扬子克拉通西南缘中元古代通安组的形成时代——锆石LA-ICPMS U-Pb年龄   总被引：5，自引：0，他引：5  

耿元生  柳永清  高林志  彭楠  江小均 《地质学报》2012,86(9):1479-1490

通安组是扬子克拉通西南缘褶皱基底的组成部分,可分为5个岩性段。本文利用凝灰质粉砂岩(样品100620-1)中碎屑锆石和侵入通安组的辉长-闪长岩脉(样品100620-1-1和样品100620-2-2)中岩浆锆石的LA-ICP-MSU-Pb年龄探讨通安组的形成时代。通安组三段中凝灰质粉砂岩的碎屑锆石有两个主要的峰值年龄,分别为1.8～1.9Ga和2.28～2.38Ga,这表明通安组三段的沉积物来自不同的物源区。该凝灰质粉砂岩中最年轻的3粒锆石的207Pb/206Pb平均年龄为1806Ma。从侵入到通安组第三段的辉长-闪长岩的岩浆锆石中获得了1513±13Ma的207Pb/206Pb加权平均年龄(样品100620-2-1)和1531±18Ma的上交点年龄(样品100620-2-2)。这些新获得的年龄数据可以限定通安组的形成时限为1.8～1.5Ga。辉长-闪长岩脉1513Ma和1531Ma的年龄数据与东川群黑山组火山凝灰岩1503±7Ma的年龄结果相似,表明侵入到通安组三段中的辉长-闪长岩脉与东川群黑山组的火山凝灰岩形成于一个岩浆旋回的同一阶段。因此,通安组三段大致相当于云南东川群的黑山组。  相似文献   

New data on detrital zircons from the sandstones of the lower Cambrian Brusov Formation (White Sea region,East-European Craton): unravelling the timing of the onset of the Arctida–Baltica collision     

《International Geology Review》2012,54(16):1945-1963

The basement of the northeastern periphery of the East-European Craton (ЕЕС) is composed of volcanic-sedimentary sequences, volcanic rocks, granitoids, and rare ophiolite complexes. Geochronological data constrain their age from ca. 750 to 500 Ma, and there is a consensus that these rocks represent relicts of a late Neoproterozoic–Cambrian Pre-Uralides–Timanides orogeny. Combining new integrated isotopic (U-Pb, Lu-Hf) and trace-element data (TerraneChrone^® approach) on detrital zircons from sandstones of the lower Cambrian Brusov Formation in the Mezen basin (White Sea region in the northeastern periphery of the EEC) with available studies on detrital zircons from Neoproterozoic–middle Cambrian (meta)sedimentary units of the northeastern periphery of the EEC allow us to conclude that (1) the onset of the Arctida–Baltica collision can now be constrained to the time interval between ca. 540 and 510 Ma and (2) the Ediacaran–early Cambrian Mezen sedimentary basin was a basin on the Timanian passive margin of Baltica up to 540 Ma, but was not a foreland basin of the Pre-Uralides–Timanides orogen.  相似文献   

Provenance of detrital zircons in the Late Triassic Sichuan foreland basin: constraints on the evolution of the Qinling Orogen and Longmen Shan thrust-fold belt in central China     

《International Geology Review》2012,54(14):1806-1824

In this article, we present in situ U–Pb and Lu–Hf isotope data for Upper Triassic detritus in the Sichuan region of northwestern South China, which was a foreland basin during the Late Triassic. The aim is to determine the provenance of sediments in the foreland basin and to constrain the evolution of the surrounding mountain belts. U–Pb age data for the Late Triassic detrital zircons generally show populations at 2.4–2.6 Ga, 1.7–1.9 Ga, 710–860 Ma, 410–460 Ma, and 210–300 Ma. By fitting the zircon data into the tectonic, sedimentologic, and palaeographic framework, we propose that the north Yangtze Block and South Qinling–Dabie Orogen were the important source areas of sediments in the northern part of the foreland basin, whereas the Longmen Shan thrust-fold belt was the main source region for detritus in other parts of the foreland basin. The South Qinling–Dabie Orogen could also have served as a physical barrier to block most detritus shed from the southern North China Block into the foreland basin during the sedimentation of the Xujiahe Formation. Our results also reveal that part of the flysch from the eastern margin of the Songpan–Ganzi region had been displaced into the Longmen Shan thrust-fold belt before the deposition of the foreland basin sediments. In addition, the Lu-Hf data indicate that Phanerozoic igneous rocks in central China show insignificant formation of the juvenile crust.  相似文献   

Permian age of the Wudaogou Group in eastern Yanbian: detrital zircon U–Pb constraints on the closure of the Palaeo-Asian Ocean in Northeast China     

《International Geology Review》2012,54(14):1754-1768

The Wudaogou Group in eastern Yanbian, Northeast China, plays a key role in constraining the timing and eastward termination of the Solonker–Xra Moron River–Changchun Suture, where the Palaeo-Asian Ocean closed. The Wudaogou Group consists of schist, gneiss, amphibolite, metasedimentary, and metavolcanic rocks, all of which underwent greenschist- to epidote–amphibolite-facies regional metamorphism, with some hornfels resulting from contact metamorphism. To determine the age of deposition, the timing and grade of metamorphism, and the tectonic setting of the Wudaogou Group, we investigated the petrography and geochronology of the metamorphic rocks in this group. Zircons from the metasedimentary rocks of this group can be divided into metamorphic zircons and detrital zircons of magmatic origin. U–Pb ages of metamorphic zircons dated by LA-ICP-MS vary from 249 ± 4 to 266 ± 4 Ma, approximating the age of regional metamorphism in the eastern Yanbian area. Detrital zircons yield U–Pb ages ranging from 253 ± 5 to 818 ± 5 Ma, and indicate that the provenance of the Wudaogou Group experienced four tectonic–thermal events between 818 and 253 Ma: Neoproterozoic (ca. 818–580 Ma), Cambro–Ordovician (ca. 500–489 Ma), Devonian–Carboniferous (ca. 422–300 Ma), and middle–late Permian (ca. 269–253 Ma). The youngest detrital zircon, with a U–Pb age of 253 ± 5 Ma, defines the maximum depositional age of the Wudaogou Group. The presence of the Cambro-Ordovician and Neoproterozoic detrital zircons implies that the source of the Wudaogou Group had an affinity with Northeast China, which leads us to conclude that the Solonker–Xra Moron River–Changchun Suture extends from Wangqing to Hunchun in eastern Yanbian, and that the Palaeo-Asian Ocean may have closed at the end of the Permian or Early Triassic period.  相似文献   

四川冕宁基性岩墙的年代学、地球化学特征及其地质意义     

李宏博  张招崇  吕林素  李永生 《地质论评》2012,58(5):952-964

本文对四川冕宁地区的基性岩墙进行了年代学、岩石学和地球化学研究。主量元素特正和微量元素标准化图解显示,基性岩墙属于拉斑玄武岩系列,具有洋岛玄武岩(OIB)的特征,与峨眉山玄武岩为同源产物,存在密切的成因关系。微量元素示踪、Th/Hf-Ta/Hf判别图表明,冕宁基性岩墙具有地幔柱成因的特征,并遭受了轻微混染。基性岩墙锆石LA-ICP-MS测年结果表明,岩墙形成年龄为256.7±4.3Ma,表明岩墙是峨眉山大火成岩省大规模岩浆作用晚期的产物。年龄测定结果还暗示了岩墙在约244Ma遭遇了一次变质事件,可能是岩浆热——机械侵蚀作用,以及印支运动诱发岩浆作用再次活跃的结果。  相似文献   

桂北地区南华系沉积物源分析——来自碎屑锆石U-Pb年龄的证据   总被引：1，自引：0，他引：1  

韩坤英  王梁  丁孝忠  任留东  高林志  刘燕学  庞健峰  薛玖红 《岩石学报》2016,32(7):2166-2180

江南造山带西南部是扬子克拉通新元古代地层发育较完整的地区之一。其中,桂北地区的南华系地层自下而上依次为:长安组、富禄组、大塘坡组和黎家坡组,沉积厚度从几十米到几千米不等,总体趋势是西厚东薄。本文对长安组、富禄组、黎家坡组的5个样品进行了碎屑锆石LA-ICP-MS U-Pb年龄测试。其中长安组碎屑锆石U-Pb年龄存在一个峰值,峰值区间为724~972Ma之间,最年轻的年龄加权平均值为746±5Ma(n=19),指示南华系长安组沉积年龄可能介于746~780Ma之间;富禄组碎屑锆石U-Pb年龄有三个峰值,主峰为705~936Ma,两个次峰分别为1823~2163Ma和2241~2673Ma之间;黎家坡组下部121109-3样品的碎屑锆石主峰值为1966~2118Ma,两个次峰为724~921Ma和2221~2688Ma;中部121109-4样品碎屑锆石主峰值为1813~2192Ma,两个次峰为748~944Ma和2296~2726Ma;上部121109-5样品碎屑锆石主峰值为1984~2193Ma,两个次峰为653~1007Ma和2215~2675Ma。桂北地区南华系长安组、富禄组、黎家坡组5个样品的年龄峰值区间相近,但主峰和次峰有明显的区别,反映了三个组沉积地层主要物源可能来自不同的地区,并经历了不同的沉积环境。碎屑锆石年龄分布特征反映了在653~1007Ma之间扬子克拉通东南缘、江南造山带西南部的桂北地区有强烈的岩浆活动,可能与Rodinia超大陆的聚合和裂解事件有关,而1792~2261Ma的岩浆活动则与Columbia超大陆的聚合和裂解事件相对应,2298~2500Ma碎屑锆石年龄可能暗示在扬子克拉通南缘存在古元古代基底,少量大于2500Ma的锆石年龄表明在扬子克拉通南缘还存在太古宙基底物质。5个样品均缺少1100~1300Ma格林威尔造山时期的记录,说明江南造山带并非处在Rodinia超级大陆的中心。总之,扬子克拉通南缘及江南造山带西南部至少经历了三期强烈的构造-岩浆热事件,这三期事件在桂北地区的南华系沉积地层中均有非常清楚的记录。  相似文献   

扬子地台西南缘古元古代末的裂解事件——来自武定地区辉绿岩锆石U Pb年龄和地球化学证据   总被引：7，自引：0，他引：7  

郭阳  王生伟  孙晓明  王子正  杨斌  廖震文  周邦国  蒋小芳  侯林  杨波 《地质学报》2014,88(9):1651-1665

云南省武定地区广泛出露元古宙辉绿岩体,本文报道了武定地区海孜辉绿岩的地球化学特征及锆石的LA-ICP-MS U-Pb年龄,结果为1767±15Ma(MSWD=0.19,n=17),表明本区广泛出露的辉绿岩群侵位时代为古元古代晚期。辉绿岩岩石化学表现为低SiO2、MgO以及高TiO2(3.24%~4.02%)、碱(K2O+Na2O)和P2O5含量(0.32%~0.45%),具有偏碱性的拉斑质玄武岩的岩石化学特征。辉绿岩的大离子半径元素如K、Rb、Ba等富集,高场强元素如Ta、Nb和Zr、Hf没有明显的亏损,其地球化学参数也多与夏威夷碱性洋岛玄武岩相近。辉绿岩的微量、稀土元素的配分模式与典型的OIB和峨眉山高Ti玄武岩具有高度一致性。海孜辉绿岩原始岩浆形成于相对较富集的过渡型地幔的部分熔融,其源区为尖晶石橄榄岩相,演化过程中,有少量下地壳物质的加入。海孜辉绿岩与扬子地台西南缘广泛出露古元古代晚期的岩浆岩一致,形成于全球性Columbia超级大陆裂解的大地构造背景。海孜辉绿岩OIB的地球化学属性,为古元古代晚期全球性Columbia超级大陆裂解的地幔柱活动提供了最重要的地球化学证据。  相似文献   

广西大明山地块寒武系碎屑锆石U Pb年龄及其构造意义   总被引：1，自引：0，他引：1  

邹和平  杜晓东  劳妙姬  丁汝鑫 《地质学报》2014,88(10):1800-1819

大明山地区位处扬子地块与华夏地块结合带的西南段,对该区寒武系碎屑锆石开展U-Pb年龄谱研究可为新元古代—早古生代扬子地块与华夏地块结合带构造属性的进一步确定和对华南大地构造演化的深入研究提供新的依据。本次研究对该区2件寒武纪砂岩样品分选出的碎屑锆石进行了LA-ICPMS U-Pb年代测定和分析。锆石的透射光及阴极发光图像、Th/U比值、稀土元素特征说明其主要为岩浆岩锆石。222个谐和年龄数据显示出5个主要年龄区间:550~560Ma、750~780 Ma、950~1020 Ma、1560~1740Ma和2390~2450Ma,其中以950~1020Ma区间表现为最突出的峰值。对比大明山与大瑶山地区的寒武系碎屑锆石年龄谱系,两者表现出相似的分布特征。最明显的年龄峰值(980Ma)揭示物源区曾是Grenville期造山带的一部分。与扬子地块和华夏地块碎屑锆石年龄谱系进行比较,结合古水流及相关地质证据,认为所研究样品的碎屑锆石主要来自华夏地块。根据现有的资料,我们更倾向于认为寒武纪时扬子—华夏之间可能没有大洋的分割,而是一陆间海(intercontinental sea)格局。本次研究还在大明山寒武系中测得8颗具有太古宙年龄的古老锆石(≥2500Ma,其中1颗≥3200Ma)。这些锆石具振荡环带结构,Th/U比值均≥0.4,稀土分布多具有明显的Ce正异常与Eu负异常,指示其来自岩浆岩,反映物源区在太古宙发生过岩浆作用。结合前人研究获得的华夏地块太古宙锆石年龄信息,认为华夏地块可能存在太古宙地壳基底或接受过古老陆块的物源供给。  相似文献   

太原西山上二叠统—下三叠统地层最大沉积年龄的碎屑锆石U Pb定年约束   总被引：4，自引：0，他引：4  

刘超  孙蓓蕾  曾凡桂 《地质学报》2014,88(8):1579-1587

二叠纪—三叠纪之交是古生界向中生界过渡的重要地质历史转折时期,发生了地史时期规模最大的生物灭绝事件。石千峰组作为华北地台二叠系—三叠系过渡阶段沉积,其时代归属对二叠系—三叠系界线的准确划分至关重要。本文应用LA-MC-ICPMS对华北中部太原西山晚二叠世—早三叠世上石盒子组、石千峰组、刘家沟组中4件砂岩样品进行碎屑锆石U-Pb定年,4件砂岩样品(SNF、XM、K8、LJG)分别给出了最年轻锆石峰值年龄270Ma、296Ma、250Ma、262Ma,表明太原西山上石盒子组师脑峰砂岩(SNF)的沉积时间不早于270Ma,石千峰组底部K8砂岩(K8)沉积时间不早于250Ma。因此,太原西山地区石千峰组应归属于早三叠世,二叠系—三叠系的界线应位于石千峰组K8砂岩之下。  相似文献   

南秦岭刘岭群砂岩碎屑锆石LA-ICP-MS U-Pb年龄及其构造意义   总被引：7，自引：0，他引：7  

陈龙耀  罗玉凌  刘晓春  曲玮  胡娟 《地质通报》2014,33(9):1363-1378

秦岭造山带的构造演化是理解华北与扬子陆块缝合过程的关键,位于商丹断裂带以南的刘岭群是揭示秦岭造山带晚古生代构造演化历史的重要窗口。采用LA-ICP-MS对刘岭群3个变质砂岩样品中的碎屑锆石进行了U-Th-Pb同位素测定,获得最年轻的一组年龄区间为377~395Ma,主要年龄峰值约为442Ma、780~850Ma和900~970Ma,表明刘岭群沉积时代可以持续到晚泥盆世,物质来源于北秦岭构造带。结合刘岭群北侧武关杂岩的最新研究成果可以确定,刘岭群和武关杂岩共同构成了华北陆块南缘中—晚泥盆世弧前盆地的沉积序列,暗示古秦岭洋的最终闭合发生在泥盆纪之后,而华北与扬子陆块碰撞的主缝合线应位于刘岭群的南侧。  相似文献