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龙门山是青藏高原东缘边界山脉,具有青藏高原地貌、龙门山高山地貌和山前冲积平原三个一级地貌单元。利用数字高程模式图像和裂变径迹年代测定方法研究和计算龙门山晚新生代剥蚀厚度与剥蚀速率,结果表明:3.6 Ma以来龙门山的剥蚀厚度介于1.91-2.16 km之间,剥蚀速率介于0.53-0.60 mm/a之间。在此基础上,开展了该地区岩石圈的弹性挠曲模拟,结果表明龙门山的隆升机制具有以构造缩短隆升和剥蚀卸载隆升相叠合的特点。3.6 Ma之前,龙门山的隆升与逆冲推覆构造负载有关,以构造缩短驱动的构造隆升为特色;3.6 Ma之后,龙门山的隆升与剥蚀卸载驱动的抬升有关,并以剥蚀卸载隆升为特色,进而提出了龙门山晚新生代以来的隆升机制以剥蚀成山作用为主的认识。 相似文献
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P. J. ELLIS 《Geostandards and Geoanalytical Research》1981,5(2):161-166
Although the Gastwirth median is fairly robust (resistant to effects of contamination), it does not, as far as is known, have appropriate confidence limits. It was suspected that it would have confidence limits similar to those of the median. This was borne out in this investigation, which was confined to symmetrical distributions. It is concluded that, for practical purposes, in approximately symmetrical distributions the confidence limits for the median can be assumed to approximate those for the Gastwirth median. 相似文献
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A method is presented fop estimation of the mode of analytical data reported by cooperating analysts in the preparation of reference materials. The method is referred to as the dominant cluster method, and the nodal value obtained is the value that shows most agreement between analysts.
Several examples demonstrate that this mode (for which approximate confidence intervals have been estimated), is not inconsistent with the recommended values that have been assigned to well-known geochemical reference samples. Features in its favour are that the calculation is simple, it is independent of the type of distribution, and outliers are automatically excluded. 相似文献
Several examples demonstrate that this mode (for which approximate confidence intervals have been estimated), is not inconsistent with the recommended values that have been assigned to well-known geochemical reference samples. Features in its favour are that the calculation is simple, it is independent of the type of distribution, and outliers are automatically excluded. 相似文献
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MICHAEL M. McGLUE GEOFFREY S. ELLIS ANDREW S. COHEN PETER W. SWARZENSKI 《Sedimentology》2012,59(4):1237-1256
Expansive playa‐lake systems situated in high‐altitude piggyback basins are important and conspicuous components of both modern and ancient cordilleran orogenic systems. Extant playa lakes provide vital habitat for numerous endemic species, whereas sediments from these deposystems may record signals of climate change or develop natural resources over geological time. Laguna de los Pozuelos (North‐west Argentina) provides the opportunity for an actualistic sedimentological and geochemical assessment of a piggyback basin playa lake in an area of critical interest for understanding Quaternary palaeoclimate dynamics. Silty clays and diatom ooze are the dominant playa‐lake centre microfacies, with concentrations of total organic carbon and biogenic silica commonly exceeding 1·5 wt% in this sub‐environment. Elemental and stable isotopic analyses point to a mixed organic matter composition in the playa‐lake centre, with substantial contributions from algae and transported aquatic macrophytes. Bulk sediment and organic mass accumulation rates in the southern playa‐lake centre approach 0·22 g cm?2 year?1 and 2·89 mg cm?2 year?1, respectively, indicating moderately rapid deposition with negligible deflation over historic time. Playa margin facies contain higher percentages of fragmented biogenic carbonate (ostracods and charophytes) and inorganically precipitated aragonite crusts due to seasonal pumping and evaporation of ground water. Organic matter accumulation is limited along these heavily bioturbated wet and dry mud flats. Fluvial–lacustrine transitional environments, which are key waterbird habitats, are either silty terminal splay (northern axis) or sandy deltas (southern axis) containing highly oxidized and partially allochthonous organic matter. Modern analogue data from Laguna de los Pozuelos provide key insights for: (i) environmental reconstructions of ancient lake sequences; and (ii) improving facies models for piggyback basins. 相似文献
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青藏高原东缘具有青藏高原地貌、龙门山高山地貌和山前冲积平原三个一级地貌单元 ,本文以岷江作为切入点 ,研究了该地区河流下蚀速率与山脉的隆升作用之间的相互关系。在建立岷江阶地序列的基础上 ,利用阶地高程和热释光年代学测年资料分别定量计算了岷江在川西高原、龙门山和成都盆地的下蚀速率 ,结果表明岷江各河段的下蚀速率明显不同 ,分别为 1.0 7～ 1.6 1mm / a、1.81m m/ a和 0 .5 9mm / a;在龙门山地区岷江的下蚀速率最高 ,约为川西高原地区的 1.5倍 ,约为成都平原地区的 3倍 ;而同一河段不同时期岷江的下蚀速率基本是连续的 ,具有很好的线性关系 ,可作为该河段整个河谷的下蚀速率。基于龙门山的表面隆升速率 (0 .3～ 0 .4 mm / a) ,在约束局部侵蚀基准面和气候变化对阶地形成的控制作用的基础上 ,本文建立了青藏高原东缘岷江下蚀速率与龙门山表面隆升速率之间的线性关系 ,结果表明河流下蚀速率约为山脉表面隆升速率的 5倍。根据龙门山表面在隆升速率和下切速率等方面均大于川西高原 ,并结合龙门山活动构造以走滑作用为主 ,笔者认为青藏高原东缘的边缘山脉以剥蚀隆升为主 ,兼有构造隆升作用。最后 ,根据岷江最大切割深度所需的时间 (3.4 8Ma)和成都盆地最古老的岷江冲积扇大邑砾岩的时间 (3.6 Ma 相似文献
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Active Tectonics of the Longmen Shan Region on the Eastern Margin of the Tibetan Plateau 总被引：14，自引：0，他引：14 
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下载免费PDF全文 ZHOU Rongjun LI Yong Alexander L.DENSMORE Michael A. ELLIS HE Yulin LI Yongzhao LI Xiaogang 《《地质学报》英文版》2007,81(4):593-604
There is a massive amount of geomorphic evidence for active tectonics in the Longmen Shan at the eastern margin of the Tibetan plateau. We have surveyed some typical geomorphic markers including the Wenchuan-Maowen, Beichuan-Yingxiu and Pengxian-Guanxian faults, terrace offsets, scarps, fault-controlled saddles, dextral shutter ridges, dextral channel offsets, graben, shatter belts, and pull-apart basins. Electron spin resonance （ESR） and thermoluminescence（TL） ages were obtained using silty sand taken from below the surface of the sediments. According to these data, we calculated the rates of thrusting and strike-slip, and the results indicate that Cenozoic tectonic shortening at the plateau margin is minor with the rate of thrusting less than 1.10 mm/a and the rate of strike-slipping less than 1.46 mm/a. The Longmen Shan is a zone of NNE-trending dextral shear with slip-dip ratio of 6：1-1.3：1. From NW to SE, the thrust component becomes smaller, whereas the strike-slip component becomes larger. 相似文献
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断层之间的相互作用及其地震地质意义 总被引：1，自引：0，他引：1
从断层间相互作用产生的同震库仑应力改变入手,提出了断层间相互作用的触震与缓震效应,探讨了断层间的相互作用对断层活动性、断层未来地震潜势及余震活动分布图像的影响.从断层间相互作用的角度分析了大陆强震准周期丛集复发行为的可能的物理机制.认为断层间的相互作用具有重大的地震地质意义,在进行断层活动习性和断层地震危险性定量评价及余震分布图像预测时,应该充分考虑断层间相互作用的影响. 相似文献
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Measures of material variation (state of homogeneity) for reference materials of powdered rocks, minerals, and ores are examined critically.
It is shown that the customary analysis of variance concluding with the F-test is not a satisfactory method for the analysis of the analytical data obtained in a homogeneity experiment. It is argued that an estimation approach is more appropriate.
Examples are given of values calculated from reference-material data, together with an explanation of how the results can be interpreted. 相似文献
It is shown that the customary analysis of variance concluding with the F-test is not a satisfactory method for the analysis of the analytical data obtained in a homogeneity experiment. It is argued that an estimation approach is more appropriate.
Examples are given of values calculated from reference-material data, together with an explanation of how the results can be interpreted. 相似文献
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Regionally metamorphosed metapelites from Rogaland, SW Norway, contain zircon formed during the decompression reaction garnet + sillimanite + quartz → cordierite. The zircon, which occurs as inclusions in cordierite coronas around garnet, is texturally, chemically and isotopically distinct from older zircon in other textural settings in the matrix. A SHRIMP U–Pb age of 955 ± 8 Ma based on analyses in thin section on the decompression zircon from the cordierite coronas, therefore dates a point on the retrograde path, estimated from garnet–cordierite equilibria to be 5.6 kbar, 710 °C. This population was under‐represented in conventional SHRIMP analyses of individual zircon in a mono‐mineralic grain mount and, in the absence of a textural context, its significance unknown. The dominant age identified from SHRIMP analyses of the grain mount, in combination with analyses from matrix zircon in thin section, was 1035 ± 9 Ma. Based on the lack of consistent textural relationships with any specific minerals in thin section, as well as rare earth element chemistry, the 1035‐Ma population is interpreted to represent zircon growth during incipient migmatization of the rocks at 6–8 kbar and c. 700 °C. This is consistent with previous estimates for the age of regional M1 metamorphism during the Sveconorwegian Orogeny. The most important outcome of this study is the successful analysis of zircon grains in a specific, well‐constrained reaction texture. Not only does this allow a precise point on the regional P–T path to be dated, but it also emphasizes the possibility of zircon formation during the retrograde component of a typical metamorphic cycle. 相似文献