夏季对流和环流10-25天季内变化-5西太平洋暖池热力状况的关系   总被引：4，自引：0，他引：4  

Ren Baohu  Huang Ronghui 《大气科学进展》2002,19(2):321-336

主要讨论了西太平洋暖池热力状况年际变化相联系的10－25天季内振荡的特征。在西太平洋暖池处于“暖”夏季和“冷”夏季两种状态时，10－25天季内振荡呈现出明显差异，在所讨论的亚洲－太平洋大部分区域，“暖”夏季时对流活动的10－25天季内变化和“冷”夏季时对流活动的10－25天季内变化表现出显的反相关关系，表明对流活动的年际变化与季内变化的相互作用。当西太平洋暖池上空对流活动的10－25天季内振荡处于最强和最弱阶段时，低层大气表现为Gill型环流响应，即气旋式（反气旋式）环流出现在最强（最弱）对流活动的西北，这种对流和环流关系在西太平洋暖池出于“暖”夏季和“冷”夏季两种状态时均成立。而当西太平洋暖池上空对流活动的10－25天季内振荡处于除此以外其他阶段时，就看不到Gill型环流响应。  相似文献   

中国风成黄土及其形成下限研究   总被引：8，自引：1，他引：8  

滕志宏  申西平 《地层学杂志》1995,19(2):81-87

“中国岩漠·砾漠·沙漠·黄土分布与主风向关系图”显示西北地区的第四纪黄土堆积是以风力为主的综合因素所形成，即就地起沙，近沙成土，一定地域的黄土在物源上隶属于一定地区的沙漠。黄土高原及新疆天山、昆仑山北麓的黄土地层结构的综合对比研究表明，典型风成黄土在不同地域和不同地貌单元上最早开始堆积的层位基本上是一致的，即均始于所有黄土剖面中的下粉砂层（Ｌ＿（１５））。该层以下的第四纪沉积类型因地而异，为非黄土沉积（湖相、冲洪积相及火山岩相等）。由黄土高原各代表性剖面的磁性地层学研究及新疆于田黄土下伏的安山玄武岩的同位素年龄测定获得黄土层开始堆积的时代为早更新世晚期，约１．２ＭａＢ．Ｐ。风成黄土的开始堆积是与黄土南缘各造山带（昆仑山、天山、祁连山及秦岭等）强烈的新构造隆升并产生区域环境效应有成因联系。这一更新世早期的事件层位得到了古生物学、新构造学、地貌学及地外物体高速撞击地球表面所产生的玻璃陨石等事件的佐证。  相似文献   

具有0．4Ma准周期的事件群发性与气候－构造旋回刍论──以黄土区为对比区   总被引：1，自引：0，他引：1  

朱照宇 《地球化学》1994,(1)

实地考察研究了中国黄土分布区及其它地区上新世末期以来的各种地质事件，用多种测年法和古土壤断代法确定了黄土、水系、沉积、侵蚀、火山、断裂等气候和构造事件的发生年代，指出第四纪事件具有一种准周期为０．４Ｍａ的同步群发性，提出了一种描述地球内外地质动力全球性变化的“气候－构造旋回”模式。  相似文献   

中朝板块中、新元古界年代地层柱与构造环境新思考   总被引：22，自引：4，他引：22  

乔秀夫  高林志  张传恒 《地质通报》2007,26(5):503-509

中国北方燕辽裂陷槽位于中朝板块北部,是巨厚中、新元古界的沉积区。中、新元古界包括长城系(1800～1600Ma)、蓟县系(1400～1000Ma)和青白口系(1000～800Ma)。上述划分是中国地质学家长期研究的共识,由全国地层委员会发布,中国地质调查局在全国地质调查填图中施行[1]。青白口系自下而上包括下马岭组、龙山组、景儿峪组,由于在下马岭组的斑脱岩中获得了锆石SHRIMPU-Pb年龄1368Ma±12Ma,从而对1000Ma作为青白口系底界的年龄乃至中国中、新元古界地质年表提出了挑战。中国地质学家必须面对新的下马岭组年龄值,拼弃传统思维,重新排定北方中、新元古界年代地层柱中各系、组的界线年龄。本文建议:长城系为1800～1600Ma;蓟县系为1600～1400Ma;新建西山系为1400～1200Ma;1200～1000Ma是一个待命名的系;新的青白口系为1000～800Ma,包括龙山组及景儿峪组。由于下马岭组中的斑脱岩反映了岛弧构造环境,从而可重塑中朝板块北部下马岭组及整个中元古界(指1800～1200Ma)为沟-弧-盆板块体系的弧后扩张盆地,即传统概念中的燕辽裂陷槽是弧后扩张的产物。沟-弧-盆板块体系可以系统地解释燕辽裂陷槽的动力学成因、各种地震灾变事件、火山活动、层控矿床等形成的地质背景。  相似文献   

A crucial role for slab break-off in the generation of major mineral deposits: insights from central and eastern Australia     

Ivo M. A. Vos  Frank P. Bierlein  Paul S. Heithersay 《Mineralium Deposita》2007,42(5):515-522

In the Lachlan Fold Belt of southeastern Australia, major orogenic gold and porphyry gold–copper deposits formed simultaneously within distinct tectonic settings during a very short time interval at ca. 440 Ma. The driving mechanism that controlled the temporal coincidence of these deposits remains largely unexplained. A review of contemporaneous metallogenic, tectonic, magmatic and sedimentological events in central and eastern Australia reveals that a change in subduction dynamics along the Australian sector of the Early Palaeozoic circum–Gondwana mega-subduction system could have influenced lithospheric stress conditions far inboard of the subduction margin. The magnitude of ore formation and the spatial extent of related events are proposed in this paper to have been controlled by the interplay of mantle processes and lithospheric changes that followed slab break-off along a portion of the mega-subduction system surrounding Gondwana at that time. Slab break-off after subduction lock-up caused mantle upwelling that, in turn, provided an instantaneous heat supply for magmatic and hydrothermal events. Coincident reorganisation of lithospheric stress conditions far inboard of the proto-Pacific margin of Australia controlled reactivation of deep-lithospheric fault structures. These fault systems provided a pathway for fluids and heat fuelled by mantle upwelling into the upper lithosphere and caused the deposition of ~440 Ma gold deposits in the Lachlan Fold Belt, as well as a range of metallogenic, tectonic and sedimentary changes elsewhere in central and eastern Australia.  相似文献   

青藏高原近25年来河流、湖泊的变迁及其影响因素   总被引：7，自引：0，他引：7  

朱大岗孟宪刚  郑达兴乔子江邵兆刚  杨朝斌韩建恩 余佳孟庆伟  吕荣平 《地质通报》2007,26(1):22-30

结合20世纪70年代中期的MSS图像和90年代末期的ETM 图像解译,对近25年来青藏高原河流、湖泊的分布现状及其变迁进行了分析。研究表明,青藏高原河流总体上变化不明显,部分地区外流水系个别河段略有摆动,内流水系少数河段发生改道、断流,入湖河流河口段发生延伸、退缩等变化。青藏高原多数天然湖泊变化较大,主要是部分湖泊面积缩小或扩大;少数湖泊解体或归并;有的已干涸的湖泊又重新汇水,有的湖泊则接近干涸。导致河流、湖泊演变的主要影响因素有气温变化、降水变化及冰川变化、气候雪线变化等。  相似文献   

Benthic community response to habitat variation: A case of study from a natural protected area,the Celestun coastal lagoon     

Daniel Pech  Pedro-Luis ArdissonNorma A. Hernández-Guevara 《Continental Shelf Research》2007

Little information currently exists on spatial and temporal benthic community variations in tropical coastal lagoons. Here, the benthic community response to habitat variation in the Celestun coastal lagoon, northwest Yucatan peninsula, was seasonally examined during the 1994–1995 climatic cycle into a grid of 12 sampling sites distributed along the salinity gradient of the lagoon. Habitat variation was assessed through physical factors associated both to the water column (e.g. salinity) and the bottom sediment (e.g. sand, silt and clay fractions). The benthic community response was assessed through species diversity measures and abundance. Under the influence of climatic seasonality, variations in habitat conditions followed by changes in the benthic community characteristics were expected. Results from two-way ANOVAs showed that for the period of study, Celestun lagoon was more heterogeneous along the spatial axis of variability than along the temporal one. Multiple regression analysis showed that salinity was spatially the main factor influencing the benthic community characteristics. Temporally, the sediment characteristics were observed to exert significant effects on the species diversity characteristics but not on abundance. Other variables assessed (dissolved oxygen, pH, temperature and water column transparency) exhibited no significant covariance with species diversity and abundance. Since generated from historical data, these results have the potential to be useful as a benchmark to the establishment of monitoring programs in the light of the increasing anthropogenic pressure on the natural resources of the lagoon and surrounding coastal area.  相似文献   

Intrusion-related Gold Deposits in Egypt     

Nagy Shawky BOTROS 《《地质学报》英文版》2021,95(3):1033-1055

Intrusion-related gold deposits(IRGDs) occur in the Eastern Desert(ED) of Egypt within magmatic districts that are exploited for tungsten and tin mineralization. IRGDs and intrusion-related rare metal deposits(IRRMDs) are almost invariably linked with the late to post collisional Younger Granites(YGs) that have three successive phases(I, II and III). At ～635–630 Ma, the ED underwent a transition in deformation style from compressional to extensional and a switch from subduction with crustal thickening to delamination with crustal thinning. This transition was concurrent with the emplacement of a short magmatic pulse(～635–630 Ma) that represents a transition between orogenic gold deposits and IRGDs. K-rich calc alkaline granites(phase I and II of the YGs) hosting IRGDs like the Hangalia deposit were emplaced during the time span 630–610 Ma. Alkaline magmatism began at 610 Ma, coexisting with the K-rich calc-alkaline magmatism over the 610–590 Ma time span, where the Fawakhir(598 ± 3 Ma) and Um Had(596 ± 2 Ma) granites that host the IRGDs were emplaced. In time, the alkaline magmatism became more alkaline giving rise to phase III of the YGs that hosts IRRMDs. A distinct metallogenic epoch comprising both IRGDs and IRRMDs, was undergoing extreme growth at ～600 Ma.  相似文献   

Recent Studies on Attributions of Climate Change in China   总被引：7，自引：0，他引：7  

ZHAO Zongci  DING Yihui  LUO Yong  Wang Shaowu 《Acta Meteorologica Sinica》2005,19(4):389-400

Attributions of floods/cooler along the Yangtze River Valley and droughts/warmer in North China forthe last 25 years have been reviewed in this paper. Both natural climate variability and human activitiesare considered. Some stronger evidences contributed to the natural climate variability, such as decadal andinterdecadal variabilities of East Asian summer monsoon, the periodicities and transitions of rainfall andtemperature changes in China, abrupt climate change, NAO, AO, AAO, ENSO, …  相似文献   

Photometric study of Centaur (60558) 2000 EC₉₈ and trans-neptunian object (55637) 2002 UX₂₅ at different phase angles     

P. Rousselot  J.-M. Petit  A. Sergeev 《Icarus》2005,176(2):478-491

We present photometric observations of Centaur (60558) 2000 EC₉₈ and trans-neptunian object (55637) 2002 UX₂₅ at different phase angles and with different filters (mainly R but also V and B for some data). Results for 2000 EC₉₈ are: (i) a rotation period of 26.802±0.042 h if a double-peaked lightcurve is assumed, (ii) a lightcurve amplitude of 0.24±0.06 for the R band, (iii) a phase curve with H=9.03±0.01 and G=−0.39±0.08 (R filter) and H=9.55±0.04 and G=−0.50±0.35 (V filter) or a slope of (R filter) and 0.22±0.06 (V filter), (iv) the color indices B-V=0.76±0.15 and V-R=0.51±0.09 (for α=0.1-0.5°) and 0.55±0.08 (for α=1.4-1.5°). The rotation period is amongst the longest ever measured for Centaurs and TNOs. We also show that our photometry was not contaminated by any cometary activity down to magnitude ?27/arcsec². For 2002 UX₂₅ the results are: (i) a rotation period of 14.382±0.001 h or 16.782±0.003 h (if a double-peaked lightcurve is assumed) (ii) a lightcurve amplitude of 0.21±0.06 for the R band (and the 16.782 h period), (iii) a phase curve with H=3.32±0.01 and G=+0.16±0.18 or a slope of (R filter), (iv) the color indices B-V=1.12±0.26 and V-R=0.61±0.12. The phase curve reveals also a possible very narrow and bright opposition surge. Because such a narrow surge appears only for one point it needs to be confirmed.  相似文献