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排序方式: 共有2342条查询结果,搜索用时 15 毫秒
941.
The high-pressure metamorphic belt (HPMB) of eciogite-blueschist in Central Qiangtang (羌塘) lies in the Longmu Co (龙木错)-Shuanghu (双湖) suture zone. To the west, the HPMB extends 500 km from Hongjishan (红脊山) to Caiduochaka (才多茶卡), east of Shuanghu; to the east it extends to Baqing (巴青) and Jitang (吉塘) in Qamdo (昌都), and then bends southward to Yunnan (云南)Province. Including the Lancangjiang (澜沧江) blueschist belt, the entire HPMB is about 2 000 km long. In Central Qiangtang, the belt is mainly composed of blueschist and eclogite, whereas in West Yunnan it contains only blueschist. The Baqing-Jitang segment is dominated by garnet phengite schist. 40Ar-39Ar dating of giaucophane and phengite from the blueschists yielded plateau ages ranging from 223 to 215 Ma, whereas SHRIMP U-Pb dating of zircon from the eclogites gives metamorphic ages of 243-217 Ma. The calculated metamorphic conditions for the blueschists are 410-460℃ and 0.67-0.75 GPa, and for the eclogites, <500 ℃ and 1.56-2.35 GPa. The metamorphic ages suggest that the Longmu Co-Shuanghu suture closed in the Late Triassic. The region south of the Longmu Co-Shuanghu-Laneang suture consists of the pan-African basement overlain by Gondwana sedimentary and meta-sedimentary rocks, whereas the region north of the suture is dominated by the Jinning (晋宁) basement and Yangtze sedimentary and metasedimentary rocks. The Qiangtang HPMB marks the closure of the paleo-Tethys Ocean. 相似文献
942.
SHRIMP Dating and Recrystallization of Metamorphic Zircons from a Granitic Gneiss in the Sulu UHP Terrane 总被引:2,自引:2,他引:0
LI HongyanInstitute of Mineral Resources Chinese Academy of Geological Sciences Beijing Geosciences Rennes Universite de Rennes Rennes Cedex France 《《地质学报》英文版》2004,78(1):146-154
An unusual zircon SHRIMP dating result of a granitic gneiss from the Qinglongshan eclogite-gneiss roadcut section is presented in this paper. The very peculiar and complicated internal structures, as well as the very low Th/U ratios (0.01-0.08) of the zircons indicate that they were formed by metamorphic recrystallization. Strongly in contrast with previously published zircon U-Pb ages of the Dabie-Sulu UHP metamorphic rocks where protolith ages of 600-800 Ma are commonly recorded, only metamorphic age of 218±5 Ma, defined by 18 analytical spots either in rim or in core of zircons, are recorded in this granitic gneiss. This age represents the time of the complete metamorphic recrystallization overprint on primary magmatic zircons. The recrystallization was derived by the UHP metamorphism, and was strengthened by the early stage of retrograde metamorphic fluid activity. 相似文献
943.
944.
通过1:25万厦门市、东山县幅区域地质调查.在福建沿海动力变质带南段中同种原岩不同变形强度的动力变质岩进行了岩石化学分析,揭示了晚侏罗世侵入岩在动力变质过程中,从未变形岩石到糜棱岩化岩石、初糜棱岩、糜棱岩、超糜棱岩的变化过程中岩石化学成分的变化规律。该研究为动力变质岩的原岩恢复提供了依据,并为岩石韧性变形过程中岩石化学成分迁移这一理论研究提供了资料。 相似文献
945.
The long term (Holocene) channel and floodplain dynamics of a low gradient, low energy, fine grained aggradational fluvial system within a formerly glaciated landscape in central Scotland, the Kelvin Valley, are described from a series of sediment stratigraphic transects and 12 14C assays in a headwater reach between Kirkintilloch and Kilsyth. The 14C assays and dated archaeological sites on the floodplain together suggest that the River Kelvin ceased to aggrade more than 2000 years ago, probably much more, so the 4–6 m of channel and floodplain deposits are almost entirely of early to mid‐Holocene age. The Kelvin Valley is characterized, despite its low flow characteristics, by a highly variable floodplain architecture, in which some transects suggest long term channel stability and strong partitioning of floodplain sedimentation and others indicate high channel mobility. This variation makes the application of general models of fluvial evolution difficult. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
946.
By observing four samples obtained from Jiangxi Province, China, under the scanning electron mi-croscope (SEM), we discovered that nano-particle layers were commonly formed on sliding planes of the penetrative foliation in metamorphic rocks. We also successfully reproduced this phenomenon with a tri-axial pressure experiment. Having gone through the granulitization-alienation-partition in the shear sliding process, the nano-particles (40-95 nm in diameter) display different individual shapes and dis-tinct layered textures. This nano-confinement layer is essentially a frictional-viscous stripe with vis-cous-elastic deformation. In the micro-domain stripe, activities in structural stress field-rheological physical field-geochemical field are very dynamic, corresponding to the three stages (i.e., shear sliding strengthening-weakening-exfoliating) of the foliation development in metamorphism rocks. As such, the viscous-elastic deformation behavior helps shed light on the understanding of the micro-dynamic mechanism of the structural shearing. 相似文献
947.
艾比湖胡杨宽度年表建立及其环境意义 总被引:3,自引:2,他引:1
在艾比湖东岸采集了3个样点的胡杨树芯标本,建立了艾比桦和东大桥两个采样点的树轮宽度年表(STD,RES和ARS年表),年表长度分别为196 a和210 a,并分析了年表的特征。对树轮标准年表与精河气象站的温度、降水量进行的相关分析发现,温度和降水对胡杨年轮宽度生长的影响较小,没有达到显著相关,表明该区域的降水和温度都不是树木生长的主要限制条件。艾比湖湖面面积变化、沙尘暴日数与树轮宽度指数的相关分析表明,艾比湖湖面面积与轮宽指数呈反向变化,而沙尘暴日数与轮宽指数呈显著正相关,特别是精河站年沙尘暴日数与东大桥当年(t)、次年(t+1)和再次年(t+2)的标准年表指数的相关系数分别达到0.31、0.61和0.57,且后两项通过了0.01显著性检验,表明二者受到共同环境因素的制约。可能由于东大桥采点位于河道附近,地下水位较高(1.4~2.7 m),在高湖面时期,与之对应的较高的地下水位反而制约了胡杨的生长,而在湖面较低的年份,地表干燥而裸露,沙尘暴频发,地下水位较低,更适宜胡杨的生长。 相似文献
948.
949.
亦论韧性剪切变形与金的成矿作用——与邵世才《试论韧性剪切变形与金的成矿》一文的讨论 总被引:2,自引:0,他引:2
剪切带型金矿是一种重要的金矿类型.韧性-超韧性深层次剪切变形是促使Au元素活化分异、形成动力变质含金热液的过程,中浅层次的韧脆性、脆性剪切变形区是Au元素聚集成矿部位.韧脆性剪切带的不同变形层次及其构造岩类型决定了剪切带型金矿床的矿化类型.剪切带型金矿床往往具有成矿时代滞后、空间规模差异、物源指示差异、韧性变形强度与Au元素含量反相关等异常特征.长期演化的造山带附近及边缘是寻找大型剪切带型金矿床的有利地区. 相似文献
950.
Dorothy Sack 《Quaternary Research》1999,52(3):316
Deposits of a transgressive-phase Lake Bonneville stillstand or oscillation are found just below the elevation of the regressive-phase Provo shoreline at numerous exposures throughout the Bonneville basin. Existence of these subProvo shoreline deposits provides a new explanation for the massive size of Provo depositional and erosional landforms, which can no longer be explained by a long stillstand at the Provo shoreline. Provo coastal landforms are large because they are superimposed on subProvo landforms. Results also help to clarify divergent interpretations regarding the relative age of the Provo shoreline and the number of times it was occupied by the water plane. Occupation of approximately the same level during both the transgressive and the regressive phase of Lake Bonneville may be coincidental, or it may indicate that a bedrock sill controlled outflow at subProvo as well as Provo time. Rise to the Bonneville level could have occurred after massive slope failure plugged the outlet pass. 相似文献