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1.
周喜文  耿元生 《岩石学报》2009,25(8):1843-1852
贺兰山孔兹岩系作为华北克拉通西部孔兹岩带的重要组成部分,其变质时代问题一直悬而未决.利用SHRIMP锆石U-Pb定年技术,对贺兰山孔兹岩系中3个代表性富铝片麻岩(石榴堇青钾长片麻岩、石榴堇青二长片麻岩与石榴黑云斜长片麻岩)样品进行了精确定年.发现这3种岩石虽处不同层位,但其碎屑锆石年龄却非常集中,各测点207Pb/206Pb年龄总体变化在2.0～2.1Ga之间,加权平均年龄则在2017～2040Ma之间.这些碎屑锆石都具有岩浆结构特征,反映当时曾存在大规模花岗质岩浆活动,所成岩体为孔兹岩系沉积提供了充足物源.另有少量大于2.5Ga的碎屑锆石(2520～2949Ma),表明本区存在太古代岩浆活动记录.本区石榴堇青二长片麻岩中发育典型的变质增生锆石,其成因很可能与黑云母的脱水熔融反应有关.利用该锆石确定贺兰山孔兹岩系的变质时代为1950±8Ma.该时代与东部大青山、乌拉山孔兹岩系变质时代相同,表明华北克拉通西部的阴山地块与鄂尔多斯地块大体是以平行的方式正面拼贴到一起的,形成了目前的孔兹岩带.  相似文献   

2.
Santunying is an important area for revealing nature of the late Neoarchean tectono-magmato-thermal events in the eastern Hebei part of the North China Craton. It is mainly composed of meta-intrusive rocks. Supracrustal rocks sporadically occur in the meta-intrusive rocks. The meta-intrusive rocks are subdivided into the Santunying tonalitic gneiss, Qiuhuayu tonalitic-trondhjemitic gneiss, Xiaoguanzhuang dioritic gneiss and Qingyangshu meta-gabbro. Respectively, SHRIMP U–Pb zircon dating on fourteen samples yielded weighted mean 207Pb/206Pb ages of 2525–2537, 2532–2546, 2530–2544 and ∼2531 Ma for magmatic zircons from them. Dioritic gneiss of the Xiaoguanzhuang gneiss contain abundant 2544–3487 Ma xenocrystic zircons. SHRIMP U–Pb dating on a garnet-biotite gneiss sample yielded a weighted mean 207Pb/206Pb age of 2537 Ma for detrital zircons. All rocks underwent strong metamorphism, deformation and anatexis, resulting in formation of leucosomes and residues, with some leucosomes concentrating to form large veins. They record a strong late Neoarchean event by metamorphic zircon ages of 2489–2519 Ma. Some rocks also record metamorphic zircon ages of 1772–1843 Ma. Magmatic zircons from the magmatic rocks show large variations in εHf(t) values ranging from −1.7 to +8.7. Combined with early studies, conclusions are: 1) Intrusive rocks with the involvement of mantle-derived materials have a narrow range of magmatic zircon ages from 2525 to 2546 Ma, and supracrustal rocks were formed during the same period. 2) Ancient crustal remnants (>2600 Ma) are present, consistent with the late Neoarchean arc magmatism involving older continental crust, similar to Phanerozoic Andean margins. 3) The Archean basement underwent a strong tectonothermal event at the end of the Neoarchean, with the metamorphic zircon ages being 10–30 million years younger than the timing of magmatism, a common feature of the North China Craton. 4) A late Paleoproterozoic tectonothermal event widely occurred in the western part of eastern Hebei, which is linked with regional ductile deformation.  相似文献   

3.
《International Geology Review》2012,54(10):1194-1211
A belt of khondalite-series rocks in the Western Block of the North China craton (NCC) are considered to represent products of the collision between the north Yinshan and the south Ordos terranes before final amalgamation of the NCC basement. The Jining Complex of Inner Mongolia occurs in the eastern part of the Khondalite Belt and is crosscut by the Trans-North China Orogen. Khondalite rocks of the Jining Complex mainly comprise sillimanite-garnet gneiss, garnet/sillimanite-bearing granite, massive porphyritic granite, garnet quartzite, calc-silicate, and marble with minor felsic gneiss and mafic granulite. LA-ICP-MS, U–Pb dating and cathodoluminescence (CL) image analysis of zircons from five rocks from the complex, i.e. Sil-Bt-Grt leptynite gneiss, Spl-Sil-Ksp-Grt vein in (Crd)-Sil-Grt gneiss, Sil-Grt-K-Fsp mylonite from a shear zone, Crd-bearing Sil-Grt gneiss, and granite were used to determine protolith and metamorphic ages of the khondalite-series rocks. Results of 315 detrital zircon grains indicate five age populations: 2410–2550 Ma, 2162 Ma, 2047–2099 Ma, 1950–1993 Ma, and 1866 Ma. CL investigation reveals that zircon grains of most samples are rounded, unzoned with low Th/U, indicating a metamorphic origin, whereas quite a few grains in some rocks are characterized by magmatic oscillatory zoning and comparatively high Th/U, and are typically overgrown by metamorphic, low CL rims with low Th/U. Three samples of Sil-Bt-Grt gneiss record oldest ages of ～2550–2480 Ma, suggesting an Archaean/early Palaeoproterozoic provenance for the Jining Complex. Ages of ～2162–2047 Ma are interpreted as the metamorphic modified inherited source of supercrustal protoliths of the khondalite-series rocks. The khondalite depositional age is defined as 2228–2027 Ma by concordant ages obtained in this research. The Sil-Ksp-Grt vein and the granite have single population ages of 1985?±?28 Ma and 1957?±?19 Ma, respectively, and are inferred to record the same metamorphic event, i.e. formation of the Khondalite Belt within the Western Block owing to the collision of the north Yinshan and the south Ordos terranes. The Sil-Grt-K-Fsp mylonite yields a single group age of 1866?±?22 Ma, which may date final suturing of the Eastern Block and the Western Block and stabilization of the NCC.  相似文献   

4.
对蚌埠淮光花岗闪长岩的岩相学和锆石阴极发光图象研究表明,淮光"混合花岗闪长岩"为岩浆结晶作用的产物,岩石形成后受到了应力作用的改造.锆石SHRIMP U-Pb定年结果和岩浆锆石的SHRIMP U-Pb年龄显示淮光花岗闪长岩形成于130.0±2.0 Ma;大多数继承锆石的年龄集中在1 800～1 900 Ma、2 300～2 517 Ma和3 443 Ma,这意味着淮光花岗闪长岩的母岩浆起源于华北地块基底的部分熔融.早白垩世(130 Ma左右)的岩浆作用是引起继承锆石和碎屑锆石Pb丢失的重要原因,同时也是华北地块东部岩石圈减薄的最重要时期.130 Ma左右的岩浆作用和岩石圈减薄应与太平洋板块的俯冲相联系.  相似文献   

5.
鲁东地区前寒武纪侵入岩其侵入活动集中于新太古代和新元古代,均遭受不同程度的区域变质和韧性剪切带的改造,形成一套花岗质片麻岩类。新太古代早期TTG质花岗岩分布于胶北隆起区莱州一栖霞一带,经受了区域变质作用,形成一套灰色片麻岩,锆石内核SHRIMPU—Pb年龄2726—2707Ma基本代表岩浆结晶年龄,锆石变质边为2500Ma;古元古代侵入岩——莱州基性一超基性岩组合形成于1900～1850Ma左右,锆石SHRIMPU—Pb年龄（1852±9）Ma,（1868±11）Ma;新元古代侵入岩主要为花岗闪长质-二长花岗质片麻岩,出露于胶南-威海造山带,锆石U～Pb定年结果集中为892～605Ma,其中荣成超单元锆石SHRIMPU—Pb年龄720～780Ma。中生代侵入岩以花岗岩类为主,集中出露于半岛北部和东南沿海一带。燕山早期侵入岩文登超单元、垛崮山超单元、玲珑超单元锆石SHRIMPU—Pb同位素年龄值集中在167～150Ma;燕山晚期侵入岩大店超单元锆石SHRIMPU～Pb年龄120±4Ma,崂山超单元锆石SHRIMPU～Pb同位素年龄值为（120±2）～（114±2）Ma。  相似文献   

6.
内蒙古狼山地区宝音图地块是兴蒙造山带微地块之一.采用SHRIMP和LA ICP-MS锆石U-Pb测年技术,对宝音图地块中变质侵入体和宝音图群石英岩中的锆石进行了同位素年代学研究,获得了变质侵入体SHRIMP锆石U-Pb年龄1672±10Ma和宝音图群石英岩的碎屑锆石U-Pb下限年龄1426Ma,限定了宝音图群的形成时代应晚于1426Ma.同时根据宝音图群碎屑锆石年龄谱构造-热事件信息与华北克拉通构造-热事件年龄谱对比的相似性,揭示了宝音图群的碎屑来源于华北克拉通,认为宝音图地块与华北克拉通更具亲缘性,可能为华北克拉通的一部分.  相似文献   

7.
尚义杂岩是冀西北地区有代表性的变质地质体,由变质表壳岩和侵入岩组成。其中的变质表壳岩曾认为是新太古代晚期蛇绿岩洋壳残片。该区也有红旗营子群存在。我们对尚义黄土窑地区尚义杂岩和红旗营子群不同类型岩石进行了锆石SHRIMP U-Pb定年。含石榴黑云斜长片麻岩(HB1410)核部锆石年龄为310~2500Ma,边部变质锆石年龄为255Ma左右。黑云片麻岩(HB1411)和石英岩(HB1415)碎屑锆石年龄都为2.5Ga左右。辉长岩(HB1518)和石英闪长岩(HB1519)岩浆锆石年龄为278~279Ma。根据这些资料和前人研究,该地区的原红旗营子群和尚义杂岩变质表壳岩主体可能不是新太古代地质作用产物,而是形成于晚古生代,由不同时代地质体组成的构造杂岩。不存在所谓的太古宙蛇绿岩残片。晚古生代时期,中亚造山带对华北克拉通北缘的影响十分强烈。  相似文献   

8.
邹雷  刘平华  刘利双  王伟  田忠华 《地球科学》2020,45(9):3313-3329
叠布斯格杂岩作为阿拉善地块变质程度最高、形成时代最老的变质岩系,是进一步深入认识阿拉善地块形成、演化与构造亲缘性的最佳对象.本文对叠布斯格杂岩中黑云斜长片麻岩开展了系统的野外地质调查、岩相学观察和锆石U-Pb年代学研究.碎屑锆石U-Pb定年和野外地质调查表明,叠布斯格杂岩中黑云斜长片麻岩碎屑锆石年龄介于2 177~2 010 Ma,最小年龄峰值为2 050 Ma,结合变质锆石年龄数据,限定其沉积时代在2 050~1 969 Ma之间.区域对比研究表明,阿拉善地块叠布斯格杂岩中黑云斜长片麻岩与西阿拉善地块龙首山杂岩、华北克拉通孔兹岩带（尤其是孔兹岩带西部）中的变沉积岩系在沉积时代与源区特征上具有高度的一致性.此外,变质锆石U-Pb定年和微量元素分析表明,叠布斯格杂岩中黑云斜长片麻岩记录了古元古代晚期1 969~1 811 Ma连续的变质年龄.对比分析阿拉善地块与孔兹岩带变沉积岩系的碎屑锆石年龄谱系-变质时代表明,阿拉善地块与孔兹岩带在古元古代可能具有相同的沉积-变质演化历史,在古元古代期间阿拉善地块应是华北克拉通孔兹岩带的西延部分.   相似文献   

9.
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   

10.
The general classification of intermediate-acid intrusive rocks in the metamorphic zone of Gaoligong Mountains as one of the metamorphic terranes of Proterozoic Gaoligong Mountains is problematic regarding the intrusion stage and age, as well as the subsequent metamorphism and deformation. In this study, we investigated granitic gneiss in the metamorphic zone of Gaoligong Mountains based on the 1:50,000 regional geological survey of Qushi Street (2011-2013) and SHRIMP U-Pb zircon geochronology. Results showed that the SHRIMP U-Pb zircon dating of granitic gneiss ranged from 163.5±5.7 Ma to 74.0±2.0 Ma. Thus, the granitic gneiss was grouped into orthometamorphic rocks (metamorphic intrusions). The dating data of granite rocks associated with intense metamorphism and deformation were divided into three groups, 163.5±5.7 to 162.3±3.1 Ma, 132.2-101.0 Ma and 99.4±3.5-74.0±2.0 Ma, which respectively represented three independent geologic events including an important magma intrusion with superimposed metamorphic effects in the late Middle Jurassic, regional dynamic metamorphism and superimposed reformation of fluid action in the early Cretaceous, and dynamic metamorphism dominated by ductile shear and metamorphism starting from the late Cretaceous.  相似文献   

11.
胶东地区的荆山群呈近东西向环绕太古宙TTG花岗质片麻岩展布,主要由成熟度高的含石墨变泥砂质岩石、钙硅酸岩和大理岩组成,变质程度达高角闪岩相-麻粒岩相,具孔兹岩系性质。变质中-基性岩侵入到荆山群。它们的侵位时代对于探讨华北克拉通东部元古宙构造演化以及对荆山群沉积时代的制约,都有重要意义。锆石SHRIMP U-Pb定年结果表明,遭受低级变质的闪长岩(S0835)岩浆锆石年龄为1852±9Ma (MSWD=2.1),遭受中高级变质的辉长岩(S0816)变质锆石年龄为1865±11Ma (MSWD=0.76)。结合区域资料,可得出如下结论:(1)荆山群孔兹岩系形成于古元古代晚期(2.2~1.9Ga);(2)古元古代期间,胶东地区从挤压体制转入伸展体制的时间在1.87Ga之前。在华北克拉通中西部的恒山、大青山地区,存在1.97~1.92Ga辉长岩,在1.92~1.83Ga期间发生变质,与本文研究结果类似。这表明华北克拉通中-西部和东部具有类似的古元古代演化历史。  相似文献   

12.
鲁西是华北克拉通太古宙基底典型分布区之一,存在新太古代早期到晚期长期连续的地质演化的记录。在泰山地区黄前水库北侧,我们对相互关系十分清楚的不同类型和时代TTG岩浆岩进行了详细野外地质观察和锆石SHRIMP U-Pb定年。早期片麻状英云闪长岩为望府山杂岩的一部分,具有深熔特征,岩浆锆石和变质锆石年龄分别为2695±7 Ma和2630±10 Ma。早期片麻状英云闪长岩被奥长花岗岩脉切割,后者的两组锆石年龄分别为2626±8 Ma和2689±12 Ma,分别代表了其形成时代和捕获锆石年龄。之后,它们又被晚期弱片麻状英云闪长岩(线峪岩体)侵入,其岩浆锆石年龄为2547±7 Ma,存在2.6~2.7 Ga捕获锆石。这些不同时代岩浆岩的形成过程是鲁西地区新太古代地质演化的一个缩影。  相似文献   

13.
The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma. Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin. Received: 16 June 1996 / Accepted: 29 January 1997  相似文献   

14.
滇西高黎贡山群变质岩的锆石年龄及其构造意义   总被引：11，自引：5，他引：6  
李再会  林仕良  丛峰  谢韬  邹光富 《岩石学报》2012,28(5):1529-1541
被认为是腾冲-梁河地块前寒武纪结晶基底的滇西高黎贡山群变质岩系,其原岩及变质时代长期争论不休。岩相学和地球化学表明,组成高黎贡山群的黑云二长片麻岩、黑云角闪斜长片麻岩和变粒岩的原岩均为岩浆岩。首次对这些变质岩进行原位锆石U-Pb定年,分别获得497.8±7.2Ma～500±14Ma、83.5±0.9Ma的岩浆结晶年龄和459±5Ma、55.2±1.1Ma的变质年龄。结合相邻区碎屑锆石年龄及其区域对比分析,认为腾冲-梁河地块高黎贡山群中以石英片岩、石英岩为主体的原始沉积岩系可能形成于新元古代,应与拉萨地块有密切的亲缘关系。在早古生代环冈瓦纳大陆周缘造山过程中被寒武纪花岗岩侵入并发生变质作用;在新特提斯俯冲过程中,经历了晚中生代的安第斯型造弧作用;在印度与欧亚大陆碰撞过程中,又经历了新生代的岩浆作用、变质作用以及走滑剪切形成糜棱岩化作用。  相似文献   

15.
秦岭拉鸡庙镁铁质岩体锆石LA-ICP-MS年代学研究   总被引：10，自引：7，他引：3  
刘军锋  孙勇  孙卫东 《岩石学报》2009,25(2):320-330
秦岭拉鸡庙镁铁质岩体位于北秦岭南缘,主要由辉长岩(80%)、苏长辉长岩(15%)和少量闪长岩等侵入杂岩组成。对采自该岩体闪长岩的锆石进行阴极发光图像、微区原位LA-ICP-MS微量元素分析和U-Pb定年。CL图像显示这些锆石可以分为两类,一类锆石呈长柱状,具有明显的岩浆生长环带;另一类则呈浑圆状,阴极发光图像复杂,部分颗粒岩浆生长环带较模糊,个别样品外围存在一窄的亮色环边,推测为后期地质事件影响的结果。对26颗锆石核部和生长边进行28次U-Pb同位素分析,获得两组206Pb/238U年龄,分别为973±60Ma和422±7Ma。分析结果显示,所有样品具有高的Th, U, REE含量,明显富集HREE,其Th/U比值普遍高于0.6,表明这些锆石应属于岩浆成因。其中,422±7Ma应该代表拉鸡庙镁铁质岩体的成岩时代,这可能与古生代扬子陆块或者是具有扬子板块属性的微陆块和华北陆块的碰撞有关,该碰撞导致了秦岭洋的闭合;而973±60Ma应为捕获锆石年龄,代表北秦岭早期与Rodinia超大陆拼合有关的岩浆事件。考虑到没有检测到典型的华北克拉通的年龄,推测元古代北秦岭更接近华南板块。  相似文献   

16.
蔡佳  刘福来  刘平华  王舫  施建荣 《岩石学报》2015,31(10):3081-3106
乌拉山-大青山孔兹岩系岩石出露于华北克拉通孔兹岩带中段,是洞悉华北克拉通前寒武纪基底构造演化历史的一个重要窗口。研究区孔兹岩系岩石包括堇青石榴黑云二长片麻岩、夕线堇青石榴黑云二长片麻岩、紫苏石榴黑云片麻岩和石榴长英质粒状岩石,系统的岩相学观察显示多种典型的减压反应结构。阴极发光图像特征显示乌拉山-大青山孔兹岩系岩石均存在大量继承性碎屑锆石和变质增生锆石,其中继承性碎屑锆石形态复杂,多显示典型岩浆结晶环带,标志着源区物质主要来源于岩浆岩。变质锆石为新生的单颗粒或围绕着继承性碎屑锆石核生长,内部结构均匀,整体的Th/U比值较低。锆石LA-ICP-MS U-Pb定年结果表明,该区孔兹岩系岩石的继承性碎屑锆石的207Pb/206Pb年龄主要集中在2400~2500Ma、~2300Ma和2000~2100Ma,进而可限定其最老沉积时代应为~2000Ma,表明乌拉山-大青山孔兹岩系的原岩形成时代为古元古代中期。乌拉山-大青山孔兹岩系中典型的变质锆石记录其变质时代为1850~1950Ma,并显示~1950Ma和~1860Ma两组年龄峰。结合前人对内蒙古孔兹岩带乌拉山-大青山地区高级变质地体的变质作用、构造演化和同位素年代学的研究结果,综合判断该期变质事件与古元古代华北克拉通西部陆块内北部的阴山陆块和南部的鄂尔多斯陆块之间的俯冲-碰撞并折返抬升至地表的动力学过程有关,其中~1950Ma代表了陆-陆碰撞形成孔兹岩带的初始阶段,而~1860Ma则代表了其折返抬升的时代。  相似文献   

17.
秦岭富水杂岩体的一些变辉长岩含有粒度较大，U、Pb含量较高的斜锆石和锆石，是U-Pb同位素测年的极好矿物。本文对秦岭富水杂岩的中粗粒角闪黑云辉长岩中的斜错石和错石分别进行了SHRIMP法和TIMS法U-Pb同位素年龄测定，获得斜锆石和锆石的U-Pb同位素年龄分别为501.4±1.2 Ma和480.0±3.4 Ma，二者相差约20 Ma；对该岩石中的斜锆石和锆石的关系及锆石的成因进行了初步研究，认为斜锆石的U-Pb同位素年龄应可解释为秦岭富水杂岩中基性岩石的形成时代，而锆石的成因比较复杂，对其U-Pb同位素年龄地质意义的合理解释需作进一步的研究。  相似文献   

18.
阿拉善东缘奥陶纪地层位于鄂尔多斯(华北地块)与北祁连早古生代造山带之间的过渡地区,该区的构造背景一直是长期争论的问题,它涉及到阿拉善地块是否与华北地块相连、奥陶系的物源以及"贺兰拗拉槽"是否存在等问题。分布于阿拉善地块东缘的中奥陶统米钵山组的碎屑锆石LA-ICP-MSU-Pb年龄测试表明,样品中数量最多的锆石年龄为900～950Ma,Alxa-1的峰值年龄为916Ma,Alxa-2的峰值年龄为953Ma,次者在494～623Ma之间,这个区间内存在多个峰值,如Alxa-1存在505Ma和588Ma两个主要峰值,Alxa-2则存在494Ma、517Ma、623Ma等几个峰值。在2.5Ga左右两个样品都存在一个弱的峰值,Alxa-1峰值为2517Ma,而Alxa-2峰值为2552Ma和2670Ma。除此之外,两个样品都有个别大于3.0Ga的成分,Alxa-1样品中最年轻的锆石为451±8Ma,Alxa-2样品则为483±4Ma。这些年龄以及沉积特征表明:(1)传统认为的奥陶纪"贺兰拗拉槽"并不存在,鄂尔多斯西南缘地区以及阿拉善东部地区当时属于北祁连早古生代周缘前陆盆地系统;(2)早古生代主要物源来自北祁连造山带,新元古代物源来自阿拉善地块;(3)鄂尔多斯西缘整个米钵山组的锆石年龄分布及其变化,指示出北祁连造山带(岛弧)逐渐靠近阿拉善地块,其间洋盆逐渐消失的过程;(4)阿拉善地块基底与华北有明显差别,阿拉善地块明显受到新元古代和古生代构造热事件的影响,两者可能是在中奥陶世或之后才拼贴在一起。  相似文献   

19.
内蒙古达茂旗北部的早古生代闪长岩侵入体产于包尔汉图-白乃庙岛弧带的西部,采用SHRIMP锆石U-Pb定年及角闪石40Ar/39Ar测年对其进行了精确的年代学研究。两件闪长岩样品分别获得的SHRIMP锆石U-Pb年龄为453±3Ma和446.8±5.3Ma,角闪石40Ar/39Ar坪年龄为459.2±2.4Ma和442.9±4.2Ma。这为研究该时期弧岩浆作用提供了新的年代学证据,并表明该岩浆侵位后,经历了结晶并快速冷却的过程,可能揭示了本区岛弧带和华北板块碰撞的构造意义。  相似文献   

20.
《Precambrian Research》2001,105(2-4):115-128
The Aasivik terrane is a ∼1500 km2 complex of gneisses dominated by ∼3600 Ma components, which has been discovered in the Archaean craton of West Greenland, ∼20–50 km south of the Paleoproterozoic Nagssugtoqidian orogen. The Aasivik terrain comprises granulite facies tonalitic to granitic gneisses with bands of mafic granulite, which include disrupted mafic dykes. Four gneiss samples of the Aasivik terrain have given imprecise SHRIMP U–Pb zircon ages of 3550–3780 Ma with strong loss of radiogenic lead and new growth of zircon probably associated with a granulite facies metamorphic event(s) at ∼2800–2700 Ma. To the Southeast, the Aasivik terrane is in tectonic contact with a late Archaean complex of granitic and metapelitic gneisses with apparently randomly distributed mafic and ultramafic units, here named the Ukaleq gneiss complex. Two granitic samples from the Ukaleq gneiss complex have U–Pb zircon ages of 2817 ± 10 and 2820 ± 12 Ma and tzircon εNd values of 2.3–5.4. Given their composition and positive εNd values, they probably represent melts of only slightly older juvenile crust. A reconnaissance SHRIMP U–Pb study of a sample of metasedimentary rock from the Ukaleq gneiss complex found ∼2750–2900 Ma zircons of probable detrital origin and that two or more generations of 2700–2500 Ma metamorphic zircons are present. This gneiss complex is provisionally interpreted as a late Archaean accretionary wedge. A sample of banded granulite facies gneiss from a complex of banded gneisses south of the Aasivik terrain here named the Tasersiaq gneiss complex has yielded two zircon populations of 3212 ± 11 and 3127 ± 12 Ma. Contacts between the three gneiss complexes are mylonites which are locally cut by late-post-kinematic granite veins with SHRIMP U–Pb zircon ages of ∼2700 Ma. The isotopic character and the relationships between the lithologies from the different gneiss complexes suggest the assembly of unrelated rocks along shear zones between 2800 and 2700 Ma. The collage of Archaean gneiss complexes were intruded by A-type granites, here named the Umiatsiaasat granites, at ∼2700 Ma, later than the tectonic intercalation of the gneiss complexes.  相似文献   

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