U-Pb systematics of zircon and titanite from the Gardnos impact structure, Norway: Evidence for impact at 546 Ma?

Zircon and titanite were investigated in impactites of the Gardnos structure, a crater formed in Sveconorwegian (ca. 1 Ga) crust, which was then overridden in the Devonian by Caledonian nappes. Observed deformation features in zircons are granular texture, planar microstructures, and likely the incorporation of organic carbon during impact causing black staining of the zircon grains. The grains were studied by scanning electron microscopy (SEM) and cathode luminescence (CL) and dated by U-Pb isotope dilution - thermo-ionization mass spectrometry (ID-TIMS). Zircon grains without impact related features have U-Pb data showing moderate discordance (5-13%) and indicating formation ages mostly in the range of 1600-1000 Ma, except detrital zircon ages as old as >2481 Ma, reflecting the diversity of target rocks in the area. Titanite with concordant ages of 995-999 Ma dates metamorphism during final juxtaposition of the Telemarkia on the Idefjorden terrane to the east. Zircon grains with demonstrated or presumed shock features yield highly discordant (14-40%) U-Pb data, with a majority of them plotting along an array with a lower intercept of about 340 Ma reflecting the influence of the Caledonian orogeny and recent Pb-loss. One zircon grain was totally reset at 379 Ma during late Caledonian metamorphism, which also caused local growth of new titanite. A specific group of zircon grains yields data with relatively high discordance for moderate U contents, and five of these analyses, including that of a grain with proven granular or aggregate texture, fit a discordia line with an upper intercept of 546 ± 5 Ma. These features are interpreted as indicating zircon break-down to an amorphous state during impact, with subsequent recrystallization into microcrystalline aggregates causing extensive to complete Pb loss. We further suggest that their crystallinity prevented Pb loss during the Caledonian orogeny, while the small subgrain size and increasing metamictisation allowed more recent disturbances. We thus interpret the 546 Ma age as the approximate time of impact.     

额尔古纳地块太平川巨斑状花岗岩的锆石U-Pb年龄和Hf同位素特征

大兴安岭北段额尔古纳地块莫尔道嘎-太平川一带分布有大量的新元古代巨斑状花岗岩,该岩体形成的确切时代及成因尚不清楚。笔者等运用LA ICP MS技术进行了锆石U Pb定年和锆石Hf同位素组成测定。锆石U Pb年龄结果揭示太平川巨斑状花岗岩形成时代为791.4 Ma。锆石Hf同位素研究显示εHf（t）为1.4~6.4,均>0,反映亏损地幔来源新生地壳物质在花岗岩的形成中起主导作用,锆石Hf单阶段的模式年龄tDM为1.09~1.28 Ga,与岩石的形成时间791.4 Ma有较长的时间间隔,表明该区花岗岩的母岩来自具有较长地壳滞留时间的地壳物质的部分熔融。结合额尔古纳已有的花岗岩锆石Hf同位素资料,认为额尔古纳地块在中、新元古代曾发生过地壳增生事件,存在1.09~1.28 Ga的中元古代晚期增生地壳。     

Inherited or not inherited: Complexities in dating the atypical ‘cold’ Chopok granite (Nízke Tatry Mountains,Slovakia)

Zircon U-Pb SIMS dating combined with in-context (in thin section) monazite and xenotime U + Th-total Pb dating was used to clarify the Palaeozoic evolution of the ‘cold’ Chopok granite (Nízke Tatry Mountains, Slovakia). Four distinct zircon, monazite and xenotime age domains testify to a prolonged evolution from igneous formation to multi-stage metasomatism and hydrothermal overprinting. The geological interpretation of age patterns from ‘cold’ granites, expected to have low zircon saturation temperatures (<800 °C) and relatively high amounts of zircon inheritance, requires special care, especially for what concerns proper attribution of zircon inheritance and igneous growth ages. These issues can be resolved using zircon saturation temperatures (T_Zrn) as proxy for the amount of zircon inheritance in combination with the temperature differences between T_Zrn and the granite solidus. In this respect, the Chopok granite is an atypical ‘cold’ granite. Due to T_Zrn being substantially lower (ca. 80 °C ± 50 °C) than the granite solidus temperature, practically no zircon inheritance was found. The zircon age data indicates that the Chopok granite is a product of an Early Ordovician (475.8 ± 3.3 Ma) magmatic event, corresponding with the widespread Early Palaeozoic magmatism recorded throughout the European Variscan belt. This is further corroborated by phosphate mineral ages. The post-magmatic activity recorded in the U-Pb systematics of zircon and phosphates overgrowths can be related to the different phases of the evolution of the Variscan orogen: Early Carboniferous (ca. 352 Ma) metasomatism documents the main Variscan orogenic event, whereas the Permo-Triassic age (ca. 255 Ma) reflects thermo-tectonic activity associated with large-scale crustal extension, contemporaneous with the initial continental leading to the break-up of Pangea.     

U–Pb isotopic dating of titanite microstructures: potential implications for the chronology and identification of large impact structures

Identifying and dating large impact structures is challenging, as many of the traditional shock indicator phases can be modified by post-impact processes. Refractory accessory phases, such as zircon, while faithful recorders of shock wave passage, commonly respond with partial U–Pb age resetting during impact events. Titanite is an accessory phase with lower Pb closure temperature than many other robust chronometers, but its potential as indicator and chronometer of impact-related processes remains poorly constrained. In this study, we examined titanite grains from the Sudbury (Ontario, Canada) and Vredefort (South Africa) impact structures, combining quantitative microstructural and U–Pb dating techniques. Titanite grains from both craters host planar microstructures and microtwins that show a common twin–host disorientation relationship of 74° about <102>. In the Vredefort impact structure, the microtwins deformed internally and developed high- and low-angle grain boundaries that resulted in the growth of neoblastic crystallites. U–Pb isotopic dating of magmatic titanite grains with deformation microtwins from the Sudbury impact structure yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1851?±?12 Ma that records either the shock heating or the crater modification stage of the impact event. The titanite grains from the Vredefort impact structure yielded primarily pre-impact ages recording the cooling of the ultra-high-temperature Ventersdorp event, but domains with microtwins or planar microstructures show evidence of U–Pb isotopic disturbance. Despite that the identified microtwins are not diagnostic of shock-metamorphic processes, our contribution demonstrates that titanite has great potential to inform studies of the terrestrial impact crater record.     

黔东南—桂北地区四堡群凝灰岩锆石SHRIMP U-Pb年龄及其地层学意义

首次获得黔桂地区晚前寒武纪四堡群凝灰岩(斑脱岩)锆石SHRIMP U-Pb年龄,结合新获得的侵位于四堡群的花岗岩锆石SHRIMP U-Pb年龄,将四堡群明确定位于新元古界。"江南造山带"普遍发育的新元古代四堡群(梵净山群、冷家溪群、双桥山群)和上覆的丹州群(下江群、板溪群、河上镇群)均为低变质绿片岩系,构成了江南古陆的变质基底。多年来四堡群一直划归中元古界,并且构成"四堡运动"的主体,其时代的定位一直影响着整个江南古陆变质基底的地层划分和对比,也制约着中国地质学家对江南造山带的地质背景和成矿条件解疑。通过对四堡群及其上覆地层中斑脱岩锆石的研究,精确地测定并获得了四堡群斑脱岩锆石的年龄841.7Ma±5.9Ma和黔东南摩天岭地区侵入四堡群的花岗岩锆石的年龄826.8Ma±5.9Ma。     

Duluth Complex FC1 Apatite and Zircon: Reference Materials for (U-Th)/He Dating?

The accuracy and validation of geo- and thermochronological dating hinges on the availability of well-characterised age reference materials. The Mesoproterozoic gabbroic anorthosite FC1 from the Duluth Complex, Minnesota is a reference material for zircon U-Pb and a suggested reference material for apatite fission-track dating. We evaluate FC1 as (U-Th)/He reference material, and determine its apatite U-Pb, and zircon and apatite (U-Th)/He age. Our dating results constrain the thermal history of FC1, showing that fast cooling occurred between ~ 1099 and 1040 Ma from ≥ 600 °C to ~ 200 °C. The zircon (U-Th)/He data from air-abraded grains give a robust isochron age of 1037 ± 25 Ma (2s) without overdispersion. The within-grain homogeneity of U and Th, the availability of FC1 zircon, and the absence of radiation-damage effects on the (U-Th)/He age support its use as reference material. Unabraded zircon grains give lower and more dispersed ages, highlighting the usefulness of air abrasion to control for α-ejection in (U-Th)/He dating. Our apatite (U-Th-Sm)/He single-grain ages vary between 180 and 300 Ma. Their wide dispersion argues against the use of FC1 apatite as (U-Th-Sm)/He reference material and makes the interpretation of their low-temperature thermal history complicated.     

广西栗木锡多金属矿床锆石和锡石U-Pb年龄及其地质意义

年代学研究是花岗岩型稀有金属矿床研究的重要内容,多种定年方法的联合有助于对岩浆演化及稀有金属元素富集成矿过程的精细刻画。论文选择栗木矿区具代表性的金竹源、老虎头和水溪庙花岗岩型钨锡铌钽矿床和（长石）石英脉型钨锡矿床,进行LA-ICP-MS锆石U-Pb和LA-MC-ICP-MS锡石U-Pb年代学研究。结果显示,老虎头细粒铁锂云母钠长石花岗岩锆石U-Pb年龄为（216.3±1.7）Ma,长石石英脉型钨锡矿床锡石UPb年龄为（210.1±4.9）Ma;两件金竹源花岗岩型钨锡铌钽矿床锡石U-Pb年龄分别为（219.6±1.5）Ma和（219.9±2.2）Ma,石英脉型钨锡矿床锡石U-Pb年龄为（217.3±3.2）Ma;水溪庙长石石英脉型钨锡矿床锡石U-Pb年龄为（210.7±2.5）Ma。本次研究可以看出,金竹源花岗岩的成岩年龄与花岗岩型钨锡铌钽矿床及石英脉型钨锡矿床的成矿年龄间隔较小,表明含矿花岗岩可能在较短时间内经历了岩浆冷凝结晶、富集成矿和热液锡矿化过程,是短暂矿化事件的产物,而非以往认为的岩浆-热液长时间演化的结果。同时,基于不同测年方法的对比结果显示,在含锡花岗岩中,锡石年龄既能代...     

东南极Windmill群岛与罗迪尼亚超大陆聚合相关构造热事件的时代:来自Bailey半岛镁铁质片麻岩和淡色片麻岩锆石SHRIMP U-Pb年龄的约束

东南极Windmill群岛变质杂岩经历的变质和岩浆事件与西澳大利亚Albany-Fraser造山带在时间上相对应,并可能与罗迪尼亚超大陆的拼合有关。Windmill群岛Bailey半岛的镁铁质片麻岩(角闪石-单斜辉石-斜方辉石-黑云母-斜长石-石英-磁铁矿-锆石)被认为具有较早的形成年龄,其中还出露属于正片麻岩的淡色片麻岩(斜长石-钾长石-石英-黑云母-锆石)。对这两种片麻岩中的锆石分别进行了SHRIMP U-Pb年龄测定,首次获得该区镁铁质片麻岩锆石核部207Pb/206Pb加权平均年龄1403±28 Ma,该年龄记录了本区中元古代早期岩浆事件,这是Windmill群岛地区记录的最早一期岩浆事件,可能受到了东部莫森大陆(Mawson Continent)构造岩浆活动的影响。铁镁质片麻岩锆石增生边的年龄为1318±34 Ma,则记录了早期构造热事件。淡色片麻岩中锆石核部年龄为1257±51 Ma,与Bailey半岛的片麻状含石榴子石花岗岩侵位年龄一致,共同记录了该区的一期岩浆活动。淡色片麻岩中锆石增生边的年龄为1197±26 Ma,记录了晚期的变质事件。这些新的年龄数据强烈支持1375~1151 Ma期间东南极Windmill群岛与西澳大利亚Albany-Fraser造山带相连接的构造模型,同时也为罗迪尼亚超大陆拼合过程提供了重要的年代学约束。      

鄂尔多斯盆地周缘地壳形成与演化历史:来自锆石U-Pb年龄与Hf同位素组成的证据

锆石U-Pb定年及Hf同位素测定结果表明,鄂尔多斯盆地周缘的华北板块北缘、兴蒙造山系及扬子板块-秦岭-大别-苏鲁造山带等构造单元系统具有明显不同的形成与演化历史。华北板块北缘锆石年龄平均值为1 837 Ma,最强烈的岩浆活动出现于2 200~1 800 Ma,该期锆石约占全部的40%;次为强烈的岩浆活动在2 800~2 200 Ma,其众数在全部锆石中约占30%;1 500~1 200 Ma、500~100 Ma这两个阶段形成的锆石在全区所占比例各约为15%。华北板块北缘最突出的特征是基本不含1 000~700 Ma期间形成的锆石,>3 000 Ma的锆石在全区分布极为有限。锆石Hf同位素亏损地幔模式年龄表明华北板块北缘平均值为2.55 Ga,较U-Pb平均年龄老,说明2 200~1 800 Ma期间形成的锆石含有较多的古老地壳再循环组分。Hf亏损地幔模式年龄最强峰值约为2.8 Ga,与全岩Nd亏损地幔模式年龄的峰值相一致,Hf模式年龄为3.0~2.25 Ga的颗粒占全部的近95%,证明华北板块北缘的地壳增生主要在太古宙至古元古代期间。Hf同位素亏损地幔模式年龄>3.0 Ga的锆石颗粒所占比例不到0.1%,另外近5%锆石的模式年龄分布于中元古代。晚古生代-中生代所形成的锆石均是先存地壳组分,尤其是中元古代增生地壳的熔融作用形成。兴蒙造山系中锆石U-Pb年龄平均值为497 Ma,最强峰分布于石炭纪(约320 Ma),石炭纪-二叠纪末(350~250 Ma)形成的锆石所占比例达30%以上。新元古代至早古生代(600~440 Ma)形成的锆石占全部锆石的55%以上,而中元古代末-新元古代期间(1 200~600 Ma)形成的锆石在全区仅占4%。中元古代以前形成的锆石非常有限,说明该区最早形成的地壳组分在兴蒙造山系的形成过程中较充分地参与到后期的岩浆作用过程中。兴蒙造山系中锆石相应的Hf同位素亏损地幔模式年龄平均为1.13 Ga,明显较相应的U-Pb年龄老,最强峰值出现于约0.6 Ga。Hf亏损地幔模式年龄为0.7~0.28 Ga的颗粒在兴蒙造山系所占比例达57%,证明该区最强烈的地壳增生发生于新元古代至古生代期间。Hf同位素亏损地幔模式年龄分布于1.5~0.7 Ga的锆石在全区约占38%,说明此期间也是该区地壳较强烈的增生期。Hf亏损地幔模式年龄大于1.5 Ga的锆石所占比例不到5%,古生代以后兴蒙造山系也基本没有明显的地壳增生。扬子与秦岭-大别-苏鲁造山带构造单元中的锆石U-Pb年龄平均为799 Ma,年龄为1 300~750 Ma的锆石在全部锆石中约占70%。晚古生代-燕山期形成的锆石约占20%。年龄在3 500~2 650 Ma、2 118~1 680 Ma的锆石在该区各约占5%。结合扬子与秦岭-大别-苏鲁造山带平均为1.56 Ga的Nd亏损地幔模式年龄特征,说明1 300~750 Ma期间该区较强烈的岩浆作用事件中有较多的古老地壳组分加入其中。锆石U-Pb年龄及Hf同位素组成均说明鄂尔多斯盆地周缘各构造单元具有不同的形成演化历史。地壳是幕式增长的,但各构造单元每幕发生的时间、强度存在明显差别。因此,由盆地中不同时代地层中碎屑锆石U-Pb年龄及Hf同位素组成及全岩Nd同位素特征的系统研究可反演盆地物源供给与周围构造单元之间的关系。     

秦岭岩群副变质岩碎屑锆石年龄谱及其地质意义探讨

报道了北秦岭地块中秦岭岩群夕线黑云石英片岩61个碎屑锆石测点的207Pb/206Pb年龄测试结果,其中15个测点在SHRIMPⅡ上进行,46个测点来自LA-ICPMS的测定结果。61个年龄值显示锆石主要来源为1·5~1·9Ga(共51个测点,占所有测点的83·6%)的古元古代末至中元古代早期的大陆地壳,1粒碎屑锆石来自新太古代岩石,5粒来自中元古代晚期的蚀源区,4个测点为0·9~1·0Ga。由于秦岭岩群被新元古代早期960~900Ma的花岗岩体侵入,新的碎屑锆石测年结果表明秦岭岩群副变质岩的沉积时代至少介于1500~960Ma之间,亦可能为中元古代末期。秦岭岩群在早古生代造山过程中受到强烈改造,但本次测定未从夕线黑云石英片岩中获得这次变质作用的年代学信息。     

福建龙岩大洋花岗岩LA-ICP-MS锆石U-Pb测年、Hf同位素组成及其地质意义

对福建龙岩大洋花岗岩的两期岩相进行了LA-ICP-MS锆石U-Pb定年和锆石Hf同位素研究。结果表明:大洋花岗岩的早期黑云母正长花岗岩年龄为(144.8±0.9)Ma,εHf(t)值为-5.58～-2.00,二阶段Hf模式年龄为1 313～1 530 Ma,晚期微斜长石花岗岩的年龄为(127.5±0.4)Ma,εHf(t)值为-7.57～-0.90,二阶段Hf模式年龄为1 246～1 668 Ma。同位素特征表明,大洋花岗岩两期岩体都形成于早白垩世,是在岩石圈伸展的底侵作用下形成的,物源主要是中元古代地壳物质,但晚期有少量幔源组分的加入。     

朝鲜半岛平南盆地中元古代岩浆事件

朝鲜平南盆地翁津地区发育中元古代黄海群和同时期(称之为瓮津期)花岗岩,花岗岩体侵入于黄海群。本文采用锆石原位微区U-Pb定年技术,对黄海群中的酸性火山岩及花岗岩进行了年龄测试。获得的数据表明,黄海群中下部层位及上部层位的酸性火山岩分别在1235±5Ma和1203±7Ma喷发,由此说明黄海群的沉积时代应为中元古代,而不是传统上认为的古元古代;两个翁津期花岗岩体(翁津和黄衣山岩体)的侵位年龄分别为1251±22Ma和1248±13Ma,为中元古代花岗质岩浆活动的产物。上述1251~1203Ma年龄的获得,表明朝鲜半岛发育中元古代岩浆作用,从而明确朝鲜黄海裂谷与华北东缘裂谷在时间上具有同期性,同时也表明中国华北与朝鲜在中元古代具有类似的发展历史。     

塔里木盆地沙雅隆起北部三道桥地区前震旦纪基底岩浆岩特征与锆石U-Pb年龄研究

对塔里木盆地北部三道桥地区前震旦纪基底的岩浆岩进行岩石学分析及时代限定研究。研究区前震旦纪基底的岩浆岩主要由钾长花岗岩、石英二长岩及角闪二辉岩组成。钾长花岗岩局部受断裂影响,发生碎裂化作用,形成碎裂化钾长花岗岩。通过对Qg2、Qg3、S53及Qg4井4口钻井的4个岩心样品进行LA-ICP-MS锆石U-Pb年代学研究,获得钾长花岗岩、石英二长岩及碎裂钾长花岗岩年龄分别为1846±1Ma、1791±1Ma、1824±2Ma,代表了古元古代岩浆岩的变质年龄;角闪二辉岩年龄为879±4Ma,代表了中新元古代火山侵入年龄。说明塔里木盆地沙雅隆起北部存在前震旦纪古老基底,这些结果也为塔里木克拉通的前寒武纪构造演化提供了新的限定。     

孙吴-嘉荫地区早中生代花岗岩的年代学、地球化学与成因

对小兴安岭北部孙吴-嘉荫地区早中生代花岗岩进行了年代学和地球化学研究,据此探讨其成因及形成的构造背景。锆石U-Pb同位素定年结果表明,研究区早中生代花岗岩分为晚三叠世和早侏罗世两期,形成时代分别为210 Ma和187~181 Ma。晚三叠世碱长花岗岩属铝质A型花岗岩,岩浆源区为新元古代从亏损地幔中增生的基性火成岩地壳。早侏罗世英云闪长岩-花岗闪长岩和二长花岗岩属埃达克岩,是由加厚下地壳物质部分熔融形成的;正长花岗岩-碱长花岗岩与同期埃达克岩具明显不同的地球化学特征,岩浆源区为中元古代从亏损地幔中增生的基性地壳物质。结合区域地质构造演化特征,认为晚三叠世花岗岩是华北板块和西伯利亚板块碰撞造山后伸展构造环境下的产物,早侏罗世花岗岩的形成与古太平洋板块俯冲产生的挤压构造环境有关。     

内蒙古红山子复式岩体地质时代的厘定及其地质意义

通过岩相学研究和LA-ICP-MS锆石U-Pb测年,对红山子岩体的主要侵入期次和侵入岩形成时代进行了厘定,明确了红山子岩体为复式岩体并探讨了其地质意义。岩相学研究表明,红山子复式岩体由粗粒碱长花岗岩、斑状黑云母花岗岩、细粒黑云母碱长花岗岩和花岗斑岩等组成; LA-ICP-MS锆石U-Pb测年结果显示:粗粒碱长花岗岩的年龄为153. 6±1. 2 Ma,斑状黑云母花岗岩年龄为151. 4±1. 1 Ma,与周边火山盆地赋矿火山岩的年龄一致,属晚侏罗世早期;细粒黑云母碱长花岗岩的年龄为131. 5±1. 8 Ma,花岗斑岩年龄为133. 3±1. 4 Ma,与侵入红山子盆地的花岗斑岩的年龄一致,属早白垩世早期。因此,红山子岩体是由燕山期2个相隔20 Ma的不同期次侵入体组成的复式岩体。研究表明,红山子铀矿床赋存在早白垩世早期花岗斑岩与晚侏罗世火山岩的内、外接触带中,暗示复式岩体早白垩世早期细粒黑云母花岗岩、花岗斑岩与晚侏罗世粗粒碱长花岗岩、斑状黑云母花岗岩的内、外接触带是有利的找矿部位,并得到了铀矿勘查实践的初步证实。     

南秦岭桂林沟斑岩型钼矿Re-Os同位素年代学及其构造意义研究

陕西省镇安县桂林沟斑岩型钼矿床位于南秦岭多金属成矿带内,其成矿围岩主要为细粒花岗岩、钾长花岗岩和蚀变的粗粒花岗岩。本文通过对桂林沟斑岩型钼矿床中辉钼矿Re-Os同位素定年以及围岩中锆石U-Pb年代学研究,旨在探讨成矿成岩的关系及其构造意义。结果表明,6件辉钼矿的Re-Os同位素年龄在195.9~198.5Ma之间,加权平均年龄为197.2±1.3Ma,表明桂林沟钼矿形成于早侏罗世。围岩细粒花岗岩、钾长花岗岩和粗粒花岗岩的锆石U-Pb年龄分别为199±1.4Ma、201±3.1Ma和198±11Ma,这说明其成岩和成矿年龄基本一致。值得注意的的是,桂林沟钼矿床的形成年龄不同于前人已报导的秦岭钼矿的三个主要成矿期,即238~213Ma、145~126Ma和116~110Ma,其稍晚于第一成矿期。200~190Ma可能代表了秦岭成矿带一期尚未认识的重要成矿事件,对于南秦岭找矿具有重要意义。该期钼矿形成于秦岭印支期碰撞之后,是在造山带垮塌引起的岩浆-热液事件过程中形成的。     

松潘-甘孜地块南缘燕山早期矽卡岩型钨钼矿床 ——来自大牛场成岩成矿年代学及锆石Hf同位素证据

矽卡岩型矿床是钨、钼、锡等矿产的重要来源之一,中国的矽卡岩型矿床绝大多数分布于中国东部,成矿时代主要为燕山期.川西九龙大牛场是在松潘-甘孜地块新发现的矽卡岩型钨钼矿床,其成岩成矿时代尚未得到精确限定.大牛场地区铁厂河花岗岩体以二长花岗岩为主,少量正长花岗岩,而钨钼矿体主要产于矽卡岩中.文章对该矿床开展锆石U-Pb定年、...     

粤东仙水沥Sn-W矿床地质特征及成岩成矿年代学研究

近年来,粤东沿海地区新识别出一期早白垩世锡多金属成矿事件,但关于区内矿床类型仍然存在争议,包括与高分异花岗岩有关和动力变质热液成因.仙水沥Sn-W矿位于粤东沿海莲花山动力变质带,前人研究认为该矿床类型为动力变质热液成因.本文在详细介绍了仙水沥矿床地质特征的基础上,开展了锡石LA-ICP-MS U-Pb定年,并对空间上与...     

东昆仑早古生代花岗岩锆石U-Pb年龄及其地质意义

应用激光烧蚀多接收器电感耦合等离子体质谱(LA-MC-ICPMS)方法,对东昆仑五龙沟地区花岗岩样品进行了锆石 U-Pb 定年研究。结果表明,黄龙沟中部的糜棱岩化二长花岗岩(B20-14)中岩浆锆石206Pb/238U年龄平均值为(417.7±2.0) Ma,黄龙沟上部的糜棱岩化二长花岗岩(B21-2)中岩浆锆石206Pb/238U年龄平均值为(419.7±2.3) Ma,深水潭粗中粒二长花岗岩(B20-8)中岩浆锆石206Pb/238U 年龄平均值为(419.9±2.0) Ma,红旗沟中部的粗中粒二长花岗岩(B25-9)岩浆锆石206Pb/238U年龄平均值为(419.0±2.0) Ma。它们代表了五龙沟地区所研究花岗岩的形成年龄,其形成时代均为晚志留世,记录了东昆仑早古生代的岩浆活动。本文获得的东昆仑五龙沟地区的晚志留世花岗岩可能与东昆仑早古生代洋盆闭合后的碰撞造山作用有关。花岗岩中1861 Ma、1666 Ma古元古代继承锆石的发现,表明东昆仑造山带的基底物质为古元古代。     

湘西南猫儿界花岗斑岩锆石U-Pb年代学、地球化学特征及其地质意义

文章对苗儿山—越城岭地区西北侧猫儿界花岗斑岩开展了锆石U-Pb年代学、岩石地球化学和Nd同位素研究,探究了岩体的形成时代、成因类型及源区性质.三件花岗斑岩样品LA-ICP-MS锆石U-Pb定年给出的206Pb/238U加权年龄分别为824.3±4.5 Ma、825.4±4.1 Ma和826.8±4.8 Ma,表明猫儿界...