柴北缘西段花岗岩锆石SHRIMP U-Pb定年及其岩石地球化学特征

柴北缘西段出露的花岗岩主要有赛什腾山、团鱼山、嗷唠河和三岔沟等岩体,这些岩体的走向为北西向,与区域构造线方向基本一致．岩体的锆石SHRIMP U—Pb定年结果表明,它们的时代从早古生代的奥陶纪到晚古生代的泥盆纪和二叠纪．其中,赛什腾山岩体为（465．4±3．5）Ma,团鱼山岩体两期侵入岩的年龄分别为（469．7±4．6）和（443．5±3．6）Ma;它们均属早古生代奥陶纪;而嗷唠河岩体的石英闪长岩为（372．1±2．6）Ma,属晚古生代泥盆纪;三岔沟岩体也由两期侵入岩组成,其年龄分别为（271．2±1．5）和（260．4±2．3）Ma,属二叠纪．花岗岩的岩石地球化学特征表明,柴北缘早古生代花岗岩具有岛弧或活动大陆边缘花岗岩的属性,原岩可能为中元古代（1．03～1．15Ga）形成的、来源于亏损地幔的拉斑玄武质洋壳,它们的形成与板块的俯冲作用有关;晚古生代花岗岩继承了早古生代花岗岩的特点,其原岩可能为中元古代（1．18—1．29Ga）的岛弧根部下地壳,岩浆物质成分以壳幔混合源为主,它们的形成与造山隆起后不同块体之间的均衡调整有关．     

东昆仑造山带中带的锆石U-Pb定年与构造演化启示

应用LA-ICPMS法和SHRIMP法测定产在东昆仑造山带东段昆中带的清水泉高级岩片的正片麻岩和斜长角闪岩的锆石U-Pb年龄．1件正片麻岩中变质重结晶锆石的加权平均^206 Pb/^238 U年龄为（517．0＋5．0/-6．0）Ma;另1件正片麻岩的继承性锆石给出其岩浆源区955,895和657Ma等3组^207 Pb／^206 Pb年龄,变质重结晶的岩浆成因锆石边给出的^206 Pb/^238 U年龄值为（559＋12／-17）和（516±13）Ma．斜长角闪岩的锆石3组加权平均^206 Pb/^238 U年龄值为（482．0＋10/-8．0）,（516．2±5．8）和（549±10）Ma．这些年龄结果分别记录了昆中带在前寒武纪和早寒武纪时期发生过的构造热事件．秦岭-阿尔金-柴北缘．昆仑造山带的地质体记录的寒武纪岩浆-变质事件表明它们在原特提斯构造演化早期可能曾发生过陆块汇聚．     

湘东北地区石蛤蟆花岗岩体SHRIMP U—Pb年龄及地球化学特征

分布于湖南东北部的石蛤蟆岩体侵位于新元古代地层中。由微细粒斑状黑云母花岗闪长岩和细粒斑状黑云母二长花岗岩等两期侵入体组成。通过锆石SHRIM PU--Pb法测得岩体侵位年龄为157土2Ma（2d）,MSWD=0．98,成岩时代为晚侏罗世。SiO2=68．26％～68．53％,K2O／Na2O=1．37～1．59,岩石属镁质、准铝质-微过铝质、高钾钙碱性-钾玄岩系列;岩石明显富集大离子亲石元素,亏损高场强元素,Rb／Sr较低（0．40～0．56）;乏REE较高（171．48～183．81）,Eu为弱负异常（δEu=0．86～0．93）,（La／Yb）N=27．11～45．87;具较高的eNd值（-5．11）和高T2DM（1．63Ga）。综合研究表明,石蛤蟆花岗岩为混合源高钾钙碱性花岗岩类（KCG）,其花岗岩浆有大量幔源物质加入。讨论认为岩体形成于构造体制转换下的地球动力学背景,是造山晚期张弛作用下的产物。     

皖南谭山岩体的锆石定年及地质意义

皖南地区广泛分布燕山期岩浆岩,但其年代学方面的工作较为薄弱。为厘定该地区燕山期岩浆岩年代学格架,本文利用LA-ICP-MS锆石U-Pb定年方法对皖南谭山岩体的正长花岗岩进行了锆石U-Pb年代学研究,两个样品的206Pb/238U加权平均年龄分别为128．5±1．7Ma和128．3±1．5Ma,基本一致,为早白垩世岩浆活动的产物。结合本地区高精度年代学数据,皖南地区中生代岩浆岩可划分为三个峰期：第一峰期为142～139Ma;第二峰期为133～130Ma;第三峰期为128～125Ma。     

鲁西上峪辉长-闪长岩的成因：年代学与岩石地球化学证据

对鲁西上峪辉长闪长岩进行了系统的年代学与地球化学研究,以便对其成因以及中生代岩石圈地幔的性质给予制约．研究表明,鲁西上峪岩体是由一套辉长闪长岩类岩石构成．锆石呈自形一半自形晶,且具有较高的Th/U比值（1．23～2．87）,意味着岩浆成因．对两个辉长闪长岩中锆石进行的LA-ICP—MSU-Pb定年结果（加权平均年龄）分别为（129±1）和（134±2）Ma,这表明该岩体的形成时代为早白垩世．除早期堆积体外（QT-19）,该类岩石的SiO2和MgO含量分别介于50．12％～56．37％和3．52％～6．37％之间;且以高Mg^#（0．54～0．63）、富Na（Na20／K20大于1）、高Cr（73×10^-6～217×10^-6）、Ni（34×10^-6-241×10^-6）为特征．该类岩石强烈富集轻稀土元素和大离子亲石元素、明显亏损高场强元素,^87St／^86Sr（t）值和εNd（t）值分别变化于0．70962～0．71081和-16．60— -13．04之间．结合鲁西铁铜沟、金岭高镁闪长岩和方城、费县玄武岩及其中地幔包体的特征,认为上峪辉长闪长岩的原始岩浆起源于受陆壳物质强烈改造的富集型上地幔．鲁西早白垩世高镁闪长岩Sr-Nd—Pb同位素的空间变化——即自南东向北西方向。^87St／^86Sr（t）值降低、εNd（t）值升高、^207Pb/^204Pb和^208Pb/^204Pb初始比值的降低——与扬子克拉通沿北西方向俯冲于华北克拉通之下的构造模式相吻合．     

基于激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)的锆石微区U-Pb精确定年

激光剥蚀电感耦合等离子体质谱(LA-ICP-M_S)为锆石U-Pb年代学提供了快速、精确的测试技术。文中利用Agilent 7900型四极杆电感耦合等离子体质谱仪(Q-ICP-M_S)和ResolutionM50-LR型193nm Ar F准分子激光剥蚀系统联机,建立了完整的锆石U-Pb年龄测试流程。在激光束斑直径40μm、能量密度3. 5J/cm2的条件下,用标准玻璃NIST 612对测试系统进行调谐,使238U的灵敏度高于30 000cps/s。对5个锆石标样(年龄为4～1 064Ma)进行了详细的定年研究,所获得的91500、GJ-1、Plesovice、FCT和蓬莱锆石的U-Pb年龄与前人报道的年龄在误差范围内是一致的,3个国际标样(91500、GJ-1、Plesovice)的测试精度优于3%,2个二级标样(FCT和蓬莱)测试精度较低,仅优于15%,结果表明该实验流程是可行的。锆石U-Pb年龄的分析误差主要来自3个方面:同位素比值测定误差、仪器灵敏度漂移和同位素分馏校正系数误差、标样推荐值误差。与国际标样相比,影响FCT和蓬莱锆石的分析误差除了以上3个因素外,还有以下3个方面:放射性成因Pb*含量过低,测试误差增大;普通Pb对其年龄影响加剧,不易精确地扣除;样品与标样匹配程度降低。因此,样品的测试精度取决于绝对年龄、普通Pb含量和标样与样品匹配程度。     

Miller Range 05035和LaPaz Icefield 02224月球陨石中锆矿物Pb/Pb离子探针定年:月海玄武岩的成因启示

Mille rRange(MIL) 05035和LaPaz Icefield(LAP)02224是两块非角砾月海玄武岩陨石.本文研究了这两块月球陨石的岩相学和矿物学特征,并用离子探针多接收模式对锆矿物进行原位Pb/Pb定年.岩相学和矿物学特征与前人研究结果一致.MIL 05035中钙锆钍矿Pb/Pb年龄为(3851±8)Ma(2σ),与前人其他方法的结果一致.该年龄指示MIL 05035可能与Asuka 881757是成对陨石,且MIL 05035代表的岩浆作用可能与39亿年前月球表面的强烈撞击事件有关.测试了LAP02224中两颗斜锆石的Pb/Pb年龄,其中一颗较大斜锆石(6μm×20μm)呈现年龄分带现象,从(3109±29)Ma(2σ)到(3547±21)Ma(2σ),远大于该陨石的全岩年龄((3.02±0.03)Ga),另一颗斜锆石年龄为(3005±17)Ma(2σ).该结果说明LAP 02224的结晶年龄至少为～3.55Ga,先前获得的3Ga全岩年龄不是该陨石的结晶年龄,而反映了后期热事件的影响.本文结果显示钙锆钍矿和斜锆石可以获得较全岩更为可靠和精确的年龄,对研究月海玄武岩的成因有着更深远的意义.     

松辽盆地南部基底花岗质岩石锆石LA-ICP-MS U-Pb定年:对盆地基底形成时代的制约

为了限定松辽盆地基底的形成时代,对松辽盆地南部7个基底花岗质岩石进行了锆石LA-ICP-MS U-Pb定年研究.锆石的阴极发光图像显示,7个基底花岗质岩石中的锆石均呈自形晶,且具有典型的岩浆生长振荡环带.测年结果表明,位于西部斜坡区洮6井(T6-1)石英闪长岩形成于(236±3)Ma;位于东南隆起区北部榆参1#(YC1-1)井下部(2126 m)闪长岩形成于(319±1)Ma,其中有(364±3)Ma的捕获锆石,其上部(1994 m)钾长花岗岩(YC1-2)形成于(361±2)Ma;位于东南隆起区南部十屋断陷内秦2井(Q2-1)、松南121井(SN121)、松南122井(SN122)和松南72井(SN72)基底花岗质岩石锆石LA-ICP-MS U-Pb定年结果分别为(161±5),(165±2),(165±1)和(161±4)Ma.统计结果表明,中侏罗世花岗质岩石构成了基底花岗岩的主体,同时基底中发育有海西期和印支期岩浆活动.这暗示松辽盆地是在中生代中侏罗世造山作用之后发展起来的中生代晚期陆内或陆缘裂谷盆地.     

Zircon SHRIMP U-Pb dating of granites from Dulan and the chronological framework of the North Qaidam UHP belt,NW China

Zircon SHRIMP dating of granites from Dulan,east segment of North Qaidam UHP belt shows that they are 406.6±3.5 Ma for Yematan-E,407.3±4.3 and 397±6 Ma for Balijiehatan-W,404.5±4.0 and 397.0±3.7 Ma for Shuiwenzhan-N,380.5±5.0 Ma for Shuiwenzhan-S,382.5±3.6 and 372.5±2.8 Ma for Chachagongma.These granites from Dulan represent the products of the third and fourth periods of Paleozoic magmatism in North Qaidam.Geochemically,the granitoids with metalumious to weak peratuminous are quartz diorite,granodiorite,and granite in composition and mainly belong to calc-alkaline series,a few samples to calc or alkali-calc series.The third period of granites is a rock association of granodiorite+granite,with initial 87Sr/86Sr ratios from 0.7082 to 0.7110 and T2DM model ages from 1.41–1.90 Ga;and the fourth period of granites is a rock association of quartz diorite+granodiorite+granite,with initial 87Sr/86Sr ratios from 0.7072 to 0.7091 and T2DM model ages from 1.07–1.38 Ga.Therefore,the third period of granites has higher initial 87Sr/86Sr ratios and T2DM model ages.On the contrary,the fourth period of granites has Nd(t)values from 0.6 to-3.0,higher than that of the third granite with Nd(t)values-3.2 to-9.3.Thus,the data comparison indicates that the third granites may derive from Paleo-proterzoic continental crust with mantle material whereas the fourth granites may derive from the Meso-proterzoic basalt crust with continental material.Combined with regional geology,we thought that the third granites were formed relative to plate exhumation and the fourth granites to delamination of the lithospheric mantle.     

SHRIMP zircon U-Pb dating and its geological significance of Chibaisong gabbro in Tonghua area,Jilin Province,China

The basic dykes are widely distributed in the Tonghua area, among which the Chibaisong No.1 gabbro has attracted many geologists’ attention to the copper-nickel sulfide deposit within it. However, its formation time has been controversial all the time. Most geologists considered that it could be formed at the late Archean or the Paleoproterozoic[1]1), while some other geologists contended that it might be formed in early Yanshannian of Mesozoic2). The forming time of the basic dyke swarm i…     

U-Pb dating of zircon fromthe bed parallel anatectic granitic intrusion in the Baoban group in Hainan Island and the tectonic implication

1 Geological setting Hainan Island is situated in the conjunction region between the Euro-Asian plate, the Indian-Australian plate and the Pacific plate, its tectonic setting and evolution is implicated in understanding the continen-tal margin accretion and evolution of East Asia and the formation of the South China sea. The Jiusuo-Lingshui fault zone divides Hainan Island into the Yaxian Pa-leozoic massif in the south and the Qiongzhong Pa-leozoic massif in the north (Fig. 1), they con…     

U-Pb dating of early Mesozoic granodioritic intrusions in southeastern Hunan Province, South China and its petrogenetic implications

The NE-trended Mesozoic granodioritic intrusions are spatially and temporally associated with the copper multi-metal mineralization in southeastern Hunan Province, South China. U-Pb dating result of single-grained zircons of four samples respectively from Shuikoushan, Baoshan, western Tongshanling and eastern Tongshanling intrusions reveals that their crystallization age spans a range from 172 Ma to 181 Ma, which also represents the oldest age of the regional copper multi-metal mineralization. Some of the zircon grains give an upper intercept age of about 1753 Ma and ²⁰⁷Pb/²⁰⁶Pb apparent age of (1752 ± 4) Ma, implying the involvement of the pre-Cambrian metamorphic (possible Middle Proterozoic) basement in their genesis. The presence of such a kind of zircon grains in these granodiorites indicates either that the parental magmas were assimilated by basement rocks during magma ascent or that lower/middle crustal rocks were one of the important components during the melting process.     

宁芜盆地凹山铁矿含矿玢岩LA-ICP-MS锆石U-Pb定年及其地质意义

凹山铁矿是宁芜火山盆地内重要的玢岩矿床之一.为进一步厘定该矿床的成矿年龄,分析其成矿动力学背景,本文对凹山铁矿含矿辉石闪长玢岩和磁铁矿样品进行了详细的稀土元素地球化学分析,并对辉石闪长玢岩样品进行了LA-ICP-MS锆石U-Pb年龄测定.测年结果显示凹山铁矿成矿母岩的形成时代为127.6±4.4 Ma,属早白垩世,该年龄可代表凹山铁矿床的成矿年龄.成矿岩浆源自于地幔或下地壳玄武岩;盆地岩石圈减薄诱发地幔成矿物质进入地壳,成矿时代对应岩石圈减薄的高峰期.     

LA-ICP-MS zircon U-Pb dating from granitoids in southern basement of Songliao basin:Constraints on ages of the basin basement

Seven LA-ICP-MS zircon U-Pb datings from granitoids in the southern basement of the Songliao basin were done in order to constrain the ages of the basin basement. The cathodoluminescence (CL) images of the zircons from seven granitoids indicate that they are euhedral-subhedral ones with striped ab-sorption and obvious oscillatory zoning rims. The dating results show that a weighted mean 206Pb/238U age is 236±3 Ma for quartz diorite (sample No.T6-1) located in the western slope of the basin,that weighted mean 206Pb/238U ages are 319±1 Ma (2126 m) and 361±2 Ma (1994 m) for diorite (sample No.YC1-1) and granite (sample No.YC1-2) located in northern part of southeastern uplift of the basin,respectively,and that weighted mean 206Pb/238U ages are 161±5 Ma,165±2 Ma,165±1 Ma and 161±4 Ma for samples Q2-1,SN121,SN122,and SN72 granitoids located in southern part of southeastern uplift of the basin,respectively. The statistical results of ages suggest that the middle Jurassic granitoids con-stitute the main part of basement granitoids,and that the Hercynian and Indo-Sino magmatisms also occur in the basin basement. It is implied that the Songliao basin should be a rift one formed in the intracontinent or active continental margin settings in the late Mesozoic after the Middle Jurassic orogeny took place.     

皖南新元古代双峰式岩墙群的年龄、地球化学特征及地质意义

皖南许村镇附近发育一套岩墙群,主要由辉长岩和花岗闪长斑岩组成,它们在时空上紧密伴生,成因上密切相关。岩石的SiO2含量集中分布在酸性和基性成分之间,缺乏中性及中酸性成分,构成一套双峰式侵入岩组合。对花岗闪长斑岩进行锆石LA-ICP-MS U-Pb年代学研究,表明双峰式岩墙侵入时间为822．1＆#177;6．6Ma。辉长岩具有正εHf （t）值（2．1～4．4）、大离子亲石元素和LREE富集,显示大陆拉斑质玄武岩地球化学和同位素组成特征;花岗闪长斑岩富含Zr、Hf和稀土元素,较高的Ga/A1比值,较低Ba、Sr、P、Ti含量,总体上地球化学特征类似A2-型花岗岩,εHf （t ）值范围（1．8～4．6）与辉长岩基本相同。许村双峰式岩墙群的基性端员辉长岩是拉张环境下华南弱亏损岩石圈地幔部分熔融产生玄武质岩浆的产物,而酸性端员花岗闪长斑岩是玄武质岩浆在上升途中受地壳混染,并发生底侵作用和由玄武岩浆提供的热源导致地壳重熔的结果。     

华北克拉通北缘—西伯利亚板块南缘的地壳速度结构特征

华北克拉通北缘—西伯利亚板块南缘（张家口—中蒙边界）的深地震测深剖面长600 km,跨越华北板块、内蒙造山带和西伯利亚板块.沿测线采用8个1.5t的爆炸震源激发地震波,使用300套数字地震仪接收,取得了高质量的地震资料.通过资料分析和处理,识别出沉积层及结晶基底的折射波（Pg）、上地壳底面的反射波（P2）、中地壳内的反射波（P3）、中地壳底面的反射波（P4）、下地壳内的反射波（P5,仅在镶黄旗—苏尼特右旗下方出现）和莫霍面的反射波（Pm）等6个震相.采用地震动力学射线方法（seis88）得到的地壳速度结构表明：（1）在华北板块与内蒙造山带之间,内蒙造山带与西伯利亚板块之间,上地壳中存在明显的高速度局部变化,在地表发育大量的古生代花岗岩体、超基性岩体.（2）在中下地壳华北板块南缘的地震波速度大,为6.3~6.7 km/s,西伯利亚板块北缘的速度小,为6.1~6.7 km/s,且界面比较平缓.原因是在内蒙造山带内地壳的缩短和隆升造山引起了中下地壳界面的剧烈起伏,不同海陆块的拼合和物质交换导致了不同区域速度的不均匀性.（3）莫霍面在赤峰断裂带（F2）以南和索伦敖包—阿鲁科尔沁旗断裂带（F4）以北较为平缓,平均深度为40~42 km.在F2—F4之间呈双莫霍面,莫霍面1明显上隆,深度为33.5 km,层速度为6.6~6.7 km/s.莫霍面2明显下凹,在西拉木伦河断裂带（F3）下方,最深达到47 km,速度达到最大为6.8~6.9 km/s,这可能是由壳幔物质混合引起的.依据莫霍面的特点,本文认为双莫霍面以南为华北板块北缘,以北为西伯利亚板块南缘,拼合位置在赤峰断裂带（F2）与索伦敖包—阿鲁科尔沁旗断裂带（F4）之间的区域.     

Zircon U–Pb dating of gabbro and diorite from the Bato pluton,northeast Japan

To constrain the timing of the tectonothermal events and formation process of a plutonic suite, U–Pb dating was carried out by laser ablation inductively coupled plasma mass spectrometry combined with cathodoluminescence imaging on zircon grains extracted from the Bato pluton, northern Yamizo Mountains, Japan. The Bato pluton consists of gabbro and diorite. Zircon grains separated from a gabbro sample had a unimodal ²³⁸U–²⁰⁶Pb age (105.7 ±1.0 Ma). It was interpreted as the solidification age of the gabbro. Cathodoluminescence observation showed that the zircon grains from a diorite sample were characterized by anhedral cores, oscillatory zoned mantles, and dark rims. The ²³⁸U–²⁰⁶Pb age of the anhedral cores ranged from 2 165 Ma to 161 Ma, indicating the assimilation of surrounding sedimentary rocks. The ²³⁸U–²⁰⁶Pb ages of the oscillatory zoned mantles and dark rims are 109.0 ±1.3 Ma and 107.7 ±1.3 Ma, respectively. Observation under polarizing microscopy suggests that the anhedral cores occurred before plagioclase and hornblende, and the oscillatory zones around the anhedral cores had crystallized at the same time as the crystallization of biotite. Moreover, the dark rims formed at the same time as the crystallization of quartz and K‐feldspar. The formation process of the gabbro‐diorite complex in the Bato pluton was inferred as follows. (i) A mafic initial magma intruded into Mesozoic sedimentary rocks, and the assimilation of these sedimentary rocks led to geochemical variation yielding a dioritic composition. Subsequently, plagioclase and hornblende of the diorite were crystallized before 109.0 ±1.3 Ma. (ii) Biotite crystallized in the middle stage around 109.0 ±1.3 Ma. (iii) Quartz and K‐feldspar of the diorite were crystallized at 107.7 ±1.3 Ma. The gabbroic magma solidified (105.7 ±1.0 Ma) after solidification of the diorite.