吕梁地区古元古代花岗片麻岩成因及变质时代:锆石和独居石U-Pb年龄及锆石Hf同位素证据

吕梁地区在华北克拉通前寒武纪研究中具有重要位置,出露大量的古元古代变质表壳岩和花岗质岩石,对研究华北克拉通古元古代地质演化历史具有重要意义。本次研究选择吕梁地区白家滩花岗片麻岩进行锆石和独居石U-Pb年代学以及锆石Hf同位素研究,2个花岗片麻岩的岩浆锆石U-Pb年龄分别为2182±16Ma和2185±24Ma,代表了其侵位时代。独居石U-Pb年龄分别为1898±7Ma和1899±14Ma,明显比锆石增生边的谐和²⁰⁷Pb/²⁰⁶Pb年龄（2180~2032Ma）年轻,说明独居石对后期变质作用的响应程度比锆石强,其U-Pb年龄更能反映白家滩花岗片麻岩经历了~1900Ma的退变质作用,与华北克拉通中部造山带的变质作用时间一致。花岗片麻岩的锆石Hf同位素亏损地幔模式年龄（t_DM）为2473~2598Ma,两阶段亏损地幔模式年龄（t_DM^C）分别为2646~2839Ma,ε_Hf（t）值分布于-1.3~+1.8之间,未显示同期幔源物质的加入,而是新太古代地壳物质部分熔融的产物,结合已有的古元古代中期（2.2~2.1Ga）的岩浆岩锆石Hf同位素数据,华北克拉通新太古代地壳在2.2~2.1Ga期间发生了广泛的重熔作用,这期岩浆活动在华北克拉通吕梁、中条、五台以及胶-辽-吉等地区广泛发育,可能形成于陆内裂谷环境。     

黑青和田玉宝石矿物学及地球化学特征研究

近年国内市场出现了一种含有黄铁矿的黑青色玉石,主要产自新疆,属于和田玉中的稀少品种。本文利用常规宝石学仪器、偏光显微镜、红外光谱、拉曼光谱、X射线粉晶衍射(XRD)、电子探针(EPMA)、激光电感耦合等离子质谱(LA-ICP-MS)以及同位素质谱仪(MC-ICP-MS)对7块黑青和田玉样品的宝石矿物学和地球化学特征进行了系统分析,结果显示,样品颜色为墨绿-黑色,折射率点测1.61,相对密度3.08~3.17,摩氏硬度6.0~6.5,主要组成矿物为透闪石,次要矿物以黄铁矿为主,同时还含有少量绿泥石、绿帘石、榍石、锆石、石墨等,具有典型的纤维交织状结构;红外与拉曼光谱特征峰显示与和田玉标准谱峰一致;样品中透闪石的主要化学成分为SiO₂、MgO、CaO和FeO,Mg/(Mg+Fe²⁺)值显示部分透闪石已过渡为阳起石;根据微量元素Cr-Ni投图判别样品为白云石大理岩型成因,稀土元素含量较少,呈左倾模式;推测成矿热液主要为岩浆水,含少量变质水;样品中黄铁矿Co/Ni>1且含少量As、Se、Cu、Zn、Pb等元素,δ³⁴S介于8.87‰~20.92‰之间,推断为岩浆热液成因且硫来源于岩浆与地层硫的混合。     

西藏班戈北部早白垩世火山岩：班公湖—怒江洋闭合的岩浆记录

对班戈县北部马前乡地区的早白垩世安山岩和英安岩进行了详细的地质填图及岩石学、年代学、地球化学和Hf同位素研究。锆石U-Pb定年获得安山岩年龄分别为（108.0±1.5）Ma和（113.6±0.9）Ma;英安岩年龄为（106.7±1.9）Ma和（113.6±0.8）Ma。安山岩富集Th和U,亏损Nb、Ta和Ti,具有变化范围较大的Mg^#值（25~63）,锆石ε_Hf（t）值（-8.6~+1.5）以负值为主,应当为幔源镁铁质熔体与壳源熔体的混合产物。英安岩具有与安山岩类似的微量元素成分特征及负的锆石ε_Hf（t）值（-12.3~-8.1）,应当是地壳部分熔融的产物。结合前人研究成果认为,这些早白垩世岩浆岩是约110 Ma沿班公湖-怒江缝合带岩浆大爆发的产物,可能与班公湖-怒江洋闭合之后的拉萨与羌塘地块陆-陆碰撞有关。     

川西松林口岩体锆石U-Pb定年及其地球化学特征

松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（212.4±0.9） Ma （MSWD=0.66）,二长花岗岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（222.4±1.1） Ma （MSWD=0.39）,形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO₂含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K₂O/Na₂O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,La_N/Yb_N比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg^#值较高（50.97~61.27）,w（Rb）/w（Sr）为0.12~0.25,Rb-（Y+Nb）图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。     

南天山拜城县波孜果尔A型花岗岩类锆石U-Pb定年及其Lu-Hf同位素组成

新疆拜城县波孜果尔A型花岗岩类岩体位于塔里木地台北缘及邻区的近东西向碱性侵入岩带上,主要岩石类型为霓石钠闪石英碱长正长岩、霓石钠闪碱长花岗岩、黑云母碱长正长岩。全岩SiO₂=68.97%~74.14%,Na₂O+K₂O=9.67%~11.19%,Al₂O₃=13.72%~15.26%,Fe₂O₃=0.18%~1.41%,FeO=0.91%~1.51%,CaO=0.35%~0.63%。稀土元素总量较高,ΣREE=298×10^-6~1286×10^-6,平均706×10^-6,轻稀土富集,重稀土亏损,强烈的Eu负异常,呈“右倾海鸥型”的稀土元素配分模式。富Nb、Ta、Zr、Hf等高场强元素,亏损Ba、K、Sr等大离子亲石元素,Zr+Nb+Ce+Y=936×10^-6~3684×10^-6,平均1813×10^-6。为A1型花岗岩。岩体形成于早二叠纪。锆石LA-ICP-MS U-Pb年龄为287.7~291.6Ma,平均289.8Ma,岩体形成后,在279.1~282Ma左右经历了后期热液流体的改造。锆石ε_Hf（t）值为-6.3~9.0,两阶段模式年龄（t_DM2）跨越古元古代晚期-新元古代中期,主要集中在中元古代。岩浆平均温度832~839℃,形成于非造山的板内构造环境,且具高温、无水、低氧逸度的成岩特点。该岩体具有壳幔混源的特点。     

西秦岭印支期高Sr/Y花岗岩类的成因及动力学背景——以同仁地区舍哈力吉岩体为例

西秦岭印支期花岗岩类分布十分广泛,形成时代集中于248~234Ma和224~211Ma两个阶段.其中,夏河岩体(248~238Ma)和温泉岩体(223~216Ma)的部分样品被厘定为埃达克岩(Sr>400×10^-6,Yb<2×10^-6),指示陆壳厚度大于50km.本文对西秦岭同仁地区舍哈力吉岩体进行了锆石U-Pb定年、岩石学、地球化学和Sr-Nd同位素研究.舍哈力吉岩体主要由石英二长岩组成,同时含有许多暗色镁铁质微粒包体(MME).寄主岩中发育少量的钾长石巨晶,并且部分巨晶具有环斑结构.舍哈力吉石英二长岩化学成分比较均一,而且也显示出类似埃达克岩的一些地球化学特点,如富SiO₂(66.07%~67.52%)和Al₂O₃(14.85%~15.95%),高Sr(560×10^-6~692×10^-6),低Y(11.4×10^-6~12.9×10^-6)和Yb(0.99×10^-6~1.09×10^-6),并具有较高的(La/Yb)_N比值(27.8~34.3)和微弱的负Eu异常(δEu=0.77~0.95).锆石U-Pb测年结果为234.1±0.5Ma,表明其形成于印支早期.岩石为偏铝质、高钾钙碱性系列且K₂O/Na₂O>1,高Mg^#(59~60)、Cr(69.1×10^-6~81.2×10^-6)和Ni(31.6×10^-6~36.1×10^-6),以富集大离子亲石元素(Rb、Ba、Th、U)而相对亏损高场强元素(Nb、Ti、P)为特征,(⁸⁷Sr/⁸⁶Sr)_i=0.7075~0.7077,ε_Nd(t)=-6.3~-6.1,亏损地幔模式年龄为1.25~1.33Ga.舍哈力吉石英二长岩起源于石榴角闪岩相古老下地壳的部分熔融,之后经历了壳幔岩浆混合作用和以斜长石为主的分离结晶作用.寄主岩的环斑结构和相对一致的地球化学特征,很可能是高温幔源熔体对壳源富钾高黏度岩浆改造所导致的晶粥快速再活化的结果.西秦岭在印支早期可能并未经历显著的地壳加厚过程.西秦岭印支早期花岗岩类形成于活动大陆边缘局部伸展环境,可能与古特提斯洋壳俯冲极性的改变有关.     

榍石LA-SF-ICP-MS U-Pb定年及对结晶和封闭温度的指示

榍石富含U、Th,贫Pb,是U-Pb定年的理想矿物之一。本文采用激光剥蚀-高分辨等离子体质谱建立榍石U-Pb定年方法,采用25~30μm激光斑束,准确测定榍石U-Pb标准样品BLR-1（~1048Ma）、OLT-1（~1014Ma）和Pakistan（~21.4Ma）,以及年轻榍石样品（<100Ma）U-Pb年龄,提高了检测准确性和空间分辨率。综合对比共生锆石和榍石U-Pb年龄、榍石颗粒微量元素和U-Pb年龄环带及不同成分岩浆岩（SiO₂含量48.1%~77.0%）中岩浆榍石的结晶温度,结果表明：岩浆演化过程中,榍石具有宽泛的结晶温度（600~900℃,峰值~750℃）,主要集中于岩浆演化中晚期结晶,榍石U-Pb同位素封闭温度接近或略低于锆石,因此同一岩浆体系中锆石与榍石的年龄差异可能反映了该熔体较晚达到榍石饱和,而非熔体热演化历史或封闭温度信息。     

西藏波密花岗岩体的年代学、地球化学特征及其意义

波密岩体位于西藏东南部,处于班公湖-怒江蛇绿混杂岩带与印度河-雅鲁藏布蛇绿混杂岩带之间,整体呈NW向延伸,面积约29km²。本文对波密花岗岩体进行了系统的岩石学、地球化学及同位素年代学研究。结果显示,波密岩体主要以黑云母石英闪长岩与黑云母花岗闪长岩为主,两个花岗闪长岩的LA-ICP-MS锆石U-Pb年龄分别为113.1±2.3Ma和113.4±2.1Ma。花岗岩类SiO₂介于64.11%~66.63%,K₂O+Na₂O=6.36%~7.54%,全碱含量较高,属于高钾钙碱系列。稀土元素含量为114.9×10^-6~182.8×10^-6,分配曲线均呈右倾趋势。另外,A/CNK为0.80~0.95,波密岩体有高K,高Si,低P的特点,大离子亲石元素(Rb、K)富集,高场强元素(Nb、Ta、P、Ti)亏损,属于偏铝质I型花岗岩。2件样品37个测点的锆石ε_Hf(t)值不均一,几乎全为负值(-13.72~-0.08),反映岩浆可能源于古老地壳;地壳模式年龄(t_DM^C)集中于891~2047Ma之间。综合分析波密岩体地球化学及锆石年龄数据,均与中冈底斯及弧背断隆带中早白垩世的岩体特征相似。因此本文推断波密岩体的成因为中冈底斯早白垩世带状岩浆大爆发事件在东部的延续。     

阿尔金南缘塔特勒克布拉克复式花岗质岩体东段片麻状花岗岩的地球化学特征、锆石U-Pb定年及其地质意义

出露于阿尔金构造带南缘北部塔特勒克布拉克复式花岗质岩体东段的片麻状花岗岩, SiO₂为71.88%~73.92%, Al₂O₃为13.39%~14.14%, K₂O+Na₂O为8.18%~8.85%, K₂O/Na₂O=1.54~2.33, A/CNK介于1.02~1.09之间, 属高钾钙碱性系列的弱过铝质岩石。该岩石富集大离子亲石元素(LILE), 亏损Nb、Ta、P、Ti等高场强元素(HFSE); ∑REE较高且变化范围大(∑REE=98.57×10^-6~579.1×10^-6, 平均338.8×10^-6), 具有明显的负Eu异常(δEu=0.22~0.71, 平均0.34), LREE相对富集, 轻重稀土分馏明显。Nb/Ta=11.78~15.83、Zr/Hf=34.94~36.82及Th/U=8.4~12.7, 结合源岩判别图解, 推断其源区物质主要来源于上地壳的变泥砂质沉积岩类。微量元素及稀土元素特征暗示原岩部分熔融残留相的矿物组合可能为石榴石+斜长石+金红石, 全岩Zr饱和温度计计算结果显示部分熔融温度>800℃, 推断该岩石形成于麻粒岩相条件下云母和角闪石脱水诱发的部分熔融。该岩石LA-ICP-MS锆石U-Pb原位定年结果为: 761±54Ma(上交点年龄), 451±1.7Ma(核部)和411.3±1.8Ma(边部), 锆石核部Th/U平均为0.64, 边部Th/U平均为0.05。结合区内超高压榴辉岩的原岩形成时代、峰期变质与退变质时代分别为约750Ma、500Ma与450Ma的研究资料(Liu et al., 2012)综合分析, 塔特勒克布拉克片麻状花岗岩的原岩时代为782.3±6.9Ma, 可能与罗迪尼亚超大陆裂解事件有关; 花岗岩结晶年龄为451±1.7Ma, 形成于俯冲碰撞造山后抬升阶段, 对应于区内深俯冲陆壳的折返时代, 此时超高压变质岩石发生了麻粒岩相的退变质作用, 随后411.3±1.8Ma又受到另一期地质事件的改造。     

北秦岭宽坪岩群变质沉积岩年代学及地质意义

宽坪岩群位于北秦岭造山带,主要由广东坪岩组斜长角闪岩、四岔口岩组云母石英片岩及谢湾岩组的大理岩组成。通过LA-MC-ICPMS锆石U-Pb测年研究,宽坪岩群谢湾岩组碎屑锆石年龄为400~3502 Ma,其中最年轻一组的²⁰⁶Pb/²³⁸U年龄在380~418 Ma,结合黑云母⁴⁰Ar/³⁹Ar（370.9±2.0）Ma的变质年龄,表明谢湾岩组形成在晚泥盆世。四岔口岩组碎屑锆石年龄介于512~3598 Ma,最年轻的一组锆石²⁰⁶Pb/²³⁸U年龄在512~549 Ma,其黑云母⁴⁰Ar/³⁹Ar变质年龄为（370.4±1.8）Ma,表明该组形成于512 Ma（早寒武世）之后,晚泥盆世之前,主体很可能形成于早古生代。宽坪岩群是由不同时代的地层和岩片构成,应该进一步解体。宽坪岩群物源来自华北陆块、秦岭造山带和扬子陆块。其变形变质时代为晚泥盆世,代表了北秦岭造山带碰撞造山的结束时代。     

Ordovician high-grade metamorphism of a newly recognised late Neoproterozoic terrane in the northern Harts Range,central Australia

Granulite facies rocks from the northernmost Harts Range Complex (Arunta Inlier, central Australia) have previously been interpreted as recording a single clockwise cycle of presumed Palaeoproterozoic metamorphism (800–875 °C and >9–10 kbar) and subsequent decompression in a kilometre‐scale, E‐W striking zone of noncoaxial, high‐grade (c. 700–735 °C and 5.8–6.4 kbar) deformation. However, new SHRIMP U‐Pb age determinations of zircon, monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the Proterozoic, but in the Ordovician (c. 470 Ma). The youngest metamorphic zircon overgrowths from two metabasites (probably meta‐volcaniclastics) yield ²⁰⁶Pb/²³⁸U ages of 478±4 Ma and 471±7 Ma, whereas those from two metapelites yield ages of 463±5 Ma and 461±4 Ma. Monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock (457±5 Ma and 462±5 Ma, respectively). Zircon, and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes. In contrast, titanite from the two metabasites yield ²⁰⁶Pb/²³⁸U ages that are much younger (411±5 Ma & 417±7 Ma, respectively) than those of coexisting zircon, which might indicate that the terrane cooled slowly following final melt crystallization. One metabasite has a second titanite population with an age of 384±7 Ma, which reflects titanite growth and/or recrystallization during the 400–300 Ma Alice Springs Orogeny. The c. 380 Ma titanite age is indistinguishable from the age of magmatic zircon from a small, late and weakly deformed plug of biotite granite that intruded the granulites at 387±4 Ma. These data suggest that the northern Harts Range has been subject to at least two periods of reworking (475–460 Ma & 400–300 Ma) during the Palaeozoic. Detrital zircon from the metapelites and metabasites, and inherited zircon from the granite, yield similar ranges of Proterozoic ages, with distinct age clusters at c. 1300–1000 and c. 650 Ma. These data imply that the deposition ages of the protoliths to the Harts Range Complex are late Neoproterozoic or early Palaeozoic, not Palaeoproterozoic as previously assumed.     

Geology and Pb-Pb Geochronology of Paleoproterozoic Volcanic and Granitic Rocks of Pitinga Province,Amazonian Craton,Northern Brazil

Pitinga Province is one of the main tin provinces of the Amazonian craton. The oldest unit in the studied area is the Iricoumé Group, which consists of rhyolites and rhyodacites with a ²⁰⁷Pb/²⁰⁶Pb zircon age of 1888 ± 3 Ma. This volcanic sequence is intruded by five A-type granite plutons. The studied portion of the Europa pluton is homogeneous, and composed of a peralkaline alkali-amphibole hypersolvus granite that yielded a ²⁰⁷Pb/²⁰⁶Pb zircon age of 1829 ± 1 Ma. The early facies of the Madeira pluton consists of a metaluminous amphibole-biotite syenogranite (rapakivi facies) with a ²⁰⁷Pb/²⁰⁶Pb zircon age of 1824 ± 2 Ma. It is intruded by a 1822 ± 1 Ma, mildly peraluminous biotite syenogranite. The later facies of this pluton consist of a porphyritic, hypersolvus, alkali-feldspar granite and an albite granite. Field relationships and an extensive drilling survey indicate that these two facies are sheet-shaped and were emplaced almost simultaneously. The hypersolvus alkali-feldspar granite has a ²⁰⁷Pb/²⁰⁶Pb zircon age of 1818 ± 2 Ma. Taking in account its field relationships with the albite granite, a similar age is assumed for the latter.

The albite granite intrudes the biotite granite and rapakivi granite facies of the Madeira pluton, which was emplaced by shallow-level cauldron subsidence. The albite granite is sheet shaped and consists of a magmatic peralkaline cryolite-bearing core facies partially surrounded by an autometa-somatic peraluminous fluorile-bearing border facies. Both albite granite facies are strongly tin-mineralized and display anomalous contents of Nb, Rb, Zr, and REE. A massive body of cryolite and pegmatitic rocks is associated with the albite granite.

The contrast in age between the Iricoume Group and the Europa + Madeira granites demonstrates that the plutons are not subvolcanic intrusions related to the extrusives. The ages of 1824 ± 2 Ma, 1822 ± 2 Ma, and 1818 ± 2 Ma obtained, respectively, for the amphibole + biotite syenogranite, biotite granite, and porphyritic hypersolvus granite of the Madeira pluton are consistent with the emplacement sequence inferred for these facies. These ages indicate that the Madeira pluton was emplaced in a relatively short time. Its facies are a little younger than the peralkaline granite of the Europa pluton, suggesting that the latter is not coeval with the Madeira peralkaline albite granite.     

Cadomian Lower-Crustal Contributions to Variscan Granite Petrogenesis (South Bohemian Pluton, Austria): Constraints from Zircon Typology and Geochronology, Whole-Rock, and Feldspar Pb-Sr Isotope Systematics

A hybrid pyroxene-bearing Weinsberg type granitoid of the SouthBohemian batholith (Austria) consists of two independent mineralassemblages that were formed during two different magmatic events.The older, inherited assemblage forms unevenly distributed millimetre-sizedmulti-grain patches of quartz + mesoperthitic alkali feldspar+ andesine/bytownite + clinopyroxene (X_Mg = 0·50–0·54)+ orthopyroxene (X_Mg = 0·35–0·42) ±ilmenite ± accessories. It is interpreted to representremnants of a mangeritic igneous rock with a superimposed granulite-faciesre-equilibration texture characterized by unzoned pyroxenesand plagioclase. The enclosing younger assemblage with alkalifeldspar + oligoclase/andesine + quartz + biotite ± accessoriescrystallized from a biotite-bearing granitic melt with feldsparsexhibiting typical magmatic zoning. Coexisting with the inheritedassemblage are zircons with a characteristic typology (S23 toD, mean J4). Zircons belonging to the granitic assemblage, onthe other hand, show a distinctly different typology (L2 toS5, mean L4) or are anhedral. A Cambrian age of formation andsubsequent re-equilibration of the inherited assemblage is inferredfrom a mean U/Pb and ²⁰⁷Pb/²⁰⁶Pb evaporation age of 523 ±5 Ma for the J4 zircons. Granitic L4 zircons show a mean ²⁰⁷Pb/²⁰⁶Pbevaporation age of 355 ± 9 Ma, interpreted as the ageof zircon growth during a Carboniferous partial melting eventin the lower crust. Granite emplacement at 345 ± 5 Mais inferred from U/Pb analysis of the anhedral zircon population.The comparably low radiogenic common Pb isotope compositionof megacrystic alkali feldspars suggests that at least somedomains of these crystals are inherited from the older, pyroxene-bearingmineral assemblage. Rb/Sr whole-rock dating is thus severelyjeopardized by the presence of the inherited alkali feldsparcrystals, leading to widely scattering data points and errorchronages of no geological significance. KEY WORDS: Austria; Bohemian Massif; geochronology; granites; Pb–Sr isotopes     

New age constraints on metamorphism,metasomatism and gold mineralisation at Plutonic Gold Mine,Marymia Inlier,Western Australia

The Plutonic Well Greenstone Belt (PWGB) is located in the Marymia Inlier between the Yilgarn and Pilbara cratons in Western Australia, and hosts a series of major Au deposits. The main episode of Au mineralisation in the PWGB was previously interpreted to have either accompanied, or shortly followed, peak metamorphism in the late Archean at ca 2650 Ma with a later, minor, event associated with the Capricorn Orogeny. Here we present new Pb isotope model ages for sulfides and Rb–Sr ages for mica, as well as a new ²⁰⁷Pb–²⁰⁶Pb age for titanite for samples from the Plutonic Gold Mine (Plutonic) at the southern end of the PWGB. The majority of the sulfides record Proterozoic Pb isotope model ages (2300–2100 Ma), constraining a significant Au mineralising event at Plutonic that occurred >300 Myr later than previously thought. A Rb–Sr age of 2296 ± 99 Ma from muscovite in an Au-bearing sample records resetting or closure of the Rb–Sr system in muscovite at about the same time. A younger Rb–Sr age of 1779 ± 46 Ma from biotite from the same sample may record further cooling, or resetting during a late-stage episode of metasomatism in the PWGB. This could have been associated with the 1820–1770 Ma Capricorn Orogeny, or a late-stage hydrothermal event potentially constrained by a new ²⁰⁷Pb–²⁰⁶Pb age of 1725 ± 26 Ma for titanite in a chlorite–carbonate vein. This titanite age correlates with a pre-existing age for a metasomatic event dated at 1719 ± 14 Ma by U–Pb ages of zircon overgrowths in a sample from the Marymia Deposit. Based on the Pb-isotope data presented here, Au mineralising events in the PWGB are inferred to have occurred at ca 2630, 2300–2100 Ma, during the Glenburgh and Capricorn orogenies, and 1730–1660 Ma. The 2300–2100 Ma event, which appears to have been significant based on the amount of sulfide of this age, correlates with the inferred age for rifting of the Marymia Inlier from the northern margin of the Yilgarn Craton. The texturally-later visible Au may have been deposited during the Glenburgh and Capricorn orogenies.     

大兴安岭扎兰屯地区前寒武纪变质岩系年龄及其构造意义

大兴安岭扎兰屯地区出露较多的前寒武纪变质岩系,包括先前认为是古元古代的兴华渡口群、新元古代的佳疙瘩组和新元古代—早寒武世的倭勒根岩群,但一直缺少精确的年代学依据。通过LA-ICP-MS锆石U-Pb同位素测年,对这3个变质岩群的原岩时代进行了厘定。结果显示,兴华渡口群中绿泥石白云母片岩的锆石~(206)Pb/~(238)U年龄加权平均值为520.1±4.3Ma(n=11,MSWD=1.6),佳疙瘩组中长英质糜棱岩锆石~(206)Pb/~(238)U年龄加权平均值为512.0±2.9Ma,倭勒根岩群中绿泥绢云片岩最年轻锆石~(206)Pb/~(238)U年龄加权平均值为491.7±11.9Ma,年龄最密集区加权平均值为516.7±4.5Ma。锆石图像特征及Th/U值均显示岩浆型锆石特征。综上所述,扎兰屯地区出露的兴华渡口群、佳疙瘩组和倭勒根群形成时代均为早古生代早期,而非先前认为的"前寒武纪"。同时,上述年龄谱系表明,该地区在480~500Ma和500~530Ma存在2期强烈的岩浆活动,应与东北地区晚泛非期岩浆-变质事件有关。     

内蒙古大青山地区英安岩LA-ICP-MS锆石U-Pb年龄及其构造意义

在内蒙古大青山地区逆冲推覆构造所截切的英安岩中获得锆石~(207)Pb/~(206)Pb表面年龄加权平均值为1870±19Ma,认为英安岩为华北克拉通古元古代末—新元古代一次裂解事件的产物.同时,据安山岩锆石U-Pb年龄谐和度(102)较好的锆石~(206)Pb/~(238)U表面年龄436±4Ma及英安岩锆石U-Pb年龄谐和度(104)较好的锆石~(206)Pb/~(238)U表面年龄153±2Ma和160±2Ma,表明大青山地区逆冲推覆构造存在构造复活或构造追踪现象。这一认识为大青山地区逆冲推覆构造的研究积累了新的资料,提供了新的研究思路。     

Mineral association and graphite inclusions in nephrite jade from Liaoning,northeast China: Implications for metamorphic conditions and ore genesis

The Liaoning Province in the northeastern part of the North China Craton(NCC) hosts several tremolite jade(nephrite) deposits. Here we investigate the Sangpiyu tremolite jade deposit where the relationship between abundant graphite inclusions within the jade remains enigmatic. We employ petrography, electron probe microanalysis, X-ray-diffraction, and Raman spectroscopy to characterize the tremolite jade and its inclusion minerals. The Sangpiyu jade is predominately composed of tremolite with minor calcite, dolomite, serpentine, titanite, zoisite, allanite, chlorite,apatite, chromite and graphite. Raman spectroscopy of graphite inclusions shows that the D1/G intensity ratio ranges from 0.78 to 0.88 in deep green samples and from 0.05 to 0.23 in dark green samples. The ranges of D1/(D1 + G) integral area ratio for these types are from 0.0548 to 0.3037 and 0.5528 to 0.7355 respectively. The formation temperature of graphite inclusions in the dark green tremolite jade is computed as 549.8 ℃, whereas that for the deep green sample is about343.2 ℃. Our results suggest that the jade formation occurred in a multi-stage process through the action of hydrothermal fluids and metamorphism possibly in a subduction-related setting at moderate to high temperatures.     

内蒙古道伦达坝铜钨锡矿床LA-ICP-MS锆石和锡石U-Pb年龄及其地质意义

道伦达坝矿床位于大兴安岭南段,是一个铜钨锡矿床,其铜、钨、锡储量均达中型。矿体呈脉状,主要产于二叠系砂板岩中的断裂破碎带中,华力西期黑云母花岗岩中的断裂破碎带中亦赋存有矿体。文章选取2件石英-萤石-白云母-电气石-锡石-黑钨矿阶段的矿石样品对其中的进行了LA-ICP-MS U-Pb定年,获得2件样品的~(207)Pb/~(206)Pb-~(238)U/~(206)Pb谐和年龄分别为(134.7±6.6)Ma(MSWD=1.4)和(136.8±7.4)Ma(MSWD=1.7),~(206)Pb/~(207)Pb-~(238)U/~(207)Pb等时线年龄分别为(132±12)Ma(MSWD=0.76)和(135±13)Ma(MSWD=0.9)。锡石定年结果表明,道伦达坝矿床形成于早白垩世。对矿区外围张家营子岩体中的斑状细粒花岗岩进行了LA-ICP-MS锆石U-Pb测年,获得的~(206)Pb/~(238)U加权平均年龄为(135±1)Ma(MSWD=1.3),该岩体的形成年龄与道伦达坝矿床的成矿年龄在误差范围内一致。本次定年结果表明道伦达坝矿床形成于早白垩世,与同期的花岗质岩浆活动有密切的成因联系,该矿床属于与花岗岩有关的岩浆热液脉型矿床。     

Zircon response to high-grade metamorphism as revealed by U–Pb and cathodoluminescence studies

Correct interpretation of zircon ages from high-grade metamorphic terrains poses a major challenge because of the differential response of the U–Pb system to metamorphism, and many aspects like pressure–temperature conditions, metamorphic mineral transformations and textural properties of the zircon crystals have to be explored. A large (c. 450?km²) coherent migmatite complex was recently discovered in the Bohemian Massif, Central European Variscides. Rocks from this complex are characterized by granulite- and amphibolite-facies mineral assemblages and, based on compositional and isotopic trends, are identified as the remnants of a magma body derived from mixing between tonalite and supracrustal rocks. Zircon crystals from the migmatites are exclusively large (200–400?μm) and yield ²⁰⁷Pb/²⁰⁶Pb evaporation ages between 342–328?Ma and single-grain zircon fractions analysed by U–Pb ID-TIMS method plot along the concordia curve between 342 and 325?Ma. High-resolution U–Pb SHRIMP analyses substantiate the existence of a resolvable age variability and yield older ²⁰⁶Pb/²³⁸U ages (342–330?Ma, weighted mean age?=?333.6?±?3.1?Ma) for inner zone domains without relict cores and younger ²⁰⁶Pb/²³⁸U ages (333–320?Ma, weighted mean age?=?326.0?±?2.8?Ma) for rim domains. Pre-metamorphic cores were identified only in one sample (²⁰⁶Pb/²³⁸U ages at 375.0?±?3.9, 420.3?±?4.4 and 426.2?±?4.4?Ma). Most zircon ages bracket the time span between granulite-facies metamorphism in the Bohemian Massif (~345?Ma) and the late-Variscan anatectic overprint (Bavarian phase, ~325?Ma). It is argued that pre-existing zircon was variously affected by these metamorphic events and that primary magmatic growth zones were replaced by secondary textures as a result of diffusion reaction processes and replacement of zircon by dissolution and recrystallization followed by new zircon rim growth. Collectively, the results show that the zircons equilibrated during high-grade metamorphism and record partial loss of radiogenic Pb during post-peak granulite events and new growth under subsequent anatectic conditions.     

北秦岭西段冥古宙锆石(4.1～3.9Ga)年代学新进展

2007年王洪亮等报道在北秦岭西段火山岩中获得一粒年龄为4079±5Ma的冥古宙捕虏锆石。之后,对这一发现开展了深入的调查研究,我们除利用SHIMP技术方法对原4079Ma的锆石进行验证外,新获得了两粒~(207)Pb/~(206)Pb年龄为4007±29Ma和3908±45Ma捕获的变质成因锆石,表明早在4.0Ga已经有变质作用的发生,这或许说明在冥古宙时期地球已经具有相当规模和厚度的地壳。同时开展的岩石学研究表明,蕴含古老锆石的母岩属于火山碎屑熔岩类而不是火山熔岩。