ROLE OF METASOMATIC PROCESSES IN RUBY-BEARING MARBLES FORMATION OF THE SOUTHERN URAL MOUNTAINS          下载免费PDF全文

《地学前缘》2017,24(3):257-262

Ruby-bearing marbles of the Southern Ural Mountains are developed in the metamorphic perimeter of granites-gneisses domes where high grade metamorphic granitization and diaphthoresis have occurred.Geological research into the development and occurrence of ruby-bearing marbles indicate that they formed as a result of repeated transformation.Their substrate consisted of an organogenous marine limestone containing Visean faunal remains.Intensive Mg metasomatism of limestone during early progressive stages of metamorphism resulted in a substrate of dolomite composition containing faunal remains with a calcite composition.Increased temperature and pressure resulted in metamorphism of early Mg metasomatites,turning them into fine-grained marble containing Visean faunal remains.Tensional stresses near the intrusive domes resulted in dedolomitization of early Mg metasomatites,giving rise to light,coarse-grained calcite marbles having polygonal-grained structure.Such carbonaceous marbles became metamorphosed around the perimeter of granite-gneiss massifs.Their rheological properties allowed for plastic flow in these marbles into areas of tectonic neutrality,forming bodies of rheomorphic marbles,sometimes even among marbled limestone.Relict bodies of Mg metasomatites underwent boudinage and rotation.Flow cleavage occurred in axial blocks of inter-dome structures and in their steep walls.Therefore platy jointing(banding,pseudo-lamination)formed in the marbles.Thickness of the plates is from several millimeters to 2-3m.Calcite underwent recrystallization with extension of grain size in the central parts of plates,sometimes amounting to 15-25cm in cross-section.Ruby-bearing marbles consist of Mg-calcite.The rock is coarse-grained,with a panidiomorphic texture.Schistosity is often observed in the plane of cleavage.Mg-calcite marble occurs among and grades into background calcite marbles,which are controlled by cleavage of flowing.It is supposed that the ruby-bearing Mg-calcite marbles bodies are elongated in the direction of dip.Their formation is caused by recrystallization under the action of rising metamorphogenic fluids at high temperatures and higher pressures(amphibolitic and epidote-amphibolitic facies).Ruby-bearing marbles formed at the end of the prograde stage of metamorphism.The early retrograde stage of metamorphism is defined by a new wave of Mg metasomatism and formation of calcite-dolomitic marbles with a poikiloblastic texture from calcite or Mg-calcite marbles.Usually the boundaries of the bodies are clear,planar,and controlled by cleavage.Studies of small bodies have shown that they are elongated in the direction of dip.Usually they contain pink corundum and/or pink spinel;red corundum is replaced by red spinel.Thus the initial marine limestones were transformed into various marbles and completely lost their primary composition and bedding as a result of metamorphism,deformation,and metasomatic transformation.Ruby-spinel mineralization in marbles is controlled by cleavage.  相似文献   

Seasonal Cumulative Effect of Ural Blocking Episodes on the Frequent Cold events in China during the Early Winter of 2020/21     

Yao YAO  Wenqi ZHANG  Dehai LUO  Linhao ZHONG  Lin PEI 《大气科学进展》2022,39(4):609-624

Starting in mid-November,China was hit by several cold events during the early winter of 2020/21.The lowest temperature observed at Beijing station on 7 January reached?19.6°C.In this paper,we show that the outbreak of the record-breaking extreme cold event can be attributed to a huge merging Ural blocking(UB)ridge over the Eurasian region.The sea-ice cover in the Kara and East Siberia Seas(KESS)in autumn was at its lowest value since 1979,which could have served as a precursor signal.Further analysis shows that several successive UB episodes occurred from 1 September 2020 to 10 January 2021.The persistent UB that occurred in late September/early October 2020 may have made an important contribution to the October historical minimum of sea ice in the KESS region.Our results also show that,after each UB episode in winter,significant upward propagation of wave activity occurred around 60°E,which resulted in weakening the stratospheric vortex.Meanwhile,each UB episode also caused a significant reduction in sea-ice extent in KESS and a significant weakening of the westerly jet in mid-high-latitude Eurasia.Results suggest that the Arctic vortex,which is supposed to enhance seasonally,became weaker and more unstable than the climatic mean under the seasonal cumulative effects of UB episodes,KESS warming,and long-lasting negative-phase North Atlantic Oscillation(NAO-).Those seasonal cumulative effects,combined with the impact of La Ni?a winter,led to the frequent occurrence of extreme cold events.  相似文献   

2010年1月2—5日乌兰察布市大雪、大风、寒潮个例分析   总被引：2，自引：0，他引：2  

常永旺  张百萍  王轶博 《内蒙古气象》2010,(4):15-17

利用常规气象观测资料,从天气环流形势的演变过程及各种物理量变化,对2010年1月2—3日乌兰察布地区普降中雪,其中集宁和兴和大雪、卓资山大到暴雪及雪后大风、寒潮过程做了客观分析。分析发现:这次过程是高空横槽转竖与地面河套气旋共同影响的结果,下游的阻塞高压是降雪的必要条件,极地冷空气南下在横槽北部堆积是出现大风、寒潮的关键。  相似文献   

Structure of the Middle Urals,east of the main Uralian Fault     

M. Friberg  G. A. Petrov 《Geological Journal》1998,33(1):37-48

In the Middle Urals, volcanic-arc and back-arc basin rocks of Ordovician to Devonian age occur in the Tagil Synform. These outboard terranes were thrust westwards in the late Carboniferous onto continental margin associations of late Proterozoic and Palaeozoic age, now exposed in the Central Uralian Uplift. The Main Uralian Fault coincides approximately with the suture separating the outboard terranes from the East European Platform margin. New fieldwork in the hinterland of the Middle Urals in the area east of the Tagil Synform has found structural evidence favouring E-directed thrusting of accreted terranes and eugeoclinal allochthons in the late Palaeozoic. The upper tectonic units are composed of ophiolite mélange and volcano-sedimentary rocks of Ordovician to Devonian age; they are thrust onto high-grade gneisses, some of possible microcontinental affinities, extensively intruded by mid-Palaeozoic granitic plutons. The nappes in the hinterland are refolded by major upright antiforms and synforms that fold the entire tectonostratigraphy. After thrust assembly, all tectonic units east of the Main Uralian Fault were intruded by late Carboniferous to early Permian granites. Reflection seismic profiles (recorded to 8 s TWT), recently reprocessed at Cornell University, image the major fold structures and demonstrate that they are restricted to the upper crust, being underlain by an extensive zone of flat-lying middle crustal reflectivity. At 10–15 km depth the latter appears to truncate all structures, including the late- to post-tectonic granitoids and extensional faults, east of the Main Uralian Fault. Previous studies (potential-field, refraction- and wide-angle-reflection seismics) have identified an anomalously deep crust under the Tagil Synform and have concluded that the root zone of the orogen is located beneath this belt. The new evidence presented here supports this interpretation, with back-thrusting of the oceanic rocks eastwards over Palaeozoic accreted terranes. © 1998 John Wiley & Sons, Ltd.  相似文献   

我国南方两次低温雨雪事件天气成因对比分析          下载免费PDF全文

吕春艳  李旭  陈军  刘艺朦  冉光镜 《沙漠与绿洲气象(新疆气象)》2024,18(1):96-104

2018年和2021年末我国南方分别发生了一次大范围的低温雨雪天气,对生活、生产造成了严重影响,因此对比分析这两次低温雨雪天气成因具有重要意义。结果表明：两次过程期间,对流层中层中高纬阻塞流场显著,阻高位于贝加尔湖西侧,脊前偏北气流在下游横槽后部堆积,使得西伯利亚高压强度增强。东传的Rossby波在阻高区域发生能量频散,利于阻高减弱、崩溃,横槽转竖引导槽后冷空气南下,导致地面强烈降温,同时在西伯利亚高压东侧和南侧,低频风温度平流是造成强降温的主要原因。低纬南支槽活跃,向北的暖湿空气与中高纬南下的冷空气汇合,造成我国南方大范围的低温雨雪、冻雨天气。与2018年过程相比,2021年过程持续时间较短,降水范围小,关键区降温幅度更大,是因为2021年过程期间Rossby波能量频散更快,阻高维持时间较短,冷空气从中高纬地区直接南下侵袭我国,而2018年冷空气在贝加尔湖附近发生堆积、西折,向南渗透时势力减弱。  相似文献   

江淮流域强暴雨过程对阻高和副高逐日变化的响应关系   总被引：3，自引：1，他引：2       下载免费PDF全文

陈菊英  冷春香  程华琼 《地球物理学进展》2006,21(3):1012-1022

江淮流域是我国暴雨频发的地区之一,而乌拉尔山阻塞高压和西太平洋副热带高压是北半球两个主要的大气环流系统.本文统计分析了1971~2003年期间乌山阻塞高压和西太平洋副高的逐日强度变化特征,研究了乌山阻塞高压和西太平洋副高对江淮流域强暴雨过程的响应关系.结果表明,江淮流域多数强暴雨过程发生在乌山阻高的减弱期,在乌山阻高的建立和加强期较少有持续性暴雨发生.乌山阻高的突然减弱是江淮流域强暴雨过程发生的强信号之一.同时,西太平洋副热带高压的加强西伸登陆是江淮流域强暴雨过程发生的必要条件之一.  相似文献   

西风带阻塞高压形成及崩溃动力机制的Euler-Lagrange理论解释          下载免费PDF全文

刘春  张春辉  刘自牧  叶秣麟 《气象科学》2023,43(3):384-392

本文主要采用Euler-Lagrange理论,讨论正压剪切流的切变参数对阻塞高压形成的影响。研究表明:存在一个临界参数,当切变参数的绝对值超过这个临界参数,正压剪切流将分歧出阻塞流型,这意味着阻塞高压的形成;反之,当切变参数的绝对值小于这个临界参数,阻塞流型将恢复到剪切流,这意味着阻塞高压的崩溃。该研究一定程度回答了阻塞流型"怎么形成"和"怎么崩溃"这一基本而关键的问题。  相似文献