Petrogenesis of granitoids from the Lachlan Fold Belt,southeastern Australia: The role of disequilibrium melting

S- and I-type granites from the Lachlan Fold Belt, southeastern Australia, have been investigated to assess the role of disequilibrium melting in their petrogenesis. Differences between the median initial εHf compositions of magmatic zircon populations and the host bulk-rock (ΔεHf^blk-zrc) range from −0.6 to +2.5 ε units, providing evidence for intra-sample (and hence inter-phase) Hf-isotopic heterogeneity. Linear variations on Harker diagrams and O and Hf isotope compositions of magmatic zircon preserved in many I- and S-type granites are inconsistent with assimilation or simple mixing hypotheses. In contrast, isotopic disequilibrium between the melt and a restite assemblage can explain the bulk-rock versus zircon differences observed in these samples.Assuming that magmatic zircon records the melt composition, differences between the bulk-rock εHf and εHf of magmatic zircon (ΔεHf^blk-zrc values) measured for I-type granites (0.4–2.5) can largely be explained by disequilibrium amphibole dehydration melting of meta-igneous protoliths that were either isotopically heterogenous at the time they were formed, or perfectly homogeneous before being aged in the crust for 0.4–1.0 billion years prior to partial melting. The Currowong Suite exhibits petrographic features and preserves geochemical and isotopic compositions that do not lend themselves to simple restite model or magma mixing explanations; however, these observations could be explained by the restite unmixing of magma batches generated from a single source rock if, as modelling has suggested, separate batches contain different melt compositions.By investigating the application of disequilibrium melting to granite genesis, this study demonstrates that isotopic heterogeneity at various sampling scales should actually be expected for the production of granites from a single source, rather than necessitating the involvement of multiple sources and mixing processes. As a result great care should be taken in the interpretation of isotope data from granitic bulk-rocks or their zircons.     

Ubiquitous post-peak zircon in an eclogite from the Kumdy-Kol,Kokchetav UHP-HP Massif (Kazakhstan): Significance of exhumation-related zircon growth and modification in continental-subduction settings

U–Pb geochronological, trace-element and Lu–Hf isotopic studies have been made on zircons from ultrahigh-pressure (UHP) mafic eclogite from the Kumdy-Kol area, one of the diamond-facies domains of the Kokchetav Massif (northern Kazakhstan). The peak eclogitic assemblage equilibrated at > 900 °C, whereas the bulk sample composition displays light rare-earth element (LREE) and Th depletion evident of partial melting. Zircons from the eclogite are represented by exclusively newly formed metamorphic grains and have U–Pb age spread over 533–459 Ma, thus ranging from the time of peak subduction burial to that of the late post-orogenic collapse. The major zircon group with concordant age estimates have a concordia age of 508.1 ±4.4 Ma, which corresponds to exhumation of the eclogite-bearing UHP crustal slice to granulite- or amphibolite-facies depths. This may indicate potentially incoherent exhumation of different crustal blocks within a single Kumdy-Kol UHP domain. Model Hf isotopic characteristics of zircons (ε_Hf(t) +1.5 to +7.8, Neoproterozoic model Hf ages of 1.02–0.79 Ga) closely resemble the whole-rock values of the Kumdy-Kol eclogites and likely reflect in situ derivation of HFSE source for newly formed grains. The ages coupled with geochemical systematics of zircons confirm that predominantly late zircon growth occurred in Th–LREE-depleted eclogitic assemblage, that experienced incipient melting and monazite dissolution in melt at granulite-facies depths, followed by amphibolite-facies rehydration during late-stage exhumation-related retrogression.     

金川铜镍硫化物样品中锇同位素比值的高精度分析

采用两种独立的190Os稀释剂、4个不同的化学流程,用等离子体质谱仪、TRITON热表面电离质谱仪和MAT-262固体质谱仪3种质谱仪器,在4个实验室分别对采自金川铜镍硫化物样品的187Os/188Os同位素比值进行分析,样品分析数量达到56个。4个实验室获得的结果分别为0.3356±0.0018(n=12,2s)、0.3363±0.0008(n=6,2s)、0.3363±0.0010(n=18,2s)和0.3353±0.0034(n=20,2s)。采用ISOPLOT软件对所得56个数据进行加权平均计算,得到187Os/188Os同位素比值为0.33602±0.00022(置信度95%)。两台TRITON热表面电离质谱仪测量的结果几乎完全一致,且精度高于MAT-262固体质谱仪和等离子体质谱仪。比较了碱熔和Carius管两种溶样方法,结果表明,对于所研究的样品,用Carius管溶矿方式可以将含锇矿物完全溶解。     

Petrogenesis of the microcrystalline-dioritic enclaves from Jiuling granitoids in the eastern segment of Jiangnan Orogen and constraints on magma source materials

Numerous dark enclaves with different shapes are found in Jiuling Neoproterozoic granitoids. Precise LA-ICP-MS U-Pb dating was conducted on zircons extracted from two microcrystalline enclave samples, yielding crystallization ages of 822.6±5.8 Ma and 822.2±6.2 Ma, respectively. The consistent ages within analytical errors with the host granitoids suggested that they were the products of the same magmatism. The microcrystalline-dioritic enclaves commonly show plastic forms and contain similar plagioclase megacrysts to the host rocks, and both of the enclaves and host granitoids showed a complex composition and structural imbalance in plagioclases. Furthermore, the apatites with a euhedral acicular shape occurred widely in the microcrystalline-dioritic enclaves. All of these petrographic features above imply magma mixing is involved in their diagenesis. The enclaves and host granitoids show a marked zircon trace element difference and Hf isotopic signatures without correlation in zircon trace element pairs but form their own system between enclaves and host granitoids. Additionally, most of the zircons show extremely high ε_Hf (t) with ε_Hf (t) =3.54–11.94 from the southern samples, and ε_Hf (t) =1.0–9.09 from the central region. Some zircons with the higher ε_Hf (t) are similar to the zircons from the juvenile island arc in the eastern segment of Jiangnan Orogen. Integrated geological and Hf isotopic characteristics suggest microcrystalline-dioritic enclaves were derived from the partial melting process of the Mesoproterozoic crust which enriched juvenile island arc materials and mixed with the granitic magma that remelted from the Mesoproterozoic continental crust which relatively enriched ancient sediments and mixed with the host granitoid in diagenesis.     

浙东白垩纪双峰式火山岩Sr、Nd同位素组成及其成因意义

浙东白垩纪火山岩以发育双峰式岩石组合为特征,其成因一直是有争议的问题。本文从其两端元岩石——玄武岩和流纹岩的Sr,Nd同位素特征出发,论证了玄武岩起源于经过俯冲来源的物质交代(或混染)的富集型地幔楔,流纹岩主要由古老变质基底重熔生成,并与玄武岩岩浆发生过低度混合。在混合过程中,玄武岩的Sr同位素组成基本未受到影响,Nd同位素组成可能发生一定的变化;流纹岩的Sr同位素组成则有明显改变。     

同位素填图与深部物质探测(Ⅱ)：揭示地壳三维架构与区域成矿规律

地球深部是大规模成矿作用的“驱动机”、“供应源”和“传输带”。深入揭示深部物质组成与分布、物质循环与能量转换、三维架构与动力过程,对理解成矿作用至关重要。岩浆岩“探针”及区域同位素(如全岩Nd、锆石Hf)填图是探索深部物质组成与演化过程的主要手段,可以探测地壳深部物质组成的三维架构,揭示新生地壳/古老地壳/再造地壳的空间分布与时空演变,从而为提升区域成矿规律认识提供深部物质制约证据,有助于成矿潜力的定量半定量评价及其区域成矿预测。文章重点总结和探讨了岩浆岩全岩Nd同位素和锆石Hf同位素区域填图在解决地壳三维架构与成矿规律方面的应用成果,深入探讨了巨量岩浆岩发育的深部驱动机制及其成矿制约,对比总结了不同类型造山带(如中亚增生造山带、青藏高原碰撞造山带、秦岭复合造山带等)和不同克拉通的地壳深部组成结构与成矿制约特色。研究显示：不论是什么造山带和克拉通,深部年轻地壳分布区制约了铜金、铜镍等矿床的形成分布;古老地壳控制了大型钼矿、铅锌矿、稀有金属等矿产;两者过渡地带常常发育铁矿等。这些研究不仅揭示了区域成矿规律,而且对成矿预测与成矿潜力评价有潜在的应用价值,有可能成为成矿规律研究特别是深部物质探测及成矿背景研究的新方向。     

Zircon U–Pb ages and Hf isotope compositions of migmatites from the North Qinling terrane and their geological implications

Migmatites are predominant in the North Qinling (NQ) orogen, but their formation ages are poorly constrained. This paper presents a combined study of cathodoluminescence imaging, U–Pb age, trace element and Hf isotopes of zircon in migmatites from the NQ unit. In the migmatites, most zircon grains occur as new, homogeneous crystals, while some are present as overgrowth rims around inherited cores. Morphological and trace element features suggest that the zircon crystals are metamorphic and formed during partial melting. The inherited cores have oscillatory zoning and yield U–Pb ages of c. 900 Ma, representing their protolith ages. The early Neoproterozoic protoliths probably formed in an active continental margin, being a response to the assembly of the supercontinent Rodinia. The migmatite zircon yields Hf model ages of 1911 ± 20 to 990 ± 22 Ma, indicating that the protoliths were derived from reworking of Palaeoproterozoic to Neoproterozoic crustal materials. The anatexis zircon yields formation ages ranging from 455 ± 5 to 420 ± 4 Ma, with a peak at c. 435 Ma. Combined with previous results, we suggest that the migmatization of the NQ terrane occurred at c. 455–400 Ma. The migmatization was c. 50 Ma later than the c. 490 Ma ultra‐high‐P (UHP) metamorphism, indicating that they occurred in two independent tectonic events. By contrast, the migmatization was coeval with the granulite facies metamorphism and the granitic magmatism in the NQ unit, which collectively argue for their formation due to the northward subduction of the Shangdan Ocean. UHP rocks were distributed mainly along the northern margin and occasionally in the inner part of the NQ unit, indicating that they were exhumed along the northern edge and detached from the basement by the subsequent migmatization process.     

内蒙古维拉斯托锌铜矿床选矿试验研究

维拉斯托锌铜多金属矿床矿石中富含多种元素,其中铜、铅、锌、砷、银、钨、钴等元素具有综合利用价值,矿石类型属于比较难选多金属矿石.采用混合浮选铜铅（-0.076 mm为65%）-依次浮选锌、砷（钴）-再浮选钨-重选（摇床）选钨的选矿工艺流程,对选矿pH值、药剂种类及用量等系列选矿条件进行了实验研究,达到较为理想的选矿效果,为矿山生产提供了技术保证.     

福建武平地区桃溪群混合岩U-Pb定年及其Hf同位素组成:对桃溪群时代及郁南运动的约束

桃溪群混合岩位于南岭东段武夷山褶皱带南段.本文通过采自桃溪附近帽村-田园两个代表性花岗片麻岩样品进行LA-ICP-MS锆石U-Pb 测年获得494～496Ma的结晶年龄,641～657Ma和799Ma两组继承锆石的206Pb/238U 表观年龄.同时对样品FJ-137进行的Hf同位素测定表明其εHf(t)变化于-2.3...     

氩同位素用于库车坳陷天然气主力气源岩判识

稀有气体是天然气中指示其地球化学特征的重要组分,放射成因氩( Arr)的年代积累效应广泛应用于同位素定年和天然气的气源对比.本文系统地讨论了 40Ar的形成机理及其运移进入气藏的过程,利用 40Ar的母体元素 K在煤和煤系泥岩中的丰度差异,分析了以煤和煤系泥岩为母源的天然气 40Ar/36Ar同位素组成上的不同,并利用这种差异对煤系中煤岩或煤系泥岩为源岩的天然气藏的主力源岩进行了判识,继而建立了利用氩同位素组成判识煤系烃源岩主力源岩的方法.利用此方法对塔里木盆地库车坳陷三叠系-侏罗系煤与煤系泥岩互层的烃源岩进行了探讨, 数学计算结果表明该区主力源岩为煤系泥岩, 煤对天然气藏的贡献较小.