Decollements in slate belts,examples from the European variscides and the Qin Ling Belt of Central China

Decollements are conspicuous features of collision belts as a result of shortening and shearing of rocks of different competencies in response to intracontinental subduction and crustal stacking. When these decollements occur at upper levels, the classical thin skin tectonics of the foredeeps without important internal strain results; at mid crustal levels slaty cleavage and foliation development occurs. In the more internal parts of the chains, in the lower crust, near the crust mantle boundary, the more severe conditions (granulitic metamorphism) result in ductile deformation in the deepest parts of the mountain belts. Examples of middle and lower crust are well documented in Central China and the Variscan Belt of Europe from field evidence and deep seismic profiling.From these examples it appears more and more likely that most of the mid-crustal slate belts showing vertical slaty cleavage at the erosion surface overly flat decollements.At greater depth large decollements must occur as well in the lower continental crust and at crust-mantle boundary. Typical features of the deep seismic vertical profiles such as the strongly layered lower crust may represent the image of such deep decollements.

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Zusammenfassung Abscherungen sind charakteristische Strukturen von Kollisions-Orogenen. Sie sind das Ergebnis von Verkürzung und Scherung verschieden kompetenter Gesteine infolge intrakontinentaler Subduktion und Krustenüberlagerung. Zu unterscheiden sind Überschiebungen oberer Zonen, wie in den Randgebirgsbereichen ohne bedeutende innere Deformation, von internen metamorphen Zonen mit Schieferung und Plättung. In den tiefen Krustenzonen und im Krusten-Mantelbereich gehen sie einher mit hochgradiger Metamorphose, allgemein in der Granulitfazies.Beispiele der mittleren und tiefen Zonen sind gut erschlossen im paleozoischen Orogen Zentralchinas und im Variszikum Europas und belegt sowohl durch die Geologie wie tiefenseismische Profile. Diese Beispiele zeigen mehr und mehr, daß geschieferte Gebirgsstockwerke mit an der Oberfläche steilstehender Schieferung von flachen Abscherungen unterlagert werden.Die typische Erscheinung einer seismisch gut geschichteten Strukturierung der Unterkruste könnte in dieser Hinsicht als Deckenbahnen interpretiert werden.

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Résumé Les décollements sont des structures typiques des chaînes de collision. Ils résultent du raccourcissement et du cisaillement de roches de différentes compétences en réponse à la subduction continentale et à l'empilement crustal. On peut distinguer des décollements superficiels surtout dans les bassins d'avant chaîne où les roches charriées ont subi une déformation interne faible à nulle (plis et chevauchements sans schistosité). Des décollements plus profonds dans le tiers supérieur de la croûte accompagnés de schistosité et de foliation, dans les parties plus internes métamorphiques des chaînes. Enfin des décollements très profonds à la base de la croûte ou entre croûte et manteau, accompagnés ou suivis d'un métamorphisme de haut degré, généralement granulitique.Ces deux derniers types de décollement sont clairement exprimés dans la chaîne Varisque d'Europe et dans la chaîne Paléozoïque Qin Ling de Chine Centrale. Il apparaît ainsi de plus en plus évident que la plupart des zones plissées à schistosité verticale, non liées à des décrochements, passent en profondeur à de grands décollements plats. On les met en évidence sur le terrain ou/et grâce à des profils de sismique réflexion écoute longue. Des aspects caractéristiques de ces profils comme par exemple la croûte inférieure litée pourraient représenter l'image sismique de tels décollements profonds.

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Quasi-hydrostatic compression of ruby to 500 Kbar

Measurements of the cell parameters of ruby to 500 Kbar under quasi-hydrostatic conditions in a diamond-anvil cell show a practically isotropic compression, the ratio c/a of the hexagonal cell parameters remaining constant. These results are consistent with previous single-crystal measurements below 100 Kbar as well as with ultrasonic elastic-constant measurements. There is no evidence for significant differences between the bulk moduli of ruby and corundum, and a review of compression and ultrasonic data yield Ko = 2.53±0.01 Mbar and Ko = 5.0 ± 0.4. Good agreement with the experimental values is found for compressions calculated from empirically or theoretically determined elastic properties.     

离子色谱法测定矿物包裹体中阴离子

本文介绍了用离子色谱法同时测定矿物包裹体中F~-、Cl~-、PO_4~(3-)、Br~-、NO_3~-、SO_4~(2-)6种阴离子的新方法。研究了流动相浓度对保留时间的影响以及消除负峰干扰的方法。     

内蒙古狼山地区的层控铀矿及其控制因素的卫片影象模式

狼山地区广泛分布着花岗岩型铀矿化和砂岩型铀矿化。本文通过对该区的遥感地质综合解译,重点研究了几个含铀盆地的砂岩型铀矿化成矿特点及其通感图象的影象特征,发现广布于早白垩世断陷盆地的砂岩型铀矿化是一典型的层控型铀矿。并通过区域构造型式的研究,强调了弧形构造的断块活动特征及其对含铀盆地和含矿层分布的控制作用;揭示了弧形构造的后期活动和环形构造、北北东向线性构造与铀矿化的再造关系。从而得出砂岩铀矿化是受地层岩相和弧、环、线构造“四位一体”条件控制的新认识。该矿化在MSS图象上呈现一定的影象特征,据此,本文概括出本区层控铀矿的影象模式。     

Dynamic Effect of Mudstone Strength Properties

This paper, comparing the dynamic test results of mudstone (silty clay) with the static ones, verifies influence of cyclic loading and loading rates on the strength of mudstone. It is found that the dynamic strength is higher than the static strength. In the case of rapid loading (rising time of pressure is 10ms ), the unconfined compressive strength for this type of soil in dynamic test is 2.3 to 2.9 times as high as that in static tests, and the strength index, Cd , is about 2.8 times as great as Cs , but ∅ values are approximately equal to each other. Repeat loading (up to 3600 cycles) has no great influence on the strength of mudstone, and under the condition of unconfined loading, the fatigue strength of mudstone is somewhat lower than its statically strength.     

西藏羊八井地热田水热蚀变

本文对羊八井地热田钻扎ZK-201、ZK-301和ZK-308的岩心进行了较系统的蚀变矿物学、岩石学和流体包体研究。划分出6个蚀变矿物共生组合及蚀变分带,讨论了蚀变过程中岩石化学变化的特点,并推测了蚀变的温度和酸碱度条件。研究表明,热田曾处于极度的活动状态,最高温度达220-240℃,由于冷水的入侵,热田在目前钻探所及范围已冷却了50-70℃。蚀变矿物分布模式表明,目前热田流体主通道位于北部,热田进一步的开发应以寻找北部深部高温流体为主。     

青海湖沉积物中的粘土矿物

本文对青海湖沉积物中的粘土矿物和沉积环境进行了初步研究。沉积物的粒度成分一般以粉砂级为主,湖周沉积物较粗,湖内沉积物较细。湖中粘土矿物以伊利石-绿泥石为主,含少量蒙脱石和高岭石等。沉积物表层未见蒙脱石,粘土中Al₂O₃、K₂O和MgO的相对百分含量的特征与海粘土的化学成分特征相似。     

事件地层学与地外灾变事件

从P∈—∈,P—T等地层界线上的特征岩石、古生物大规模灭绝和Ir及ξ~(13)C的异常等研究表明,与K—R界线一样,在这些界线上也可能存在有地外灾变事件。同时文中提出了界线灾变事件、界线灾变期、界线灾变环境、界线层、界线粘土层、梅树村地质事件等与研究事件地层学有关的一系列新概念。     

Oxygen isotopes in mantle related and geothermally altered magmatites of the Transhimalayan (Gangdese) ranges

In closed magma systems SiO₂ approximately measures differentiation progress and oxygen isotopes can seem to obey Rayleigh fractionation only as a consequence of the behaviour of SiO₂. The main role of ¹⁸O is as a sensitive indicator of contamination, either at the start of differentiation ( ¹⁸O_init) or as a proportion of fractionation in AFC. Plots of ¹⁸O vs SiO₂-allow to determine initial ¹⁸O values for different sequences for source comparison. For NBS-28=9.60, the ¹⁸O at 48% SiO₂-varies between a high 6.4 for Kiglapait (Kalamarides 1984), 5.9 for Transhimalaya, 5.8 for Hachijo-Jima (Matsuhisa 1979), 5.6 for Koloula (Chivas et al. 1982) and a low 5.3 for the Darran Complex, New Zealand. The Transhimalayan batholiths (Gangdese belt) were emplaced in the Ladakh-Lhasa terrane, between the present-day Banggong-Nujiang, and Indus-Yarlung Tsangbo suture zones, after its accretion to Eurasia. The gradient of the least contaminated continuous ( ¹⁸O vs SiO₂-igneous trend line is similar to that of Koloula, and AFC calculations suggest a low secondary assimilation rate of less than 0.05 times the rate of crystallisation. Outliers enriched in ¹⁸O are frequent in the Lhasa, and apparently rare in the Ladakh transsect. Low- ¹⁸O (5.0–0) granitoids and andesites on the Lhasa-Yangbajain axis are the result of present day or recent near-surface geothermal activity; their quartzes still trace the granitoids to the Transhimalaya ¹⁸O trend line, but the distribution of low total rock or feldspar ¹⁸O values could be a guide to more recent heat flow and thermally marked tectonic lineaments. Two ignimbrites from Maqiang show hardly any ¹⁸O-contamination by crustal material.