Discussion of Some Problems as to the East Asian Subtropical Monsoon   总被引：2，自引：0，他引：2       下载免费PDF全文

HE Jinhai  ZHAO Ping  ZHU Congwen  ZHANG Renhe  TANG Xu  CHEN Longxun  ZHOU Xiuji 《Acta Meteorologica Sinica》2008,22(4):419-434

Based on NCEP/NCAR gridded reanalysis, TRMM precipitation data, CMAP, and rainfall observations in East China, a study is conducted with focus on the timing and distinctive establishment of the rainy season of the East Asian subtropical monsoon （EASM） in relation to the South China Sea （SCS） tropical summer monsoon （SCSM）. A possible mechanism for the EASM is investigated. The results suggest that 1） the EASM rainy season begins at first over the south of the Jiangnan region to the north of South China in late March to early April （i.e., pentads 16-18）, and then the early flooding period in South China starts when southerly winds enhance and convective rainfall increases pronouncedly; 2） the establishment of the EASM rainy season is earlier than that of its counterpart, the SCSM. The EASM and the SCSM each is featured with its own independent rain belt, strong southwesterly wind, intense vertical motion, and robust low-level water vapor convergence. The SCSM interacts with the EASM, causing the EASM rainy belt to move northward. The two systems are responsible for the floods/droughts over the eastern China; and 3） in mid-late March, the eastern Asian landmass （especially the Tibetan Plateau） has its thermal condition changing from a cold to a heat source for the atmosphere. A reversal of the zonal thermal contrast and related temperature and pressure contrasts between the landmass and the western Pacific happens. The argument about whether or not the dynamic and thermal effects of the landmass really act as a mechanism for the earlier establishment of the EASM rain belt is discussed and to be further clarified. Finally, the article presents some common understandings and disagreements regarding the EASM.  相似文献   

Late quaternary palaeoclimate in the savannas of South America     

Maria La Salgado-Labouriau 《第四纪科学杂志》1997,12(5):371-379

The paper reviews Late Quaternary palynological evidence from eight sites in the savannas of northern South America. The sites reviewed are Lake Valencia (10°N), Carajas (6°S), Aguas Emendadas (15°S), Crominia (17°S), Salitre (19°S), Lagoa de Serra Negra (18°S), Lagoa Santa (20°S) and Lagoa dos Olhos (20°S). Four of the sites show evidence for a climate more humid than at present from ca. 36 ka BP to ca. 22–18 ka BP. Maximum dryness was reached at 14 ka to 10.5 ka BP at Lake Valencia. There was an increase in moisture from 8.8 ka BP at Lake Valencia and from 7 ka BP in Central Brazil. The presence of charcoal indicates human impact from ca. 8.6 ka BP. ©1997 John Wiley & Sons, Ltd.  相似文献   

Biostratigraphy,sedimentology and sequence stratigraphy of the Tournaisian–Viséan transitional strata in South China (Guangxi)     

L. Hance  Ph. Muchez  H.-F. Hou  X. Wu 《Geological Journal》1997,32(4):337-357

The biostratigraphy and sedimentological evolution of the Tournaisian–Viséan (T–V) transitional strata in South China (Guangxi) have been investigated. The sediments were deposited on a carbonate platform and in slope and basinal environments. In the T–V transitional strata, six foraminiferal associations have been distinguished which allow correlation between the shallow and deep water deposits. A careful examination of the evolutionary stages of the foraminifer Eoparastaffella provides a more accurate criterion for the definition of the T–V boundary, but does not significantly modify the historical one. The distinction of two morphotypes is based on the elevation of the last whorl and the peripheral outline. Tournaisian specimens of Eoparastaffella have a well rounded periphery (morphotype 1) contrasting with the subangular periphery of younger Viséan specimens (morphotype 2). A coefficient can be deduced from simple biometric measurements for more precisely defining the T–V boundary. The sequence stratigraphy of the T–V strata in South China has been reconstructed by combining biostratigraphical and sedimentological data. It allowed the correlation of the T–V transitional strata between the platform area and the slope and basinal locations. Late Tournaisian strata were deposited during a highstand systems tract. Near the end of the Tournaisian, a major drop in relative sea-level led to the development of an unconformity in the platform area. Lowstand deposits formed during latest Tournaisian time in the basin where a detailed biostratigraphic framework has been devised. Sediments deposited during the ensuing transgressive systems tract overlie the late Tournaisian highstand sediments in the platform area and the latest Tournaisian lowstand deposits in the basin. A major drop in relative sea-level near the end of the Tournaisian has been recognized worldwide. Therefore, the possibility of using the sequence stratigraphy of the T–V strata in South China for worldwide correlations should be investigated. © 1997 John Wiley & Sons, Ltd.  相似文献   

南洞庭湖湿地景观文化的结构与特征研究   总被引：1，自引：0，他引：1  

王保忠  何平  安树青  王彩霞  王保明  沈守云 《湿地科学》2005,3(4):241-248

洞庭湖是我国传统的风景名胜区,也是世界上唯一一个由三个国际重要湿地组成的湖泊。作为洞庭湖的最重要组成部分,南洞庭湖国际重要湿地蕴藏着独特的景观文化资源,在长江文明、中华文明乃至世界文明的发展中占有重要地位。根据1999～2005年的调查结果,系统地分析了南洞庭湖湿地景观文化资源的结构特征：①物质文化（稻耕文化、船文化、建筑文化、生产文化、工程文化等）;②精神文化（端午节、民俗艺术、湖乡忌禁、饮食文化、抗洪抢险、植物文化等）;③制度文化（傩文化、楚文化、历史遗迹、湿地文物等）;阐述了湿地文化的起源及地位,重点研究了15种景观文化内容。研究结果表明,南洞庭湖景观文化的本质特征（湿地文化与水文化）具有国际重要湿地背景,典型的湘楚文化特点,突出的湿地特色,独特的世界遗产特点,同时具有高度的真实性及完整性。  相似文献   

蚀变岩帽的特征、成因以及在华南的分布探讨     

陈静  周涛发  张乐骏  孙艺  WHITE Noel C  李旋旋 《岩石学报》2020,36(11):3380-3396

Sillitoe（1995）蚀变岩帽（Lithocap）的定义为大范围富黄铁矿的硅化、高级泥化和泥化蚀变,在地质环境上位于古地表和浅成中-酸性岩浆侵入体之间。蚀变岩帽往往显示为突出的正地形,有助于寻找隐伏的斑岩矿化体。但蚀变岩帽在地表的范围往往多达几十个平方千米,又常常掩盖下覆斑岩矿床的蚀变矿化特征及其地球化学印记,因此大型的蚀变岩帽又给勘探工作带来一定的挑战。蚀变岩帽相关矿床的勘探需以地质填图为基础,结合近红外光谱分析（SWIR）进行蚀变填图,以及全岩地球化学以及矿物地球化学表现的元素或元素组合异常,来帮助定位热源或深部斑岩体。遥感和地球物理中的激电响应,也可以辅助定位岩体。华南地区的蚀变岩帽主要分布于长江中下游成矿带和东南沿海火山岩带。前人对安徽庐枞盆地中的矾山蚀变岩帽进行了系统研究,确定了矾山蚀变岩帽形成于白垩纪,与围岩砖桥组火山岩年龄一致。同位素和流体包裹体工作证明了形成矾山蚀变岩帽的流体主要为深部岩浆热液中的酸性气体与浅部大气降水的混合,在浅部高渗透率的火山岩及其岩性界面反应,广泛发育了一套硅化和高级泥化蚀变,指示与矾山相关可能存在斑岩和高硫型浅成低温热液铜金矿床。福建紫金山地区有中国最大的高硫型浅成低温热液矿床,主要赋存于紫金山蚀变岩帽中。紫金山蚀变岩帽的地质特征和蚀变分带已经研究的较为详细,但目前深部的侵入体还没有发现。浙江的蚀变岩帽是中国非金属矿产的重要来源,包括明矾石矿、地开石矿和红柱石矿等,这些蚀变岩帽与金属矿化的关系尚未有相关研究。根据目前的资料总结,有较多的蚀变岩帽分布在中国华南,这些蚀变岩帽特征典型,但目前的研究程度尚浅。现有的研究结果表明,华南的蚀变岩帽的成矿潜力巨大,可能存在一条巨型的斑岩-浅成低温矿床成矿带,具有广阔的找矿勘查前景,建议加强蚀变岩帽及相关矿床的找矿与研究工作。  相似文献   

南秦岭早古生代玄武岩的岩浆源区及演化过程   总被引：1，自引：1，他引：0  

张方毅  赖绍聪  秦江锋  朱韧之  赵少伟  杨航  朱毓  张泽中 《岩石学报》2020,36(7):2149-2162

南秦岭地区早古生代玄武岩中发育的大量单斜辉石斑晶为研究火山岩的深部演化过程及源区属性提供了重要的载体。本文通过对早古生代玄武岩及其中的单斜辉石斑晶进行矿物学、岩石学及地球化学分析,讨论火山岩的演化历程及源区属性。电子探针分析结果表明玄武岩中单斜辉石斑晶属于透辉石,其成分与全岩成分并不平衡,暗示岩石经历了单斜辉石的堆晶作用。通过质量平衡计算得到了与单斜辉石斑晶平衡的熔体并计算了单斜辉石结晶的温压条件,结果显示单斜辉石斑晶结晶压力为7.6～14.0kbar,温度为1201～1268℃。高压下的分离结晶作用导致了单斜辉石成为主要的结晶相。重建后的玄武岩具有高镁、高钙、富钛,富集高场强元素Nb、Ta,亏损Rb、K、Sr和P,Dy/Yb比值高的地球化学特征,指示其源区为含单斜辉石、磷灰石及石榴石的交代岩石圈地幔。同地区发现的玄武质角砾也具高镁及高钙的特征,其富集Ba、Nb、Ta、Ti及低Dy/Yb比值表明源区为含单斜辉石、角闪石及尖晶石的交代岩石圈地幔。  相似文献   

Nature and Evolution of Pre-Neoproterozoic Continental Crust in South China: A Review and Tectonic Implications     

WANG Kai  DONG Shuwen  YAO Weihu  ZHAO Tianyu 《《地质学报》英文版》2020,94(6):1731-1756

South China as an amalgamation of the Yangtze and Cathaysia blocks is composed of Archean to Mesoproterozoic basement overlain by Neoproterozoic and younger cover. Both the constituent Yangtze and Cathaysia blocks contain well-preserved Neoproterozoic rocks that have been extensively studied in terms of the age and tectonic nature, but less is known about their earlier crustal history due to the incomplete rock record. Recent efforts in investigating the yet survived crustal nature based on isotopic and elemental signatures preserved in igneous and sedimentary rocks have steadily improved our knowledge about the pre-Neoproterozoic continental crustal evolution in South China. In this paper, we summarize the up-to-date pre-Neoproterozoic records, including petrological, geochronological, geochemical and geophysical data, across South China, and discuss its spatiotemporal patterns of the pre-Neoproterozoic crust and the relevant tectonic events. While the xenocrystic/inherited and detrital zircon records suggest widespread Archean (mainly ca. 2.5 Ga) crustal components within both the Yangtze and Cathaysia blocks, exposed Archean rocks are only limited to isolated crustal provinces in the Yangtze Block. These Archean rocks are dominated by TTGs (tonalite-trondhjemite-granodiorite) with varied ages (3.3–2.5 Ga) and zircon Hf isotopes, indicating a compositionally heterogeneous nature of the Archean Yangtze Block and, by inference, the development of multiple ancient terranes. The early Paleoproterozoic (2.4–2.2 Ga) tectonomagmatic events characterize the western Yangtze Block and are supportive of an east-west subdivision of the Yangtze basement, whereas the late Paleoproterozoic (2.1–1.7 Ga) orogeneses may have affected a larger area covering both the western and eastern parts of the Yangtze Block, and also the Cathaysia Block. The eastern Yangtze Block with generally northeastward-younging late Paleoproterozoic magmatism and metamorphism likely experienced a prolonged 2.05–1.75 Ga orogenic process welding the various Archean proto-continents, consistent with the documentation of a buried late Paleoproterozoic orogenic belt imaged by deep seismic profiling from its central part and of a slightly older ophiolitic mélange in the northern part. The Cathaysia Block was probably involved in a short-lived 1.9–1.8 Ga orogenic event. The two orogeneses overlapped in time and may have contributed to the cratonization of a possible unified South China, and are referred to be linked with the assembly of the Nuna Supercontinent. The subsequent late Paleoproterozoic to early Mesoproterozoic rift successions and intrusions (1.7–1.5 Ga) in the southwestern Yangtze Block, and the ca. 1.43 Ga rifting in Hainan Island of the Cathaysia Block could be responses to the Nuna break-up. Late Mesoproterozoic (1.2–1.0 Ga) magmatism of varied age and nature in different localities of the Yangtze Block is reflective of a complex tectonic process in the context of the assembly of the Rodinia Supercontinent. Similar-aged metamorphism (1.3–1.0 Ga) is recorded in Hainan Island, reflecting the Grenvillian continental collision during the Rodinia assembly, but further studies are necessary to better constrain the late Mesoproterozoic tectonic framework of South China.  相似文献   

藏南地区新生代多阶段构造演化及其动力学的探讨     

刘德民  杨巍然  郭铁鹰 《地学前缘》2020,27(1):194-203

开合构造是一种全球构造假说,该假说基础为地球上的一切物质和地质体都存在开合表现;可以用开合构造观解释一些板块构造理论登陆后不能合理解释的地质现象。文章在结合前人基础地质资料基础上,分析藏南地区基本的构造单元划分;强调动态构造单元划分,提出了被重力拆离断层改造叠加的逆断层区以及被拆离断层改造的正断层区。在主流观点提出碰撞挤压造山形成青藏高原时,野外科学考察发现了绒布寺伸展正断层的存在。文章认为绒布寺伸展正断层与主中央逆冲断层形成时间比藏南拆离系要早,两者构成了藏南挤出构造的两个边界;而藏南拆离系是晚期形成的,局部叠加在主中央逆冲断层之上,并且珠峰北追踪了早期绒布寺正断层呈相对高角度产出。3条断裂构造系统是不同时期、不同构造背景下的产物。藏南由前人所划分的飞来峰、构造窗等逆冲推覆构造系统中的构造单元,往往挤压逆冲特征表现不明显,却表现出由新的地层覆盖在老地层之上而显示地层柱缺失的特征。文章认为这些是滑覆构造的表现,是藏南地区晚期重力滑覆作用的产物。用开合构造理论将该地区新生代构造演化划分为由开转换为合;然后由合转换为开,构成一个完整开合演化历史,在这多阶段构造演化过程中,地球深部的热能、地球内部的重力势能以及构造引起的附加应力能起到关键作用。  相似文献   

黔南上司地区石炭系有孔虫:兼论华南维宪阶有孔虫生物地层序列     

沈阳  王训练  李玉坤  杨志华  岑武轩  王雪兵 《地学前缘》2020,27(6):213-233

石炭纪时期有孔虫具有演化快、分布广、数量丰富、分异度高的特点,对于地层的划分对比具有极为重要的意义。与全球其他重要的石炭纪沉积区相比,华南有孔虫生物地层划分精度相对较低。本文首次较为系统地报道了华南石炭系代表性岩石地层单位旧司组和上司组下部丰富的有孔虫化石及其在剖面上的分布情况,并综合现有关于华南的有孔虫化石资料,将华南维宪阶划分为7个有孔虫化石带,自下而上分别为Eoparastaffella simplex带、Viseidiscus/Planoarchaediscus带、Paraarchaediscus带、Pojarkovella nibelis带、Koskinotextularia带、Bradyina带和Janischewskina带。这些有孔虫带可与全球其他典型的石炭纪沉积区进行很好的对比,从而为相关的研究提供一个较为精细的地层格架。通过对黔南上司地区有孔虫的研究,提议中国石炭系区域性年代地层单位上司阶底界可用有孔虫Bradyina的首现定义,并将上司阶与西欧的Warnantian亚阶中上部和俄罗斯的Aleksinian亚阶—Venevian亚阶对比,对应国际维宪阶上部,为全球石炭系年代地层对比提供了可靠的化石依据。  相似文献   

Nanpanjiang basin: A window on the tectonic development of south China during Triassic assembly of the southeastern and eastern Asia     

《Gondwana Research》2020

As the largest siliciclastic sink in the South China block, the Triassic Nanpanjiang basin is generally thought of as a foreland basin related to Indosinian collision between the South China and Indochina blocks. Our basin analysis, spanning an eight years period, provides details of Lopingian to Middle Triassic stratigraphic fill and tectonic subsidence of the basin. Field observation and sedimentological analyses reveal that the basin was not filled by a monotonous turbidite system and suggest instead the development of five primary depositional units constituted by deep-water turbidite systems, mass-transport deposits, condensed drapes, shallow-water isolated carbonate platforms, and volcano-volcaniclastic rocks. The stratigraphic completeness of the basin, the coexistence of widespread but localized carbonate platforms within axially filled deep-water basin, tectonically generated cyclothems of transverse mass-transport deposits along intrabasinal faults and basin fill of extrusive rocks of bimodal composition together apparently call in question the claim that crustal shortening prevailed during the Late Permian to pre-Norian Triassic. Patterns of basin fill, differential tectonic subsidence and very high subsidence rate of the region adjacent to master fault are more closely match the pattern expected for extensional to transtensional basin in a back-arc setting. The crustal extension in the southwestern South China was not consistent with hypothesized Indosinian collision between South China and Indochina blocks, but more likely developed in response to northwestward subduction of the paleo-Pacific plate. Our results, combined with regional considerations, lead to a new model for the Triassic tectonic evolution of South China during Triassic assembly of the southeastern and eastern Asia.  相似文献