CHIME monazite ages of metasediments from the Altai orogen in northwestern China: Devonian and Permian ages of metamorphism and their significance   总被引：3，自引：0，他引：3  

Chang-Qing  Zheng  Takenori  Kato  Masaki  Enami  Xue-Chun  Xu 《Island Arc》2007,16(4):598-604

Abstract   The chemical Th-U-total Pb isochron method (CHIME) has been applied to determine the ages of monazite grains from metasediments of greenscshist-amphibolite facies in the Altai orogen, northwest China. The area of distribution of these metamorphic rocks is divided into the Permian (261–268 Ma) central-western and Devonian (377–382 Ma) eastern units on the basis of their metamorphic ages. The Devonian CHIME ages are consistent with the Pb–Pb ages of granitoid in the eastern unit, and support the idea that emplacement of the granitoids was synchronous with regional metamorphism at deep levels. The Permian metamorphic ages (the present study) and igneous ages previously reported from the central-western unit can be interpreted in terms of subduction of crustal material and oceanic plate, and rapid exhumation.  相似文献   

动力变质作用形成的天然气分析   总被引：2，自引：0，他引：2  

陶士振  刘德良  杨晓勇  戴金星 《大地构造与成矿学》2000,24(1):24-30

动力变质作用导致岩石的机械破碎 ,在碳酸盐岩地区由于断裂的动力增温作用使得岩石发生变质反应释放出二氧化碳。同时在断裂发育过程中流体的参与、岩脉的热作用对碳酸盐岩的变质热分解也起了一定的作用 ,并使变质反应复杂化。我国东部郯庐断裂带范围内碳酸盐岩或其它类型的含碳岩石较为发育 ,并具备动力变质成气和成藏的有利地质条件。  相似文献   

Anomalies on the Cambro-Ordovician passive margin of Scotland     

B.J. Bluck 《Proceedings of the Geologists' Association. Geologists' Association》2007,118(1):55-62

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Field report:Research along the Yarlung Suture Zone in Southern Tibet,a persistent geological frontier     

Andrew K.Laskowski  Lin Ding  Fu-Long Cai  Yao-Fei Chen  Song-Lin He 《地学前缘(英文版)》2018,9(2):591-594

The Yarlung Suture Zone in Southern Tibet marks the boundary between India and Asia-formerly separated by an ocean basin-and is a critical record of the tectonic processes that created the Tibetan Plateau. The Yarlung Suture Zone is also a frontier research area, as difficulty of access has limited research activity, providing ample opportunities for new discoveries. This paper documents field research conducted by the authors along the Yarlung suture zone in eastern Xigaze(Shigatse, Rikaze)County, ~250 km west of the city of Lhasa, in July 2017. The goal of this research was to map the Suture Zone structure in detail, and more specifically to understand the branching relationships between two major fault systems-the Great Counter Thrust and Gangdese Thrust. A summary of early geological exploration is included to provide context for this research.  相似文献   

山东省莱州-安丘铁成矿带成矿规律探析          下载免费PDF全文

董银峰  徐金欣  赵金  李明波  杜振明 《山东国土资源》2015,31(5)

成矿带内主要赋矿层位为古元古代粉子山群和荆山群变质地层,铁矿成因可归纳3种成因类型,即层控沉积变质型、受断裂构造控制的高中温热液型和岩浆熔离型。沉积变质铁矿层控特征明显,其赋存层位为古元古代粉子山群小宋组;热液型铁矿严格受断裂构造、层间构造所控制,不论在垂向或水平方向上与蛇纹岩或磁铁蛇纹岩均呈过渡关系,矿体多呈形态复杂的透镜状产于古元古代粉子山群小宋组和荆山群野头组祥山段;岩浆熔离型铁矿位于昌邑大店断裂与平度断裂相接部位,成矿母岩为古元古代莱州岩套西水夼细粒变辉长岩,矿体赋存于古元古代荆山群野头组中。  相似文献   

伊吾Eucrite陨石的岩石学、矿物学特征及其成因     

高天静  冯彩霞  宋光明  刘燊  李世杰 《地质学报》2021,95(9):2901-2908

Howardite-Eucrite-Diogenite(HED)族陨石是地球上目前发现数量最多的无球粒陨石类型,已发现的 HED族陨石主要来自于南极和非洲西北部的沙漠,本研究的 HED族陨石国际命名为Yiwu 001 ,发现于中国新疆维吾尔自治区伊吾县境内.系统的矿物学和岩石学研究显示,该陨石属于单矿物碎屑角砾岩 Eucrite,主要矿物为易变辉石(38%)、普通辉石(8%)和斜长石(46%),副矿物主要为二氧化硅、陨硫铁、铬铁矿、钛铁矿.根据主要矿物的粒径,对该陨石开展了区域划分:粗粒、细粒和极细粒,辉石对应的粒径均值分别为 550 μm、100 μm 和 60 μm.粗粒和部分细粒区域具次辉绿结构,细粒和极细粒区域发育麻粒结构.陨石中细粒玄武岩包裹着以椭球体为主的粗粒和拉长的极细粒玄武岩,极细粒玄武岩呈定向构造.Yiwu 001 陨石原岩可能为内含粗粒玄武岩捕虏体的玄武岩,定向构造指示可能发生过近静态的部分熔融.该陨石在晚期经历了复杂的热变质作用,为 5 型变质类型,主要表现在出溶辉石条带、麻粒结构和三联点结构.  相似文献   

Relationship between Thermal Metamorphism of Coal and the Periodic Variation Law of Geochemical Behavior of Elements: A Study on the C2 Coal Seam in the Fengfeng Mining Area of the Handan Coalfield in Hebei,China     

YANG Jianye  QIN Shenjun  ZHANG Weiguo  LIU Shande  XU Fei 《《地质学报》英文版》2021,95(5):1684-1694

This study highlights the response of the periodic variation of the geochemical behavior of elements to the thermal metamorphism of coal by considering the differentiation mode and differentiation degree of elements of the C2 coal seam in the Fengfeng mining area of the Handan Coalfield in Hebei, China. The periodic variation of the geochemical behavior of elements was observed to change towards a certain direction as the degree of metamorphism of a geological body increased. Based on the coincidence degree (or similarity degree) between the geochemical behavior of elements and periodic variation of elements, the 57 elements in this study were divided into two levels. The periodic variation of the geochemical behavior of first-level elements was largely synchronous with that of their first ionization energy, suggesting that only one differentiation mode exists and the elements are mainly inorganically associated. The differentiation mode of the second-level elements deviated to a certain extent from their first ionization energy; the larger the deviation, the more complicated and diverse was the differentiation mode. Among the second-level elements, the grade of coal metamorphism has evident and intuitive effects on the proportion of elements with particular structural features, such as the 4q+3 type of elements and the odd-odd elements. In addition, the distribution of elements in organic and inorganic matter within coal are subject to the structural features of the elements. The differentiation mode and differentiation intensity of elements could be characterized by the hierarchical parameter and differentiation intensity. The hierarchical parameter and differentiation intensity of certain elements showed a good positive or negative correlation with Rmax in coal. The 57 elements in this study were quantitatively ordered according to the degree of magmatic hydrothermal fluid influence and thermal metamorphism of coal through graphs depicting the goodness of fit, correlation coefficient with Rmax, and differentiation intensity. The results of this study are consistent with the results of previous field research, illustrating the scientific significance and application value of this study on the periodic variation of the geochemical behavior of elements.  相似文献   

Cambrian metamorphism of the Qaidam block:Constraints from phase equilibrium modeling and monazite U-Pb datingSCIEI北大核心CSCD     

滕霞  张建新  毛小红  路增龙  周桂生  武亚威  郭祺 《岩石学报》2022,(11):3247-3258

柴达木地块位于青藏高原东北缘的祁连-阿尔金-昆仑早古生代造山系之中,它的西段出露一套(超)高温变质岩组合:变泥质岩、长英质片麻岩、基性麻粒岩、钙硅酸盐岩、含橄榄石大理岩及少量Mg-Al麻粒岩。本文以相平衡模拟和独居石U-Pb年代学为主要手段,限定柴西缘变泥质岩的变质作用P-T-t轨迹。变泥质岩记录了顺时针P-T轨迹,其中,压力峰期条件约为0.89GPa和800℃,温度峰期条件约为0.64GPa和825℃,退变质条件为0.58GPa和800℃至0.37±0.05GPa和702±50℃。变泥质岩的独居石U-Pb年龄集中在517~496Ma之间,三个样品的加权平均年龄分别为508±2Ma(MSWD=2.0)、506±1Ma(MSWD=1.7)、506±1Ma(MSWD=1.3)。本文将其解释为独居石的形成年龄,并认为独居石主要形成于退变质过程中的残留熔体结晶阶段(0.58GPa和800℃左右)。结合已有的工作可以得出,柴达木地块西段麻粒岩相变质作用具有顺时针P-T轨迹和1000~1300℃/GPa的峰期T/P值,并且在高温变质条件(>800℃)持续了超过30Myr。该类高T/P型变质作用最有可能发生在大型碰撞造山带内,可以与冈瓦纳大陆内部的晚泛非期的高T/P型变质作用对比,很可能是与冈瓦纳大陆最终拼合有关的晚泛非期造山事件的体现。  相似文献   

Unravelling the protracted U-Pb zircon geochronological record of high to ultrahigh temperature metamorphic rocks: Implications for provenance investigations     

《地学前缘(英文版)》2023,14(2):101515

The assessment of detrital zircon age records is a key method in basin analysis, but it is prone to several biases that may compromise accurate sedimentary provenance investigations. High to ultrahigh temperature (HT-UHT) metamorphism (especially if T > 850 °C) is herein presented as a natural cause of bias in provenance studies based on U-Pb detrital zircon ages, since zircon from rocks submitted to these extreme and often prolonged conditions frequently yield protracted, apparently concordant, geochronological records. Such age spreading can result from disturbance of the primary U-Pb zircon system, likewise from (re)crystallization processes during multiple and/or prolonged metamorphic events. In this contribution, available geochronological data on Archean, Neoproterozoic and Palaeozoic HT-UHT metamorphic rocks, acquired by different techniques (SIMS and LA-ICP-MS) and showing distinct compositions, are reassessed to demonstrate HT-UHT metamorphism may result in modes and age distributions of unclear geological meaning. As a consequence, it may induce misinterpretations on U-Pb detrital zircon provenance analyses, particularly in sedimentary rocks metamorphosed under such extreme temperature conditions. To evaluate the presence of HT-UHT metamorphism-related bias in the detrital zircon record, we suggest a workflow for data acquisition and interpretation, combining a multi-proxy approach with: (i) in situ U-Pb dating coupled with Hf analyses to retrieve the isotopic composition of the sources, and (ii) the integration of a petrochronological investigation to typify fingerprints of the HT-UHT metamorphic event. The proposed workflow is validated in the investigation of one theoretical and one natural example allowing a better characterization of the sedimentary sources, maximum depositional ages, and the tectonic setting of the basin. Our workflow allows to the appraisal of biases imposed by HT-UHT metamorphism and resulting disturbances in the U-Pb detrital zircon record, particularly for sedimentary rocks that underwent HT-UHT metamorphism and, finally, suggests ways to overcome these issues.  相似文献   

陕北三叠纪煤田中—特高油产率煤分布规律及成因机理     

马丽  段中会  贺丹  周蕾  吕婷婷  闫和平  王锐 《中国煤炭地质》2022,(1)

以子长矿区内分布的300余组钻孔数据为基础,研究了陕北三叠纪煤田煤炭资源的物理化学性质,按照《煤中焦油含量分级》(MT/T1179—2019),划分了中油产率煤(7.0%<ω(Tar_d)<12.0%)和高油产率煤(12.0%<ω(Tar_d)<15.0%)的分布范围,预测了中—特高油产率煤的资源量。研究了矿区主采煤层3号煤层和5号煤层的煤质、沉积环境、变质程度等,认为矿区内中—特高油产率煤具一低两高的特征:镜质体反射率高(0.61%~0.83%)、变质程度低、挥发分高(35.78%~45.64%),认为成煤环境及变质程度是影响煤层富油的关键因素,研究区内5号煤层的焦油产率略高于3号煤层。  相似文献