the chondrite-normalized rare earth element distribution of clastic fine grained sedimentary rocks is accepted to be parallel to the distribution of REE in the upper continental crust, an estimate of upper crustal Th abundances can be made. Using reasonable assumptions of certain elemental ratios (K/U, Th/U, K/Rb) in the upper crust, minimum estimates of the abundances of K, U and Rb can also be made for the post-Archean and Archean upper crusts.The post-Archean values (K = 2.9%; Rb = 115 ppm; Th = 11.1 ppm; U = 2.9 ppm) compare favourably to some previous estimates made from direct sampling and theoretical considerations and help confirm a granodiorite present day upper continental crust. The Archean data (K = 0.92%; Rb = 30ppm; Th = 3.5 ppm; U = 0.92 ppm) support models which suggest a significantly more mafic exposed crust at that time.     

Formation of sedimentary basins of graben type by extension of the continental crust

A mechanism for causing graben-like subsidence by crustal stretching in response to tension is suggested, based partly on previous hypotheses of Vening Meinesz, Artemjev and Artyushkov, Bott and Fuchs. The mechanism requires rheological subdivision of the crust into a brittle upper layer about 10–20 km thick overlying a ductile lower crust. The brittle layer responds to tension by normal faulting and wedge subsidence; the ductile layer responds by local or regional thinning and by lateral flow of material from beneath the subsiding wedge causing complementary uplift by horst formation or elastic upbending. A graben width of between 30 and 60 km is predicted in absence of basement inhomogeneity. Computations of the energy budget indicate that sedimentary basins of more than 5 km thickness can form by the mechanism provided that water pressure reduces the friction on the faults. The mechanism can explain relatively rapid beginning and end of subsidence, and spasmodic sinking may occur. A wide variety of observed graben-like basins can be explained by the hypothesis, including classical rift valleys and the Mesozoic basins of UK and the North Sea, but it is inapplicable to broad unfaulted cratonic or shelf subsidence.     

Compression and tension in the earth's crust

Summary Variations in density in the basaltic layer and the upper mantle are postulated as being due to mineral conversions as result of high temperature and pressure variations. This theory has been developed in order to explain the elevation of mountain chains, median ocean rises and deep sea trenches as being caused by compressional and tensional stressfields.

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Zusammenfassung Es wird angenommen, daß Dichte-Änderungen in der Basalt-Schale und dem oberen Teile des Erdmantels von Mineralumwandlungen infolge hoher Temperatur- und Druck-Änderungen herrühren. Diese Theorie wird ausgebaut, um die Hebung von Kettengebirgen und ozeanischen Rücken und die Bildung von Tiefseegräben auf Grund von Zug- und Druckspannungs-Feldem zu erklären.

     

Geodynamics of the Early Precambrian,Part 2: Formation of continental crust and sedimentary basins,specificity of the lithosphere

This part of work is aimed at consideration of problems concerning evolution of geodynamic processes based on characteristic structures of the Early Precambrian and their rocks. Considered in the paper are structures characterizing existence of mature continental crust (sedimentary basins), development of the crust (metamorphic belts and granitoids) and underlying upper mantle (lithospheric keel), and amalgamation of crustal domains (continents, microcontinents, terrains) into supercontinents. Geodynamic phenomena of the Early Precambrian comparable with the Phanerozoic ones are distinguishable, on the one hand, and their changes with time of evolutionary character are detectable, on the other. The latter are satisfactorily explainable by secular lowering of the mantle temperature in general and above the top of mantle plumes.     

Contemporary technogenic movements of the earth's crust

Technogenic movements, caused by Man's activities, are subdivided on the basis of their causative factors, which are: changes in hydrodynamic and hydrostatic conditions at depth during the process of withdrawal and injection of fluids, the effect of static pressure during mining operations, the redistribution of static loads on the surface, and dynamic interactions during explosions. During the removal of fluids and solid rocks from below, downwarping of near-surface portions of the sedimentary shell and crust takes place, which cannot for the most part be regarded as tectonic.

The creation of additional loads during the construction of large cities and the building of large reservoirs cause downwarping of the crust on the order of a few tens of centimeters with a velocity on the order of 1 cm/yr, and also earthquakes of magnitude up to 5-6. The patterns of manifestation of this type of movement are considered on the basis of three major dams: North America (Lake Mead), Africa (Kariba), and India (Koyna).

During underground nuclear explosions in Nevada, substantial faults were engendered over an extent of hundreds of meters up to kilometers for a distance of up to 6 km from the point of detonation.

Technogenic movements may embrace not only the sedimentary shell, but also the consolidated crust. In their characteristics, and also the areas and depths of the sectors of the crust involved, the technogenic movements in a number of cases cannot be distinguished from present-day natural tectonic movements, in every case local. —Authors.     

Regularities of rare-earth element distribution in the sedimentary shell and in the crust of the earth

After summarizing the vast analytical material it was possible to establish the differences in rare-earth element (REE) distribution in geosynclines and on platforms. It is shown that the heavier REE composition in sediments of geosynclines and the lighter one in sediments of platforms was initially created by processes of endogenic differentiation and then inherited by sedimentary series of these zones. On the basis of the calculation of the REE content in rocks of various shells of the Earth crust the increase of the role of heavy lanthanides into the depths of the crust is shown. The obtained estimate of REE abundance in the lithosphere led to the conclusion that the crust of our planet, despite the repeated reworking of its matter by sedimentary processes, metamorphism and granitization, has inherited features peculiar to products of tholeiitic magmatism—the most widely spread type of mantle fusion.     

The formation of ultradeep sedimentary basins through metamorphism with rock contraction in continental crust

Sedimentary covers are up to 15–20 km thick in ultradeep sedimentary basins. Joint interpretation of seismic reflection sounding and gravimetric data indicates that eclogites are located in the basins under the Moho. In these rocks the velocities of P-waves are close to those in mantle peridotites. The basins show only moderate crustal stretching and their formation was caused primarily by the transformation of gabbroids into dense eclogites in the lower part of the continental crust. The transformation took place episodically as mantle fluids infiltrated the lower crust and it was ensured by pressure rise in the lower crust occurring with the accumulation of sediments. Moderate metamorphism developed in silicic upper crust as temperature and pressure increased under thick sedimentary covers. In iron-rich metasedimentary rocks, deep metamorphism resulted in the density increase, and P-wave velocities there increased to those characteristic of the oceanic crust.     

应力路径对地表变形特性影响的数值模拟

针对不同环境条件及工程因素对地表变形影响的不同特点,研究了不同应力状态下土的变形特性,得出其影响地表变形的基本规律。通过典型三轴试验对比分析了变形规律,由试验数据空间反演了各应力路径下的本构模型空间,编制相应的模块嵌入有限元程序,模拟了几种不同路径下地表沉降算例,得到了导致地表变形的几个基本规律：①不同的地表变形问题对应的应力路径千差万别,需要用不同的应力路径条件下的本构模型进行分析;②应力路径的影响是不可忽略的,甚至在诸多因素中起主导作用;③数值建模方法建立起来的模型通过权值系列的不同反映应力路径的影响,能较好应用于此类问题的分析;④CTC与TC路径极限体变相差近20 %;⑤CTC路径的剪缩区范围比CTE路径大,两种路径下剪缩体应变值最大相差近17.3 %;CTE路径较CTC路径的剪胀更为明显,剪胀体应变最大相对差值近98 %。     

Folding and faulting of strain-hardening sedimentary rocks

The question of whether single- or multi-layers of sedimentary rocks will fault or fold when subjected to layer-parallel shortening is investigated by means of the theory of elastic-plastic, strain-hardening materials, which should closely describe the properties of sedimentary rocks at high levels in the Earth's crust. The most attractive feature of the theory is that folding and faulting, intimately related in nature, are different responses of the same idealized material to different conditions.When single-layers of sedimentary rock behave much as strain-hardening materials they are unlikely to fold, rather they tend to fault, because contrasts in elasticity and strength properties of sedimentary rocks are low. Amplifications of folds in such materials are negligible whether contacts between layer and media are bonded or free to slip for single layers of dolomite, limestone, sandstone, or siltstone in media of shale. Multilayers of these same rocks fault rather than fold if contacts are bonded, but they fold readily if contacts between layers are frictionless, or have low yield strengths, for example due to high pore-water pressure. Faults may accompany the folds, occurring where compression is increased in cores of folds. Where there is predominant reverse faulting in sedimentary sequences, there probably were few structural units.     

On the origin and evolution of the earth's crust and magmas

This paper discusses some controversial petrological ideas, expressed in the geonomic literature of our time.Origin and evolution of the crust: According to classical magmatism the sialic crust is segregated from the mantle in the course of the Earth's evolution, causing a growth of the continental crust. Arguments against this concept are advanced.According to neo-huttonism the sialic crust developed from the outside in an early phase of the Earth's history. This might have occurred according to the hot-Earth theory on the origin of our planet (Rittmann), or according to the cold-Earth theory of cosmogenesis (Urey; Berlage).The matter of this envelop of proto-sial has then been geochemically recycled countless times during the major part of the Earth's history (neo-huttonism), transforming it into the sialic crust as we know it (Nieuwenkamp). During the later part of the evolution, in post-Algonkian times, a new process came to the fore. Extensive parts of the sialic crust were incorporated and digested by the mantle; in these areas an oceanic crust came into being. This physicochemical process of burning holes in the sialic crust has been called the Mediterranean type of oceanization (van Bemmelen).Origin and evolution of the magmas: Distinction is made between basaltic magmas segregated from the upper mantle, and the calcalkaline suite of magma derived from the sialic crust and its sedimentary cover. This classification corresponds withRittmann's bimodality concept, andNieuwenkamp's distinction between an oceanic and a continental metabolism. Moreover, transitions are found between the two fundamental types of crust (continental and oceanic) and the corresponding suites of magma. These transitions occur especially in small ocean basins with a foundering, intermediary type of crust and thick piles of sediments (Menard). In these areas the process of Mediterranean oceanization is active.The final chapter discusses the synthetic model of the origin and evolution of the Earth's crust and magmas according to the undation theory.

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Zusammenfassung Diese Arbeit bespricht einige umstrittene petrologische Gedanken, welche in letzter Zeit in der geonomischen Literatur publiziert wurden.Herkunft und Entwicklung der Kruste. Nach dem Konzept des klassischen Magmatismus wurde die sialische Kruste im Laufe der Erdentwicklung vom Mantel ausgeschieden, was von einem Wachstum der sialischen Kruste begleitet wurde. Argumente gegen diese Auffassung werden angeführt.Nach den neo-huttonischen Vorstellungen wurde die Kruste von außen her in einer frühen Phase der Erdgeschichte gebildet. Die Bildung einer protosialischen Hülle könnte entweder ganz im Anfang stattfinden (nach der Theorie einer heißen Urerde vonRittmann), oder kurz nach der Agglomeration einer kalten Urerde (nach den Vorstellungen vonUrey undBerlage).Die Umwandlung dieser Protosialhülle in eine sialische Kruste geschah während den zahllosen geochemischen Zyklen der Erdgeschichte (Neo-huttonismus nachNieuwenkamp). Im letzten Teil der Erdgeschichte wurde eine neue Phase der planetarischen Entwicklung erreicht. Ausgedehnte Teile der sialischen Kruste wurden vom Mantel angefressen, verschluckt und verdaut, wobei die Ozeane mit basaltischer Kruste entstanden. Diese relativ jungen physischchemischen Prozesse der Aufnahme der Sialkruste im Mantel wird Mediterraner Typus der Ozeanisation genannt (van Bemmelen).Herkunft und Entwicklung der Magmen. Ein Unterschied wird gemacht zwischen basaltischen Magmen, die ihre Herkunft im oberen Mantel haben, und der kalk-alkalischen (Pazifischen) Magmenreihe, die von der sialischen Kruste und ihrer Sedimenthülle abgeleitet wird. Diese Unterscheidung stimmt überein mitRittmanns Auffassung der Bimodalität der Magmen, undNieuwenkamps Einteilung in ozeanischen und kontinentalen Metabolismus.Außerdem treten auch Übergänge auf zwischen diesen zwei Grundtypen der Kruste und den sie begleitenden Magmen. Diese Übergänge können beobachtet werden in den kleinen ozeanischen Becken der Gegenwart, mit absinkender Kruste intermediärer Art und mächtiger Sedimentfüllung (Menard). In diesen Gebieten ist der Prozeß der Mediterranen Ozeanisation im Gange.Das Schlußkapitel bespricht das synthetische Modell der Herkunft und Entwicklung der Erdkruste und der Magmen nach der Undations-Theorie.

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Résumé Cette contribution analyse quelques idées controversables, sur les problèmes fondamentaux du volcanisme publiées récemment dans la littérature géonomique.Origine et développement de l'écorce terrestre. Selon la théorie classique du magmatisme, la croûte sialique est le produit du manteau (supérieur). Elle s'est dégagée pendant l'évolution de notre planète et ce processus résultait dans un accroissement en volume de l'écorce sialique. Des arguments contre cette théorie sont étalés.Selon la théorie « neo-huttonique », l'écorce sialique se formait de l'extérieur de notre planète au commencement de son évolution.Rittmann suppose une proto-planète chaude, tandis queUrey etBerlage supposent une agglomération relativement froide. Cette enveloppe proto-sialique fut formée immédiatement ou peu de temps après cette agglomération planétaire. Puis le matériel de cette enveloppe fut soumis aux cycles géochimiques qui produisaient l'écorce continentale que les géologues de terrain peuvent étudier (Nieuwenkamp).Dans la dernière phase de l'évolution terrestre un nouveau phénomène géochimique devient de plus en plus important. Des parties de la croûte sialique sont corrodées et englouties par le manteau. Dans ces régions l'écorce continentale est transformée en écorce océanique. Ce processus de transformation de la croûte continentale est nommé le type méditerranéen de l'océanisation (van Bemmelen).Origine et développement des magmes. On peut distinguer entre les magmes basaltiques, qui sont dégagés par le manteau et les magmes calco-alkalins (suite Pacifique) qui sont dérivés de la croûte sialique et son épiderme sédimentaire. Cette distinction correspond à l'idée deRittmann sur la » bimodalité « des magmes et l'idée deNieuwenkamp sur deux types de « métabolisme » (continental et océanique) de la terre. En outre, on peut observer des transitions entre ces deux types fondamenteaux de l'écorce (continentale et océanique) et de magmes (basaltiques et granodioritiques). Ces transitions sont actives dans de petits bassins océaniques (récemment décrits parMenard) dans lesquels l'écorce continentale est en train de transformation et descente. Cette écorce intermédiaire est couverte par des piles de sédiments d'une épaisseur énorme.Dans le chapitre dernier l'auteur avance un modèle synthétique sur ces problèmes fondamentaux de l'évolution de notre planète selon la théorie des ondations de la surface terrestre.

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday     

Slow movements of the earth's crust and the creation of earthquakes

The article discusses problems of the application of data on vertical movements of the earth's crust to earthquake forecasting. A mathematical and numerical correlation between the internal tensions under the earth's crust and the vertical uplifts of the earth's surface is established.     

Geothermal model of the earth's crust in the pannonian basin

A geothermal model of the hyperthermal zone of the Pannonian basin is constructed. On the basis of results of seismic measurements along five deep seismic sounding profiles on the territory of the basin and the surrounding areas and also of measurements of heat flow, heat production by radioactive elements and thermal conductivity of rocks, the variation of temperature with depth and maps of Mono-temperatures and heat flux through this surface are calculated and constructed, respectively. It is shown by numerical-model calculations that the heat anomaly of the Pannonian basin indicated by a number of surface measurements is mainly of mantle origin. Inhomogeneities of the heat-flow increase with depth down to the upper mantle and the temperature on the Moho-surface below the hyperthermal zone has values on average 400–500°C more than those in the surrounding areas. Heat flux through the Moho under the Pannonian basin is also higher by about 40–50 mW m⁻². On the basis of the present calculations, it can be suggested that the upper mantle is probably partially molten beneath the annonian basin. As a most reasonable source mechanism of formation of this heat anomaly, the frictional heating arising in areas of induced secondary convection that probably has proceeded also beneath the basin from the Triassic to the Miocene is suggested here.     

大面积土体堆载地基变形一般规律分析

大面积土体堆载是典型的一维固结问题,但是大面积堆载的地基土变形规律与常规小范围堆载有显著差别。本文通过收集整理多项软土地区大面积土体堆载工程实测资料,结合工程地质情况,总结了大面积堆载的一般规律。从这些工程的实测结果看,大面积堆载与小范围堆载相比,其影响范围大、固结时间长、孔隙水压力消散缓慢、变形量大,这些规律对工程设计具有一定参考价值和指导意义。     

A statistical model of the earth's crust: Method and results

A model of the earth's crust has been adopted for interpretation of seismic reflection profiles in Kazakhstan. Within it, the smooth variation of seismic velocities with depth becomes complicated by small random fluctuations of various scales. These velocity fluctuations are manifested in oscillations of amplitudes and arrival times of the recorded signals.

The inhomogeneity of the medium is characterized by its coefficient of intrinsic attenuation. Investigation of this coefficient shows that for the crust, its mean value (at a frequency of 7 Hz) is equal to 10⁻³ km ⁻¹ and that over the depth interval of 10–25 km its value is very small, almost zero. It is therefore most surprising that this same depth interval (10–25 km) contains nothing unusual within the cross-section of its determined component wave velocity.     

Stress amplification in the upper crust and the development of normal faulting

Finite element analysis of lithosphere deformation, incorporating failure criteria based on the Modified Griffith Theory for an elastic upper crust and a visco-elastic rheology for the lower crust and lithospheric mantle, demonstrates that normal faulting as a result of comparatively small, horizontal tensile stresses acting throughout the lithosphere can occur by the phenomenon of stress amplification. The use of a simple, Newtonian viscosity or of power law creep for the visco-elastic material does not significantly change the results. The time to failure is dependent upon the magnitude of the applied stress and the effective viscosity of the underlying material. For an applied stress of 20 MPa and a constant viscosity of 10²³ Pa s failure is predicted after 1.19 Ma, with a fault plane hade of about 30°. A decrease of one order of magnitude in the viscosity of the lower crust results in a slightly shorter time to failure whereas an increase of one order of magnitude results in a very much greater failure time.     

Structure of the earth's crust in Jordan from potential field data

Gravity and magnetic data were collected and used to study the crustal structure of Jordan. Three new geophysical maps of Jordan were created: a Moho discontinuity map, a crystalline basement surface map, and a map showing the lowest limit of magnetic blocks. Depths of the Curie Isotherm were also calculated. Results indicate that the depth to the Moho discontinuity in Jordan varies from 32 to 33 km in the northwest to 38 km in the southeast. The basement complex rocks outcrop on the surface in the southwest but lie at about 8 km in the northeast. The Curie Isotherm (585 °C) lies at a depth of about 10 km in the area east of the Dead Sea and dips southeastward towards the Al-Sirhan (Wadi Sirhan), southeast Jordan, where it is located at 35 km depth. Local isostasy of rock masses (blocks) in Jordan does not occur. Nevertheless, this does not rule out the possible existence of isostasy in a regional scale at greater depths within the mantle.     

Active faulting at the Eurasian, North American and Pacific plates junction

The active faults known and inferred in the area where the major Pacific, North American and Eurasian plates come together group into two belts. One of them comprises the faults striking roughly parallel to the Pacific ocean margin. The extreme members of the belt are the longitudinal faults of islands arcs, in its oceanic flank, and the faults along the continental margins of marginal seas, in its continental flank. The available data show that all these faults move with some strike-slip component, which is always right-lateral. We suggest that characteristic right-lateral, either partially or dominantly, kinematics of the fault movements has its source in oblique convergence of the Pacific plate with continental Eurasian and North American plates. The second belt of active faults transverses the extreme northeast Asia as a continental extension of the active mid-Arctic spreading ridge. The two active fault belts do not cross but come close to each other at the northern margin of the Sea of Okhotsk marking thus the point where the Pacific, North American and Eurasian plates meet.     

The state of stresses in the upper part of the earth's crust

The measurement of the absolute stresses in the earth's crust was begun in Sweden in 1951, is still proceeding in Scandinavia and has been extended to other parts of the world. The presence in the earth's crust in these areas of a general horizontal stress field has been established, which at any point is usually several times the dead weight of the overlying rock, and highly directional. The sum of the horizontal principal stresses,σ₁ + σ₂, is 180 kgf/cm² at the crust surface and increases linearly with depth; for instance at 1,000 m it is 1,000 kgf/cm².The existence of horizontal fissuring of the bedrock down to great depth is discussed, as is the reason for their appearance. The upper part of the earth's crust seems to be in a state of dynamic but not static equilibrium. The stability of wide underground openings is discussed. An account is given of the technique for measuring the absolute rock stress.     

Solar energy and problem of developments of sialic layer of the earth's crust

The sialitic layer is visualized as a gigantic weathered crust which has developed over the primordial basaltic crust of the planet, under the influence of climatic processes motivated by solar energy. – V.P. Sokoloff.