Relationship between Crustal 3D Density Structure and the Earthquakes in the Longmenshan Range and Adjacent Areas

This paper presents the 3D density structure of crust in the Longmenshan range and adjacent areas,with constraints from seismic and density data.The density structure of crust shows that the immense boundary plane of density distribution in relation to the Longmeshan fault belt is extended downward to～80 km deep.This density boundary plane dips towards the northwest and crosses the Moho.With the proximity to the Longmenshan fault belt,it has a larger magnitude of undulation in the upper and middle crust ...     

Origin, Age and Significance of Pseudotachylites from the Eastern Dabieshan Orogenic Belt, China

Recent field survey in the eastern Dabieshan Mountains has revealed extensive occurrences of pseudotachylite. The pseudotachylite tends to occur as simple veins and injected networks along the NE-SW-trending fracture zones or shear zones, which are parallel to the Tanlu fault zone and cut all the pre-Cretaceous geological bodies. The characteristics of both the microstructures gained by the optical microscope and SEM imaging and the geochemistry between the pseudotachylites and their host rocks show that the pseudotachylites were formed mainly by ultracataclasis of their wall rocks in which they occur. The bulk K-Ar ages of the pseudotachylites yielded a narrow range of 81 -93 Ma, and moreover the laser-probe 40Ar/39Ar dating of phengite overprinting on the pseudotachylite gave a weighted mean age of 78.9 Ma. These results show that the pseudotachylites from the eastern Dabieshan Mountains formed along the NE-SW-trending fault zone during the uplifting of the orogenic belt at 80-90 Ma, which places impor     

内蒙古西乌珠穆沁旗阿木山组上段碳酸盐岩微相与沉积环境分析

内蒙古西乌珠穆沁旗晚石炭世-早二叠世阿木山组上段主要为发育在碳酸盐岩台地边缘内的一套深灰色-灰色的块状生物碎屑碳酸盐岩.根据微相组分、微相类型和沉积环境总结出8种碳酸盐岩微相类型,分别为叶状藻粒泥灰岩-泥粒灰岩、含鲕粒团块颗粒灰岩、含少量生物碎屑的泥状灰岩、球粒生屑泥粒灰岩、Antheria po-lygonalis珊...     

关于藏北改则地区夏岗江植物群及其地层时代的修订意见

在20世纪80年代,关于藏北改则县夏岗江雪山地区的夏岗江植物群及其所在的坚扎弄组曾存在着早二叠世和晚二叠世2种不同的时代意见。2002年,敌布错组发现后,古植物学家认为敌布错组和坚扎弄组的植物化石面貌相同或相似,同属于夏岗江植物群。由于敌布错组被认为不整合覆盖在中二叠世下拉组之上,因此,地质学家认为敌布错组、坚扎弄组及其所含的夏岗江植物群的时代为晚二叠世。然而,最近敌布错组之下的所谓的下拉组中发现了早三叠世—晚三叠世的牙形石,同时在坚扎弄组和敌布错组中发现了晚三叠世—早中侏罗世的孢粉化石,因此,夏岗江植物群及其所在地层的时代不是原来认为的晚二叠世,而是晚三叠世—早、中侏罗世。     

关于“侵入岩谱系单位填图方法”有关问题的讨论

本文简单地阐述了岩浆作用的多样性，指出不能以同源岩浆演化一种岩浆作用方式来概括或代表所有的岩浆活动，通过对“侵入岩谱系单位填图方法”在实际应用中存在的一些问题的讨论，指出同源岩浆演化理论尚不完善，不能人为地夸大同源岩浆演化理论的作用，未经深入研究和试验不宜把这个方法应用于所有时代和任何构造背景的花岗岩类。     

An Experimental Study of Mixture Corrosion Effects of Carbonate Rocks in the Transitional Zone of Littoral Karst Areas

The mechanism for development of littoral karst differs from that of inland karst, and the mixture corrosion effects are one of the most important factors that control the development of littoral karst. Through seven groups of static experiments carried out in a closed CO2-H2O system, basic conclusions can be drawn as follows: (1) the basic law of corrosion process in a transitional zone of seawater-freshwater in littoral karst areas is identical with that in the fresh water, i.e., the lithologic characteristics and rock structure are the main factors which control the development of littoral karst; (2) the mixture corrosion rate of the carbonate rock in the above transitional zone is faster than that in fresh water or seawater; (3) the mechanism for development of carbonate rocks differs at various pressures of CO2 in a transitional zone in littoral karst areas.     

辽西牛营子地区晚三叠世逆冲构造

燕山陆内造山带侏罗纪的构造及其研究已广为报道，但确凿的三叠纪构造分析明显不足，对辽西凌源牛营子地区详细的构造地质调查揭示该区晚三叠世晚期存在的逆冲构造，盆地东部中侏罗世郭家店组之下覆盖着一套晚三叠世逆冲叠瓦构造，其运动指向，黄土坡以西逆冲叠瓦构造由西向东推覆；黄土坡以北弧形断裂由北向南逆冲，为派生的运动。逆冲断裂带控制的槽地之中发育同逆冲期邓杖子组灰岩－－白云岩质角砾砾岩，我们的资料表明，对杖子组时代应属晚三叠世晚期，与晚三叠世老虎沟组基本是连续过渡的，原定牛营子盆地早－中侏罗世地层是倒置的，正常的晚三叠世－中侏罗世地层序列自下而上应为老虎沟组，邓杖子组，水泉沟组，郭家店组，晚三叠世晚期逆冲构造事实的确定说明，燕山陆内造山带至少从晚三叠世起就经历了强烈的变形，其早期形变历史对于认识区域构造演化和陆内变形的发展过程具有重要意义。     

Isotopic Geochronological Evidence for the Caledonian Xiongdian Eclogite in the Northwestern Dabie Mountains,China

A typical HP/MT (high pressure/medium temperature) eclogite from Xiongdian, northwestern Dabie Mountains, has been geochronologically studied using the single-zircon U-Pb, 40Ar-39Ar and Sm-Nd methods. Prismatic zircons occurring as inclusions within garnets define a minimum crystallization age of 399.5±1.6 Ma. 40Ar-39Ar dating on amphibole gives a plateau age.of 399.2 ± 4 Ma, which is interpreted as a retrogression age of amphibolite facies. This integrated study enables us to conclude that the age of high-pressure metamorphism is older than 399.5 ± 1.6 Ma, suggesting Caledonian collision between the North China and Yangtze plates. Round zircon within the aggregate of quartz and muscovite gives a concordant age of 301± 2 Ma, reflecting a later retrogression event. An age profile of post-eclogite metamorphism is documented, including amphibolite facies metamorphism at 399.2 Ma shortly after eclogitization and later retrogressive metamorphism at 301 Ma. Sm-Nd mineral isochron of garnet+omphacite gives     

新疆北部前寒武系划分和对比

库鲁克塔格是新疆北部前寒武系分布较广,地层层序相对完整的地区.作者以库鲁克塔格为地层模型区,以同位素第龄为格架,初步确定了本区群级地层单元的界线及归属.在岩石地层、生物地层、化学地层等各种方法相互印证的基础上,建立并完善了前寒武纪的地层层序.