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1.
The Northern Qilian high-pressure metamorphic belt has experienced multiple deformation-metamorphism, which consists of at least four stages.In 550.8-526 Ma, eclogites were formed. High temperature and pressure caused the escape of a large quantity of gas-liquid fluids from rocks while silicate melt was generated. In the late stage, small amounts of CO2 and H2O infiltrating along fractures were introduced.In the formation of glaucophane schist (447-362 Ma), devolatilization reactions were dominated during the subduction-uplift stage of the paleoplate.In the uplift-exhumation stage (400-380 Ma) the increase of internal space of fractures in the rocks favoured fluid infiltration and concentration. These fluids participated in hydration reactions in the retro-metamorphism. The fluids participating in the mineral reactions have the compositions of CaCl2-NaCl-H2O.In subsequent thrusting (<380 Ma), the metamorphic terrain was uplifted to the shallower crust and ductile-shearing deformation took place, which c  相似文献   

2.
40Ar-39Ar dating of albite from the Meishan and Taocun iron deposits yields plateau ages of 122.90±0.16 Ma and 124.89±0.30 Ma, and isochron ages of 122.60±0.16 Ma and 124.90±0.29 Ma, respectively. Phlogopite from the Zhongshan-Gushan ore field has a plateau age of 126.7±0.17 Ma and an isochron age of 127.21±1.63 Ma. Analysis of regional geodynamic evolution of the middle-lower Yangtze River region suggests that the porphyry iron deposits were formed as a result of large-scale lithosphere delamination and strong sinistral strike-slip movement of the Tancheng Lujiang fault zone. The copper, molybdenum and gold deposit system in the middle-lower Yangtze River region was formed during the stress transition period of the eastern China continent.  相似文献   

3.
A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ ^13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8Ma. At the core depth of 197-170m (about 2.8-2.5Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarses and and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5Ma and 0.8Ma (at the core depth of 170-38.5m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5m (about 0.8-0Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000m a.s.l.  相似文献   

4.
Lake geomorphology and high-level lacustrine deposits since the mid-late Pleistocene are well preserved in lakes of the Qinghai-Tibet Plateau. According to geological surveys of 17 lake districts in different locations of the plateau, combined with interpretations of satellite images and topographic maps, the authors studied the timing of formation and scopes of the pan-lake areas of the plateau and their paleoclimate. The latest two high lake levels （overflow surfaces） on the Qinghai-Tibet Plateau in the Quaternary occurred at N40 to 30/35 ka and N65 to 53 ka respectively. In these time intervals, the plateau was covered by huge interconnected pan-lake systems with a total area of -36 km^2 and a total volume of lake water of 〉530 million km^2, which are about 38 times and 659 times larger than those of the modern lakes respectively. Before this pan-lake period in the late Pleistocene, there had been three high lake levels that occurred at N 132-112 ka, 110-95 ka and 91-72/-83-75 ka respectively, suggesting that the late Quaternary climate on the plateau was unstable and changed rapidly. The -40-30 ka high lake level also appeared in the Tengger desert north of the plateau, suggesting that there existed very strong summer monsoons from South Asia then; the variation in solar radiation with a 20,000 precessional period has special importance for the high-altitude Qinghai-Tibet Plateau in the low-latitude zone of the Earth. Around 30 ka, the pan-lakes at the peripheries of the Qinghai-Tibet Plateau drained out suddenly with rapid uplift of the plateau and cooling. In a short time the huge amount of cold lake water emptied into the Indian Ocean and Western Pacific. The draining event of the pan-lakes brought about the environmental changes of rivers and lakes at peripheries of the plateau.  相似文献   

5.
The Dongchuang gold deposit in the Xiaoqinling area is an orogenic-type lode gold deposit. It is one of the few superlarge (>100 t Au) deposits in China. Although it has been argued that it was formed in the Mesozoic, related isotopic age data have not been reported in previous studies. Based on detailed geological study, the authors have carried out isotopic dating on various metallogenic generations. The ore-forming process of the Dongchuang gold deposit consists of four stages: coarse-grained pyrite-bearing quartz veins (stage Ⅰ), fine-grained pyrite-quartz veinlets (stage Ⅱ), multi-sulfides (stage Ⅲ) and carbonate-quartz veinlets (stage IV). Ar-Ar dating on mineral separates of stages Ⅰ, Ⅱ and Ⅲ yields plateau ages of 142.9±2.9 Ma, 132.2±2.6 Ma and 128.3±6.2 Ma, respectively. Sericite separates from stage Ⅱ assemblage also yield an Ar-Ar isochron age of 132.6±2.7 Ma, similar to the Ar-Ar plateau age. These results suggest that the Dongchuang gold deposit was mainly formed during 143-128 M  相似文献   

6.
The Dachang superlarge Sn-polymetal deposit in Guangxi, China, is one of the largest tin deposit all over the world. However, this deposit has long been in debate as to its origin. One of the opinions is that the Dachang deposit was formed by replacement of hydrothermal solution originating from Yanshanian granites, and the other is that this deposit was formed by submarine exhalation in the Devonian. This paper presents some new isotopic geochronology data obtained with the 40Ar-39Ar method for quartz and sanidine from massive ore in the No. 91 and No. 100 orebodies. Analytic results show that the No. 91 orebody was formed at 94.52±0.33 Ma (the plateau age obtained with the 40Ar-39Ar method for quartz) or 91.4±2.9 Ma (the plateau age obtained with the 40Ar-39Ar method for feldspar), while the No. 100 orebody was formed at 94.56±0.45 Ma (the plateau age obtained with the 40Ar-39Ar method for quartz), suggesting that both the No. 91 and the No. 100 orebodies were formed at the Late Yanshanian instead o  相似文献   

7.
We clarified three stages of dolomitization and secondary changes by studying the petrology and geochemistry characteristics of dolomite from the Ma55–Ma510 sub-members of the Ordovician Majiagou Formation in the Jingxi area in the Ordos Basin: (1) Syngenetic microbial dolomitization is characterized by formation of dolomite with a mainly micrite structure and horse tooth-shape dolomite cements. (2) Seepage reflux dolomitization during the penecontemporaneous period superposed adjustment functions such as recrystallization and stabilization in the middle-deep burial stage, forming dolomites mainly consisting of micro crystal and powder crystal structure. (3) Powder dolomite, fine dolomite, and medium-coarse crystalline dolomite formed in pores and fractures in the middle-deep burial stage. The secondary concussive transgression-regression under a regressive background is an important condition for the occurrence of many stages of dolomitization in the study area. The basin was an occlusive epicontinental sea environment in the Ma5 member of the Ordovician Majiagou Formation sedimentary period. In the sediments, sulfate content was high, which is conducive to the preservation of microbial activity and microbial dolomitization. Micritic dolomite formed by microbial dolomitization provides good migration pathways for seepage reflux dolomitization. Affected by evaporation seawater with increased Mg/Ca ratio, seepage reflux dolomitization was widely developed and formed large-scale dolomite, and underwater uplifts and slopes are favorable areas for dolomite. In the middle-deep burial stage, dolomitizing fluid in the stratum recrystallized or stabilized the previous dolomite and formed a small amount of euhedral dolomite in the pores and fractures.  相似文献   

8.
Palygorskite is a typical indicator mineral of the arid and strong evaporation environment. Distribution of palygorskite in loess-red clay sequences may act as an important indicator for reconstruction of the paleoenvironment and paleoclimate. In this paper, field emission scanning electron microscope and high-resolution transmission electron microscope observations on the red clay-loess-paleosol of the Renjiapo profile at Lingtai, Gansu Province indicate that palygorskite occurs widely in red clay sequences formed before 3.6 Ma, but no occurrence has been found in eolian sediments since 3.2 Ma. Micromorphological features and microstructure of palygorskite show that it is an autogenic mineral formed during pedogenesis, and transformed from iilite-montmorilionite under the pore water action. In the Lingtai profile, the disappearance horizon of palygorskite is consistent with those of increasing magnetic susceptibility, dust flux and depositional rate. The distribution of palygorskite in the profile indicates that the interval of around 3.6 Ma was an important transformation period of the East Asian paleomonsoon, when changes took place in the East Asia paleoclimate pattern, i.e. a high-frequency strong fluctuation alternative evolution of the environment. Therefore, palygorskite is a key indicator mineral of the East Asian paleomonsoon evolution of that time.  相似文献   

9.
Three melting events of the earth's crust occurred during the period of 220-120 Ma in the Shandong Pe-ninsula. Three subcycles of granitoid magma including six rock series were generated in the faulted granitoidmagma belt. The parent magma of several rock series formed earliest originated from the lower crust ofgranulite facies; following the increase of geothermal temperature the source magma would migrate into themiddle crust of amphibolite facies. In the diapiric granitoid magma belt, the granitoid magma was formed firstin granitic layer of the upper crust, and then in the middle crust. In each subcycle the generation of magmastarted with the generation of more mafic one and finished with low eutectic one; they were formed in the formof layered melting in a particular position of the crust.  相似文献   

10.
According to the alternation of terrestrial beds and transgressive beds, the sedimentary sequence of the South Yellow Sea since the Olduvai subchron can be divided into 15 stratigraphical intervals. According to the facies analysis, there are 7 transgressive beds and one bed with transgression marks, and classical transgressive-regressive facies sequence also appears in the major transgressive beds.Palaeogeographic evolution in the shelf area involved 4 periods: (1) 1.70-0.5 Ma B. P. was the stage for the development of the Palaeo-Yangtze River alluvial plain and delta. Tide influenced -river channel sediments formed during the Olduvai have been found in borehole QC2. The river mouth was located near 124°E and during the transgressive stage from 0.97-0.73 Ma B.P. to the east of 122.2°E, a large-scale undersea delta was formed. In the regressive stage, the shelf area became an alluvial plain. (2) 0.50-0.75 Ma B.P. was a multi-transgressive fluctuation stage during which 3 transgressive beds (HVI, HV, H  相似文献   

11.
青藏高原多期次隆升的环境效应   总被引：28，自引：0，他引：28  
青藏高原隆升对中国西部环境变迁起着决定性影响。通过对柴达木、吐鲁番—哈密、塔里木盆地的演化及其与青藏高原隆升的耦合研究,以柴达木盆地为时空坐标,认为高原隆升可分为三大阶段:(1)古近纪期间青藏高原隆升仅限于冈底斯山一带。当时,受行星纬向气候带控制,中国西北地区为干旱亚热带草原和热带雨林环境,大面积准平原化、泛盆地化,在构造上处于伸展-夷平的拉张环境,与现今亚洲大陆东部相似;(2)青藏高原整体的初次隆升发生在中新世早—中期(23~11·7Ma)。因青藏高原和大兴安岭的阻隔,古近纪的纬向气候带逐渐转变为中亚季候风,古黄土(22Ma)、三趾马动物群的发育,说明高原北缘当时为干旱的荒漠草原环境。同时,这次隆升引起中—晚中新世中国西部广袤地域古地形-构造面貌的变化;(3)形成现今高原面貌的末次快速隆升发生在0·9~0·8Ma。早更新世晚期,印度洋快速扩张,印度板块向中亚大陆脉冲式(A型)陆内俯冲,使得高原快速挤压隆升。这次隆升不仅使高原本身的环境骤变,出现第四纪以来最大的冰川,形成世界上最大的高寒草原,而且引起了全球气候的变化,促使北极圈冰盖的形成。同时,高原隆升使高原内部和周边出现强烈的挤压构造变形,如柴达木、河西走廊、塔里木、吐鲁番—哈密、准噶尔等诸盆地内几万米厚度中—新生界的构造变形与昆仑山、祁连山、天山、阿尔泰山的挤出式双向推覆隆升,形成了中国西北的盆-山地貌。现今,随着青藏高原的持续隆升,高寒草原开始退化,造成中国西北地区大面积的荒漠化,成为制约我国西部生态环境的重要因素。  相似文献   

12.
关于晚新生代准1.2Ma周期构造气候旋回   总被引：8，自引：2，他引：6  
构造气候旋回的理论要点是构造作用驱动气候变化,因而不同于Milankovitch冰期气候旋回,但两者又都是受地球轨道要素控制的。本文主要根据青藏高原和黄土高原的晚新生代地质记录,以磁性地层为时间标尺,以黄道倾斜(ε)最大变幅位置为模式年龄,划分最近8Ma的准1.2Ma周期构造气候旋回的主旋回层,即MTC7、MTC6、MTC5、MTC4、MTC3、MTC2、MTC1、MTC0,它们的界线年龄分别为7.3、6.1、4.9、3.7、2.5、1.3和0.2MaBP。在此基础上,分析了青藏高原构造隆升和黄土高原风尘沉积各自显示的准1.2Ma周期的演变特征,表明它们之间具有构造驱动气候的因果关系。文中还探讨了最近7.3MaBP的古环境变迁,获得了有关晚新生代东亚季风形成演变和环境分异是在轨道气候旋回背景下受构造气候旋回控制的新认识。   相似文献   

13.
本文用末次冰期北美大冰盖南缘的风尘堆积记录来重建末次盛冰期的亚极地环境变化.磁化率、有机碳含量和潜育化程度的资料表明,末次盛冰期的前期(约21000～15000aB P.)植被覆盖较差,而后期(15000～10000aB.P.)植被覆盖较好,15 000aB.P.环境发生了急剧的变化,磁化率曲线显示了大约1000a的氧化-还原周期.这种大约1000a的环境变化周期很可能由低纬地区的海洋和大气的扰动所驱动,这种扰动的能量通过北美大冰盖及时地传递到北大西洋.  相似文献   

14.
第四纪中国自然环境变迁的原因机制   总被引：6，自引：1，他引：6  
作者在重建晚第三纪和第四纪古气候环境的基础上,着重讨论了晚第三纪和第四纪古气候之间的显著差异以及引起中国第四纪自然环境大幅度变迁的主要原因机制。中国新生代晚期构造运动导致自然环境的巨大变迁,其中青藏高原隆起的影响尤为突出。作者认为,青藏高原隆起及其反馈作用、季风环流的加强以及全球气候变化的影响,协同成为中国第四纪气候大幅度变化的主要原因,当然也是新生代晚期以来,尤其是中更新世以来中国自然环境变迁的主要原因机制。  相似文献   

15.
 The Qinghai–Tibet Plateau uplifted >3000 m in the Quaternary period. The average rate of uplift was 1–1.1 mm/year. The uplifting has remolded the geomorphology of China. The landform in China was changed from west-low and east-high to west-high and east-low in three steps. The Qinghai-Tibet Plateau uplift is an important factor that affected the climate and the environment of China in the Quaternary period. It controls atmospheric circulation and climatic change in Asia and even the northern hemisphere, by dividing the westerlies into two branches: south and north. The plateau gradually became a heat source in summer and a cold source in winter. The uplift had a decisive effect on the formation of the East-Asia monsoon, which increased the climatic differences between the glacial period and the interglacial period. The climate and environment of China are characterized by the influences of the plateau uplift. The east of China became the south-east monsoon area, whereas the south-west became the south-west monsoon area and the north-west turned into an arid inland region. The Gobi and large-scale deserts that formed in the inland basins are ceaselessly extending. The climate of northern China became more arid as the Qinghai-Tibet Plateau continued to uplift. The Plateau uplift affected glacial evolvement and loess formation, and propelled the migration of cold- and warm-blooded animals, which differed from other regions of the world at the same latitude. Received: 30 August 1999 · Accepted: 18 April 2000  相似文献   

16.
系统分析青藏高原新生代中新世50余个沉积盆地的类型、构造背景、岩石地层序列,对青藏高原中新世构造岩相古地理演化特征进行分析和探讨。中新世,青藏高原海相沉积已经全面退出,全部转为陆相沉积,约23Ma时高原及周边不整合面广布,标志高原整体隆升。塔里木、柴达木及西宁-兰州、羌塘、可可西里等地区主体表现为大面积的构造压陷湖盆沉积。约17.2Ma左右,阿尔金山显著隆升,使柴达木盆地西叉沟一带再无生物礁灰岩出现,且在盆地西部出现了短暂的沉积间断。这一时期,柴达木盆地西部开始进入湖退期,而东南部则快速湖进;同时,大约17.7Ma索尔库里山间盆地初始凹陷形成。另外,高原腹地五道梁-沱沱河盆地受南部唐古拉山的挤压抬升,在16Ma左右结束了五道梁组的沉积,在可可西里—唢呐湖一带则再次凹陷接受唢呐湖组沉积,形成高原腹地的大型压陷湖盆。13～10Ma期间,藏南南北向断陷盆地的形成,是高原隆升到足够高度开始垮塌的标志;约8Ma以来,高原东北部几乎所有湖盆均进入湖退期,普遍出现冲积扇、辫状河和水下扇砂砾岩堆积。  相似文献   

17.
奚晓霞 《沉积学报》1998,16(2):155-160
Cl-是封闭湖盆中反映气候变化的敏感指标。临夏盆地晚新生代地层Cl-含量变化表明,气候的长期演化呈现明显的阶段性与周期性,在约6.3Ma气候突然产生显著的由湿变干,并于5.3～4.5Ma达到极端干旱,其干旱程度是第四纪早期的33倍,低频上,气候呈现出约400万年的干湿波动,在晚中新世与早上新世,与同周期的全球热冷（凉）波动相对,而在第四纪早期,则与冷暖相对,可能反映亚洲季风系统于晚上新世才开始逐步形成,并于第四纪初建立,3.4Ma开始强烈隆升的青藏高原可能与此密切相关。  相似文献   

18.
WHEN THE KUNLUN MTS.PASS AREA UPLIFTED TO PRESENT ELEVATIONChineseNationalkeyProjectforBasicResearchonTibetanPlateau (G19980 40 80 0 )  相似文献   

19.
青藏高原气候变化的若干事实及其年际振荡的成因探讨   总被引：1，自引：0，他引：1  
利用1961-2012年青藏高原88个气象台站逐月气温、降水以及温室气体等气候系统监测资料和CMIP5输出的未来气候变化情景数据,分析了近52年来青藏高原气候变化暖湿化的若干事实,揭示了其年际振荡与温室气体、高原加热场、高原季风、AO等气候系统因子的关系,预测了未来20~40年青藏高原可能的气候变化趋势。研究表明：近52年来青藏高原在总体保持气候变暖的趋势下自2006年以来出现了某些增暖趋于缓和的迹象,较全球变化滞后了8年左右;降水量的增加在青藏高原具有明显的普遍性和显著性,气候变湿较变暖具有一定的滞后性,降水量变化的5年短周期日趋不显著,而12年、25年较长周期逐渐明显且仍呈增多趋势。由于温室气体、气溶胶持续增加、高原夏季风趋强、ENSO事件和太阳辐射减少,青藏高原气候持续增暖但有所缓和;春季高原加热场增强、高原夏季风爆发提前且保持强劲,使得高原春、夏季和年降水量增加,而秋、冬季AO相对稳定少动,东亚大槽强度无明显变化,高原冬季风变化不甚显著,导致了高原秋、冬季降水量无明显变化。未来20~40年青藏高原仍有可能继续保持气温升高、降水增加趋势。  相似文献   

20.
为揭示循化盆地沉积物对古气候及青藏高原隆升过程的指示作用, 采用X射线衍射(XRD)、扫描电子显微镜(SEM)方法对循化盆地中新世沉积物中粘土矿物组成、微观形貌进行了深入研究.结果表明, 沉积物中粘土矿物以伊利石、蒙脱石为主, 绿泥石、高岭石和坡缕石含量较低; 粘土矿物相对含量及伊利石结晶度变化特征指示, 在23.1~21.2 Ma期间, 古气候以温暖潮湿为主; 21.2~14.3 Ma期间古气候以冷干为主, 出现短暂的相对暖湿时段; 14.3~10.6 Ma期间, 古气候以相对暖湿为主; 10.6~9.3 Ma时期, 气候以冷干为主; 9.3~5.2 Ma期间, 气候虽有冷干与暖湿波动, 但总体上以暖湿为主.在21.2 Ma和5.8 Ma时期发生的明显强降温事件, 可能与青藏高原的阶段性隆升有关.   相似文献   

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