Zircon U-Pb geochronology of basement metamorphic rocks in the Songliao Basin

Zircon LA-ICP MS U-Pb dating of six metamorphic rocks and a metagranite (breccia) from southern basement of the Songliao Basin are reported in order to constrain the formation ages of basement. The basement metamorphic rocks in the Songliao Basin mainly consist of metagabbro (L45-1), amphibolite (SN117), metarhyolitical tuff (G190), sericite (Ser) schist (N103), chlorite (Chl) schist (T5-1), biotite (Bi)-actinolite (Act)-quartz (Q) schist (Y205), and metagranite (L44-1). The cathodoluminesence (CL) images of the zircons from metagabbro (L45-1) and metagranite (L44-1) indicate that they have cores of magmatic origin and rims of metamorphic overgrowths. Their U-Pb isotopic ages are 1808±21 Ma and 1873±13 Ma, respectively. The zircons with oscillatory zoning from amphibolite (SN117) and Chl schist (T5-1), being similar to those of mafic igneous rocks, yield ages of 274 ± 3.4 Ma and 264 ± 3.2 Ma, re-spectively. The zircons from metarhyolitical tuff (G190) and Ser schist (N103) display typical magmatic growth zoning and yield ages of 424 ± 4.5 Ma and 287 ± 5.1Ma, respectively. Most of zircons from Bi-Act-Q schist (Y205) are round in shape and different in absorption degree in the CL images, implying their sedimentary detritals. U-Pb dating yield concordant ages of 427 ± 3.1Ma, 455 ± 12 Ma, 696 ± 13 Ma, 1384±62 Ma, 1649±36 Ma, 1778±18 Ma, 2450±9 Ma, 2579±10 Ma, 2793±4 Ma and 2953±14 Ma. The above-mentioned results indicate that the Precambrian crystalline basement (1808―1873 Ma) exists in the southern Songliao Basin and could be related to tectonic thrust, and that the Early Paleozoic (424―490 Ma) and Late Paleozoic magmatisms (264―292 Ma) also occur in the basin basement, which are consistent with the ages of the detrital zircons from Bi-Act-Q schist in the basement.     

Zircon U-Pb geochronology of the volcanic rocks from Fanchang-Ningwu volcanic basins in the Lower Yangtze region and its geological implications

The latest eruptions in two important Mesozoic volcanic basins of Fanchang and Ningwu located in the middle-lower reaches of the Yangtze River formed the bimodal volcanic rocks of the Kedoushan Formation and ultrapotassic volcanic rocks of the Niangniangshan Formation, respectively. The representative volcanic rocks of the two Formations were selected for LA-ICPMS zircon U-Pb dating. The results indicate that there exist a large amount of magmatic zircons as indicated by high Th/U ratios in these volcanic rocks. The weighted mean age of 21 analyses is 130.7±1.1 Ma for the Kedoushan Formation, and that of 20 analyses is 130.6±1.1 Ma for the Niangniangshan Formation. These U-Pb ages are interpreted to represent the formation times of the volcanic rocks. In combination with other known geochronological data for Mesozoic volcanic rocks from the Lower Yangtze region, it is proposed that the latest volcanic activations in the Jinniu, Luzong, Fanchang and Ningwu volcanic basins probably came to end prior to ca. 128 Ma. There is no significant time interval between the early and later volcanic activities in the Luzong and Ningwu basins, suggesting a short duration of volcanic activities and thus implying the onset of an extensional tectonic setting at about 130 Ma in the Lower Yangtze region. Integrated studies reveal that the Early Cretaceous magmatic activities and their geochronological framework in the Lower Yangtze region are a response to progressively dynamic deep processes that started with the transformation of tectonic setting from compression to extension, followed by delaminating of the lower part of the thickened lithosphere, lithospheric thinning, asthenosphere upwelling, and crust-mantle interaction.     

准噶尔盆地西北缘和布克赛尔玄武岩锆石U-Pb年龄及其地质意义

目的确定准噶尔盆地西北缘和布克赛尔玄武岩的形成时代,并探讨其地质意义。方法在锆石阴极发光内部结构研究的基础上,进行LA-ICP-MS锆石U-Pb测年。结果玄武岩形成时限在291～310 Ma。结论玄武岩喷发形成时代不是晚奥陶世,而更可能是在早二叠世。其中,最老的继承性单颗粒碎屑锆石谐和年龄为(2 395±27)Ma,推测该区应存在前寒武纪古老地块。因此,准噶尔盆地西北缘由两条蛇绿岩、蛇绿混杂岩带围限的区带,应是由蛇绿岩、蛇绿混杂岩地体、岛弧岩浆杂岩和微古陆块共同组成的古生代增生带。     

准噶尔盆地中部钻井岩心凝灰质砂岩锆石U-Pb年龄及其地质意义

对准噶尔盆地中央凹陷内部钻井岩心凝灰质细砂岩样品进行岩石学及LA-ICP-MS锆石U-Pb测年,探讨研究区的地层沉积时代及基底构造属性。结果表明:(1)碎屑锆石的年龄分布范围为(270±2)Ma~(568±3)Ma,具有多峰的分布特征,表明其碎屑物质来源较为复杂。岩浆锆石样品最小年龄为270 Ma,代表该样品的沉积时代为中二叠世。(2)研究还获得(568±3)Ma新元古代和(1 790±14)Ma的古元古代锆石年龄,这可为准噶尔盆地存在前寒武纪古老结晶基底提供依据。同时研究还获得晚古生代363~401Ma,300~358 Ma,270~299 Ma的年龄纪录,反映准噶尔盆地基底经历了多阶段复杂陆壳演化过程。     

Zircon U-Pb ages of the basement rocks beneath the Songliao Basin, NE China

The basement of the Songliao Basin is mainly composed of slightly-metamorphosed or unmetamorphosed Paleozoic strata, granites and gneiss. Petrographical studies indicate that the gneiss was originally the granitic intrusions which were deformed in the later stage. One undeformed granitic rock sample gives a U-Pb age of (305±2) Ma, and the mylonitic granite yields a U-Pb age of (165±3) Ma. Both of the two samples contain no inherited zircon, which suggests that there is no large-scale Precambrian crystalline basement beneath the Songliao Basin.     

Hf isotopes of zircon megacrysts from the Cenozoic basalts in eastern China

Cenozoic basalts are widely distributed in eastern China, and some of them contain zircon megacrysts which are considered to be constituent mineral of the subcontinental lithospheric mantle （SCLM） and petrogenetically related to mantle metasomatism induced by addition of crustal materials. Using the Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry （LA-MC-ICPMS）, zircon megacrysts from the Cenozoic basalts at Changle in Shandong, Mingxi in Fujian, and Penglai in Hainan provinces have been used for Hf isotopic analyses. The data indicate that there is no significant deviation for the different zircon grains in each locale, except those from Penglai. The obtained ^176Hf /^177Hf ratios are 0.28302- 0.28308 for Changle, 0.28297-0.28300 for Mingxi, and 0.28288-0.28293 for Penglai, with corresponding ear values of 8.7-10.8, 7.0-7.9, and 3.9-5.7, respectively. These data display that there existed some regional heterogeneity, but the Hf model ages clustere in the Phanerozoic. Therefore, it is inferred that metasomatism of the lithospheric mantle beneath eastern China took place in the Phanerozoic, most probably in the Mesozoic-Cenozoic. However, the formation time of the iithospheric mantle is not clearly constrained based on the present Hf isotopic data.     

巢湖地区侵入岩锆石定年

安徽巢北地区坐落着一个"M"型的山脉,近年来对该地区的构造、地层和古生物化石已有很多的研究积累,但对于岩浆岩,由于分布和发育有限而研究程度较低。文章应用LA-ICP-MS锆石微区分析技术对该地区出露的岩体进行了精确定年。结果显示,岩体中含大量岩浆成因锆石,以高的w(Th)/w(U)比和振荡结晶环带为特征。样品中16个测点的n(206Pb)/n(238 U)加权平均年龄为(100.8±1.3)Ma,代表该岩体的形成年龄。巢北地区位于下扬子北缘,近年来关于下扬子地区中生代岩浆岩研究的年龄数据尚无小于100 Ma的报道,而在本区西侧紧邻的郯庐断裂带南缘上,其岩浆岩的形成时代介于132~103 Ma之间。因此,巢北地区侵入岩在时代和成因上,和郯庐断裂带的联系更加密切。     

新疆西准噶尔萨尔托海地区英安岩锆石U-Pb年龄及其对达拉布特蛇绿岩侵位时限的约束

新疆西准噶尔达拉布特蛇绿岩在其北东段萨尔托海地区被下石炭统火山岩-沉积岩不整合覆盖。对这套沉积-火山岩系中的英安岩进行 LA-ICP-MS 锆石 U-Pb 定年, 获得 ²⁰⁶Pb/²³⁸U 加权平均年龄为 349±2 Ma(早石炭世杜内期)。英安岩REE 分配型式具有轻稀土富集、重稀土相对平坦、Eu 负异常明显的特点。微量元素原始地幔标准化图解中, 所有样品的标准化丰度都随着元素不相容性的增加而增大。与经典的弧英安岩以及埃达克火山岩相比, 太勒古拉组英安岩 Sr 含量平均值为 195 μg/g, Sr/Y 平均值为 5.2, La/Yb 平均值为4.6, 远小于经典的弧英安岩和埃达克岩。结合太勒古拉组变形、变质微弱的特点, 认为早石炭世英安岩形成于板内裂谷环境, 且在早石炭世之前达拉布特蛇绿岩已经就位。     

Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China

Continental volcanic rocks and volcaniclastic sedi-mentary conglomerates of the Cangshuipu Formation oc- cur as wedge-shaped Neoproterozoic strata in the Yiyang region, Hunan Province. They overlie with a high-angle unconformity the Lengjiaxi Group of the Upper Meso- proterozoic Eonothem. The wedge-shaped Neoproterozoic strata of the continental clastic rocks and the Mesopro-terozoic deep marine flysch turbidites of the Lengjiaxi Group represent two distinct stages of basin-tectonic evo-…     

准噶尔南缘糜棱岩锆石定年及其地质意义

目的确定准噶尔盆地南缘糜棱岩的侵位时代。方法在锆石阴极荧光内部结构研究的基础上,进行LA-ICP-MS锆石原位U-Pb定年。结果测年结果显示花岗岩侵位年龄可分为两组：418—460Ma和914—979Ma。结论准噶尔盆地南缘至少发生过二期主构造热事件：早古生代加里东期和元古宙吕梁运动期。     

Petrogenesis of keratophyes in the Pingshui Group, Zhejiang: Constraints from zircon U-Pb ages and Hf isotopes

Zircon LA-ICP-MS U-Pb ages and Hf isotopic as well as whole-rock geochemical data are reported for keratophyes in the Pingshui Group, Zhejiang. The results are used to discuss their petrogenesis and geological significance. The keratophyes were dated at 904±8 to 906±10 Ma. These intermediate-felsic rocks are characterized by high LREE contents and depletion of HREE and HFSE (e.g., Nb, Ta, Ti, P), resembling arc-derived rocks. The keratophyes exhibit positive εHf(t) values of 8.6 to 15.4, consistent with the...     

东秦岭沙河湾岩体成因——来自锆石U-Pb定年及其Hf同位素的证据

目的 确定东秦岭沙河湾花岗岩体形成时代、源区性质及其成因.方法 在锆石内部结构的CL图像研究基础上,用LA-ICFMS和MC-ICPMS测定锆石U-Pb年龄及Hf同位素组成,探讨寄主花岗岩、暗色闪长质包体及及围岩中闪长质脉体锆石U-Pb年代学及Hf同位素组成特征.结果 寄主花岗岩、暗色包体及其围岩中闪长质脉体分别存在210 Ma和197 Ma,197 Ma和188 Ma以及230M a和210 Ma两组年龄的锆石;对应的εHf(t)值在一个略微偏正或负的范围内变化,指示该岩体非单一源区岩浆物质所能形成,至少是两个源区岩浆混合作用的结果.结论 该岩体是以新元古带古老地壳物质熔融为主体的壳源岩浆与源自略富集地幔的幔源岩浆高度混合的产物.这一壳、幔岩浆混合作用首先以230Ma的幔源岩浆活动为标志,并可能在210 Ma前就由于幔源岩浆活动热源的持续积累而诱发了该区地壳物质的部分熔融,形成以壳源岩浆为主的岩浆房.此后.约在200 Ma深部幔源基性岩浆进入壳源酸性岩浆房发生岩浆混合,并一直持续到185 Ma左右,证明了秦岭中生代壳、幔岩浆混合作用持续了大约60 Ma.     

Age and genesis of the Myanmar jadeite: Constraints from U-Pb ages and Hf isotopes of zircon inclusions

Myanmar jadeite (jadeitite) is well known for its economical value and distinctive tectonic locality within the collisional belt between India and Eurasian plates. However, it is less studied for its genesis and geodynamic implications due to precipitous topography, adverse weather and local military conflicts in the area. By means of combined ICP-MS and LA-MC-ICPMS techniques, we have carried out in-situ trace elements, U-Pb and Lu-Hf isotopes for zircon inclusions in a piece of jadeite gem sample. CL imaging suggests that the zircons are metasomatic in origin, and contain mineral inclusions of jadeite and omphacite. Seventy-five analyses on 16 grains of the zircons yield a U-Pb age of 158 ± 2 Ma. The Myanmar zircons differ from other types in that they have no significant Eu anomalies despite high HREE concentrations. Measured ¹⁷⁶Hf/¹⁷⁷Hf ratios range from 0.282976 to 0.283122, with an average value of 0.283066 ± 7; ε_Hf(t) value of 13.8 ± 0.3 (n=75). These results indicate that the Myanmar jadeite was formed in the Late Jurassic, probably by interaction of fluid released from subducted oceanic slab with mantle wedge. Therefore, its formation has no genetic relationship to the continental collision between Indian and Euroasian plates. Supported by National Natural Science Foundation of China (Grant No. 40673039) and the Science Plan Foundation of Guangdong (Grant No. 2007B031200005)     

新疆东准噶尔铜华岭中酸性侵入体锆石U-Pb年代学研究

伊吾县铜华岭中酸性侵入体位于新疆北部东准噶尔阿尔曼太断裂和克拉麦里断裂之间的野马泉岛弧区, 岩性主要为闪长玢岩、英云闪长岩和二长花岗岩等。通过锆石LA-ICP-MS U-Pb年代学方法, 对这3种岩性进行精确定年, 其²⁰⁶Pb/₂₃₈U的加权平均年龄分别为427.4±3.2,422.8±3.2和418.5±2.6Ma,说明铜华岭岩体是早古生代岩浆活动的产物, 为东准噶尔早古生代造山带演化提供了花岗岩证据。     

准噶尔盆地东道海子凹陷平地泉组烃源岩地球化学特征

对准噶尔盆地腹部东道海子凹陷二叠系平地泉组烃源岩地球化学特征进行评价,通过对烃源岩有机质丰度、类型与成熟度及烃源岩厚度特征分析表明,平地泉组发育湖相泥岩,在凹陷内分布广泛、厚度大,为东道海子凹陷的主力烃源岩;凹陷东北部滴南地区平地泉组烃源岩为中等-好的烃源岩,有机质类型为Ⅱ2型-Ⅲ型,热演化达到成熟-生油高峰阶段;平地泉组门限深度为2 350m,生油高峰深度为2 900m左右。结合邻区资料,认为东道海子凹陷主体平地泉组烃源岩有机质丰度高、类型较好,达到生油高峰-高成熟阶段,具有较高的资源潜力。     

准噶尔盆地车排子凸起新近系沙湾组重矿物、U-Pb年代学特征及物源分析

综合岩石学特征、砂岩碎屑组分特征、重矿物组合特征和锆石U-Pb年代学特征, 探讨准噶尔盆地车排子凸起新近系沙湾组沙一段的沉积特征和物源演化过程。结果表明, 车排子凸起存在南北双物源体系, 沙一段以粗碎屑沉积为主。在一砂组沉积阶段, 扎依尔山为北部物源区, 发育小规模扇三角洲沉积; 中天山及北天山造山带为南部物源区, 发育辫状河三角洲沉积。在二砂组沉积阶段, 中天山供给减弱, 北天山供给加强, 盆地水体加深, 南部辫状河三角洲前端分布小型滨浅湖滩坝。南部物源变化的主要原因可能是受印度板块和欧亚板块碰撞的远程影响, 天山在新生代中新世中期经历强烈的挤压和抬升过程, 造成北天山隆升, 为车排子凸起提供物源。     

Zircon SHRIMP U-Pb dating of meta-diorite from the basement of the Songliao Basin and its geological significance

Located in the east portion of the North Orogenic Belt, the Songliao Basin is bounded by the Da Hinggan Mountains in the west, the Xiao Hinggan Mountains in the north, the Zhangguangcai Range in the east, and the North China Craton (NCC) in the south (Fig…     

水汶盆地碎斑熔岩LA-ICP-MS锆石U-Pb年龄及地球化学特征

广西水汶火山盆地西垌组四段碎斑熔岩锆石LA-ICP-MS U-Pb测年结果显示其形成年龄为(83.4±0.9)Ma,属晚白垩世火山-岩浆活动的产物.碎斑熔岩富SiO2(73.57％～ 74.29％),富K2O(4.91％～ 5.61％),低P2O5 (0.03％～0.04％),准铝-弱过铝质(A/NKC为0.99 ～ 1.03),富集Rb,Th以及La,Ce,Nd等轻稀土元素,亏损Ba,Nb,Ta,Sr,P,Ti,Rb/Sr比值高(1.16～ 1.73),Y和Th含量与Rb含量之间具有正的相关性,过碱指数(AI值),Zr+Nb+Ce+Y值、FeO*/MgO值、10000×Ga/A1值均小于典型的A型花岗岩,与高分异Ⅰ型花岗岩地球化学特征十分相似,应该是太平洋板块俯冲作用背景下,形成于弧后拉张构造环境的高分异Ⅰ型碎斑熔岩.     

火山岩油气藏地球物理预测技术及准噶尔勘探实例

火山岩储层识别和预测中最常用和有效的地震技术是正演模拟技术、地震属性分析技术、波阻抗反演技术和相干分析技术,并有各自的适用条件。对准噶尔盆地3个研究区的火山岩地震反射特征进行研究,建立准噶尔盆地4种火山岩地震相模式。通过准噶尔盆地火山岩油气藏的勘探实践,认为火山岩储层综合预测应该包含岩相预测、岩性预测、裂缝预测3个方面。     

准噶尔盆地石炭系烃源岩地球化学特征研究

系统分析了准噶尔盆地石炭系烃源岩有机质丰度、有机质类型及成熟度等特征,应用综合地球化学指标对有机质类型进行判定.石炭系烃源岩有机质丰度高,上统好于下统.其有机质类型表现为下统好于上统,下统以混合偏腐泥型为主,上统以混合型偏腐殖型为主,煤系以腐殖型为主.下统烃源岩几乎都在成熟—过成熟范围内,利于生成成熟油气和凝析油,上统利于生气.并通过纵向上各主要烃源岩层对比,总结出重碳同位素、饱和烃色谱不含β胡萝卜烷、规则甾烷以C27呈显著优势的"V"型分布是石炭系烃源岩的几个标志性地球化学特征.