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。     

滇西新构造运动时期陆内伸展作用

上新世一第四纪为滇西的新构造运动时期,代表了本区喜马拉雅造山期后的伸展作用时间,除形成区域性的角度不整合外,还形成了一系列小规模的转换拉张盆地,并产生大规模玄武岩浆喷发。洱源—遮放地震深度-速度剖面的P波速度,显示本区岩石圈具4层结构,即上部壳层、韧性壳层、下部固态壳层和地幔岩石圈。各层对比表明,地幔隆起导致热隆伸展作用及热流上涌,并在壳幔界面产生局部混熔,下部壳层发生区域深变质作用;韧性壳层产生强烈纯剪流动,上部壳层则以脆性—脆韧性走滑断层及层圈式滑脱被动地调整;地壳均衡作用不断地调整地幔隆起与地壳厚度的关系。     

Kinematics of crustal stacking and dispersion in the south-eastern Bohemian Massif

The south-eastern Bohemian Massif consolidated during the Late Variscan orogeny by the oblique collision of two continental crustal blocks after closure of an oceanic realm. One microcontinent comprises portions which are now distributed among Moravian and Moldanubian units and which are characterized by Late Proterozoic tectonothermal events, especially by granitoid intrusions. The other microcontinent includes the Gföhl gneiss and granulites (Gföhl nappe) of probable Early Palaeozoic protolith ages. Both continental blocks are separated by an ophiolite-like assemblage, which is preserved in portions of the Raabs unit.Oblique crustal stacking is accompanied by north-eastward propagation of nappes in a dextral transpressive regime. Exhumation of previously thickened crust is achieved by equally oriented bulk extension but partitioned in distinct displacement paths. Coeval stacking and extension at different crustal levels is suggested.Correspondence to: H. Fritz     

北京云蒙山花岗岩基的岩石变形及其成因

云蒙山花刚岩基由１２个侵入体组成，岩基中的片麻状花岗岩是在１２６±２１Ｍａ时侵入的型花岗岩，根据岩基中花岗岩与围岩的变形循征，确定岩基的侵位机制为底辟定位型，花岗岩中的变形组构与环绕岩基的糜棱岩的岩基定位晚期、花岗岩浆完全结晶之前形成。由于云蒙山花岗岩基的强力定位，导致密怀变质核杂岩在燕山晚期再次发生伸展构造运动。     

豫西东秦岭造山带低压变质带的变质变形和变质反应

豫西西峡北部低压变质带受到４次变形改造。低压变质作用主要发生在Ｄ１和Ｄ２变形间期，形成黑云母－红柱石、石榴石－红柱石、十字石－红柱石和堇青石－红柱石４个递增变质带。由矿物变质反应识别出堇青石－红柱石带ｐ－Ｔ趋势具有减压增温特点，这一演化特征可能反映变质作用具有地壳拉张的地球动力学特点。     

滇西北及邻区现代构造应力场

通过滇西北及邻区大量活动断层擦痕的测量和利用由断层滑动方向反演构造应力张量的计算方法，获得滇西北及邻区现代构造应力场特征：区域现代构造应力场以水平作用为主，在滇西北地区，最大主应力方向为北北东；在滇西北外围地区，最大主应力方向为北北西或北西。在构造应力场分析的基础上，依据活动断裂构架及运动组合特征，提出了滇西北反“Ｓ’型右旋扩展的构造成因模型     

云开隆起低压麻粒岩相变质作用时代的重要发现

首次报道云开隆起低压麻粒岩９５０Ｍａ左右的变质作用年龄，结合麻粒岩的岩相学以及区域地质特征，指出晋宁期云开地区处于拉张的构造环境。     

可拓聚类预测方法在地质灾害危险性评价中的应用

基于可拓学的物元模型和聚类分析原理,提出了地质灾害危险性评价的可拓聚类预测方法。本文根据地质灾害危险性的9个影响因子,构建了经典域物元和节域物元,应用物元理论和可拓集中的关联函数建立预测模型,通过聚类分析得到地质灾害危险性的预测结果。并将可拓聚类预测方法用于对云南昭通地区滑坡、泥石流危险性评价之中,实例研究表明了可拓聚类预测方法用于地质灾害危险性评价的有效可行性。