滇西澜沧岩群碎屑锆石U-Pb定年及其地质意义   总被引：1，自引：0，他引：1       下载免费PDF全文

徐云飞  丛峰  刘军平  孙柏东  黄晓明 《沉积与特提斯地质》2018,38(2):103-112

虽然前人对澜沧岩群做了大量的研究,但缺乏同位素年代学方面的研究。此次研究针对澜沧江南段菖蒲塘-大田山地区澜沧岩群绢白云母石英片岩进行碎屑锆石U-Pb定年,为澜沧岩群的形成时代增添年代学证据。极大多数(129粒)锆石阴极发光(CL)图像显示其有明显的结晶振荡环带,指示其为岩浆成因的碎屑锆石,129粒碎屑锆石具有多组峰值年龄,最年轻一组年龄加权平均值为452±26Ma,表明澜沧岩群最早沉积时限不早于452±26Ma;极少数(1粒)锆石具弱阴极发光,缺乏内部结构特点,认为其为变质重结晶锆石,变质结晶锆石U-Pb年龄为255±3Ma,与前人研究所得澜沧岩群变质时代基本吻合。综合分析,澜沧岩群的沉积时限不早于452±26Ma,在二叠纪末期可能发生变质作用。  相似文献   

青海南山吾口侵入岩体锆石U-Pb年代学、地球化学特征及其地质意义          下载免费PDF全文

郝亚青  杨启安  石玉莲  李生虎 《沉积与特提斯地质》2018,38(4):13-23

本文对青海南山吾口正长花岗岩和花岗闪长岩进行了岩石学、岩石地球化学及年代学研究。首次测得吾口侵入岩体正长花岗岩的锆石206Pb/238U年龄为253. 8±3. 3Ma(MSWD=0. 96),形成时代为晚二叠世。岩石中Al_2O_3为(14. 13～16. 51)×10~(-2),K_2O为(1. 66～3. 59)×10~(-2),A/NK=1. 15～2. 35,A/CNK=0. 75～1. 03,TFe O/(TFe O+MgO)=0. 53～0. 81,岩石具偏铝质中-高钾钙碱性花岗岩特征;吾口岩体表现为富集大离子亲石元素Rb、K等,亏损高场强元素Nb、Ta、Ba等;轻重稀土分异较明显,具右倾特征,中等负Eu异常(δEu=0. 44～0. 68),具壳幔岩浆混合特征。吾口岩体代表了阿尼玛卿洋盆向北削减俯冲运动在青海南山构造带与西秦岭造山带和南祁连造山带的构造转换衔接部位的构造演化的地质记录。该侵入岩体形成时代及构造环境的确定,为研究印支早期青海南山构造演化及动力学机制提供重要依据。  相似文献   

新疆西南天山阿万达金矿区赋矿围岩物源及形成时代:碎屑锆石U-Pb年代学制约          下载免费PDF全文

付宇  丁清峰  吴昌志 《高校地质学报》2018,24(3):353

阿万达金矿位于西南天山造山带内。此次研究在简要总结其矿床地质特征基础上,对与阿万达金矿成矿密切相关的阿克苏群中硅质片岩围岩分别进行了岩石地球化学分析和LA-ICP-MS碎屑锆石U-Pb定年研究,以期对围岩的沉积环境、物源及形成时代进行讨论。岩石地球化学分析结果显示,阿万达金矿赋矿围岩中硅质片岩的原岩可能为一套成熟度较低的泥岩或砂岩,物源主要为石英岩质沉积物,沉积环境可能处于活动大陆弧内的沉积盆地内。U-Pb定年结果显示,其碎屑锆石定年数据主要形成了加权平均年龄值为405 Ma或406 Ma的年龄峰,其谐和年龄最小峰值即405 Ma可以作为其最大沉积年龄。因此笔者认为阿克苏群中硅质片岩的沉积时代并不是前人所定的长城纪,而是不老于早泥盆世。另外,这一地层的物源组成具有多样性,～405 Ma碎屑锆石占主体,可能与哈尔克山北缘火山弧内的早泥盆世岩浆活动有关;～745Ma的碎屑锆石的出现,表明其物源有少部分来自新元古代岩石;极少数～2.50 Ga的碎屑锆石的出现,反映了华北地台对本地层有物源上的贡献。  相似文献   

Isotope stratigraphy and U-Pb dating of detrital zircons from the Vendian-Cambrian deposits of the North Muya block     

I.A. Vishnevskaya  E.F. Letnikova  N.A. Kanygina  A.I. Proshenkin  N.G. Soloshenko  E.V. Vetrov  V.Yu. Kiseleva 《Russian Geology and Geophysics》2018,59(11):1433-1449

U-Pb dating of detrital zircons from the sandstones of the Mamakan Formation has been made. Geochemical and isotope parameters of the carbonate deposits of the Yanguda Formation in the Vendian-Cambrian cover of the North Muya continental block have been estimated. It has been established that only the Neoproterozoic (630-915 Ma) rocks of the North Muya block were the provenances of terrigenous material. In the least altered carbonate rocks of the Yanguda Formation, the ⁸⁷Sr/⁸⁶Sr ratio is within 0.70814-0.70879 and δ¹³C varies from -0.4 to + 1.9‰. Comparison of the evaluated isotope parameters with those of carbonate rocks of typical Vendian-Cambrian sections shows that the carbonate deposits of the Yanguda Formation accumulated in the Early Cambrian, about 520 Ma. Sedimentation of the Mamakan and Yanguda Formations took place in the local sedimentary basin in the Vendian-Early Cambrian, in the absence of tectonic activity within the North Muya block. Detrital material that formed during the destruction of the rocks of the Siberian Platform basement and cover was not supplied into the basin.  相似文献   

Ore-bearing fluids of the Eldorado gold deposit (Yenisei Ridge,Russia)     

N.A. Gibsher  A.A. Tomilenko  A.M. Sazonov  T.A. Bul’bak  M.O. Khomenko  M.A. Ryabukha  E.O. Shaparenko  S.A. Sil’yanov  N.A. Nekrasova 《Russian Geology and Geophysics》2018,59(8):983-996

The Eldorado low-sulfide gold-quartz deposit, with gold reserves of more than 60 tons, is located in the damage zone of the Ishimba Fault in the Yenisei Ridge and is hosted by Riphean epidote-amphibolite metamorphic rocks (Sukhoi Pit Group). Orebodies occur in four roughly parallel heavily fractured zones where rocks were subject to metamorphism under stress and heat impacts. They consist of sulfide-bearing schists with veins of gray or milky-white quartz varieties. Gray quartz predominating in gold-bearing orebodies contains graphite and amorphous carbon identified by Raman spectroscopy; the contents of gold and amorphous carbon are in positive correlation. As inferred from thermobarometry, gas chromatography, gas chromatography-mass spectrometry, and Raman spectroscopy of fluid inclusions in sulfides, carbonates, and gray and white quartz, gold mineralization formed under the effect of reduced H₂O-CO₂-HC fluids with temperatures of 180 to 490 °C, salinity of 9 to 22 wt.% NaCl equiv, and pressures of 0.1 to 2.3 kbar. Judging by the presence of 11% mantle helium (³He) in fluid inclusions from quartz and the sulfur isotope composition (7.1-17.4‰ δ³⁴S) of sulfides, ore-bearing fluids ascended from a mantle source along shear zones, where they “boiled”. While the fluids were ascending, the metalliferous S- and N-bearing hydrocarbon (HC) compounds they carried broke down to produce crystalline sulfides, gold, and disseminated graphite and amorphous carbon (the latter imparts the gray color to quartz). Barren veins of milky-white quartz formed from oxidized mainly aqueous fluids with a salinity of < 15 wt.% NaCl equiv at 150-350 °C. Chloride brines (> 30 wt.% NaCl equiv) at 150-260 °C impregnated the gold-bearing quartz veins and produced the lower strata of the hydrothermal-granitoid section. The gold mineralization (795-710 Ma) was roughly coeval to local high-temperature stress metamorphism (836-745 Ma) and intrusion of the Kalama multiphase complex (880-752 Ma).  相似文献   

Zircon U–Pb and Wolframite Sm–Nd Dating of the Bayinsukhtu Tungsten Deposit in Southern Mongolia and its Geological Significance     

《Resource Geology》2018,68(4):337-351

The Bayinsukhtu tungsten deposit is a newly discovered quartz‐vein tungsten deposit in the Xing'an–Mongolia Orogenic Belt (XMOB) in southern Mongolia, hosted by the Bayinsukhtu granite porphyry. The granite porphyry is located mainly south of the study area, over 3 km². The rock consists of quartz and feldspar phenocrysts in a fine‐grained matrix, also mainly composed of feldspar and quartz. The granite porphyry samples demonstrate high SiO₂ and high alkalinity. All samples also straddle the high‐potassium calc‐alkaline series. In a plot of the molar ratios of A/NK versus A/CNK, the granites are metaluminous. The chondrite‐normalized REE patterns are characterized by large negative Eu anomalies and fractionated LREEs. The U–Pb age of zircons from the granite porphyry is 298.8 ± 1.8 Ma, and the Sm–Nd age of the five wolframite samples from the tungsten deposit is 303 ± 19 Ma. The cooling age of the granite porphyry and tungsten mineralization is within the error of measurement and is of the Late Carboniferous age. Geological and geochronological evidence shows that the tungsten mineralization and the granite porphyry at Bayinsukhtu are genetically closely related and that they are results of Carboniferous magmatism. Their tectonic setting is related to the accretion of the Central Asian Orogenic Belt during the late Paleozoic era.  相似文献   

吉林东部敦(化)—密(山)断裂带内碱性粗面岩同位素年代学、岩石化学及地质意义     

邸新  贾海明  于宏斌  聂立军 《世界地质》2018,37(4):1047

吉林敦化—密山断裂带北段琵河口—黄泥河镇之间新发现有多处的霓辉粗面岩,岩石以普遍富含碱性矿物霓辉石为特点,均呈整合接触覆盖于船底山期碱性玄武岩之上,具高位喷发、低位充填特点,全岩K--Ar年龄测定结果 (25. 64±0. 53 Ma、27. 36±0. 45 Ma、28. 45±0. 56 Ma、28. 55±0. 43Ma、28. 63±0. 45 Ma、28. 65±0. 61 Ma)属渐新世。地球化学数据显示,霓辉粗面岩SiO_2质量分数均值为59. 05%,富碱、高钾,亏损大离子亲石元素(Sr、Ba、V、Cr),富集高场强元素(Nb、Ta、Hf、Zr)和轻稀土元素(LREE),∑REE含量很高,具有右倾型稀土分配型式,显示明显Eu负异常。研究表明,霓辉粗面岩是由碱性玄武质岩浆经强烈分离结晶作用形成的,揭示该区渐新世处于一种强烈的拉张环境,幔源岩浆经历了由碱性玄武岩-碱性粗面岩的演化过程。  相似文献   

Rutile R632 – A New Natural Reference Material for U‐Pb and Zr Determination          下载免费PDF全文

Emelie Axelsson  Jonas Pape  Jasper Berndt  Fernando Corfu  Klaus Mezger  Michael M. Raith 《Geostandards and Geoanalytical Research》2018,42(3):319-338

A new natural rutile reference material is presented, suitable for U‐Pb dating and Zr‐in‐rutile thermometry by microbeam methods. U‐Pb dating of rutile R632 using laser ablation ICP‐MS with both magnetic sector field and quadrupole instruments as well as isotope dilution‐thermal ionisation mass spectrometry yielded a concordia age of 496 ± 2 Ma. The high U content (> 300 μg g^?1) enabled measurement of high‐precision U‐Pb ages despite its young age. The sample was found to have a Zr content of 4294 ± 196 μg g^?1, which makes it an excellent complementary reference material for Zr‐in‐rutile thermometry. Individual rutile grains have homogeneous compositions of a number of other trace elements including V, Cr, Fe, Nb, Mo, Sn, Sb, Hf, Ta and W. This newly characterised material significantly expands the range of available rutile reference materials relevant for age and temperature determinations.  相似文献   

青海南山地区角孔变质岩地质特征、年代学及其地质意义     

李佐臣  裴先治  李瑞保  裴磊  张永明  王旭斌  刘成军  陈有炘  王盟 《地质通报》2018,37(4):570-588

青海南山达不祖乎山北部一带的角孔变质岩系原划为早中三叠世隆务河组。通过野外实测地质剖面和路线地质调查,查明该套地层单元野外产出状态及岩石组合特征,并对其物质来源和形成时代进行分析,对进一步研究该区晚古生代-早中生代的构造演化具有重要意义。该套变质岩系为一套长石石英岩、石英岩、大理岩和黑云石英片岩组合,由下向上划分为3个岩段,叠置厚度大于3186.3m。根据碎屑锆石年龄分布特征,可大致划分为5个年龄组段,分别为250～304Ma、405～546Ma、649～1077Ma、1402～1620Ma和1861～2990Ma,其中250～304Ma可进一步划分为250～269Ma和289～304Ma两个亚组。综合前人研究资料与区域构造岩浆活动,将青海南山地区角孔变质岩的沉积时代限定为二叠纪,物源主要来自祁连造山带加里东期和晋宁期岩浆弧,柴北缘构造带海西期岩浆弧也提供了部分物质,晚古生代—早中生代经历了陆内裂陷、洋盆拉张及俯冲碰撞的构造演化过程。  相似文献   

大兴安岭伊勒呼里山早白垩世碱长花岗岩年龄、地球化学特征及其地质意义   总被引：1，自引：1，他引：0  

尹志刚  宫兆民  张跃龙  韩宇  王阳  曹忠强  李海娜  李敏 《地质通报》2018,37(6):1061-1074

对大兴安岭伊勒呼里山早白垩世碱长花岗岩进行了岩相学、地球化学、LA-ICP-MS锆石U-Pb定年研究。伊勒呼里山地区碱长花岗岩主量元素具有富Si、富碱,贫Mg、Ca的特征;微量元素亏损Sr、P、Eu、Ti,富集K、Rb、Th等不相容元素,元素地球化学特征表明,岩体为铝质A型花岗岩(A/CNK=0.88~1.21,A/NK=0.94~1.49)。测年结果显示,粗中粒碱长花岗岩的锆石年龄为140.3±1.0Ma,细中粒碱长花岗岩锆石年龄为137.9±0.8Ma,均形成于早白垩世。结合区域研究资料,伊勒呼里山地区碱长花岗岩岩体的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展密切相关,其岩浆源区可能为地壳物质的部分熔融。  相似文献