河北丰宁牛圈银金矿床构造地质特征

牛圈银金多金属矿,华北地洼北缘。成矿条件明显受燕山晚期地洼活动－陆壳伸展运动所形成的断裂构造和火山机构控制,矿床呈隐爆角砾岩筒状,具浅成低温热液型矿床特征。     

Late Palaeozoic NE–SW ductile–brittle extension in the La Serre horst,eastern France

In the La Serre horst of the Alpine foreland, the pre-Triassic La Serre median fault zone separates a Late Devonian–Early Carboniferous granite from an ignimbrite of unknown age and from Permian deposits. Motion along this fault zone took place first in ductile conditions and then evolved in brittle conditions. Both ductile and brittle shear criteria indicate a top-NE normal-dextral displacement. Similar motions are reported along faults bounding Late Palaeozoic intramontane coal basins located in the Massif Central and correspond to a widespread NE–SW Late to Post-Orogenic extension that affected the Variscan basement during Late Carboniferous to Early Permian times. To cite this article: G. Coromina, O. Fabbri, C. R. Geoscience 336 (2004).     

浅析断陷盆地多幕拉张与油气的关系--以南堡凹陷的多幕裂陷作用为例

南堡凹陷为渤海湾盆地北侧的一个小型叠合型含油气凹陷 ,中新生代以来 ,该区经历了 4幕裂谷作用演化和 1幕构造再活化作用的改造 .其 4幕裂谷作用包括燕山早期裂谷一幕发育期、燕山晚期裂谷二幕发育期、老第三纪始新世—渐新世中期裂谷三幕发育期及老第三纪渐新世中期—新第三纪中新世早期裂谷四幕发育期 .新第三纪中新世中期以来 ,该区构造性质发生明显转变 ,即由中新世早期的构造衰弱期转化为新的构造活化期 ,主要表现在 :断裂作用加剧、拉张作用增强、沉积速率加快 .上述各幕构造过程对南堡凹陷的油气生成及富集规律具有明显不同的控制作用     

小城镇空间结构变迁的形式和动力

小城镇向心增长的空间过程主要表现为郊区城镇化、内城更新改造、反向扩展3种形式，是小城镇对农村人流、物流的集聚和内部空间结构的优化。小城镇离心增长的空间过程主要表现为城镇郊区化、产业区位变迁、外向扩展3种形式，是小城镇生产力发展到一定阶段后城镇要素向近郊区的扩散。小城镇向心增长和离心增长是集聚与扩散相互作用的表现，社会经济发展是小城镇空间变迁的根本动力，功能－形态互适机制是其演变的主要机制。     

Regional variation in exhumation and strain rate of the high-pressure Sambagawa metamorphic rocks in central Shikoku, south-west Japan

Regional variation in the P–T path of the Sambagawa metamorphic rocks, central Shikoku, Japan has been inferred from compositional zoning of metamorphic amphibole. Rocks constituting the northern part (Saruta River area) exhibit a hairpin type P–T path, where winchite/actinolite grew at the prograde stage, the peak metamorphism was recorded by the growth of barroisite to hornblende and sodic amphibole to winchite/actinolite grew at the retrograde stage. In the southern part (Asemi River area), rocks exhibit a clockwise type P–T path, where barroisite to hornblende core is rimmed by winchite to actinolite. The difference in P–T path could suggest a faster exhumation rate (i.e. more rapid decompression) in the southern than in the northern part. On the other hand, physical conditions of deformation during the exhumation stage have been independently inferred from microstructures in deformed quartz. Recrystallized quartz grains in rocks from the low‐grade (chlorite and garnet) zones are much more stretched in the southern part (aspect ratio ≥ 4.0) than in the northern part (aspect ratio< 4.0), indicating a higher strain rate in the former than in the latter. These facts may indicate that the exhumation and strain rates are correlated (i.e. the exhumation rate increases with increasing the strain rate). The difference in the exhumation rate inferred from amphibole zoning between the northern and southern parts could be explained by an extensional model involving normal faulting, where the lower plate can be exhumed faster than the upper plate due to the displacement along the fault. Furthermore, the model may explain the positive correlation between the exhumation and strain rates, because the lower plate tended to support more stress than the upper plate.     

变质核杂岩研究进展、基本特征及成因探讨

本文对比了国内外变质核杂岩的基本特征后，重点探讨了几个问题：变质核杂岩发育的构造位置，既有如科迪勒拉变质核杂岩的陆缘冒地斜中心的，又有大量是陆内的。它们的基本结构更普通的是三层式，即在核杂岩和上部不变质的以发育正断层为特点的盖层之间，通常发育一套以浅变质的、发生过强烈近水平剪切所致的韧性流变的中间层状岩系；从韧性流变层的不均匀分布，反映出地热状态的横向不均一性；变质核杂岩的几何学、运动学、热状态及岩浆作用和变质作用等表明，幔源热隆、地壳的热软化、重力上浮及水平应力的联合作用可能是其隆升的原因。     

Some observations on brittle-ductile toggle

In low temperature deformation of polymineralic rocks the constituent minerals often show contrasting deformation mechanisms. In naturally deformed arkoses, feldspathic quartzites and grits under greenschist to almandine-amphibolite fades condition, feldspar deforms by microboudinage (rigid-brittle behaviour), while quartz flows by a combination of dislocation creep, pressure solution and solution transfer. Boudin segments develop and separate in a phased sequential manner while quartz matrix flows in a ductile manner, indicating a brittle-ductile toggle during progressive deformation. Both the pressure solution and dislocation creep flows are volume-conservative. Therefore, a net volume increase during the above deformations is a necessity, unless compensated by a solution-transfer process. Hydrofracturing probably played a role in microboudinage formation as the ambient level of differential stress is estimated to be low around 45–75 MPa. To develop a synthetic flow law for the above type of deformation in arkoses, one needs to consider the significance of different rate-controlling mechanisms. As feldspar pull-aparts are syntectonically filled with quartz or metamorphic minerals crystallizing during progressive deformation, successive microboudin segmentation will depend on how fast/slow the matrix quartz moves to the open crack or the sealing takes place by transfer of appropriate solute components by pressure solution or solution transfer, the real rate-controlling process.     

Classical confidence intervals and Bayesian probability estimates for ends of local taxon ranges

The observed local range of a fossil taxon in a stratigraphic section is almost certainly a truncated version of the true local range. True endpoints are parameters that may be estimated using only the assumption that fossil finds are distributed randomly between them. If thickness is rescaled so that true endpoints lie at 0 and 1, the joint distribution of gap lengths between fossil finds is given by the Dirichlet distribution. Observed ends of the range are maximum likelihood estimators of true endpoints, but they are biased seriously. Extension of the observed range at each end by a distance equal to the average gap length yields unbiased point estimators. Classical statistics can generate confidence intervals for ends of the taxon range; but with Bayesian inference, the probability that true endpoints lie in a certain region can be stated. For a 95% confidence level (classical) or a 95% probability (Bayesian), the range extensions exceed the observed range if the range is established on less than six finds; if only two finds are used, such range extensions are an order of magnitude longer than the observed range. Evidently the standard biostratigraphic practice that identifies zonal boundaries as horizons rather than confidence intervals may not be justified at the resolution of typical fossiliferous sections.     

内蒙古中部早元古代造山事件中麻粒岩相低压变质作用

内蒙古中部早元古代麻粒岩相低压变质地壳,根据富铝片麻岩中的长石种类和岩石组合,可划分为南北2个带、6个岩石组合。它们代表着不同的变质层状岩系序列及其所经历的变质作用的温度、压力条件和构造背景。矿物的包裹结构和反应边组构,记录了高温低压矿物组合取代了中温高压矿物组合:石榴子石+石英→紫苏辉石+斜长石,蓝晶石→矽线石及石榴子石+蓝晶石/矽线石+石英→堇青石。岩石的变形组构、矿物组合的转变关系和变质作用的PTt轨迹表明:本区与变质作用同期的高温正滑韧性剪切作用,是麻粒岩相低压变质地壳形成的主要原因。由中温高压变质环境转入高温低压变质环境是造山事件中推覆作用与拉伸作用联合作用的结果。