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1.
分布于鲁东胶北地区蓬莱群为一套浅变质沉积岩，角度不整合覆盖在太古宙胶东群、元古宙粉子山群上。关于蓬莱群的沉积时代尚存较大的争议，认为是震旦纪或古生代沉积形成的。蓬莱群和五莲杂岩、北淮阳变质岩带都是位于大别-苏鲁超高压变质造山带北部的重要岩石构造单元。本文报道蓬莱群沉积岩碎屑锆石年龄和始同位素分析资料，并探讨其可能的物质来源。
在栖霞地区采集了14个蓬莱群样品，主要岩石为石英岩、千枚岩、片岩、页岩，从其中4个挑出了锆石样品。分选出的碎屑锆石均为浅棕色，浑圆状，反映锆石经历了搬运作用。CL图像显示绝大多数锆石颗粒具有清晰的韵律环带内部结构，具有岩浆成因特征。在中国科学院地质与地球物理所固体同位素地球化学实验室IsoProbe-T质谱计上，采用即蒸即测方法，测得锆石207Pb/206Pb比值，其对应的年龄值主要分布在1000~1800 Ma,峰值为1200 Ma和1600 Ma左右（图1)。应用中国科学院地质与地球物理所多通道等离子质谱计Neptune MC-ICP-MS测定碎屑锆石 同位素组成。根据所获得的同位素组成，计算得到比同位素模式年龄TDM(Hf）分布在1300~3200 Ma之间，峰值为1700 Ma左右；对应的初始εHf(1200 Ma）和εHf (1600 Ma）平均值分别为-5.8和2.9（图2)。
碎屑锆石1350~1800 Ma年龄段，特别是峰期的1600 Ma，可能对应全球广泛分布的非造山事件，可能和Columbia超大陆的裂解有一定的联系。大部分锆石初始εHf (1600 Ma）值大于0，可以说明岩浆来源为幔源。而1050~1300 Ma的锆石则可能与Rodinia超大陆的汇聚形成阶段或Grenville造山事件有较密切的联系。华北克拉通大量地出露太古宙末期（2500 Ma左右）和早元古代末期(1800 Ma左右）的岩石，但在所分析的蓬莱群沉积岩几乎没有显示，可能可以排除华北克拉通为主要的沉积物源。所获得的碎屑锆石年龄虽在扬子板块有一定的出露，但缺少与Rodinia裂解有关的晚元古代700~800 Ma的岩浆锆石信息。上述资料可能暗示沉积时代为1000~800 Ma之间，但与目前的古生物证据不吻合。因此，这些碎屑锆石年龄和铅同位素数据尚不能肯定蓬莱群变质沉积岩是来源于扬子陆块，还是游离于华北、扬子的一个微陆块。如果是一个微陆块，该微陆块与Columbia裂解作用和Grenville造山作用有关，但可能未遭受到Rodinia超大陆裂解事件的影响。 相似文献
2.
点苍山-哀牢山杂岩带多期变质作用:嘎洒地区变沉积岩锆石微量元素与U-Pb年代学制约 总被引：2，自引：2，他引：0
点苍山-哀牢山杂岩带位于青藏高原东南缘,为云南三江地区一条重要的造山带,由扬子板块和印支板块于晚二叠世-中晚三叠世碰撞拼合而成。杂岩带主要由各类副片麻岩、片岩、石英岩、大理岩和斜长角闪岩构成,岩石发育强烈糜棱岩化和深熔作用。本文选取哀牢山北段新平嘎洒地区变沉积岩为研究对象,通过对变沉积岩锆石的阴极发光图像、微量元素、矿物包裹体组合、表面形态和U-Pb年龄的综合研究,揭示出嘎洒地区哀牢山杂岩经历了两期变质事件:其中,含石榴子石斜长二云母片岩中30颗变质锆石获得了较为一致的206Pb/238U年龄215±6Ma~227±5Ma,加权平均年龄为222.3±1.2Ma(n=30,MSWD=0.27),这些锆石具有浑圆状或椭圆状形态、较为均匀的阴极发光图像、平坦的HREE配分模式((Lu/Gd)N=0.73~4.08)和弱的负Eu异常,这些特征与典型的高级变质岩中变质锆石相似,而锆石的Th/U比值较为分散为0.06~0.84,平均值为0.45,可能与变质过程中富Th矿物独居石分解有关。变质年龄与杂岩带中点苍山和元阳地区变质岩中、晚三叠世变质年龄极为吻合,指示这期变质事件与中-晚三叠世古特提斯洋闭合-造山有关,标志着点苍山-哀牢山杂岩带为三江地区一条重要的古缝合线。此外,嘎洒地区夕线石榴黑云二长片麻岩的岩相学特征显示,岩石经历了石榴子石的转熔作用,除两颗锆石年龄为35.4Ma外,28颗锆石(增生边)给出了误差范围内较为一致的206Pb/238U年龄(27.3±0.5Ma~31.9±0.5Ma),加权平均年龄为29.4±0.53Ma(n=28,MSWD=2.0)。这些锆石的增生边中的矿物包裹体组合为夕线石+钾长石+黑云母+石英+独居石,且具有较低的Th/U比值(0.01~0.1),平坦的重稀土(HREE)配分模式((Lu/Gd)N=0.45~7.59)和中等程度的负Eu异常,这些特征指示该类锆石为典型的变质锆石。变质年龄与新生代红河-哀牢山剪切带内大量发现的同剪切岩浆岩、变质岩的年龄较为一致,指示这期年轻的变质事件与岩石圈尺度大规模剪切运动有关。此外,两类变沉积岩中6颗继承性碎屑锆石的年龄分布范围为528~783Ma,这些锆石具有锥形的锆石形态,清晰的振荡环带,表面发育蚀痕和凹坑,较高的Th/U比(0.1),陡倾的HREE配分曲线,表明这些锆石为经过剥蚀-搬运-沉积的岩浆锆石,具有继承性碎屑锆石的特征,说明哀牢山杂岩变沉积岩中至少应包含新元古代和早古生代的沉积物源,指示研究区哀牢山杂岩带部分岩石并不属于真正意义上的扬子结晶基底。 相似文献
3.
朝鲜平南盆地古元古界-下古生界沉积岩碎屑锆石年龄谱对比及意义 总被引：3，自引：3，他引：0
中朝古陆(华北古陆)平南盆地面积~25000km~2,位于朝鲜半岛中部,发育从中元古界到下古生界地层,但经历了低级变质作用(绿片岩相及以下)。变质基底岩石中有一套角闪岩相-麻粒岩相的变质的古元古界地层。本文根据盆地不同时代沉积岩碎屑锆石/变质锆石U-Pb LA-ICP MS年龄数据讨论沉积源区的变化,并对区域演化进行制约。甑山群/杂岩为盆地基底岩系,变质砂岩样品中碎屑锆石出现ca.2500~2100Ma的年龄峰值。另外,36.5亿年的碎屑锆石是朝鲜迄今发现的最古老碎屑锆石;夕线榴片麻岩样品记录了~1850Ma(1859±9Ma)的变质年龄;推测甑山群沉积于ca.2100~1900Ma,变质于1850 Ma。黄海群局限分布于朝鲜半岛中部,碎屑锆石年龄谱显示~1850 Ma的峰值,可见~1250 Ma的年龄,推测对应物源为古元古代基底岩浆岩和变质岩系;结合其上覆直岘群的沉积时代,推测地层沉积于ca.1250~1000Ma。直岘群是平南盆地分布最广的地层之一,底部长峰组样品显示明显的~1850Ma的峰值,而其上第二个和第三个组则显示明显的ca.1400~1600Ma和ca.1000~1200 Ma年龄峰值,~1850 Ma年龄很少;推测直岘群开始沉积时,物源主体是盆地基底岩系,但之后出现大量中元古代物质;推测其沉积时代为ca.1000~900Ma。黄州群有~1850Ma和~2500Ma的峰值,另外,还有较少的ca.1000~1200Ma及1400~1600 Ma年龄,表明沉积物源主体仍是基底岩系,可能有中新元古代沉积岩(黄州群-直岘群)的再沉积。这些沉积岩碎屑锆石年龄峰值与辽东和山东半岛沉积地层相似,并且中新元古代地层中均有大量1000~1200Ma及1400~1600Ma的物质,推测可能来自华北古陆之外,如圣弗朗西斯科克拉通。 相似文献
4.
秦岭-桐柏-大别造山带是华北板块和扬子板块碰撞拼合的产物.桐柏造山带作为古生代秦岭增生造山带与中生代大别碰撞造山带之间的纽带,记录了两大板块之间从洋壳俯冲、地体增生到最终的碰撞造山过程.本文选取桐柏造山带龟山杂岩为研究对象,对其中变沉积岩、斜长角闪岩和花岗质脉体进行了岩相学、矿物学和锆石U-Pb年代学研究.结果指示变沉积岩碎屑锆石年龄峰值主要为～411 Ma,次要年龄峰值为～490 Ma,最年轻四颗碎屑锆石的加权平均年龄为352±11 Ma.斜长角闪岩原岩结晶时代为498±18 Ma,花岗质脉形成时代为412.8±4.4 Ma,两者中变质锆石加权平均年龄为320±10 Ma,指示它们共同经历了早石炭世变质作用.变质峰期温压条件为T=571～632℃,P=0.59～0.76 GPa,属于中压相系角闪岩相变质.区域年代对比分析显示,龟山杂岩变沉积岩物源来自于北侧的北秦岭地体,属于弧前沉积,沉积时代下限为早石炭世早期.结合前人研究,本文认为在古秦岭洋向北的俯冲过程中,上述沉积岩与斜长角闪岩因构造作用拼贴在一起,于～320 Ma发生中压角闪岩相变质作用.该研究结果也指示了古秦岭洋最终闭合时间可能晚于早石炭世早期. 相似文献
5.
冀东地区始太古代早期—冥古宙锆石发现 总被引：1，自引：0，他引：1
最古老大陆地壳的形成、组成和演化是阐释地球壳幔物质分异、构造演化的逻辑起点。由于长期地质作用改造,地球上保存的古老陆壳物质十分稀少,寻找和研究都极具挑战性。在冀东卢龙喇叭山地区,早期研究发现含有大量3.4~3.8 Ga碎屑锆石的铬云母石英岩,岩石特征和碎屑锆石年龄分布与迁安黄柏峪地区的铬云母石英岩十分类似。本文对喇叭山地区与铬云母石英岩共生的变质碎屑沉积岩进行了锆石定年。黑云斜长片麻岩(J2006)94个数据点分析,碎屑锆石普遍显示强烈铅丢失,数据点主要沿上交点年龄为~3.8 Ga和~3.45 Ga的两条不一致线分布。获得3084±6 Ma的变质锆石年龄。长石石英岩(J2009)68个数据点分析,除大量3.4~3.8 Ga碎屑锆石外,还发现3.92~4.0 Ga碎屑锆石(6颗)。始太古代早期—冥古宙碎屑锆石的发现表明华北克拉通无疑存在4.0 Ga以上的形成演化历史。本文新定义的曹庄-喇叭山岩系形成于3.1~3.4 Ga之间,主要由变质碎屑沉积岩和变质基性-超基性岩组成,可能代表了地幔柱与大陆壳相互作用的构造环境。根据碎屑锆石形态特征和不同样品碎屑锆石年龄分布存在差异,物源区具有近源和规模大的特征,存在3.92~4.0 Ga、3.8 Ga、3.6~3.7 Ga和3.4~3.45 Ga等不同期次花岗质岩浆作用。 相似文献
6.
北秦岭二郎坪杂岩变沉积岩碎屑锆石年代学及其构造地质意义 总被引：6，自引：4，他引：2
碎屑锆石为沉积岩中最稳定的矿物,其年龄谱系不仅可限定沉积物的最大沉积年龄与物源性质,而且能够为探讨其形成构造环境提供关键约束。作为北秦岭构造带主要构造岩石地层单元之一,二郎坪杂岩由北、中、南三个构造岩片——北部碎屑岩片、中部蛇绿岩片和南部变碎屑岩片组成。本文对二郎坪杂岩南部变碎屑岩片中的碎屑锆石进行了LA-ICP-MS U-Pb年龄测试研究,获得样品锆石谐和年龄值分布在500±7Ma~3894±5Ma之间,1个年龄高频集中区为0.9~1.0Ga,6个次要年龄集中区分别为500~600Ma、750~850Ma、1.35~1.48Ga、1.6~1.75Ga、2.6~2.7Ga和3.0~3.4Ga。研究结果表明:1)最小峰值年龄限定二郎坪杂岩南部碎屑岩片原岩的最大沉积时代为500Ma,结合西庄河花岗闪长岩侵入南部岩片的地质事实,南部岩片的形成时代应为早古生代寒武-奥陶纪(500~475Ma),明显早于中部蛇绿岩片中的火山岩的形成时代(463~475Ma);2)通过与邻区地质事件年龄谱峰及其锆石阴极发光图像特征的对比,二郎坪杂岩变碎屑岩原岩的物源分别主要来自南部秦岭杂岩中的早新元古代花岗岩和北部华北南缘熊耳群中元古代火山岩,其物源具有双源性,暗示其形成于与伸展作用相关的裂谷或弧后盆地构造背景,而二郎坪蛇绿岩片所代表的古洋盆可能正是在此基础上发育产生的;3)结合区域地质背景资料分析,二郎坪杂岩中的沉积碎屑岩片可能形成于商丹洋向北俯冲期间所产生的弧后伸展盆地构造环境;4)通过与宽坪岩群沉积岩中的碎屑锆石年龄数据的对比,揭示二者碎屑锆石具有相似的年龄谱峰,结合宽坪群变沉积岩中发现大量疑源类、几丁虫和虫颚等早-中奥陶世化石组合以及二郎坪杂岩蛇绿岩片中的火山岩夹层硅质岩中发现早-中奥陶世牙形石和放射虫的研究,分析认为二者沉积物的沉积时代相近,沉积物源几乎完全一致,暗示它们形成的构造环境可能具有一致性;5)二郎坪蛇绿岩片中的典型的与洋壳俯冲有成因联系的弧火山岩的形成时代(463~475Ma)明显迟后于区内高压-超高压岩石的峰期变质时代(514~484Ma)约20~30Myr,清楚地表明二郎坪洋壳拖曳秦岭杂岩发生陆壳俯冲-深俯冲作用的可能性不大;6)二郎坪杂岩南部碎屑岩片和宽坪岩群碎屑沉积物中碎屑锆石中最主要的年龄集中区(0.9~1.0Ga)的物源来自秦岭杂岩中的早新元古代花岗质岩石,而缺少秦岭杂岩中的早古生代岩浆岩和HP/UHP变质岩石锆石的年龄信息,明确指示二郎坪与宽坪盆地沉积时,秦岭杂岩重要组成的早新元古代花岗质岩石已出露于地表接受剥蚀,而秦岭杂岩中出露的HP/UHP岩石和早古生代岩浆岩未抬升出露地表,即秦岭杂岩现今出露的前早古生代陆壳物质不是整体而是部分经历了陆壳俯冲-深俯冲作用。 相似文献
7.
荆山岩群是胶北地体最重要的古元古代变沉积岩系之一,经历了高角闪岩相?麻粒岩相变质与韧性变形,准确限定其沉积时代与物质来源对探究胶?辽?吉带古元古代构造演化过程具有重要意义.本文利用LA-ICP-MS（激光剥蚀电感耦合等离子质谱仪）对旌旗山地区荆山岩群禄格庄岩组中长石石英岩进行了锆石U-Pb测年和稀土元素分析.根据碎屑锆石内部结构和年龄结果,认为在最年轻一组碎屑锆石中谐和的207Pb/206Pb加权平均年龄2 120 Ma,可以大致限定其原岩的最大沉积时代,两件样品获得的变质年龄分别为1 886±12 Ma与1 969±23 Ma,结合区内禄格庄岩组被2 103~2 085 Ma二长花岗质片麻岩侵入的地质关系,初步限定旌旗山地区禄格庄岩组的沉积时代约为2 100 Ma.长石石英岩中有效碎屑锆石年龄谱图呈现2 105 Ma主峰值年龄和2 185 Ma次峰值年龄,指示旌旗山地区禄格庄岩组的主要物源为古元古代（2 200~ 2 100 Ma）中?酸性岩浆岩或再循环的产物,同时接受了少量太古宙的碎屑物质.综合胶?辽?吉带已发表的其他相关数据,认为以荆山岩群禄格庄岩组为代表的胶?辽?吉带南侧底部变沉积岩沉积时可能位于弧后盆地靠近岛弧一侧,以粉子山岩群小宋岩组为代表的胶?辽?吉带北侧底部变沉积岩则可能位于弧后盆地靠近太古宙大陆一侧. 相似文献
8.
秦岭南缘勉略构造带略阳关天门地区发育有一套绿片岩相-低角闪岩相岩石组合,是勉略构造带内强烈韧性变形的变质沉积岩系,其形成时代和构造属性长期存在争议,制约区域大地构造演化的研究。为查明其形成时代与构造背景,对其中的变质细碎屑岩进行系统的岩石学、碎屑锆石U-Pb年代学和岩石地球化学研究。2件碎屑锆石U-Pb年龄样品的年龄分布特征相似,主要年龄区间为新元古代早中期(ca.880~800 Ma),并且显示出ca.830 Ma的显著峰值;最年轻的一组碎屑锆石年龄为747~736 Ma(平均年龄742±6 Ma)。地球化学研究结果表明,关天门变沉积岩原岩应为一套细碎屑岩偶夹碳酸盐岩的沉积组合,原岩经历了较低程度的化学风化和沉积物再旋回,其物源主要为大陆岛弧背景下的中-酸性岩浆岩。结合区域已有研究成果,认为关天门变沉积岩的物源主要为碧口微地块、汉南—米仓山微地块的新元古代早中期岩浆弧。通过野外地质调查,并与已有的区域碎屑锆石年龄谱系进行对比,认为关天门变沉积岩岩片的沉积时代应晚于碧口微地块横丹群形成的时间(720 Ma),即关天门变沉积岩岩片的沉积时限应晚于720 Ma,形成于新元古代中期伸展裂陷体制,是Rodinia超大陆裂解过程的响应。 相似文献
9.
阿尔金喀腊大湾地区卓阿布拉克组沉积岩系年代及其地质意义——来自碎屑锆石LA-ICP-MS U-Pb年龄的证据 总被引：1，自引：1，他引：0
以阿尔金喀腊大湾地区卓阿布拉克组沉积岩系砾岩为研究对象,应用LA-ICP-MS方法对碎屑锆石进行U-Pb同位素年龄测定,探讨其形成时代、物源组成和构造背景。研究结果表明:(1)碎屑锆石年龄谱明显分为2组:522~427Ma和638~1766Ma,另有2个古老的同位素年龄数据分别为2450Ma、3394Ma;(2)最年轻的碎屑锆石年龄为427±4Ma,说明该砾岩的形成时代晚于427Ma,沉积岩系可能形成于晚志留世—早泥盆世(427~410Ma);卓阿布拉克组存在晚寒武世—早泥盆世的物质组成,应将其解体重新划分;(3)碎屑锆石峰值年龄为456Ma,表明喀腊大湾地区存在该时期的岩浆活动;522~427Ma的年龄数据约占总体的81%,构成了砾岩中最主要的碎屑锆石群体,说明在早古生代,尤其是晚寒武世—奥陶纪形成的岩浆岩是砾岩最重要的物源,该沉积岩系是敦煌地块向南俯冲、碰撞产生的一系列火成岩在造山剥蚀后的沉积响应;(4)结合目前北祁连造山带的研究进展和研究区碎屑锆石的研究结果,初步认为喀腊大湾地区卓阿布拉克组沉积岩系和北祁连天祝组、鹿角沟组具有相似的沉积年龄和物质来源,可能同为北祁连-北阿尔金局限洋盆闭合后,陆-陆或弧-陆碰撞造山的产物。 相似文献
10.
滇西腾冲地块高黎贡群变质沉积岩时代与原特提斯洋俯冲/增生：来自碎屑锆石U- Pb定年和岩石地球化学证据 总被引：4，自引：0，他引：4
滇西腾冲地块高黎贡群变质沉积岩时代和构造背景的厘定对正确认识原特提斯构造域演化过程及腾冲地块与冈瓦纳大陆之间的关系十分关键。岩石学、岩石地球化学结果表明,高黎贡群变质岩由变质沉积岩和变质岩浆岩组成,前者以片岩和副片麻岩为主,夹少量大理岩和石英岩,其原岩由一套杂砂岩、泥岩夹少量灰岩、硅质岩岩石组合,为深海-半深海相沉积物,形成于活动大陆边缘环境。碎屑锆石LA-ICP-MS U-Pb定年结果表明高黎贡群变质沉积岩中的锆石主要来源于与罗迪尼亚、冈瓦纳超大陆拼合及原特提斯洋俯冲有关的岩浆岩(900~1000Ma和500~600Ma),少量来源于中元古代地层(1500~1600Ma和2300~2400Ma)。4件样品中最年轻碎屑锆石群的加权平均年龄(507~510Ma)及没有出现有意义的小于470Ma碎屑锆石,表明高黎贡群变质沉积岩原岩形成于510~470Ma,是晚寒武世-早奥陶世早期原特提斯洋壳向冈瓦纳大陆下俯冲过程中,在俯冲带上盘沉积的含有大量该期火成岩碎屑的斜坡相沉积物。 相似文献
11.
Identifying granite sources by SHRIMP U-Pb zircon geochronology: an application to the Lachlan foldbelt 总被引：24，自引：1，他引：23
Sue Keay David Steele William Compston 《Contributions to Mineralogy and Petrology》1999,137(4):323-341
The potential genetic link between granites and their host sediments can be assessed using zircon age inheritance patterns.
In the Lachlan fold belt, southeastern Australia, granites and associated high-grade metasedimentary rocks intrude low-grade
Ordovician country rock. This relationship is well-exposed in the Tallangatta region, northeast Victoria (part of the Wagga-Omeo
Metamorphic Complex). In this region granites (two I-types and two S-types) have intruded during the mid-late Silurian between
approximately 410–430 Ma based on the ages of magmatic zircons. The age spectra for inherited zircons from the granites have
been compared with those of detrital zircons from the enclosing low- and high-grade metasediments. In broad terms, both for
detrital zircons in all four sediments and for inherited zircons in three of the four granites, the dominant ages are early
Paleozoic and Late Precambrian, with sporadic older Precambrian ages extending up to 3.5 Ga. The ages of the youngest detrital
zircons from the low-grade Lockhart and Talgarno terranes limit the time of sedimentation to ca. 466 Ma or younger. The youngest
detrital zircons from two samples of the high-grade Gundowring terrane are 473 Ma, making these sediments Ordovician or younger,
not Cambrian as originally suggested. However, the individual age spectra for the four selected metasediments are not well
matched when closely examined. The age spectra of the inherited zircons in the granites also do not adequately match those
in any of the metasediments. Thus, the metasediments might not be representative of the actual source rocks of the granites.
While the exact source of the granites cannot be identified from the analysed samples, the existence of a large population
of ca. 495 Ma inherited zircon grains in the S-type granites requires that the granite source contains a significant proportion
of Cambrian or younger material. This does not preclude the existence of a Precambrian basement to the Lachlan fold belt but
indicates that at the level of S-type magma generation, a Cambrian and/or younger protolith is required.
Received: 28 August 1998 / Accepted: 7 July 1999 相似文献
12.
Stefan Wyhlidal Werner F. Thöny Peter Tropper Urs Klötzli Volkmar Mair 《Swiss Journal of Geoscience》2010,103(2):273-281
Laser ablation ICP-MS U–Pb zircon geochronology of detrital zircons from a contact metamorphic sample of the Brixen Quartzphyllite
from the innermost part of the contact aureole adjacent to the Brixen granodiorite yielded three different Precambrian concordia
ages: zircon cores and an older generation of zircons give a maximum age of 2,023 ± 31 Ma, zircon rims and a younger generation
of single grains yield a concordia age of 882 ± 19 Ma. A third generation of single zircon grains yields an age of 638 ± 20 Ma.
In contrast to Austroalpine quartzphyllite complexes from the Eastern Alps neither Cambrian/Ordovician (570–450 Ma) nor Carboniferous
(360–340 Ma) ages on single zircons have been observed so far in these samples. These ages provide evidence of a complex pre-Variscan
evolution of the Southalpine basement since these data suggest a possible affinity of the Southalpine basement to Gondwana-related
tectonic elements as well as to a possible Cadomian hinterland. This study shows that dating detrital zircons of the Brixen
Quartzphyllites has great potential for providing age constraints on the complex geological evolution of the Southalpine basement. 相似文献
13.
林寺山组是胶莱盆地莱阳群底部重要的地层单元之一.准确限定其沉积时代与物源性质对于客观重建华北陆块东部晚中生代大地构造格局以及周缘造山带/前寒武纪变质基底晚中生代的折返过程具有重要的制约作用.以莱阳盆地蛇窝泊地区莱阳群林寺山组细砾岩为研究对象,对其开展了野外地质调查、岩相学观察、锆石U-Pb测年与锆石稀土元素分析等综合研究,并获得了如下初步认识.（1）林寺山组细砾岩中最小一组碎屑锆石加权平均年龄分别为129±1 Ma与127±5 Ma,结合区域上不整合于莱阳群之上青山群火山岩锆石谐和年龄为119±1 Ma,推测蛇窝泊地区林寺山组沉积时代介于127~119 Ma.（2）蛇窝泊地区林寺山组细砾岩的碎屑锆石年龄变化于2 858~126 Ma之间,并以新太古代晚期与白垩纪早期碎屑锆石为主.前古元古代的碎屑锆石主要来源于胶北前寒武纪变质岩,表明胶北太古宙-古元古代变质岩至少在白垩纪早期已折返至近地表.（3）160~120 Ma岩浆型碎屑锆石主要来源于胶东同时代的中酸性侵入体,暗示在白垩纪早期至少部分160~120 Ma中酸性侵入体已抬升至地表.（4）林寺山组发育少量的二叠纪（280 Ma）和印支期（213 Ma）变质锆石,表明胶东地区可能存在二叠纪约280 Ma区域变质-变形事件,同时暗示早白垩世苏鲁超高压变质岩已经折返到地表. 相似文献
14.
华北克拉通古元古代末-新元古代地质事件——来自北京西山地区寒武系和侏罗系碎屑锆石LA-ICP-MSU-Pb年代学的证据 总被引：15，自引：10，他引：5
华北克拉通是否同华南克拉通一样保存有与Rodinia超大陆聚合和裂解有关的年龄记录是理解华北克拉通元古宙构造演化的重要科学问题.本文对位于华北克拉通燕辽裂陷槽的北京西山地区的寒武系和侏罗系碎屑岩进行锆石LA-ICP-MS U-Pb年代学研究,目的是通过碎屑锆石年龄揭示华北克拉通前寒武纪尤其是古元古代末-新元古代重要地质事件.定年结果显示,北京西山寒武系徐庄组的钙质细砂岩中碎屑锆石年龄峰值主要集中在～1.38Ga和～1.14Ga.此外,还有～ 1.56Ga、～912Ma、～814Ma、～740Ma、～630Ma和～507Ma的年龄组.侏罗系窑坡组长石质岩屑细砂岩和粉砂质泥岩中碎屑锆石年龄峰值主要集中在～2.5Ga、1.88～1.8Ga、～1.74Ga、～1.6Ga和186Ma.此外,还有～2.77Ga、～2.0Ga、～1.2Ga、～488Ma、～256Ma和～233 Ma的年龄组.这三个岩石具有较低的成分和结构成熟度,指示较近的物源区,其碎屑物质可能大部分来自华北克拉通内部和北缘,因此其碎屑锆石的年龄组可记录华北克拉通前寒武纪重要地质事件.～2.77Ga、～2.5Ga、2.1～ 2.0Ga和1.88～1.8Ga的年龄组分别对应华北克拉通早前寒武纪发生地壳生长、克拉通化、裂谷和造山等重要地质事件;～ 1.74Ga、～ 1.6Ga、～ 1.56Ga、～1.38Ga、～912Ma和～814Ma的年龄组记录了华北克拉通最终克拉通化后开始的古元古代末-新元古代的多期裂谷事件.与1.3～ 1.0Ga、～740Ma和～630Ma的年龄组相对应的岩石在华北克拉通出现甚少,而该时期的岩浆岩和变质岩在华南克拉通广泛发育,且可能与Rodinia超大陆汇聚和裂解的不同阶段相对应.华北克拉通显生宙碎屑岩中碎屑锆石保存的古元古代末-新元古代地质事件的记录对探讨华北克拉通在元古宙的地质演化及华北克拉通与华南克拉通的关系可提供重要的依据. 相似文献
15.
N. A. Kanygina A. A. Tretyakov V. P. Kovach K. E. Degtyarev Kuo-Lun Wang A. B. Kotov 《Doklady Earth Sciences》2018,479(1):320-323
For the first time, the U–Pb age is determined for detrital zircons of quartzite–schist sequences, which are part of the Precambrian basement of the Aktau–Mointy Block (Central Kazakhstan) along with Neoproterozoic felsic volcanic (925–920 Ma) and granitic (945–917 Ma) rocks [6]. We analyzed 219 zircon grains from small-grained quartzites of the northern part of the block (Mt. Bol’shoi Alabas) including 206 grains with concordant age (1149–1273, 1276–1975, 2354–2592 Ma). These ages indicate the Mesoproterozoic, Paleoproterozoic, and Neoarchean rocks as provenances. The youngest statistically significant age peak of 1209 Ma indicates that the quartzite–schist sequences accumulated 1200–900 Ma ago (at the end of the Mesoproterozoic and beginning of the Neoproterozoic) prior to the formation of the Early Neoproterozoic felsic rocks and granites. 相似文献
16.
《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
17.
内蒙古孔兹岩带乌拉山-大青山地区古元古代孔兹岩系年代学研究 总被引：11，自引：8，他引：3
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
18.
《地学前缘(英文版)》2016,7(5)
U-Pb analyses were carried out on detrital zircon grains from major river-mouth sediments draining South Korea to infer provenance characteristics and the crustal growth history of the southern Korean Peninsula, using a laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS). The Korean Peninsula is located in the East Asian continental margin and mainly comprises three Precambrian massifs and two metamorphic belts in between them. We obtained 515 concordant to slightly discordant zircon ages ranging from ca. 3566 to ca. 48 Ma. Regardless of river-mouth location, predominance of Mesozoic(249e79 Ma) and Paleoproterozoic(2491e1691 Ma) ages with subordinate Archean ages indicates that the zircon ages reflect present exposures of plutonic/metamorphic rocks in the drainage basins of the South Korean rivers and the crustal growth of the southern Korean Peninsula was focused in these two periods. Comparison of detrital zircon-age data between the North and South Korean river sediments reveals that the Paleoproterozoic zircon age distributions of both regions are nearly identical,while the Neoproterozoice Paleozoic ages exist and the Mesozoic ages are dominant in southern Korean Peninsula. This result suggests that Precambrian terrains in Korea record the similar pre-Mesozoic magmatic history and that the influence of Mesozoic magmatism was mainly focused in South Korea. 相似文献
19.
V. N. Kozhevnikov N. G. Berezhnaya S. L. Presnyakov E. N. Lepekhina A. V. Antonov S. A. Sergeev 《Stratigraphy and Geological Correlation》2006,14(3):240-259
Individual grains of zircon from the Archean Kostomuksha, North Karelian and Matkalakhta greenstone belts, which are situated respectively in western, northern and eastern Karelia, are studied using the ion microprobe SHRIMP II. As a result, the oldest 207Pb/206Pb ages of 3151 ± 4.6 and 3329 ± 16 Ma are first determined for detrital zircons from northern and eastern Karelia. The 207Pb/206Pb ages estimated for two subsequent metamorphic events of Archean Eon in eastern Karelia correspond to 3.25 and 3.17–3.10 Ga. The age value of 2711 ± 9.6 Ma is determined for silicic volcano-plutonic complex and quartz stockwork in northern Karelia and the date 2821 ± 15 Ma for magmatic rocks of eastern Karelia. Silicic volcanics from an oceanic plateau section in the Kostomuksha belt are dated at 2791.7 ± 6.1 Ma for the first time in the Archean of Fennoscandia. The oldest detrital zircons from siliciclastic metasediments determine the stabilization time of Archean continental nuclei in East Fennoscandia. The younger generation of greenstone belts is exemplified in the Karelian craton by the Matkalakhta and Kostomuksha structures comprising rock associations less than 2.82 Ga old, mafic rocks of the Kontokki Group included. Geological history of these belts corresponds to geodynamic mesocycle 90–110 Ma long and to the Archean global epoch of metallogeny, which was responsible for origin of most valuable deposits of base and precious metals. 相似文献
20.
《International Geology Review》2012,54(16):2036-2056
ABSTRACTThe Chinese Southwest Tianshan Orogenic Belt is located along the boundary between the Central Asian Orogenic Belt (CAOB) and the Tarim Block (TB), NW China. It records the convergence of the Tarim Block and the Middle Tianshan, and is, therefore, a crucial region for understanding the Eurasia continental growth and evolution. The Wulagen (geographical name) metasedimentary rocks of the Wuqia area (mainly metamorphic sandstones and mica schists) form one of the metamorphic terranes in the Southwestern Tianshan Orogenic Belt. The geochronology of these rocks is poorly known, which hampers our understanding of the tectonic evolution of the belt. We analyzed 517 zircon grains for detrital zircon U–Pb dating and 93 zircon grains for in situ Lu–Hf isotopic compositions from the Wulagen metasedimentary rocks. The analyzed zircon grains yield Neoarchean to late Paleozoic U–Pb ages with major age peaks at ~2543 Ma, 1814 Ma, 830 Ma, 460 Ma, and the youngest cluster of zircon (magmatogene) ages is 395 Ma. The zircon U–Pb data show that the late Paleozoic (Early Devonian) is the maximum depositional age of the Wulagen metasedimentary rocks, rather than the previously considered Precambrian period. The zircons with Paleozoic ages yield εHf(t) values of ?22.0 to +11.3 and two-stage model ages (TDM2) of 3.95 to 1.30 Ga, suggesting that the parental magmas were formed from partial melting of pre-existing crustal rocks. Our zircon U–Pb geochronology and Hf isotopic data indicate the major source regions for the Wulagen metasedimentary rocks was the Kyrgyzstan North Tianshan. The zircon age population of 600–400 Ma (peak at ~460 Ma) has negative εHf(t) values (?15.0 to ?0.6) and Mesoproterozoic two-stage model ages, suggesting that the early Paleozoic magmatism resulted mainly from the melting of ancient crust, which played an important role in crustal evolution in the southern CAOB. 相似文献