云南东北部拱王山末次冰期   总被引：1，自引：0，他引：1  

张威  崔之久  冯金良  YI Chaolu  YANG Jianqiang 《地理学报(英文版)》2005,15(4):448-458

1 Introduction The Gongwang mountains constitute one of the few high m ountains of irrefutable late Pleistocene glaciation in eastern China. This area is one of the m ost extensively studied Quaternary geologicallocationsin eastern China and the interpret…  相似文献   

Rivers turned to rock: Late Quaternary alluvial induration influencing the behaviour and morphology of an anabranching river in the Australian monsoon tropics     

Gerald C. Nanson  Brian G. Jones  David M. Price  Timothy J. Pietsch 《Geomorphology》2005,70(3-4):398

Late Quaternary alluvial induration has greatly influenced contemporary channel morphology on the anabranching Gilbert River in the monsoon tropics of the Gulf of Carpentaria. The Gilbert, one of a number of rivers in this region, has contributed to an extensive system of coalescing low-gradient and partly indurated riverine plains. Extensive channel sands were deposited by enhanced flow conditions during marine oxygen isotope (OI) Stage 5. Subsequent flow declined, probably associated with increased aridity, however, enhanced runoff recurred again in OI Stages 4–3 (65–50 ka). Aridity then capped these plains with 4–7 m of mud. A widespread network of sandy distributary channels was incised into this muddy surface from sometime after the Last Glacial Maximum (LGM) to the mid Holocene during a fluvial episode more active than the present but less so than those of OI Stages 5 and 3. This network is still partly active but with channel avulsion and abandonment now occurring largely proximal to the main Gilbert flow path.A tropical climate and reactive catchment lithology have enhanced chemical weathering and lithification of alluvium along the river resulting in the formation of small rapids, waterfalls and inset gorges, features characteristic more of bedrock than alluvial systems. Thermoluminescence (TL) and comparative optically stimulated luminescence (OSL) ages of the sediments are presented along with U/Th ages of pedogenic calcrete and Fe/Mn oxyhydroxide/ oxide accumulations. They show that calcrete precipitated during the Late Quaternary at times similar to those that favoured ferricrete formation, possibly because of an alternating wet–dry climate. Intense chemical alteration of the alluvium leading to induration appears to have prevailed for much of the Late Quaternary but, probably due to exceptional dryness, not during the LGM. The result has been restricted channel migration and a reduced capacity for the channel to adjust and accommodate sudden changes in bedload. Consequent avulsions have caused local stream powers to increase by an order of magnitude, inducing knickpoint erosion, local incision and the sudden influx of additional bedload that has triggered further avulsions. The Gilbert River, while less energetic than its Pleistocene ancestors, is clearly an avulsive system, and emphasizes the importance in some tropical rivers of alluvial induration for reinforcing the banks, generating nickpoints, reworking sediment and thereby developing and maintaining an indurated and anabranching river style.  相似文献   

Sedimentation rates in the Wanggang salt marshes, Jiangsu   总被引：1，自引：0，他引：1  

WANGAijun GAOShu JIAJianjun PANShaoming 《地理学报(英文版)》2005,15(2):199-209

1 IntroductionLand-ocean interaction in coastalzone is one of the key m atters of the International G eosphereand Biosphere Program (IG BP). The key problem s of the second phase in the next decadeinclude the m aterial cycle, the system evolution process …  相似文献   

新疆阿尔泰造山带构造作用的锆石裂变径迹分析   总被引：1，自引：0，他引：1  

袁万明  董金泉  保增宽  安银昌 《地球学报》2005,26(Z1):239-243

在新疆阿尔泰造山带所获得的19个锆石裂变径迹年龄变化于155-243Ma之间，明显地分为2组，分别对应于2个构造活动期，早期为155-189Ma，晚期为189-243Ma。这与磷灰石裂变径迹年龄反映的62-100Ma和100-160Ma两个构造期完全一致。早期和晚期构造活动期持续的时间分别为54-60Ma和34-38Ma，而这两个构造期之间的间隔时间，则从早到晚由83-89Ma变为89-93Ma。同时，锆石裂变径迹年龄与距特斯巴汗断裂和巴寨断裂的距离有关，反映这两条断裂带对区域构造演化的控制作用。  相似文献   

Magmatic-to-hydrothermal crystallization in the W–Sn mineralized Mole Granite (NSW, Australia): Part I: Crystallization of zircon and REE-phosphates over three million years—a geochemical and U–Pb geochronological study     

Urs Schaltegger  Thomas Pettke  Andreas Audtat  Eric Reusser  Christoph A. Heinrich 《Chemical Geology》2005,220(3-4):215-235

Zircon, monazite and xenotime crystallized over a temperature interval of several hundred degrees at the magmatic to hydrothermal transition of the Sn and W mineralized Mole Granite. Magmatic zircon and monazite, thought to have crystallized from hydrous silicate melt, were dated by conventional U–Pb techniques at an age of 247.6 ± 0.4 and 247.7 ± 0.5 Ma, respectively. Xenotime occurring in hydrothermal quartz is found to be significantly younger at 246.2 ± 0.5 Ma and is interpreted to represent hydrothermal growth. From associated fluid inclusions it is concluded that it precipitated from a hydrothermal brine ≤ 600 °C, which is below the accepted closure temperature for U–Pb in this mineral. These data are compatible with a two-stage crystallization process: precipitation of zircon and monazite as magmatic liquidus phases in deep crustal magma followed by complete crystallization and intimately associated Sn–W mineralization after intrusion of the shallow, sill-like body of the Mole Granite. Later hydrothermal formation of monazite in a biotite–fluorite–topaz reaction rim around a mineralized vein was dated at 244.4 ± 1.4 Ma, which distinctly postdates the Mole Granite and is possibly related to a younger hidden intrusion and its hydrothermal fluid system.

Obtaining precise age data for magmatic and hydrothermal minerals of the Mole Granite is hampered by uncertainties introduced by different corrections required for multiple highly radiogenic minerals crystallising from evolved hydrous granites, including ²³⁰Th disequilibrium due to Th/U fractionation during monazite and possibly xenotime crystallization, variable Th/U ratios of the fluids from which xenotime was precipitating, elevated contents of common lead, and post-crystallization lead loss in zircon, enhanced by the fluid-saturated environment. The data imply that monazite can also survive as a liquidus phase in protracted magmatic systems over periods of 10⁶ years. The outlined model is in agreement with prominent chemical core-rim variation of the zircon.  相似文献   

Use of fallout 137Cs for documenting the chronology of overbank sediments from the river Sava, Croatia, and interpreting their geochemical patterns     

Gordana Pavlovic  Delko Barisic  Ivanka Lovrencic  Visnja Orescanin  Esad Prohic 《Environmental Geology》2005,47(4):475-481

This paper attempts to determine the impact of former Pb-Zn-Ba mining activities in Slovenian drainage basin on overbank sediments of the Sava river (West Croatia). Among the four studied sequences (S7, S8, S9, S10), the most upstream profile S7 showed the most pronounced impact of ore mining. Mercury was enriched more than 100-fold; Pb and Zn had a strong positive correlation (r > 0.99). Two factor models clearly revealed the Pb-Ba-Hg association in the lower-lying carbonate (CA) population of all four profiles, but only in the overlying silicate (SI) population of profile S7. Factor analysis confirmed this association in the total sediment (90 samples) as well as separately in the CA (33 samples) and SI (57 samples) populations. Based on a comparison with an undisturbed soil profile, the vertical distribution of ¹³⁷Cs in profile S7 was interpreted to be the combination of caesium deposition caused by a flood in 1964 and by post-depositional redistribution.  相似文献   

电子探针化学测年技术及其在地学中的应用   总被引：2，自引：0，他引：2  

郭国林潘家永  刘成东郭福生 《华东地质学院学报》2005,28(1):39-42

电子探针主要应用于固体无机材料的微区化学成分定量测定和表面形貌研究。近十年来电子探针化学测年技术发展迅速，并取得了丰富的研究成果。本文在简单介绍该技术发展历程后，进一步详细介绍该技术的基本原理、样品制备与分析、年龄计算方法等内容，最后讨论了该技术的优缺点，同时指出电子探针测年技术在地学中的具有广泛的应用前景。  相似文献   

Timing of Magma Mixing in the Gangdisě Magmatic Belt during the India-Asia Collision： Zircon SHRIMP U-Pb Dating     

MO Xuanxue  DONG Guochen  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,79(1):66-76

Abstract  Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Qüxü batholith is the most typical MME‐bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U‐Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions. Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge‐scale magma mixing in the Gangdisê belt took place 15–20 million years after the initiation of the India‐Asia continental collision, genetically related to the underplating of subduction‐collision‐induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass‐energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.  相似文献   

Provenance and Magmatic-Metamorphic Evolution of a Variscan Island-Arc Complex: Constraints from U-Pb Dating, Petrology, and Geospeedometry of the Kyffhauser Crystalline Complex, Central Germany     

ZEH  ARMIN; GERDES  AXEL; WILL  THOMAS M.; MILLAR  IAN L. 《Journal of Petrology》2005,46(7):1393-1420

The Kyffhäuser Crystalline Complex, Central Germany, formspart of the Mid-German Crystalline Rise, which is assumed torepresent the Variscan collision zone between the East Avalonianterrane and the Armorican terrane assemblage. High-precisionU–Pb zircon and monazite dating indicates that sedimentaryrocks of the Kyffhäuser Crystalline Complex are youngerthan c. 470 Ma and were intruded by gabbros and diorites between345 ± 4 and 340 ± 1 Ma. These intrusions had magmatictemperatures between 850 and 900°C, and caused a contactmetamorphic overprint of the sediments at P–T conditionsof 690–750°C and 5–7 kbar, corresponding toan intrusion depth of 19–25 km. At 337 ± 1 Ma themagmatic–metamorphic suite was intruded by granites, syenitesand diorites at a shallow crustal level of some 7–11 km.This is inferred from a diorite, and conforms to P–T pathsobtained from the metasediments, indicating a nearly isothermaldecompression from 5–7 to 2–4 kbar at 690–750°C.Subsequently, the metamorphic–magmatic sequence underwentaccelerated cooling to below 400°C, as constrained by garnetgeospeedometry and a previously published K–Ar muscoviteage of 333 ± 7 Ma. With respect to P–T–D–tdata from surrounding units, rapid exhumation of the KCC canbe interpreted to result from NW-directed crustal shorteningduring the Viséan. KEY WORDS: contact metamorphism; U–Pb dating; hornblende; garnet; Mid-German Crystalline Rise; P–T pseudosection  相似文献   

Geochronologic Constraints on the Magmatic Underplating of the Gangdisê Belt in the India-Eurasia Collision: Evidence of SHRIMP II Zircon U-Pb Dating     

DONG Guochen  MO Xuanxue  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,(6)

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