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991.
桂东鹰扬关群火山岩时代和构造环境的重新厘定:对钦杭结合带西南段构造格局的制约 总被引:2,自引:0,他引:2
鹰扬关群在湘—粤—桂三省交界地区广泛发育,为一套以绿片岩相变质的细碧岩、(石英)角斑岩及相关的火山碎屑岩为主,含有细碎屑岩和碳酸盐岩组合。该群的成岩背景过去一直认为是Rodinia超大陆裂解背景下的大陆裂谷环境,时代归属为新元古代。岩石学、地球化学和锆石LA-ICP-MS U-Pb定年结果表明,鹰扬关群火山岩主要属于基性-中性火山(碎屑)岩类,在岩石化学成分上表现为明显富集大离子亲石元素(LILE,包括U、Th、Ba、K和Rb等)和轻稀土元素,而Nb、Ta、P和Ti等高场强元素和重稀土元素相对亏损,反映其具有俯冲-消减作用形成的岛弧-弧后盆地型火山岩地球化学特征;获得鹰扬关群中变角斑岩的锆石LA-ICP-MS U-Pb谐和年龄为(415.1±2.1)Ma(n=13,MSWD=1.8),表明其为加里东期海相火山喷发的产物。结合云开地块北缘存在有早古生代MORB型和岛弧型变质基性火山岩的资料表明,扬子板块和华夏板块结合带(称之为钦—杭结合带)西南段有早古生代的古洋盆,鹰扬关群岛弧-弧后盆地型火山岩可能是钦—杭结合带南西段早古生代洋陆俯冲-消减过程的地质记录,钦—杭结合带西南段加里东期的构造格局是俯冲增生造山带而不是陆内造山带。 相似文献
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994.
利用多普勒双偏振多参数气象雷达,结合地面LD-Ⅱ闪电定位仪资料,对一次中尺度对流强风暴云的雷电过程进行观测分析。结果表明,闪电发生前后,对流云上部的差分传播相移率KDP、差分反射率因子ZDR和差相移φDP有明显的变化,反映出云中冰相粒子排列取向随云中电场分布结构的变化而变化。这种闪电发生时冰相粒子排列取向存在明显变化的信息,说明用多参数气象雷达探测的技术以及开展雷电预警预报是可行的。 相似文献
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996.
2008年北京奥运会期间大气气溶胶物理特征分析 总被引:5,自引:0,他引:5
应用MODIS卫星的气溶胶产品资料和地面的光学粒子计数器的资料,对比分析了北京地区2006、2007、2008年7~9月的气溶胶光学厚度、细粒子光学厚度、Angstrom指数、气溶胶粒子数浓度谱及体积谱,发现2008年北京奥运会期间(7月20日~9月20日)的气溶胶光学厚度比2006、2007年同期明显降低,气溶胶细模态光学厚度占总光学厚度的比上升,Angstrom指数上升,气溶胶细粒子数浓度没有明显相对变化,而粗粒子数浓度则减少约50%.利用大气标高,将MODIS反演的气溶胶柱的质量浓度转化为地面气溶胶质量浓度.用粒子计数器得到的体积谱,在假定气溶胶粒子密度的情况下,计算出其质量浓度.将这两种方法得到的气溶胶质量浓度与国家环境保护部公布的空气质量指数换算得到的可吸入颗粒物(PM10)质量浓度进行比较.结果表明:北京奥运期间空气质量总体达到了国家二级空气质量标准;与2006、2007年同期相比,2008年气溶胶PM10质量浓度明显下降,而这主要是由气溶胶粗粒子的减少引起的. 相似文献
997.
998.
一个海气耦合模式对东亚夏季气候预测潜力的评估 总被引:1,自引:0,他引:1
利用一个具有较高分辨率的海气耦合模式SINTEX-F(Scale Interaction Experiment-Frontier Research Center for Global Change coupled GCM)的多年回报结果,评估了该海气耦合模式对东亚区域,尤其是中国地区气候异常的预测潜力.与观测实况的比较结果表明:SINTEX-F模式对夏季降水、500 hPa高度场和地表气温都有一定的预测技巧,但是相比而言降水与高度场的回报技巧要高于地表气温;而且耦合模式对东亚地区气候异常的主要空间分布和年际变化特征也有较好的预测潜力,对500 hPa高度场效果较好;对降水异常的年际变化也有一定的预测潜力,尤其是我国中部地区效果较好,但是模式预测的降水异常的幅值较观测相对偏弱;此外对我国西部的极端气候也有一定的预测潜力. 相似文献
999.
RESIDUAL POST-IR IRSL SIGNALS OF POTASSIUM FELDSPAR FROM MODERN SAG POND DEPOSITS OF CENTRAL ALTYN TAGH FAULT: IMPLICATION FOR DATING YOUNG PALEOSEISMIC EVENTS 下载免费PDF全文
The Altyn Tagh Fault(ATF)is one of the most prominent active strike-slip faults in the India-Eurasia collision. Fresh features of surface ruptures, which are attributed to seismic events taking place in the last millennium, are identified at several sites along the Che'erchen River to Qingshui River section on the central part of ATF. Accurate chronology of these earthquake events would help understand the spatial-temporal relationship of the recent earthquakes. However, great difficulties are encountered. The central ATF is located in the arid area, and the vegetation cover is so limited that rare organic materials appropriate for radiocarbon dating can be found in the sediments. Luminescence dating technique may serve as an alternative to directly determine the burial ages of the earthquake related sediments. The optically stimulated luminescence(OSL)signal of quartz, which has been widely employed for luminescence dating, displays unwanted charateristics for accurate dating. Firstly, the quartz OSL signal is not sensitive to irradiation, which leads to low signal-to-noise ratio or even no measurable quartz OSL signal. Secondly, the targeted samples of the last millennium are very young, and the radiation dose received during the burial is expected to be less than 3~4Gy, which futher deteriorates the signal-to-noise ratio of the quartz OSL signal. Therefore, quartz OSL signal is not appropriate for dating the sediments relevant to the recent earthquakes on ATF.
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(De)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL170 signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the De plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL170 signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL170 De values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of De distribution of well sorted and stratified sag pond deposits is consistent with the minimum De value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum De values from the MAM-3 and the FMM. The minimum De values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL170 age would be overestimated by 200~300a.
The post-IR IRSL170 procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed. 相似文献
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(De)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL170 signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the De plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL170 signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL170 De values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of De distribution of well sorted and stratified sag pond deposits is consistent with the minimum De value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum De values from the MAM-3 and the FMM. The minimum De values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL170 age would be overestimated by 200~300a.
The post-IR IRSL170 procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed. 相似文献
1000.