中国东部富碱侵入岩铅同位素研究

对中国东部11个铅同位素省45个中生代富碱侵入岩体，进行了65个长石和全岩的铅同位素测定，并结合前人资料分析后认为，各铅同位索省富碱侵入岩铅同位索组成特征模式与所在铅同位素省中生代中酸性花岗岩类岩石的长石铅同位素组成特征完全相同，呈等值变化。     

长石铅和矿石铅同位素组成及其地质意义

中国东部中生代花岗岩类岩石的长石铅和矿石铅同位素组成,严格地受不同构造带基底岩石的性质和年龄所控制,至少可分为5个铅同位素构造省,即华北地台省、秦岭省、下扬子省、南岭省和东南沿海省。每个省具独特的矿化类型和矿石金属组合。     

东秦岭造山带花岗岩类长石铅同位素组成及其构造学意义

本文对东秦岭造山带内２７个花岗岩类央体４８件长石样品进行了铅同位素成分的测定，结果表明，本区的南秦岭不同时代花岗岩类以贫铀铅和钍铅为特征，具有明显的铅同位素块体效应，反映它们属地同一个铅同位素构造－地球化学省；而本区的北秦岭区岗岩类从晚元古代到早古生长，长石铅同位素组成以富铀铅和钍铅的为特征，但从晚古生长开始，花岗岩类长石铅同位素组成明显发生变化，以贫铀铅和钍铅为特征，反映晚古生长及其后形成花岗质     

大别造山带和扬子陆块北缘中生代玄武岩铅同位素组成及构造意义

大别造山带在地球化学分区上属于扬子大板块还是华北大板块一直存在争议。近年来，一些学者根据其显生宙矿石铅和花岗岩长石铅（揭示地壳铅）具有低铅同位素成分特征，将大别造山带整体划归华北大板块。本文对大别造山带南部（黄陂、新洲、大悟地区）、腹地（麻城地区）和扬子陆块北缘（黄石地区）晚中生代碱性玄武岩铅同位素组成（揭示地幔铅）研究表明，大别造山带具有高放射性成因铅同位素特征，与扬子铅同位素省中南扬子亚省基本一致。扬子陆块北缘（黄石地区）晚中生代碱性玄武岩铅同位素组成与扬子铅同位素省中北扬子亚省基本一致。铅同位素组成特征和Th-U-Pb体系变异趋势均表明：（1）大别造山带晚中生代地幔属于扬子地幔，与华北地幔存在明显区别；（2）大别造山带壳、幔铅同位素成分上存在明显的非耦合特征，反映大别造山带壳幔演化历史的复杂性。     

桐柏地区变质杂岩和侵入岩类Pb同位素组成特征及其地质意义

桐柏地区存在两个铅同位素组成明显不同的基底块体,在桐柏－商城断裂北侧,基底岩石以高放射性成因铅同位素组成为特征,而桐柏－商城断裂南侧,基底岩石以低放射性成因铅同位素组成为特征,它们分别可与南阳盆地以西的北秦岭和南秦岭构造带中基底岩石的铅同位素组成相对比,从而证明桐柏地区是秦岭造山带的构造东延部分．同时,通过桐柏地区侵入岩铅同位素组成特征的分析表明,早古生代侵入岩浆主要来源于北秦岭高放射性成因铅同位素组成的块体,而中生代侵入岩浆则来源于南秦岭低放射性成因铅同位素组成的块体,指示在南阳盆地以东,相当于北秦岭构造块体的地壳深部存在南秦岭的陆壳物质,反映南秦岭的陆壳物质早期向北俯冲叠置于北秦岭块体之下,并作为北秦岭中生代花岗质岩浆的源区     

郯庐断裂带晚中生代富碱侵入岩Nd、Sr、Pb同位素特征及源区性质探讨

郯庐断裂带是中国东部一条巨大的深大断裂带,它纵切华北克拉通、扬子克拉通、兴蒙-吉黑造山带和大别-苏鲁造山带四个大地构造单元,特别是在该断裂带出露许多晚中生代富碱侵入岩体,构成一条长达近2000km的富碱侵入岩带.本文是在前人研究基础上首次从大尺度对整个郯庐断裂带富碱侵入岩的Nd、Sr、Pb同位素做了比较系统深入的研究,发现四个大地构造单元的富碱侵入岩具有明显不同的Nd、Sr、Pb同位素特征,暗示四大构造单元富碱侵入岩的源区性质差别较大:兴蒙-吉黑造山带晚中生代富碱侵入岩源于和亏损地幔有成因联系的年青地壳(εNd(t)为ft.,平均值 2.25);华北克拉通、扬子克拉通和大别-苏鲁造山带三大构造单元晚中生代富碱侵入岩都主要源于EMI型富集地幔(εNd(t)均为负值).但是这三大构造单元岩石圈地幔富集程度差别较大.大别-苏鲁造山带岩石圈地幔相对富集程度最高(εNd(t)平均值为-17.06);华北克拉通次之(εNd(t)平均值为-10.03);扬子克拉通岩石圈地幔富集程度最低(εNd(t)平均值为-6.41).本文认为大别.苏鲁造山带岩石圈地幔相对最富集的原因可能是在早中生代扬子克拉通陆壳向华北克拉通深俯冲之后的折返过程中,因压力释放有利于熔/流体的形成、析出和向上交代并改造华北岩石圈地幔使之成为富集地幔.     

辽宁刘屯金矿床地质特征及成因

刘屯金矿床为含金硫化物石英脉型,矿体直接围岩为晚太古代混合花岗岩。区域上建平群大营子组为金的矿源层,金成矿与中生代构造岩浆活动密切相关。含金石英脉(矿脉)严格地受近东西向断裂构造控制。据硫同位素组成证明矿石、围岩、中生代侵入岩具有同一性,为幔源硫。氢氧同位素组成则显示了成矿溶液的多成因特征。矿石中铅同位素为古老的铅体系,与中生代岩体的长石铅属同一源地。通过时矿床成因的探讨,认为是"岩浆热源-混合热液"型复成因金矿床,成矿时代为燕山期。     

小秦岭地区文峪和东闯石英脉型金矿床铅及硫同位素研究

小秦岭地区文峪和东闯金矿床均是华北地台南缘的大型金矿床，金和金(铅）矿化主要在太古宙太华群变质岩层内呈脉状产出，并且同中生代燕山期花岗岩类具密切的时空分布关系。文章对文峪金矿床、东闯金（铅）矿床、花岗岩类侵入岩和变质岩地层的硫和铅同位素组成进行了系统研究，对不同地质体的硫和铅同位素变化特征进行了详细讨论。研究结果表明：中生代花岗岩体起源于太古言变质岩的重熔和岩浆结晶分异作用。金的成矿作用发生在中生代燕山期，成矿物质主要来自花岗岩类侵入岩，岩浆热流体对太古富变质岩地层的淋滤作用亦为金矿床的形成提供了部分物质来源。     

滇西上地幔铅同位素演化模式及滇西富碱斑岩铅同位素组成的诠释

大量的Pb同位素数据资料表明,滇西上地幔铅具两阶段演化历史,但又不是很好地吻合Stacey-Kramers的两阶段模式。本文依据Stacey-Kramers建造两阶段模式的基本原理,结合滇西地区上地幔铅同位素组成资料,拟合出了能更好地反映滇西上地幔铅同位素演化历史的二阶段模式并应用此模式对滇西富碱斑岩及其相关岩石的铅同位素组成做出诠释。     

华南绍兴-恩平富碱侵入岩带的厘定及其动力学意义初探

根据野外地质及室内岩相学、矿物成分和岩石化学的研究，从华南腹地厘定了一条重要的中生代NE向富碱侵入岩带－绍兴－恩平富碱侵入岩带。该岩带全长约1400km，宽100－150km，不仅发育有狭义的碱性岩（方沸黑云橄榄黄长岩、白榴黄长煌斑岩、霞石正长岩、霓辉石正长岩、黑榴石正长岩和含霓石石英正长岩）和碱性花岗岩（钠闪石花岗岩、霓辉石钠闪石花岗岩），还发育有大量的正长岩类－二长岩类－碱长花岗岩或晶洞钾长花岗岩。这些富碱侵入岩主要形成于晚中生代。绍兴－恩平燕山期富碱侵入岩带的厘定将对研究华南中生代的动力学的背景与演化具有重要的意义。     

Links between Mesozoic intermediate–felsic igneous rocks and lower crustal granulite xenoliths,North China Craton: O and Pb isotopic evidence

We present and compare whole-rock and zircon O and Pb isotopic compositions for the Hannuoba granulite xenoliths and Mesozoic intermediate-to-felsic igneous rocks from the Zhangjiakou region, northern margin of the North China Craton, northeast China. The xenoliths have an overall Pb isotopic range similar to rocks from the regionally exposed Neoarchaean granulite terrain. Mesozoic zircons from different types of granulite xenoliths have a narrow range of δ¹⁸O values (6.0–7.7‰) higher than normal mantle δ¹⁸O values (～5.7‰). Mesozoic intermediate–felsic igneous rocks have O and Pb isotopic compositions indistinguishable from the Hannuoba intermediate–mafic granulite xenoliths. Our new data suggest that the Mesozoic igneous rocks and granulite xenoliths are genetically linked and that both were derived from the late Neoarchaean lower crust. This argues against previous proposals that the granulite xenoliths are either products of Mesozoic basaltic underplating or formed by mixing between mantle-derived and pre-existing crustal magmas.     

Origin and formational history of some Pb-Zn deposits from Alborz and Central Iran: Pb isotope constraints

Several Pb-Zn deposits and occurrences within Iran are hosted by Mesozoic–Tertiary-aged sedimentary and igneous rocks. This study reports new Pb isotope analyses for galena from 14 Pb-Zn deposits in the Alborz and Central Iran structural zones. In general, Pb isotope ratios are extremely variable with data plotting between the upper crustal and orogenic curves in a plumbotectonic diagram. The latter may be attributed to Pb inputs from crustal and mantle end-members. Most of the galena samples are characterized by high ²⁰⁷Pb/²⁰⁴Pb ratios, suggesting significant input of Pb from old continental crust or pelagic sediment. Pb isotope data also indicate that some of the deposits, which are hosted by sedimentary rocks in Central Iran and Alborz, have similar Pb isotopic compositions and hence suggest similar source regions. Most of the galenas yield Pb model ‘ages’ that vary between ~140 and ~250 Ma, indicating that mineralization resulted from the extraction of ore-bearing fluids from Upper Triassic–Lower Jurassic sequences. The similarity in Pb isotope ratios for the Pb-Zn deposits located within these zones suggests analogous crustal evolution histories. Our preferred interpretation is that Pb-Zn mineralization within the sedimentary and igneous rocks of the Central Iran and Alborz tectonic regions occurred following a Late Cretaceous–Tertiary accretionary stage of crustal thickening in Iran.     

Pb-Nd Isotopes Indicate the Origin of Island Arc Terranes in the Early Paleozoic Pacific

The Takaka Terrane in New Zealand is one of the best exposed arc fragments of the early Paleozoic Australian-Antarctic convergent margin and constitutes one of the most outboard terranes of this margin in paleogeographic reconstructions. Pb-Nd isotope compositions of clinopyroxenes from the Cambrian Devil River Volcanics of the Takaka Terrane enable identification of the location of the terrane in the Paleo-Pacific Ocean. The Devil River Volcanics, a suite of primitive arc and back-arc rocks, are interbedded with the partly continent-derived Haupiri Group sediments. Extremely radiogenic Pb and unradiogenic Nd compositions in the arc rocks cannot be explained by assimilation of the Haupiri Group sediments or a continental basement of such a composition. Pb isotope compositions of the Takaka Terrane sediments are much less radiogenic and overlap with crustal compositions of the Lachlan Fold Belt in Australia, suggesting that both units are derived from one source, the Australian-Antarctic Pacific margin. Pb-Nd isotope compositions in the Devil River Volcanics reflect contamination of their mantle sources by subducted sediments derived from Archean provinces in either Antarctica or Laurentia. Both provinces show characteristically high 207Pb/204Pb500 and were located at the Pacific rim in the Cambrian. Mixing between mantle and Proterozoic continental material from present western South America or eastern Laurentia cannot explain the high 207Pb/204Pb500 in the New Zealand rocks. As in New Zealand, extreme spreads in Pb-Nd isotope compositions in other Cambrian volcano-sedimentary sequences in southeast Australia and Tasmania can be explained by the same model, suggesting that all these fragments originated along the Australian-Antarctic Gondwana margin. Pb isotope compositions of arc rocks, therefore, provide a new tool for terrane analysis in the early Paleozoic Pacific ocean.     

宁芜地区玢岩铁矿Pb同位素研究

本文对宁芜地区铁矿床中磷灰石和矿石进行了Pb同位素测定。磷灰石的208Pb-232Th等时线年龄为124Ma,与辉长闪长(玢)岩和钠长石岩的形成年龄均相吻合,为成矿时代与成岩时代相近提供了佐证。岩体长石Pb同位素显示,宁芜地区中生代火成岩的原始岩浆受到了大陆壳深部3.3Ga的古老岩系的混染。矿床中矿石铅主要来自赋矿母岩浆。成矿流体具有异常高的Th/U值,表明Th相对U的明显富集,这可能反映了流体中卤素为主要的矿物质迁移载体。     

Characteristics of the Density and Magnetic Susceptibility of Rocks in Northern Borneo and their Constraints on the Lithologic Identification of the Mesozoic Rocks in the Southern South China Sea

Based on the volume magnetic susceptibility and specific gravity measurements and mineral and lithologic identification results for 540 samples,the rock type,density,and magnetic susceptibility of rocks from northern Borneo were analyzed,and the applicability of gravity and magnetic data to the lithologic identification of the Mesozoic strata in the southern South China Sea was assessed accordingly.The results show that there are 3 types and 25 subtypes of rocks in northern Borneo,mainly intermediate-mafic igneous rocks and exogenous clastic sedimentary rocks,with small amounts of endogenous sedimentary rocks,felsic igneous rocks,and metamorphic rocks.The rocks that are very strongly-strongly magnetic and have high-medium densities are mostly igneous rocks,tuffaceous sandstones,and their metamorphic equivalents.The rocks that are weakly magnetic-non-magnetic and have medium-very low densities are mostly conglomerates,sandstones,siltstones,mudstones,and coal.The rocks that are weakly magnetic-diamagnetic and have highmedium densities are mostly limestones and siliceous rocks.The Cenozoic rocks are characterized by low densities and medium susceptibilities;the Mesozoic rocks are characterized by medium densities and medium-high susceptibilities;and the pre-Mesozoic rocks are characterized by high densities and low magnetism.Based on these results and the distribution characteristics of the various rock types,it was found that the pre-Mesozoic rocks produce weak regional gravity anomalies;the Mesozoic sedimentary rocks produce negative regional gravity anomalies;whereas the Mesozoic igneous rocks produce positive regional gravity anomalies;and the Cenozoic igneous rocks produce positive regional gravity anomalies.The regional high magnetic anomalies in the southern part of the South China Sea originate from the Mesozoic mafic igneous rocks and their metamorphic equivalents;and the regional medium magnetic anomalies may be produced by the felsic igneous rocks and their metamorphic equivalents.Accordingly,the identification of the Mesozoic lithology in the southern South China Sea shows that the Mesozoic sedimentary rocks are distributed over a large area of the southern South China Sea.Thus,it is concluded that the Mesozoic strata in this area have the potential for oil and gas exploration.     

桐柏-大别造山带高压变质单元岩石Pb同位素组成

铅同位素组成对于研究构造分区与演化、块体相互作用以及识别地壳中不同块体的上、下层次关系等具有重要意义.桐柏-大别造山带高压变质单元岩石的全岩Pb同位素组成研究表明, 在该造山带不同区段, 高压变质岩系二云钠长片麻岩与榴辉岩具有相似的Pb同位素组成, 表现为上部地壳高放射成因的Pb同位素组成特征, 其中Pb同位素组成为: 206Pb/204Pb=17.599~18.310, 207Pb/204Pb=15.318~15.615, 208Pb/204Pb=37.968~39.143.大别和桐柏地区高压变质岩系Pb同位素组成的一致性进一步证明了大别地区与桐柏地区的高压变质岩系是可以相连的, 它们应属于同一构造单元.高压变质岩系Pb同位素比值总体高于超高压变质岩系, 验证了桐柏-大别造山带扬子俯冲陆壳从下部岩系到上部岩系Pb同位素比值呈规律增长这一Pb同位素化学特征.侵入于高压变质岩系中的面理化(含榴)花岗岩, 其Pb同位素组成与高压变质岩系相比相对较低, 而与超高压变质岩系及其中的面理化(含榴)花岗岩相似, 为: 206Pb/204Pb=17.128~17.434, 207Pb/204Pb=15.313~15.422, 208Pb/204Pb=37.631~38.122.这表明高压变质岩系和超高压变质岩系中的面理化(含榴)花岗岩具有相同的岩浆来源.结合面理化(含榴)花岗岩具有A型花岗岩的地球化学特征分析, 它们的岩浆物质可能来自超高压变质岩折返至中下地壳的减压退变和部分熔融.      

浙江省中生代火成岩的Nd-Sr同位素研究

本文报道了浙江省21个中生代火成岩的Nd-Sr同位素组成,其中火山岩的ε_Nd值为-12.6——4.9,I_Sr值为0.70613-0.71079,t_DM年龄为1945-1296Ma;花岗岩类的ε_Nd值为-12.9——5.8,I_Sr值为0.70533-0.71208,t_DM年龄为1900-1230Ma,表明两者具有相似的同位素组成。这种相似性在同一火山-侵入杂岩体中表现更为明显,意味着两者在时、空、源方面具有同一性。与扬子地块的相比,华夏地块的中生代火成岩具有较低的ε_Nd值,较高的I_Sr值和较古老的Nd模式年龄,这种差异可能主要同这两个区域内基底变质岩在形成时代和成分上的差异有关。通过Sm-Nd同位素组成的对比研究,笔者认为,浙江境内的中生代火成岩可能主要是由基底变质沉积岩衍生的。原始岩浆的形成可能同中、下地壳岩石的熔融有关。     

郯庐断裂带张八岭隆起段晚中生代岩浆岩继承锆石U-Pb年代学:源区属性及构造意义

大别与苏鲁造山带之间的郯庐断裂带张八岭隆起段,构成了华北与扬子板块之间的断裂边界。该边界带的深部结构状态长期以来存在着不同的认识。本文利用张八岭隆起带沿线出露的晚中生代岩浆岩中继承锆石U-Pb年代学信息,结合地球物理资料及Nd、Pb、Hf同位素资料,分析了其深部的岩浆源区属性及结构状态。张八岭隆起带北段晚中生代岩浆岩继承锆石年龄以1.9~2.7Ga为主,最大峰值年龄为2.5Ga;南段继承锆石年龄以2.2~2.6Ga为主,峰值年龄也为2.5Ga;郯庐断裂带庐江段则以含大量新元古代锆石为特征,在0.7Ga形成显著的分布峰值,并有早元古和少量太古代年龄信息。分析结果表明,张八岭隆起带北段的晚中生代岩浆岩源区为华北下地壳,南段的源区兼有华北和扬子陆壳的信息,而更南部庐江段则以扬子地壳源区为特征。电法剖面揭示,郯庐断裂主边界在张八岭隆起带下向南东倾斜,从而深部存在华北地壳;而南部庐江段转变为向北西陡倾,从而深部皆为扬子地壳。郯庐断裂深部产状特征支持其印支期应为斜向汇聚边界。而其中三叠纪继承锆石的缺失指示隆起带上变质岩应为原地岩石,而非来自大别造山带。     

Pb Isotope Mapping in the Tongbai-Dabie Orogenic Belt, Central China

Tongbai-Dabie orogenic belt in Central China is a part of the collisional belt between the Yangtze and North China cratons. It represents one of the most extensive ultrahigh-pressure （UHP） and high-pressure （HP） metamorphic rocks in the world. The Pb isotope mapping in this area is a significant method to constrain the crustal structure and tectonic evolution and to identify the tectonic boundaries within the vertical tectonic stack. Based on the Pb isotope compositions of the Dabie complex （DBC）, the Tongbai complex （TBC）, UHP and HP metamorphic rocks and associated foliated granites, the lower metamorphosed rocks from North Huaiyang （NHY） tectonic belt, and Cretaceous granites in the Tongbai-Dabie orogenic belt, we determined the Pb isotope geochemical map of the Tongbai-Dabie orogenic belt. The Pb isotope map shows that the Pb isotope compositions are similar within each geological body or lithotectonic unit, but the Pb isotope compositions of different lithotectonic units show systematic variations in the Tongbai-Dabie orogenic belt. The NHY tectonic belt contrasts strongly with the Tongbai-Dabie UHP.HP metamorphic belt in Pb isotope compositions. It is suggested that the line along the Xiaotian-Mozitan fault, the north limit of the Tongbai-Dabie UHP and HP metamorphic rocks, represents an important tectonic boundary. Within the Tongbai-Dabie HP -UHP metamorphic belt, to the south of Xiaotian-Mozitan fault, the vertical variations of Pb isotope compositions in different lithotectonic units and the spatial relationship among different major lithotectonic units have been constrained.