Accretion and exhumation at a Variscan active margin, recorded in the Saxothuringian flysch

The Saxothuringian flysch basin, on the north flank of the Central European Variscides, was fed and eventually overthrust by the northwestern, active margin of the Tepla-Barrandian terrane. Clast spectra, mineral composition and isotopic ages of detrital mica and zircon have been analyzed in order to constrain accretion and exhumation of rocks in the orogenic wedge. The earliest clastic sediments preserved are of early Famennian age (ca. 370?Ma). They are exposed immediately to the NW of the suture, and belong to the par-autochthon of the foreland. Besides ultramafic (?ophiolite) material, these rocks contain clasts derived from Early Paleozoic continental slope sediments, originally deposited at the NW margin of the Saxothuringian basin. These findings, together with the paleogeographic position of the Famennian clastics debris on the northwestern passive margin, indicate that the Saxothuringian narrow ocean had been closed by that time. Microprobe analyses of detrital hornblendes suggest derivation from the “Randamphibolit” unit, now present in the middle part of the Saxothuringian allochthon (Münchberg nappes). Detrital zircons of metamorphic rocks formed a little earlier (ca. 380?Ma) indicate rapid recycling at the tectonic front. The middle part of the flysch sequence (ca. early to middle Viséan), both in the par-autochthon and in the allochthon, contains abundant clasts of Paleozoic rocks derived from the northwestern slope and rise, together with debris of Cadomian basement, 500-Ma granitoids and 380?Ma (early Variscan) crystalline rocks. All of these source rocks were still available in the youngest part of the flysch (c. middle to late Viséan), but some clasts record, in addition, accretion of the northwestern shelf. Our findings permit deduction of minimum rates of tectonic shortening well in excess of 10–30?mm per year, and rates of exhumation of ca. 3?mm/a, and possibly more.     

若尔盖高原及其周围山地的冻土和环境

若尔盖高原内部年平均气温０．６～３．３℃，气温年较差１９．１～２１．２℃，已不具备多年冻土形成和保存的气候条件。据１９９２年７月间试坑和钻孔测温，在１．０～２．２ｍ深处地温为５～８．４℃，浅层地下水温６．０～７．８℃，由此判断不存在多年冻土，季节冻结深度为１．０～２．０ｍ。据冻土现象和试坑资料判断，周围山地海拔４１５０～４２００ｍ以上发育山地岛状多年冻土。区内沼泽演化表明，部分沼泽已疏干或向疏干趋势发展，草场退化和草原沙化已成为本区生态环境的重要问题，并已影响畜牧业发展     

Barotropic local instability and severe storm process

By means of barotropic model, the characteristic and initial value problems are investigated to reveal the local two-dimensional barotropic instability of the nonuniform current to the dynamic mechanism of the formation of the Yangtze-Huaihe River severe storm in July 1991. Analytical theory and numerical experiment show that (i) the unstable developing modes are chiefly the two periods of about 44 d and 10 d, which are fundamentally consistent with that of the precipitation change of the Yangtze-Huaihe River. (ii) The growth rate of the local perturbation is dominated by the meridional wave numbern = 1–5 and zonal wave numberk = 1–12, i.e. the severe storm over the Yangtze-Huaihe River results from the interaction of the systems at different latitudes and waves of different scales, (iii) The perturbation over the Yangtze-Huaihe River possesses the property of local intensification, which slowly migrates westward over the lower and middle reaches of the Yangtze-Huaihe River. (iv) The growth rate of the instability, especially the propagation velocity of the perturbation, is sensitive to the external parameters ū and α. Project supported by the National Natural Science Foundation of China.     

Environmental evolution of Zoigê Basin since 900 kaB.P. and comparison study with Loess Plateau

The Zoige Basin is located in the eastern margin of the Qinghai-Xizang Plateau, in which two cores, RH and RM, have been drilled, with the depths of 120 m and 310 m respectively. The former with the bottom age of 826 kaB. P. has been divided into 21 stages according to the multi-proxy analysis, which could be basically compared with the oxygen isotope record of deep-sea core. The palaeoclimatic and palaeoenvironmental process of the Zoigê Basin over the past 900 kaB. P. is reconstructed, and the comparison of core RH with the Luochuan Loess record is made.     

Evolution of Quaternary groundwater system in North China Plain

The Quaternary groundwater system in the North China Plain is formed mainly through the terrestrial water flow action on the united geological and tectonic backgrounds. The analysis of groundwater dynamic field, simulation of groundwater geochemistry, and the¹⁴C dating and extraction of isotope information have provided more evidence for recognizing and assessing the evolution of groundwater circulation system and studying the past global changes. The exploitation and utilization of groundwater on a large scale and overexploitation have given rise to the decline of regional groundwater level, change of flow field, decrease of water resources and downward movement of saline water body. The water environment has entered a new evolution stage in which it is intensely disturbed by the mankind’s activities. Project supported by the National Natural Science Foundation of China.     

Spatial-temporal Frame,Evolution and Mineralization of the Northern Qilian Metallogenic Province

Four metallogenic epochs occurred in different tectonic environments during theevolution of the Northern Qilian metallogenic province through the geological time. The Mid-dle Proterozoic metallogenic epoch witnessed the tectonic environment of crustal breakupcaused by mantle diapirism, in which ultramafic-mafic rocks were intruded along beep faultbelts and the superlarge Jinchuan magmatic Cu-Ni sulphide deposit was formed. In theMiddle-Late Proterozoic metallogenic epoch the crust was further broken to form anintracontinental rift, in which the Chenjiamiao style massive Cu-Fe sulphide deposits hosted bybasic volcanic tuff were formed in the lower volcano-sedimentary sequence, while the largesedex type Jingtieshan style Fe-Cu deposits were formed within the upper abyssal carbon-richargillaceous sedimentary sequence. The Early Palaeozoic saw the aulacogen environment, with-in which the Baiyinchang style superlarge massive base and precious metal sulphide depositshosted by quartz keratophyric tuff were formed in the Middle-Late Cambrian rifted island arcand the massive Cu-Zn sulphide deposits and magmatic chromite deposits associated with theophiolite suite were formed in the Early-Middle Ordovician, and the Honggou style massiveCu-Fe sulphide deposits hosted by spilite were formed in the Late Ordovician back-arc basinenvironment. In the Late Palaeozoic-Meso-Cenozoic, the metallogenic province went into anintracontinental orogenic stage characterized by compressive tectonic environment, in whichthere occurred carbonate-quartz vein type and tectono-alteration gold deposits associated withductile-shear structures.     

金川矿区露采边坡超基性岩体工程地质特性研究

超基性岩体在金川矿区露采边坡稳定性评价中占有重要地位, 它是整体边坡的支撑体。本文研究了该岩体的物质组成、赋存环境、物理力学性质、岩体结构特征等。在此基础上, 对超基性岩体质量进行了评价。     

地球演化中最大的两级节律

地球演化中表现出的最大两级节律为１０×１０８ａ和２×１０８ａ。每２个相邻节律可合并为一个周期，因而地球演化的最大两级周期为２０×１０８ａ和４×１０８ａ。岩石学、地层学和构造地质学方面诸多证据都说明这种划分的合理性。对于地球演化中的这类大型节律及周期性的成因机制，用笔者已提出的“地球多级驻波脉动理论模型”可以得到较合理的解释。     

吕梁山北段变质岩系变形分解作用初探

吕梁山北段变岩系中，变形分解现象从宏观到微观的各级尺度上均有表现。平面上强弱变形带（域）常呈网结状形态产出，剖面上随深度的加深，强弱变形带（域）互为消长。在变形分解作用一，角闪石转化为黑云母、绿泥石、斜长石牌号降低。固流限较低的矿物发生溶解，或充填缍裂隙形成同构造分泌结晶脉，或在一定条件下形成变斑晶，致使岩石的结构构造由块状向片麻状、片状转化。Ｍｇ、Ｆｅ、Ｔｉ、Ｐ、Ｋ、Ｒｂ增高，Ｓｉ、Ｎａ、Ｓｒ降     

华北南部地区——古生界构造演化及其油气远景

华北南部地区的地质演化与华北其他地区一样，经历了结晶基底形成，中一晚元古代台内裂谷发育、古生代稳定地台沉积和中一新生代活化等发展过程。但本区受秦岭褶皱带构造活动的强列影响。因而具有相对独特的构造演化特征和油气控制条件。早寒武世中期，古秦岭海槽伸展扩张，沉积了一套全区广泛分布的以碳酸盐岩为主夹泥页岩的地层；晚寒武世开始，古秦岭海槽向北俯冲挤压，在本区南部出现一个平行于海槽的大陆边缘隆起；中奥陶世发生