宁镇地区安基山岩体锆石LA ICPMS U Pb 定年及意义   总被引：1，自引：0，他引：1  

刘建敏  闫峻  李全忠  刘晓强 《地质论评》2014,60(1):190-200

宁镇地区安基山岩体最早被厘定为高Sr低Y型岩石(Adakite),为深入理解安基山岩体的成因与深部地质作用演化过程,本文利用LA ICPMS锆石U Pb定年方法对安基山岩体的花岗闪长斑岩进行了年代学研究,获得其206Pb/238U加权平均年龄为 1088±12 Ma,表明岩浆侵位时代为早白垩世。另外,结合本地区高精度年代学数据,构筑了长江中下游地区中生代岩浆岩的精细年代学格架,划分为四个阶段：148~133 Ma（第一阶段）、131~127 Ma（第二阶段）、126~123 Ma（第三阶段）以及109~102 Ma（第四阶段）。  相似文献   

西秦岭舒家坝地区泥盆纪舒家坝群碎屑锆石LA-ICP-MSU-Pb年龄：源区特征与形成时代     

王元元  ;裴先治  ;刘成军  ;李瑞保  ;李佐臣  ;魏博  ;任厚州  ;陈伟男  ;刘图杰  ;胥晓春 《中国区域地质》2014,(7):1015-1027

以西秦岭舒家坝地区泥盆纪舒家坝群碎屑岩为研究对象,进行碎屑锆石LA-ICP-MS U-Pb年龄研究,探讨其形成时代、物源组成和构造背景。所测样品最小锆石年龄组的年龄加权平均值为413Ma,代表了舒家坝群的沉积下限,结合前人研究的古生物资料将其形成时代限定为中泥盆世。所获碎屑锆石年龄可划分为4个谱段：震旦纪—古生代年龄谱段619～409Ma,峰值为445Ma;新元古代年龄谱段930～735Ma,峰值为849Ma;中元古代年龄谱段1760～1033Ma;新太古代—古元古代年龄谱段3095～2478Ma。综合研究认为,舒家坝群的物源具多元性,包括西秦岭北缘构造带、北祁连造山带东段和华北板块基底,其中北祁连造山带东段和西秦岭北缘构造带是舒家坝群沉积的主要物源区,且后者占主导地位。结合区域地质资料,根据其物源组成特征判断,舒家坝群形成于陆—陆或弧—陆碰撞后由挤压转换为伸展环境的局部裂陷盆地。  相似文献   

柴北缘都兰高压麻粒岩的锆石U-Pb定年及其地质意义   总被引：3，自引：0，他引：3  

于胜尧  张建新  李金平  孟繁聪 《岩石矿物学杂志》2010,29(2):139-150

在柴北缘高压-超高压变质带的东端都兰地区,高压麻粒岩以透镜体的形式存在于石榴白云母片岩、花岗质片麻岩以及斜长角闪岩中。高压麻粒岩的主体为基性麻粒岩,并含少量中酸性麻粒岩。基性麻粒岩主要由石榴子石、单斜辉石、斜长石和石英等组成,而中酸性麻粒岩峰期矿物组合为:石榴子石+斜长石+钾长石+蓝晶石+石英±单斜辉石。根据显微构造和反应结构特征,主要识别出3期变质作用:①峰期高压麻粒岩相阶段(M1);②退变质高角闪岩相阶段(M2);③绿片岩相/低角闪岩相阶段(M3)。选取典型的中酸性麻粒岩样品进行了锆石LA-ICP-MSU-Pb原位定年分析,获得加权平均年龄为446.9±6.5Ma,且CL图像显示锆石内部发育石榴子石、单斜辉石、斜长石等矿物包体,反映锆石可能形成在峰期高压麻粒岩相变质条件下。岩石学和年代学结果显示都兰高压麻粒岩和邻近的榴辉岩同时形成于同一俯冲带的不同热构造环境,高压麻粒岩并非榴辉岩热松弛作用形成的,两者具有各自独立的变质演化历史。  相似文献   

Two cycles of voluminous pyroclastic volcanism and sedimentation related to episodic granite emplacement during the late Archean: Eastern Yilgarn Craton,Western Australia     

Richard J. Squire  Charlotte M. Allen  Ray A.F. Cas  Ian H. Campbell  Richard S. Blewett  Alexander A. Nemchin 《Precambrian Research》2010

The thick piles of late-Archean volcaniclastic sedimentary successions that overlie the voluminous greenstone units of the eastern Yilgarn Craton, Western Australia, record the important transition from the cessation in mafic-ultramafic volcanism to cratonisation between about 2690 and 2655 Ma. Unfortunately, an inability to clearly subdivide the superficially similar sedimentary successions and correlate them between the various geological terranes and domains of the eastern Yilgarn Craton has led to uncertainty about the timing and nature of the region's palaeogeographic and palaeotectonic evolution. Here, we present the results of some 2025 U–Pb laser-ablation-ICP-MS analyses and 323 Sensitive High-Resolution Ion Microprobe (SHRIMP) analyses of detrital zircons from 14 late-Archean felsic clastic successions of the eastern Yilgarn Craton, which have enabled correlation of clastic successions. The results of our data, together with those compiled from previous studies, show that the post-greenstone sedimentary successions include two major cycles that both commenced with voluminous pyroclastic volcanism and ended with widespread exhumation and erosion associated with granite emplacement. Cycle One commences with an influx of rapidly reworked feldspar-rich pyroclastic debris. These units, here-named the Early Black Flag Group, are dominated by a single population of detrital zircons with an average age of 2690–2680 Ma. Thick (up to 2 km) dolerite bodies, such as the Golden Mile Dolerite, intrude the upper parts of the Early Black Flag Group at about 2680 Ma. Incipient development of large granite domes during Cycle One created extensional basins predominantly near their southeastern and northwestern margins (e.g., St Ives, Wallaby, Kanowna Belle and Agnew), into which the Early Black Flag Group and overlying coarse mafic conglomerate facies of the Late Black Flag Group were deposited. The clast compositions and detrital-zircon ages of the late Black Flag Group detritus match closely the nearby and/or stratigraphically underlying successions, thus suggesting relatively local provenance. Cycle Two involved a similar progression to that observed in Cycle One, but the age and composition of the detritus were notably different. Deposition of rapidly reworked quartz-rich pyroclastic deposits dominated by a single detrital-zircon age population of 2670–2660 Ma heralded the beginning of Cycle Two. These coarse-grained quartz-rich units, are name here the Early Merougil Group. The mean ages of the detrital zircons from the Early Merougil Group match closely the age of the peak in high-Ca (quartz-rich) granite magmatism in the Yilgarn Craton and thus probably represent the surface expression of the same event. Successions of the Late Merougil Group are dominated by coarse felsic conglomerate with abundant volcanic quartz. Although the detrital zircons in these successions have a broad spread of age, the principal sub-populations have ages of about 2665 Ma and thus match closely those of the Early Merougil Group. These successions occur most commonly at the northwestern and southeastern margins of the granite batholiths and thus are interpreted to represent resedimented units dominted by the stratigraphically underlying packages of the Early Merougil Group. The Kurrawang Group is the youngest sedimentary units identified in this study and is dominated by polymictic conglomerate with clasts of banded iron formation (BIF), granite and quartzite near the base and quartz-rich sandstone units containing detrital zircons aged up to 3500 Ma near the top. These units record provenance from deeper and/or more-distal sources. We suggest here that the principal driver for the major episodes of volcanism, sedimentation and deformation associated with basin development was the progressive emplacement of large granite batholiths. This interpretation has important implication for palaeogeographic and palaeotectonic evolution of all late-Archean terranes around the world.  相似文献   

Penglai Zircon Megacrysts: A Potential New Working Reference Material for Microbeam Determination of Hf–O Isotopes and U–Pb Age     

Xian-Hua Li  Weng-Guo Long  Qiu-Li Li  Yu Liu  Yong-Fei Zheng  Yue-Heng Yang  Kevin R. Chamberlain  De-Fang Wan  Cun-Hua Guo  Xuan-Ce Wang  Hua Tao 《Geostandards and Geoanalytical Research》2010,34(2):117-134

We introduce a potential new working reference material – natural zircon megacrysts from an Early Pliocene alkaline basalt (from Penglai, northern Hainan Island, southern China) – for the microbeam determination of O and Hf isotopes, and U–Pb age dating. The Penglai zircon megacrysts were found to be fairly homogeneous in Hf and O isotopes based on large numbers of measurements by LA-multiple collector (MC)-ICP-MS and SIMS, respectively. Precise determinations of O isotopes by isotope ratio mass spectrometry (IRMS) and Hf isotopes by solution MC-ICP-MS were in good agreement with the statistical mean of microbeam measurements. The mean δ¹⁸O value of 5.31 ± 0.10‰ (2s) by IRMS and the mean ¹⁷⁶Hf/¹⁷⁷Hf value of 0.282906 ± 0.0000010 (2s) by solution MC-ICP-MS are the best reference values for the Penglai zircons. SIMS and isotope dilution-TIMS measurements yielded consistent ²⁰⁶Pb/²³⁸U ages within analytical uncertainties, and the preferred ²⁰⁶Pb/²³⁸U age was found to be 4.4 ± 0.1 Ma (95% confidence interval). The young age and variably high common Pb content make the Penglai zircons unsuitable as a primary U–Pb age reference material for calibration of unknown samples by microbeam analysis; however, they can be used as a secondary working reference material for quality control of U–Pb age determination for young (particularly < 10 Ma) zircon samples.  相似文献   

湖北宜昌地区第四纪沉积物中锆石的U-Pb年龄特征及其物源意义   总被引：2，自引：0，他引：2  

向芳  杨栋  田馨  李志宏  罗来 《矿物岩石》2011,31(2)

对于长江三峡的贯通近年来基本认为是第四纪以来的事件,但在具体贯通时间的认识上仍存在差异。紧邻三峡出口、具有第四纪以来完整地层和较好出露层位的江汉盆地西缘宜昌地区的第四纪沉积物沉积特征及测年资料显示,该地区的云池组为冲积扇—扇三角洲相沉积,善溪窑组下部为扇三角洲沉积,上部为湖相沉积。对云池组、善溪窑组、长江5级和4级阶地的015,024,YC02,00B剖面等4个典型剖面砾石层中砂质填隙物的锆石进行矿物学研究和LA-ICP-MS U-Pb年龄测定,发现015,024剖面中锆石主要来源于三峡以东的黄陵穹窿、武当地块,少量来自鄂陕边境的庙川地区和湘鄂交接的华容地区,均为三峡以东的物质来源。而长江第5,4级阶地沉积物中的锆石不仅存在上述三峡以东物源区的物质,同时出现三峡以西米仓山—大巴山地区、龙门山—攀枝花地区,以及川西巴塘—德格地区岩浆岩物源的物质,也具有来自峨眉山玄武岩的特征岩浆锆石的存在,从而证实了以015,024剖面为代表的沉积并非前人认为的长江阶地产物,同时也表明三峡的贯通应在024剖面沉积结束以后,YC02剖面沉积以前,即长江三峡贯通的时间应该在0.75 Ma以后。  相似文献   

西藏拉萨地块过铝质花岗岩中继承锆石的物源区示踪及其古地理意义   总被引：5，自引：2，他引：3  

朱弟成  赵志丹  牛耀龄  王青  管琪  刘勇胜  莫宣学 《岩石学报》2011,27(7):1917-1930

富含继承锆石的过铝质花岗岩一般来源于富铝质岩石(如变泥质岩)的部分熔融,因而分析这些继承锆石的U-Pb年龄可以像分析沉积岩碎屑锆石的U-Pb年龄一样,提供过铝质花岗岩源区物质中碎屑沉积物物源区的丰富信息。本文报道了中部拉萨地块早侏罗世过铝质花岗岩的全岩地球化学和锆石U-Pb年代学数据,结合拉萨地块已有二叠纪和晚三叠世过铝质花岗岩的继承锆石年代学数据,总结了目前已有的拉萨地块过铝质花岗岩的继承锆石U-Pb年龄特征(共199个谐和测点)。这些过铝质花岗岩属强过铝质S型花岗岩,其中的继承锆石定义了1250~1100Ma(峰值1181±14Ma)和550~450Ma(峰值494±7Ma)2个最突出的年龄群,分别可比于拉萨地块古生代沉积岩的碎屑锆石年龄峰值(约1170Ma)和寒武纪火山岩的侵位时代,明显不同于西羌塘、安多和特提斯喜马拉雅新元古代-古生代沉积岩中的碎屑锆石年龄频谱。拉萨地块过铝质花岗岩中约1181Ma的继承锆石,可能与拉萨地块古生代沉积岩中的同期碎屑锆石一样,都来自澳大利亚南西部Albany-Fraser造山带和东南极Wilkes等地,而约494的继承锆石,既可能来自澳大利亚西部,也可能来自拉萨地块本地。本文提供了拉萨地块与澳大利亚大陆北缘具有古地理联系的过铝质花岗岩继承锆石U-Pb年龄证据。拉萨地块的研究实践表明,采用过铝质花岗岩继承锆石和古生代沉积岩碎屑锆石相结合的锆石U-Pb年代学方法,可为重建冈瓦纳大陆北缘其它微陆块的古地理和构造岩浆演化提供重要约束。  相似文献   

天山南北麓中-新生界碎屑锆石U-Pb年代学记录、物源体系分析与陆内盆山演化   总被引：4，自引：1，他引：3  

李忠  彭守涛 《岩石学报》2013,29(3):739-755

大批量、原位高精度碎屑矿物同位素分析为盆地(盆山)动力学等前沿领域的研究注入了新的活力.针对天山北麓(准噶尔盆地南缘)、天山南麓(塔里木盆地北缘)中生界及新生界露头剖面,重点通过13个(新补充4个)砂岩样品的碎屑锆石U-Pb同位素的LA-ICP-MS分析,本文解析了其年代学、物源特征及其构造属性等高分辨率信息,并开展了沉积记录与物源体系对比,探索了天山及其邻近盆地的表壳演化过程与地球动力学机制.研究显示,上三叠统-中侏罗统天山南麓碎屑锆石U-Pb年龄构成相对单一,年龄偏老(峰值区间380～450Ma),而同层位天山北麓碎屑锆石物源年龄构成总体宽泛复杂(160 ～470Ma);上侏罗统-下白垩统天山南麓碎屑锆石年龄构成复杂化(150 ～ 470Ma),而天山北麓则趋于相对简单(但仍然保留250～ 430Ma较宽范围);新近统以上,天山南、北麓主物源碎屑锆石年龄构成均趋向单一,即南麓年龄偏老(峰值区间380 ～460Ma),而北麓偏新(峰值区间260～310Ma).可能说明山盆构造分异活动可以分为四个阶段:中晚三叠世-中侏罗世平稳或渐弱,天山主分水岭位于南天山;晚侏罗世-早白垩世天山区域整体抬升剥露加剧,并伴随主分水岭相对北移;晚白垩世-古近纪相对较弱,而新近纪再度活跃并达到最强,南、北天山强烈隆升,分水岭各成系统.这也反映同期在欧亚板块南缘的一系列拼合-碰撞作用中,拉萨、印度板块对天山地区陆内构造变形和改造作用效果明显,而羌塘块体的影响较小;另一方面,与晚侏罗-早白垩世拉萨板块碰撞事件相关的天山隆升导致陆内区域气候-沉积演化的重要转折,但天山南北盆地局域气候-沉积记录的分异在新近纪印度板块碰撞以前是有限的.  相似文献   

新疆库鲁克塔格西段奥陶纪花岗岩体地质特征及构造意义   总被引：1，自引：0，他引：1  

郭瑞清  秦切  木合塔尔·扎日  赵亮亮  孙敏佳  魏震 《地学前缘》2013,20(4):251-263

塔里木盆地北缘是塔里木克拉通与南天山造山带结合部位,发育近东西展布的古生代花岗质侵入岩带,该侵入岩带对探究塔里木北缘构造背景及属性乃至南天山洋演化至关重要。文中研究岩体位于库鲁克塔格西段的博斯腾湖南岸,主要岩性为二长花岗岩,LA ICP MS U Pb锆石年龄分别为(458±3) Ma和(454.6±4.6) Ma,代表花岗岩结晶年龄。地球化学特征显示,花岗岩的SiO2质量分数为71.03%～74.39%,K2O质量分数为4.14%～5.07%,A/CNK=1.03～1.08,属弱过铝质高钾钙碱性I型花岗岩;(La/Yb)N为16.41～37.59,δEu=0.44～0.79,具轻稀土富集、重稀土相对亏损的特征;在原始地幔标准化蛛网图上,样品均明显富集K、Rb、Ba、Th等大离子亲石元素,亏损Ta、Nb、P、Ti等高场强元素。花岗岩岩浆源于下地壳的部分熔融,在熔融过程中源区残留石榴子石和斜长石。综合区域地质资料及前人成果,认为花岗岩形成的动力和热力来源与南天山洋向南俯冲有关,推测在早古生代南天山洋存在双向俯冲,并从奥陶纪开始向南俯冲消减,一直延续到早石炭世,到晚石炭世闭合。  相似文献   

吉林中部晚二叠世红山组碎屑锆石年龄及其地质意义     

辛玉莲  聂立军  周凯  邸新 《地质与资源》2011,20(3):201-204

在吉林1/5万退抟等四幅区域地质调查中,通过详细的野外地质调查和前人成果的综合研究,对测区内一直悬而未决的前中生代地层重新划分为新兴岩组和红山组;采用LA-ICPMS技术,对碎屑岩中的碎屑锆石进行U-Pb测年,确定了红山组沉积时限下限为晚二叠世.这对研究造山带变质岩沉积时限提出了较好的借鉴.  相似文献