闽西南玮埔岩体和赣南菖蒲混合岩锆石La—ICPMSU-Pb年代学：对武夷山加里东运动时代的制约

闽西玮埔岩体和赣南菖蒲混合岩位于武夷山构造带南部地区.对NNE向展布的闽西玮埔岩体两个样品进行了锫石La-ICPMS U-Pb测年,获得的年龄为447.1±4.7Ma·和440.8±3.4Ma,证明这个岩体不是原来认为的印支期花岗岩,而属于加里东岩体.赣南菖蒲混合岩发育于罗浮岩体的北侧,早期将罗浮岩体归于燕山早期岩体.对混合岩进行的锫石La-ICPMS U-Pb测年,获得的年龄为445.9±3.8Ma,确定这个岩体为加里东期.这些新的高精度年龄学数据为武夷山加里东构造运动时限和性质提供了精确约束.     

闽西南清流地区加里东期花岗岩锆石U-Pb年代学及Hf同位素组成研究

通过对玮埔岩体两个代表性样品进行锆石的LA-ICP-MSU-Pb测年获得的206Pb/238U加权平均年龄分别为(429.9±3.0)Ma、(446.3±4.0)Ma,证明该岩体确实不是最早认为的印支期花岗岩,而是加里东期岩体。同时对宁化岩体一个样品的锆石LA-ICP-MSU-Pb测年结果得到206Pb/238U加权平均年龄为(448.2±2.5)Ma,同样属于加里东期岩体。进一步对闽西南清流地区玮埔和宁化岩体的锆石Lu-Hf同位素组成分析表明,εHf(t)值主要集中在-0.8～-10.4之间,且Hf二阶段模式年龄(TDM2)集中在1.72～2.34Ga之间,表明其岩浆源区来自华夏地块元古代地壳物质。并结合其他己发表的相关年代学和地球化学资料,可以推断包括玮埔和宁化岩体在内的华南内陆地区加里东期花岗岩很可能是元古宙基底深熔而成的产物;其形成与陆内地壳物质叠置加厚所引起的再造作用关系紧密。     

赣南印支期清溪岩体的锆石U-Pb年代学研究及其含矿性评价

清溪岩体是赣南地区缺少精确年龄数据的含稀土岩体之一。对赣南清溪岩体中的锆石样品进行了U-Pb法年代学研究,测年结果显示该岩体主体年龄为229.3±0.8Ma和227.0±1.0Ma,属于印支期产物,并不是前人认为的属于加里东期。对清溪岩体进行了岩石学、地球化学的研究,简要论述了其含矿性,认为清溪岩体主体为黑云母花岗岩,为过铝质钾玄岩系,轻稀土和重稀土中等分馏,负Eu异常不明显。岩石化学资料数据显示,该岩体稀土总量较高,具备成矿母岩的基本条件。     

赣南岐山岩体深熔-幕式岩浆活动:来自锆石U Pb精细年代学研究

武夷山地区加里东期深熔混合岩化-岩浆作用普遍,且两者时代一致或相近,但是加里东期深熔作用的启动时间尚不明确。赣南寻乌县岐山岩体位于武夷山构造带南部,该岩体形成时代缺乏精确的年代学依据。基于锆石LA-ICP-MS U-Pb测年手段,在该岩体中发现两期锆石,早期锆石为深熔成因,晚期为岩浆成因。本次研究获得的晚期锆石形成时代为445~440Ma,具有从外向内年龄渐新的规律,表明该岩体形成于晚奥陶世晚期-早志留世,可能是从源区上升的不同批次岩浆就位的结果,即该岩体为加里东期深熔-幕式、多期次岩浆活动的结果。边缘部位与岩体中心部位分别获得早期深熔锆石加权平均年龄值(458±4Ma)与岩浆锆石加权平均年龄值(460±4Ma),两者在误差范围内一致。表明武夷山地区在加里东早期,大约460Ma左右发生了一期深熔-岩浆活动,为武夷山构造带加里东运动深熔作用的启动时代提供了制约。     

武夷地块北东部迪口地区下元岩体和红叶岗岩体锆石La-ICP-MS U-Pb年龄及其地质意义

迪口地区的下元岩体和红叶岗岩体位于武夷山地区东、西武夷俯冲碰撞增生杂岩带(450～440 Ma)中。我们对下元岩体中的三个岩石样品进行了锆石La-ICP-MS U-Pb测年,获得岩体的侵位结晶年龄分别为420±4 Ma、430±4 Ma和434±4 Ma,证明该岩体为加里东岩体,而非早期认为的印支期花岗岩。红叶岗岩体进行La-ICP-MS锆石U-Pb测年获得的年龄为398±4 Ma,表明红叶岗岩体为加里东晚期岩体,而非前人认为的燕山期花岗岩。结合武夷山地区最新的研究成果分析,我们认为迪口地区下元岩体和红叶岗岩体可能形成于东、西武夷地块碰撞后拉张裂解环境。迪口地区下元岩体和红叶岗岩体的侵位时代为武夷地块加里东期的构造演化提供了更进一步的时代约束。     

江西信丰安西岩体同位素年龄及其地质意义

前人多将信丰县安西岩体划归燕山早期,“九五”期间笔者从事1∶5万安西镇幅区调工作 ,获得岩浆结晶锆石U -Pb同位素年龄423.4±4.9Ma、416.9±9.9Ma,以及残留的继承性锆石的U -Pb同位素年龄1545±214Ma、2021±182Ma等 ,为安西岩体的侵位、赣南加里东运动以及华南古老基底岩系的存在等提供了新的年龄资料。     

湖南九嶷山复式花岗岩体SHRIMP锆石定年及其地质意义

应用SHRIMP锆石U-Pb法获得九嶷山复式花岗岩中的主要岩体形成年龄为:雪花顶花岗岩(432±21)Ma、金鸡岭花岗岩(156±2)Ma、砂子岭花岗岩(157±1)Ma和西山火山-侵入杂岩(156±2)Ma。结果显示砂子岭岩体属燕山早期而非印支期;西山火山-侵入杂岩属燕山早期而非燕山晚期。花岗岩中继承锆石复杂,其形成时代为1579Ma、2108Ma和2669Ma,提供了九嶷山地区存在古-中元古代,甚至太古代基底的年龄信息。新元古代(912Ma)锆石的大量出现为扬子陆块和华夏陆块碰撞带通过本区的认识提供了一个间接证据。     

赣南燕山期水头岩体的锆石铀-铅年代学研究及其含矿性评价

水头岩体是目前赣南地区缺少精确年龄数据的复式岩体之一。对赣南水头岩体中的锆石样品进行了U-Pb法年代学研究,测年结果显示该岩体主体年龄为(142.7±0.6)Ma,属于燕山期的产物,并不是前人认为的加里东期。但也存在前期(海西期和加里东期)的同位素年龄信息记录,说明该岩体是复式岩体,存在至少三期岩浆活动。对水头岩体进行了岩石学、地球化学研究,简要论述了岩石成因及含矿性。水头岩体主体为黑云母花岗岩,为过铝质钾玄岩系,轻稀土和重稀土中等分馏,负Eu异常明显。初步认为水头岩体是原地重熔交代作用形成的复式岩体。岩石化学资料数据显示,该岩体具备稀土成矿母岩的基本条件。     

青海西部祁漫塔格山卡尔却卡铜多金属矿床似斑状 黑云二长花岗岩LA-ICP-MS锆石U-Pb年龄

祁漫塔格卡尔却卡铜多金属矿体主要产于花岗闪长岩、似斑状黑云母二长花岗岩体与寒武纪—奥陶纪滩间山群接触部位的矽卡岩带和二长花岗岩中。本次对矿区Ⅶ号带矽卡岩与矿体紧邻的似斑状黑云母二长花岗岩体进行LA-ICP-MS锆石U-Pb测年,获得年龄为410.1Ma±2.6Ma。结合前人获得的花岗闪长岩SHRIMP锆石U-Pb年龄（237 Ma±2Ma）和矿石矿物辉钼矿Re-Os模式年龄（239Ma）,认为岩体成岩和成矿时代都发生在印支期,卡而却卡铜多金属矿成矿作用不仅与印支期中酸性侵入岩有关,也与加里东晚期酸性侵入岩有关。祁漫塔格地区矿床形成时代主要集中于加里东中晚期和印支晚期,尽管加里东期岩体在地表出露规模远没有印支期岩体规模宏大,但是加里东晚期岩体对成矿作用的贡献也应该引起足够的重视。     

粤西罗定—信宜地区花岗岩的同位素地质年龄

在粤西桂东云开大山一带锆石铀铅测定表明,大脑顶花岗岩体形成于下古生代(460±9.6Ma);荔枝垌混合花岗岩具有明显的混合花岗岩锆石点群分布的特点,所有锆石点均集中在不一致线的下端。与一致曲线的下交点为316±8 Ma,为混合花岗岩中新生锆石的结晶年龄。混合岩化作用发生在加里东晚期的可能性最大,甚至可延至海西早期。同岩体中单矿物K-Ar测定值一般都较岩体的形成时代新,分别为184及215Ma。铷-缌全岩等时线法对本区的混合岩、混合花岗岩及变质岩的定年均不适用。     

U–Pb dating of detrital zircons for sediment provenance studies—a comparison of laser ablation ICPMS and SIMS techniques

New developments in U–Pb dating of zircons by laser ablation (LA) ICPMS are described and, for the first time, a direct comparison of detrital zircons dated by LA ICPMS and SIMS methods is presented. True real-time mass bias correction is made by aspirating a Tl/U tracer at the same time as laser ablation. The method is similar to that described in Horn et al. (2000), except that enriched ²³³U rather than ²³⁵U is used in the tracer solution. Correction for laser-induced Pb/U elemental fractionation is based on a mathematical treatment of time-resolved data that is independent of laser ablation characteristics and does not require external standardisation. Internal corrections for mass bias and elemental fractionation eliminate the effects of variable sample matrix on isotopic ratios and improve the accuracy of U–Pb dating by laser ablation ICPMS. With the proper error propagation, the precision of U–Pb age determinations is only slightly worse than SIMS-based ion probe dating. However, LA ICPMS is capable of much more rapid analysis of the large number of zircons required for sediment provenance studies. There is excellent agreement between concordant laser ablation ICPMS and SIMS analyses of detrital zircons extracted from lower Silurian metasandstone from the Ulven Group (Skarfjell Formation) in the west Norwegian Caledonian nappes. Both LA ICPMS and SIMS U–Pb zircon ages indicate that sedimentary detritus of the Ulven Group was supplied from a terrain containing zircons of Archean, Proterozoic and early Ordovician age.     

吉林中部伊通地区放牛沟火山岩的形成时代及其地质意义

对伊通地区的放牛沟火山岩,以及后期侵入该火山岩的后庙岭花岗质侵入体进行了LA-ICP-MS锆石U-Pb年代学研究。3个样品中的锆石均呈自形-半自形晶,CL图像显示出明显的岩浆振荡生长环带,结合大多数锆石具有较高的Th/U比值(0.23~3.55),暗示了它们的岩浆成因。放牛沟火山岩由变玄武安山岩和变安山岩组成,其中变安山岩样品中锆石22个测点的~(206)Pb/~(238)U年龄加权平均值分为3组:420±4 Ma,402±3 Ma及280±1 Ma,其中280±1 Ma代表了安山岩的形成年龄;变玄武安山岩样品中锆石30个测点的~(206)Pb/~(238)U年龄加权平均值分为两组:401±1 Ma及279±1 Ma,后者代表了玄武安山岩的形成年龄;后庙岭花岗质侵入体中锆石18个测点的~(206)Pb/~(238)U年龄加权平均值为256±2 Ma。上述锆石U-Pb定年结果表明,放牛沟火山岩形成于早二叠世,而非前人认为的早古生代。对后庙岭侵入体的定年结果,进一步暗示放牛沟多金属硫铁矿床的成矿时代为二叠纪。     

Zircon Trace Element Constraints on U-Pb Dating: A Case Study of the Huayuangong A-type Granite in the Lower Yangtze Region,Eastern China

For magmatic rocks, it is often found that zircon 206 Pb/238 U and 207 Pb/235 U ratios continuously plot on the concordia line with a relatively large age span for the same sample, which gives rise to large dating errors or even unrealistic dating results. As the trace element concentrations of zircon can reflect its equilibrated magma characteristics, they can be used to determine whether all the analytical spots on the zircons selected to calculate the weighted mean age are cogenetic and formed in a single magma chamber. This work utilizes the results of zircon trace element concentrations and U-Pb isotopic analyses to explore the screening of reasonable U-Pb ages, which can be used to determine a more accurate intrusion crystallization age. The late Mesozoic Huayuangong granitic pluton complex, which is located in the Lower Yangtze region, eastern China, was selected for a case study. The Huayuangong pluton comprises the central intrusion and the marginal intrusion. Two samples from the marginal intrusion yielded consistent zircon weighted mean 206 Pb/238 U ages of 124.6 ± 2.0 Ma and 125.9 ± 1.6 Ma. These analytical spots also exhibit Zr/Hf and Th/U ratios concordant with the evolution of a single magma, from which the dated zircons crystallized. However, for the central intrusion, the analytical spots on zircons from two samples all show a continuous distribution on the concordia line with a relatively large age span. For each sample from the central intrusion, the zircon Zr/Hf ratios do not conform to a single magma evolutionary trend, but rather can be divided into two groups. We propose that zircon Zr/Hf ratios can provide a new constraint on U-Pb zircon dating and zircon Th/U ratios can also be used as a supplementary indicator to constrain zircon dating and determine the origins of the zircons and whether magma mixing has occurred. By screening zircon analytical spots using these two indicators, the two samples from the central intrusion of the Huayuangong pluton produce results of 122.8 ± 4.3 Ma and 122.9 ± 2.2 Ma, which are consistent with the field observations that the central intrusion is slightly younger than the marginal intrusion.     

Late Jurassic–Early Cretaceous Plutonism in the Northern Part of the Precambrian North China Craton: SHRIMP Zircon U–Pb Dating of Diorites and Granites from the Yunmengshan Geopark, Beijing

The Yunmengshan Geopark in northern Beijing is located within the Yanshan range. It contains the Yunmengshan batholith, which is dominated by two plutons: the Yunmengshan gneissic granite and the Shicheng gneissic diorite. Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U–Pb ages from 145 to 141 Ma, whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma. Dikes that cut the Yunmengshan diorite record SHRIMP zircon U–Pb age of 162±2 and 156±4 Ma. The cumulative plots of zircons from the diorites show a peak age of 155 Ma, without inherited zircon cores, and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton, whose igneous zircons contain inherited zircon cores. The data presented here show that there were two pulses of magmatism: early diorites, followed c13 Ma later by true granites, which incorporated material from an older continental crust.     

新疆西准噶尔克拉玛依岩体中暗色岩墙的形成时代及地质意义 ——来自锆石LA-ICP-MS和角闪石Ar-Ar定年的证据

新疆西准噶尔克拉玛依岩体以及周围地层中存在着大量暗色闪长玢岩岩墙,是岩浆物质贯入3组走向不同的裂隙形成的。对其中一个闪长玢岩岩墙样品进行锆石LA-ICP-MS年代学测试,得到303.1±1.2Ma的锆石²⁰⁶Pb/²³⁸U加权平均年龄,对从该闪长玢岩中分离出的角闪石进行Ar-Ar年代学测试,得到312.1±2.8Ma的坪年龄(1120～1400℃)和313.6±6.9Ma的反等时线年龄。对该闪长玢岩岩墙附近的含角闪石黑云母二长花岗岩进行的锆石LA-ICP-MS年代学测试,获得其²⁰⁶Pb/²³⁸U加权平均年龄为319.0±1.0Ma。对侵入石炭纪地层的一个花岗斑岩岩脉样品进行锆石LA-ICP-MS年代学测试,得到了315.3±1.0Ma的²⁰⁶Pb/²³⁸U加权平均年龄。上述年代学测试结果表明克拉玛依市以西地区的暗色岩墙形成时代是石炭纪末期,不是前人所说的二叠纪。在这些岩墙形成之前,该区在石炭纪晚期还发育以克拉玛依岩体及附近酸性岩脉为代表的花岗质岩浆活动。上述围岩和岩墙的年代学资料揭示出该区闪长玢岩岩墙所占据的裂隙形成时代在315～303Ma之间,为新疆西准噶尔地区晚古生代地球动力学背景及岩浆活动的深入研究,提供了时间方面的约束。     

西昆仑慕士塔格岩体的LA ICP MS锆石U Pb定年:对古特提斯碰撞时限的制约

慕士塔格岩体是西昆仑造山带出露面积最大的侵入体,主要由黑云母二长花岗岩、似斑状黑云母二长花岗岩和花岗闪长岩组成,其中发育大量的暗色微细粒包体和基性岩浆条带。根据锆石的阴极发光图像以及Th、U、REE元素等特征,所测试的锆石均为典型的岩浆结晶锆石,利用LA-ICP-MS锆石U-Pb定年,测得岩体东西部分的加权平均206Pb/238U年龄分别为229.6±0.8Ma(MSWD=0.44)、232.8±1.5Ma(MSWD=0.21),两者在误差范围内一致,综合获得该岩体年龄为231.4±0.7Ma(MSWD=1.5),属于中三叠世晚期。根据岩石学、锆石内部结构及其REE元素特征,结合前人地球化学资料,该岩体应为壳幔岩浆混合成因。结合区域地质资料,慕士塔格岩体应是从挤压的主碰撞期向伸展后碰撞期转换的产物,表明古特提斯主碰撞作用发生在中三叠世晚期之前,之后开始进入古特提斯后碰撞阶段。     

The Southward Extension of Cathaysia Block: Evidence from Zircon UPb Dates of Borehole Volcanics in the Northern South China Sea

Five Paleogene volcanics sampled from the northern South China Sea were analyzed via LA-ICP-MS zircon U-Pb dating,including basalt and andesite from Borehole SCSV1 and volcanic agglomerate from Borehole SCSV2,respectively.A total of 162 zircon U-Pb dates for them cover an age range from Neoarchean to Eocene,in which the pre-Paleocene data dominate.The Paleogene dates of 62.5±2.2 Ma and 42.1±2.9 Ma are associated with two igneous episodes prior to opening of South China Sea basin.Those pre-Paleocene zircons are inherited zircons mostly with magmatogenic oscillatory zones,and have REE features of crustal zircon.Zircon U-Pb dates of 2518–2481 Ma,1933– 1724 Ma,and 1094–1040 Ma from the SCSV1 volcanics,and 2810–2718 Ma,2458–2421 Ma,and 1850 –993.4 Ma from the SCSV2 volcanics reveal part of Precambrian evolution of the northern South China Sea,well comparable with age records dated from the Cathaysia block.The data of 927.0±6.9 Ma and 781±38 Ma dated from the SCSV2 coincide with amalgamation between Yangtze and Cathaysia blocks and breakup of the Rodinia,respectively.The age records of Caledonian orogeny from the Cathaysia block are widely found from our volcanic samples with concordant mean ages of 432.0±5.8 Ma from the SCSV1 and of 437±15 Ma from the SCSV2.The part of the northern South China Sea resembling the Cathaysia underwent Indosinian and Yanshannian tectonothermal events.Their age signatures from the SCSV1 cover 266.5±3.5 Ma,241.1±6.0 Ma,184.0±4.2 Ma,160.9±4.2 Ma and 102.8±2.6 Ma,and from the SCSV2 are 244±15 Ma,158.1±3.5 Ma,141±13 Ma and 96.3±2.1 Ma.Our pre-Paleogene U-Pb age spectra of zircons from the borehole volcanics indicate that the northern South China Sea underwent an evolution from formation of Precambrian basement,Caledonian orogeny,and Indosinian orogeny to Yanshannian magmatism.This process can be well comparable with the tectonic evolution of South China,largely supporting the areas of the northern South China Sea as part of southward extension of the Cathaysia.     

Zircon U–Pb ages and Hf isotope compositions of migmatite from the North Dabie terrane in China: constraints on partial melting

Migmatite gneisses are widespread in the Dabie orogen, but their formation ages are poorly constrained. Eight samples of migmatite, including leucosome, melanosome, and banded gneiss, were selected for U–Pb dating and Hf isotope analysis. Most metamorphic zircon occurs as overgrowths around inherited igneous cores or as newly grown grains. Morphological and internal structure features suggest that their growth is associated with partial melting. According to the Hf isotope ratio relationships between metamorphic zircon and inherited cores, three formation mechanisms for metamorphic zircon can be determined, which are dissolution–reprecipitation of pre‐existing zircon, breakdown of Zr‐bearing phase other than zircon in a closed system and crystallization from externally derived Zr‐bearing melt. Four samples contain magmatic zircon cores, yielding upper intercept U–Pb ages of 807 ± 35–768 ± 12 Ma suggesting that the protoliths of the migmatites are Neoproterozoic in age. The migmatite zircon yields weighted mean two‐stage Hf model ages of 2513 ± 97–894 ± 54 Ma, indicating reworking of both juvenile and ancient crustal materials at the time of their protolith formation. The metamorphic zircons give U–Pb ages of 145 ± 2–120 ± 2 Ma. The oldest age indicates that partial melting commenced prior to 145 Ma, which also constrains the onset of extensional tectonism in this region to pre‐145 Ma. The youngest age of 120 Ma was obtained from an undeformed granitic vein, indicating that deformation in this area was complete at this time. Two major episodes of partial melting were dated at 139 ± 1 and 123 ± 1Ma. The first episode of partial melting is obviously older than the timing of post‐collision magmatism, corresponding to regional extension. The second episode of partial melting is coeval with the widespread post‐collision magmatism, indicating the gravitational collapse and delamination of the orogenic lithospheric keel of the Dabie orogen, which were possibly triggered by the uprising of the Cretaceous mid‐Pacific superplume.     

藏东类乌齐地区花岗质片麻岩锆石Cameca U-Pb定年及其地质意义

西藏东部类乌齐一带吉塘岩群中新识别出一套花岗质片麻岩。花岗质片麻岩中锆石Th/U比值较高(Th/U0.49),阴极发光图像显示锆石内部韵律环带明显,具典型岩浆锆石成因的特征。Cameca锆石U-Pb同位素加权平均年龄为282.1Ma±0.9Ma,表明花岗岩岩体形成于早二叠世,暗示澜沧江结合带在早二叠世存在岩浆增生事件。