Determination of High Field Strength Elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g−1 Levels in Geological Reference Materials by Magnetic Sector ICP-MS after HF/HClO4 High Pressure Digestion

Six low abundance rock reference materials (basalt BIR-1, dunite DTS-1, dolerite DNC-1, peridotite PCC-1, serpentine UB-N and basalt TAFAHI) have been analysed for high field strength elements (Zr, Nb, Hf, Ta, Th and U), Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g⁻¹ levels (in rock) by magnetic sector inductively coupled plasma-mass spectrometry after HF/HClO₄ high pressure decomposition. The adopted method uses only indium as an internal standard. Detection limits were found to be in the range of 0.08 to 16.2 pg ml⁻¹ in solution (equivalent to 0.08 to 16.2 ng g⁻¹ in rock). Our data for high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi for the six selected low abundance geological reference materials show general agreement with previously published data. Our Ta values in DTS-1 and PCC-1 (1.3 and 0.5 ng g⁻¹) are lower than in previously published studies, providing smooth primitive mantle distribution patterns. Lower values were also found for Tl in BIR-1, DTS-1 and PCC-1 (2, 0.4 and 0.8 ng g⁻¹). Compared with quadrupole ICP-MS studies, the proposed magnetic sector ICP-MS method can generally provide better detection limits, so that the measurement of high field strength elements, Rb, Sr, Mo, Sb, Cs, Tl and Bi at ng g⁻¹ levels can be achieved without pre-concentration, ion exchange separation or other specialised techniques.     

西藏冈底斯西段鲁尔玛晚三叠世二长闪长岩的成因

晚三叠世及以前岩浆活动研究的缺乏严重制约了雅鲁藏布新特提斯洋演化模式的讨论.为探讨冈底斯西段打加错地区晚三叠世岩浆活动的地球动力学背景,对鲁尔玛二长闪长岩开展了岩石学、地球化学和年代学研究工作.利用LA-ICP-MS方法测得2件二长闪长岩样品的锆石206Pb/238U年龄加权平均值为212.1±0.6 Ma(MSWD=0.97)和212.8±0.2 Ma(MSWD=0.74),表明鲁尔玛中性岩浆活动发生在晚三叠世.二长闪长岩主要由斜长石、钾长石、普通角闪石等组成,并含少量石英、普通辉石、黑云母、磁铁矿、磷灰石等,具有中等的SiO₂(50.75%~54.69%)含量,高的K₂O(2.71%~3.99%)和总碱(K₂O+Na₂O=5.84%~8.65%)含量,以及中等的A1₂O₃(13.77%~19.17%)含量,较高的CaO(4.90%~10.14%)含量.里特曼指数(σ₄₃)为3.40~7.65,A/CNK值为0.56~1.00,表明鲁尔玛二长闪长岩属于准铝质钾玄岩系列岩石.岩石富集轻稀土元素(LREE)和大离子亲石元素(LILE),相对亏损重稀土元素和高场强元素(HFSE),轻重稀土分异较弱(LREE/HREE=7.45~11.10),并具轻微的Eu负异常(δEu=0.83~0.95),无Ce异常(0.93~1.04).相对较低的87Sr/86Sr初始比值((87Sr/86Sr)_t=0.705 532~0.706 135,平均0.705 852)、正的ε_Hf(t)值(4.97~14.10,平均8.77)、年轻的地壳模式年龄(T_DM2=348~930 Ma,平均为686 Ma),(143Nd/144Nd)_t和ε_Hf(t)分别为0.512 639~0.512 669(平均为0.512 657)和0.08~0.67(平均为0.43),(206Pb/204Pb)_t、(207Pb/204Pb)_t和(208Pb/204Pb)_t分别为:18.235~18.521(平均为18.411)、15.593~15.651(平均为15.617)和39.948~38.579(平均为38.401),指示二长闪长岩起源于新生地壳.Sr-Nd-Pb-Hf同位素及微量元素特征表明鲁尔玛二长闪长岩为新生地壳部分熔融的产物.研究结果揭示,鲁尔玛二长闪长岩体是晚三叠雅鲁藏布新特提斯洋北向俯冲初期,新生地壳熔融形成的准铝质碱性钾玄岩系岩石.该岩体的研究表明,在晚三叠世(~213 Ma),冈底斯西段的打加错地区,雅鲁藏布新特提斯洋壳已经向北俯冲到南拉萨微陆块之下.      

The Preparation and Characterisation of Two New Geological Survey of Japan Geochemical Reference Materials: Copper ore JCu-1 and Zinc ore JZn-1

Two new geochemical reference materials, copper ore JCu-1 and zinc ore JZn-1 have been prepared by the Geological Survey of Japan (GSJ) for the determination of major and minor elements and isotopic compositions. JCu-1 is a sample of Cu-bearing sulfide ore typical of the Kamaishi mine in Iwate Prefecture, Japan, and is composed mainly of hedenbergite, chalcopyrite, quartz and calcite. Pyrrhotite, magnetite and actinolitic amphibole were also commonly found. The Zn-rich ore, JZn-1 is a crude ore from the Kamioka Pb-Zn mine in Gifu Prefecture, Japan. The sample consists of hedenbergite, quartz, calcite, sphalerite and epidote as main crystalline phase. Homogeneity test results showed that all studied constituents including ore elements such as Cu, Pb and Zn can be considered to be homogeneously distributed. Provisional collaborative analyses were carried out in ten laboratories, and the data were evaluated using a robust statistical method using z-scores. Recommended values for a number of major elements including TiO₂, Al₂O₃, MnO, MgO, CaO, Na₂O, K₂O, Fe (total), Zn, Cu and Pb were established. In addition, information values for eighteen major, minor and trace elements are presented to support future collaborative analyses.     

胶东范家庄地区晚侏罗世低镁埃达克质花岗岩成因及构造背景

胶东地区广泛发育一系列晚侏罗世岩浆作用产生的埃达克质岩,其成因机制及构造背景研究为揭示胶东地区中生代构造演化提供了重要证据.选取出露于胶东苏鲁地区的范家庄花岗岩进行锆石U-Pb年龄、全岩主微量元素和Sr-Nd-Pb同位素组成分析,探讨了岩石成因及成岩构造背景.锆石U-Pb年龄结果表明范家庄花岗岩侵位于晚侏罗世（161±2 Ma）.岩石主微量数据具有富硅（SiO₂=68.94%~71.00%）、高铝（Al₂O₃>15.17%）、低镁（MgO=0.32%~0.41%）;高Sr、低Y、Yb含量以及高（La/Yb）_N（>38.59）比值的特点,同位素测试结果显示相对高的（87Sr/86Sr）_i比值（0.709 28~0.711 41）、相对较低的ε_Nd（t）值（-20.5~-14.1）和高放射性Pb同位素组成（206Pb/204Pb）_t=16.853~17.207,（207Pb/204Pb）_t=15.436~15.495,（208Pb/204Pb）_t=37.340~37.629.综合分析认为,范家庄岩体属于低镁埃达克质岩,产于增厚下地壳部分熔融,源区以扬子板块下地壳组分为主,混合有华北板块下地壳成分.晚侏罗世伊泽奈奇板块俯冲形成的弧后拉张环境诱发重力不稳定或者岩石圈伸展造成加厚的造山带垮塌,软流圈上涌的导致加厚地壳部分熔融可能是形成胶东范家庄低镁埃达克岩的地球动力学背景.      

中亚造山带南缘甘肃北山地区花牛山闪长玢岩地球化学特征及地质意义

为揭示中亚造山带南段洋?陆构造演化时限及动力学背景,对中亚造山带南缘北山地区花牛山晚古生代闪长玢岩进行年代学、主微量及Sr-Nd-Pb同位素研究.闪长玢岩LA-ICP-MS锆石U-Pb年龄为287.6±7.5 Ma,SiO₂为53.92%~54.84%,K₂O+Na₂O为6.34%~6.82%,高Al₂O₃（14.66%~15.23%）低MgO（3.20%~3.99%）,Mg#值为40.26~46.50;轻稀土元素富集（（La/Yb）_N=20.07~21.33）,弱负Eu异常（δEu=0.79~0.82）;明显富集Cs、Rb、Ba、K、Th及Pb,弱富集Zr和Hf,亏损Nb、Ta、Ti、P和Sr;（87Sr/86Sr）_i值在0.707 009~0.708 799之间,（143Nd/144Nd）_i值介于0.512 248~0.512 272,ε_Nd（t）值为-0.39~+0.09.这些特征指示闪长玢岩源于地幔物质熔融,岩浆演化过程中发生地壳同化混染.结合区域地质背景,花牛山闪长玢岩的形成与北山南部辉铜山?帐房山洋盆北向俯冲闭合后的板内伸展构造背景相关,指示中亚造山带南缘北山南部于早二叠世时已经进入陆内构造阶段.      

A 3.1 billion year old marble and the 87Sr/86Sr of late-Archean seawater

A marble band in the ≈ 2.75 Gyr old Ramagiri schist belt in the Dharwar craton of south India gave a Pb–Pb age of 3.075 ± 0.095 Gyr. The geochemical data, including high Sr and low Ba and Mn indicate seawater origin for the parent rock, and that there was insignificant geochemical exchange between the marble and the surrounding rocks. The calculated initial Nd isotopic composition and μ₁ indicate an older continental crustal source for the Nd and Pb. The initial ⁸⁷Sr/⁸⁶Sr of the marble is 0.70128, which is higher than the calculated mantle value at ≈ 3 Ga. Although pre-3 Gyr old marine carbonate rocks are thought to be buffered by mantle Sr, the Ramagiri marble contains evolved, crustal Sr. Despite this, the marble has the lowest measured ⁸⁷Sr/⁸⁶Sr among carbonates and represents one of the least radiogenic periods in seawater Sr isotope composition.     

Suppression of Matrix Effects in ICP-MS by High Power Operation of ICP: Application to Precise Determination of Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U at ng g-1 Levels in Milligram Silicate Samples

We found that the suppression of signals for ⁸⁸Sr, ¹⁴⁰Ce and ²³⁸U in rock solution caused by rock matrix in ICP-MS (matrix effects) was reduced at high power operation (1.7 kW) of the ICP. To make the signal suppression by the matrix negligible, minimum dilution factors (DF) of the rock solution for Sr, Ce and U were 600, 400 and 113 at 1.1, 1.4 and 1.7 kW, respectively. Based on these findings, a rapid and precise determination method for Rb, Sr, Y, Cs, Ba, REE, Pb, Th and U using FI (flow injection)-ICP-MS was developed. The amount of the sample solution required for FI-ICP-MS was 0.2 ml, so that 1.8 mg sample was sufficient for analysis with a detection limit of several ng g^-1. Using this method, we determined the trace element concentrations in the USGS rock reference materials, DTS-1, PCC-1, BCR-1 and AGV-1, and the GSJ rock reference materials, JP-1, JB-1, -2, -3, JA-1, -2 and -3. The reproducibilities (RSD %) in replicate analyses (n=5) of BCR-1, AGV-1, JB-1, -2, -3, JA-1, -2, and -3 were < 6 %, and typically 2.5%. The difference between the average concentrations of this study for BCR-1 and those of the reference values were < 2%. Therefore, it was concluded that the method can give reliable data for trace elements in silicate rocks.     

Geochemical Characteristics of the Akiyoshi Limestones, Japan and Their Bearing on Exploration for Blind Skarn Deposits

Abstract. Carboniferous-Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ¹⁸O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ¹³C values are small. The δ¹⁸O values are negatively correlated with Mn and Fe contents. Samples with high δ¹⁸O (>25%) and δ¹³C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ¹⁸O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H₂O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ¹⁸O, δ¹³C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW-SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb-Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary.     

NEW SET OF LOW CONCENTRATION STANDARDS FOR LA, CE, SM, YB, LU, Y, SC, V, NB AND TA IN SILICATES

We have developed a set of four synthetic standards for the rare earth and high field strength elements designed for use in the determination of those elements in silicates. The base material is a glass nominally at the eutectic of the MgO-Al₂O₃-SiO₂ ternary system. The nominal doping level was 2 wt% of the elements as oxides. To avoid problems associated with peak interference, the elements were doped in four separate glasses.     

Phlogopite in the generation of olivine-melilitites from Namaqualand, South Africa and implications for element fractionation processes in the upper mantle

Major and trace element and Sr, Nd and Pb isotope analyses are presented for thirteen olivine-melilitites from Namaqualand, South Africa. Major element variations are consistent with derivation from carbonated garnet-peridotite at depths of at least 100 km and trace element abundances indicate melt fractions of 4%. Ubiquitous negative K anomalies and low, buffered K₂O concentrations are interpreted to reflect the effect of residual phlogopite during melting. It is suggested that phlogopite stability and low melt potassium saturation concentrations are enhanced by high CO₂/(CO₂ + H₂O) conditions. Residual phlogopite can also account for low measured Rb/Sr, Ba/Sr and Th/U ratios in the melilitites. REE abundances are controlled by residual garnet and hence Sm/Nd ratios are low (0.13–0.18). U/Pb ratios vary from 0.05 to 5 and are a function of Pb concentration which is in turn controlled by residual Pb-rich phase (probably sulphide). Nd and Sr isotopes are comparable with OIB from St. Helena, although two samples extend to higher ⁸⁷Sr/⁸⁶Sr ratios. Present day Pb isotopes are much more variable and partly reflect radiogenic growth since emplacement as a result of the highly variable U/Pb ratios.

Many of the trace element characteristics of the melilitites are distinct from those of within-plate potassic magmas despite both being derived from phlogopite-bearing, enriched mantle source regions. This can be attributed to the depth at which source enrichment occurred and the subsequent control exerted by phlogopite and carbonate during melting. In contrast to melilitites, potassic magmas are derived from shallower depths under low CO₂/(CO₂ + H₂O) conditions and at higher temperatures at which phlogopite melts more readily.

The incompatible element ratios of the melilitites are also similar to those both observed in HIMU ocean island basalts (OIB) and inferred for HIMU OIB source regions from isotope variations (viz, low Sm/Nd, Rb/Sr, K/Nb, Th/U and high U/Pb and Ce/Pb). It is suggested that HIMU OIB's may be derived from sources that have been subject to enrichment by a melt generated in the presence of residual phlogopite.     

A Gold-bearing Alkaline Pluton in Eastern Linxi District, Inner Mongolia: Its Geochemistry and Metallogenic Significance

Abstract: The Biliutai pluton, as the host of a small gold deposit, containing dark-gray enclaves, intruded into the Lower Permian volcanic-sedimentary formations in east Inner Mongolia, China. The host rocks and enclaves formed simultaneously at about 200 Ma (Rb–Sr isochron age with initial ⁸⁷Sr/⁸⁶Sr of 0.704). The _Nd (T) values for the enclaves (from +4.4 to +4.6) are similar to their host rocks (+3.2 to +4.8), although the values for the host rocks are relatively variable. Both enclaves and host rocks are enriched in large ion lithosphere elements and light rare earth elements but depleted in high field strength elements and heavy rare earth elements. These observations suggest that the magma was produced from subduction-modified mantle sources. The age of the mantle enrichment event, evaluated using depleted mantle Nd model ages, is 0.61 - 0.83 Ga. These geochemical characteristics constrain the metallogeny of the Biliutai pluton, and imply that the ore-forming materials probably were derived from lithospheric mantle.     

Flotation Separation of Trace Elements from Alkaline-Earth Matrices by Co(III) Hexamethylenedithiocarbamate before ICP-AES Determination

A method for the selective separation of Ag, Cd, Cr, Cu, Ni, Pb and Zn in traces from solutions of calcite (CaCO₃), dolomite (CaMg(CO₃)₂) and gypsum (CaSO₄.2H₂O) before their determination by inductively coupled plasma-atomic emission spectrometry (ICP-AES) is presented. The expected interferences of Ca and Mg on intensities of trace analytes were removed by collecting the elements of interest with cobalt(III) hexamethylenedithiocar-bamate, Co(HMDTC)₃. The flotation of aqueous solutions (1 l) of calcite, dolomite and gypsum was performed at pH 6.0, by 1.5 mg l⁻¹ Co and 0.6 mmol l⁻¹ HMDTC⁻. To minimise the effect of the reaction between Ca/Mg, which restrains the function of the surfactant, careful selection of the most suitable foaming reagent was necessary. The accuracy of the method was established by analysing natural alkaline-earth minerals by the standard addition method as well as using the dolomite reference materials GBW 07114 and GSJ JDo-1. The ICP-AES limits of detection following flotation on different minerals were found to be 0.080 μg g⁻¹ for Cd, 0.105 μg g⁻¹ for Ag, 0.142 μg g⁻¹ for Cu, 0.195 μg g⁻¹ for Cr, 0.212 μg g⁻¹ for Ni, 0.235 μg g⁻¹ for Zn and 0.450 μg g⁻¹ for Pb.     

Isotopic equilibrium/disequilibrium in granites, metasedimentary rocks and migmatites (Damara orogen, Namibia)—a consequence of polymetamorphism and melting

The overwhelming part of the continental crust in the high-grade part of the Damara orogen of Namibia consists of S-type granites, metasedimentary rocks and migmatites. At Oetmoed (central Damara orogen) two different S-type granites occur. Their negative ε_Nd values (− 3.3 to − 5.9), moderately high initial ⁸⁷Sr/⁸⁶Sr ratios (0.714–0.731), moderately high ²⁰⁶Pb/²⁰⁴Pb (18.21–18.70) and ²⁰⁸Pb/²⁰⁴Pb (37.74–37.89) isotope ratios suggest that they originated by melting of mainly mid-Proterozoic metasedimentary material. Metasedimentary country rocks have initial ε_Nd of − 4.2 to − 5.6, initial ⁸⁷Sr/⁸⁶Sr of 0.718–0.725, ²⁰⁶Pb/²⁰⁴Pb ratios of 18.32–18.69 and ²⁰⁸Pb/²⁰⁴Pb ratios of 37.91–38.45 compatible with their variation in Rb/Sr, U/Pb and Th/Pb ratios. Some migmatites and residual metasedimentary xenoliths tend to have more variable ε_Nd values (initial ε_Nd: − 4.2 to − 7.1), initial Sr isotope ratios (⁸⁷Sr/⁸⁶Sr: 0.708–0.735) and less radiogenic ²⁰⁶Pb/²⁰⁴Pb (18.22–18.53) and ²⁰⁸Pb/²⁰⁴Pb (37.78–38.10) isotope compositions than the metasedimentary rocks. On a Rb–Sr isochron plot the metasedimentary rocks and various migmatites plot on a straight line that corresponds to an age of c. 550 Ma which is interpreted to indicate major fractionation of the Rb–Sr system at that time. However, initial ⁸⁷Sr/⁸⁶Sr ratios of the melanosomes of the stromatic migmatites (calculated for their U–Pb monazite and Sm–Nd garnet ages of c. 510 Ma) are more radiogenic (⁸⁷Sr/⁸⁶Sr: 0.725) than those obtained on their corresponding leucosomes (⁸⁷Sr/⁸⁶Sr: 0.718) implying disequilibrium conditions during migmatization that have not lead to complete homogenization of the Rb–Sr system. However, the leucosomes have similar Nd isotope characteristics than the inferred residues (melanosomes) indicating the robustness of the Sm–Nd isotope system during high-grade metamorphism and melting. On a Rb–Sr isochron plot residual metasedimentary xenoliths show residual slopes of c. 66 Ma (calculated for an U–Pb monazite age of 470 Ma) again indicating major fractionation of Rb/Sr at c. 540 Ma. However, at 540 Ma, these xenoliths have unradiogenic Sr isotope compositions of c. 0.7052, indicating depleted metasedimentary sources at depth. Based on the distinct Pb isotope composition of the metasedimentary rocks and S-type granites, metasedimentary rocks similar to the country rocks are unlikely sources for the S-type granites. Moreover, a combination of Sr, Nd, Pb and O isotopes favours a three-component mixing model (metasedimentary rocks, altered volcanogenic material, meta-igneous crust) that may explain the isotopic variabilty of the granites. The mid-crustal origin of the different types of granite emphasises the importance of recycling and reprocessing of pre-existing differentiated material and precludes a direct mantle contribution during the petrogenesis of the orogenic granites in the central Damara orogen of Namibia.     

拉萨地体西段达若地区古新世花岗斑岩成因:锆石U-Pb年代学、岩石地球化学和Sr-Nd-Pb-Hf同位素的约束

前人对林子宗群典中组火山岩的成因研究较为深入,却忽略了侵位于其中的大量花岗斑岩.在野外地质调查的基础上,对拉萨地体西段达若地区花岗斑岩进行了年代学、岩石地球化学和Sr-Nd-Pb-Hf同位素研究.结果显示,2件花岗斑岩的成岩年龄分别为61.9±0.3 Ma(MSWD=0.17)和61.1±0.6 Ma(MSWD=0.69),为古新世岩浆活动的产物;岩石中未见角闪石及富铝矿物,属高钾钙碱性－钾玄岩系列,具有高SiO₂(76.16%~82.78%,平均为78.28%)、高碱(K₂O+Na₂O=4.16%~6.93%,平均为6.09%)、低CaO(0.11%~0.16%,平均为0.14%)和P₂O₅(0.02%~0.04%,平均为0.03%)的特点,富集Rb、Th、K和LREE,亏损Ba、Nb、Sr、P、Ti和HREE,轻、重稀土元素分馏强烈,负Eu异常显著,属强过铝质的高分异I型花岗岩.岩石富含放射成因Pb,(208Pb/204Pb)_t、(207Pb/204Pb)_t和(206Pb/204Pb)_t值分别为为38.737~38.944、15.661~15.682和18.079~18.624,且具有较高的(87Sr/86Sr)_i值(0.722 739~0.744 497)、ε_Nd(t)值(－6.82~－6.67),锆石ε_Hf(t)值(－4.97~－1.54)为较为分散而低弱的负值,Hf同位素二阶段亏损地幔模式年龄(T_DM2)介于1 083~1 273 Ma,Nd-Hf同位素之间发生了一定程度的解耦.综合研究表明,达若花岗斑岩形成于印度－欧亚大陆主碰撞板块汇聚(65~41 Ma)的早阶段,主要为滞后的俯冲新特提斯洋壳与地幔岩石相互作用形成的母岩浆底侵于拉萨地体古老地壳之下致使其重熔,并与少部分幔源岩浆混合之后,经高程度的结晶分异作用形成.      

东天山阿奇山-雅满苏构造带小东山火山岩的成因和意义:年代学、主微量元素及Sr-Nd-Hf同位素地球化学约束

阿奇山-雅满苏构造带是东天山造山带的重要组成部分,其大地构造属性至今仍存在争议.小东山火山岩出露于阿奇山-雅满苏构造带的西段,包括基性到酸性系列火山岩,是认识阿奇山-雅满苏构造带属性和演化的有效“岩石探针”.本次工作对其开展了系统的岩石学、锆石U-Pb年代学、元素和同位素地球化学研究.研究结果表明,小东山火山岩主要由花岗斑岩、英安斑岩、安山岩、玄武岩以及橄榄玄武岩组成,元素协变关系指示该套火山岩系列属于同源岩浆的演化产物.锆石LA-ICP-MS U-Pb测年结果显示,小东山火山岩年龄为318~308 Ma,形成于晚石炭世.该套火山岩SiO₂含量变化范围较大（48.10%~76.82%）,Al₂O₃含量整体较低且变化范围较小.从基性岩到酸性岩,稀土总量逐渐增加,Eu/Eu*值逐渐降低.中酸性火山岩大离子亲石元素Rb、K、Pb、Sr等相对富集,高场强元素Nb、Ta、Ti、P、Th等强烈亏损.而基性火山岩主要表现为Nb、Ta、Zr、Hf、Ti负异常,K、Pb、P正异常.所有火山岩均以低（87Sr/86Sr）_i（0.704 50~0.707 14）、高ε_Nd（t）（+3.16~+5.71）以及高ε_Hf值（+5.45~+12.18）为特征.上述元素和同位素地球化学特征指示了小东山火山岩形成于岛弧构造环境,起源于交代地幔楔的部分熔融并经过了结晶分异作用.结合前人对区域构造-岩浆活动的认识,本文认为小东山火山岩所在的阿奇山-雅满苏岛弧带是在石炭纪古天山洋向南俯冲过程中形成.      

拉萨地块措勤-隆格尔地区铁矿床成岩时代、岩石成因及构造环境指示

为深入了解中北部拉萨地块构造背景,利用LA-ICP-MS技术对洛布勒铁矿床成矿花岗闪长岩锆石进行了U-Th-Pb同位素测定,分析了隆格尔、洛布勒铁矿床侵入岩岩石地球化学和Sr-Nd-Pb同位素组成.获得洛布勒花岗闪长岩锆石U-Pb年龄为111.3±1.6 Ma(MSWD=0.61,n=9).隆格尔和洛布勒铁矿床侵入岩高硅(66.63%~69.02%和64.33%~64.82%)、富碱(全碱为5.91%~6.40%和5.81%~6.05%)、低A/CNK(0.91~0.97和0.94~0.95)、SiO2与P2O5含量负相关;稀土元素总量较低(∑REE为123.11×10^-6~148.83×10^-6和96.17×10^-6~101.92×10^-6),球粒陨石标准化配分模式图右倾,弱Eu负异常(0.70~0.82和0.79~0.81),富集大离子亲石元素Rb、Th、U、K、Pb等,亏损Ba和高场强元素Nb、Ta、Sr、Ti等.隆格尔花岗岩全岩和斜长石(206Pb/204Pb)t为18.474和18.626,(207Pb/204Pb)t为15.657和15.722,(208Pb/204Pb)t为38.592和39.145,(87Sr/86Sr)i为0.704 757 6和0.707 047 3,(143Nd/144Nd)i为0.512 281和0.512 339,εNd(t)为-4.13和-2.99,tDM2为1.15 Ga和1.24 Ga;洛布勒花岗闪长岩(206Pb/204Pb)t比值为18.281,(207Pb/204Pb)t比值为15.616,(208Pb/204Pb)t比值为38.369,(87Sr/86Sr)i为0.706 551 4;(143Nd/144Nd)i为0.512 309,εNd(t)为-3.62,tDM2为1.20 Ga.结果表明,措勤-隆格尔铁矿床成矿侵入岩为中钾-高钾钙碱性岩I型花岗岩,为早白垩世晚期岛弧岩浆活动产物,岩浆源于地壳物质部分熔融,岩浆演化过程经历了壳幔岩浆混合和围岩混染.结合前人研究成果,通过对比白垩纪中北部拉萨地块和南部羌塘地块成矿事件的差异,提出中北部拉萨地块113±3 Ma岩浆活动和Fe(-Cu)成矿事件与向南俯冲的班公湖-怒江洋壳发生断离有关.     

拉萨地块西部狮泉河地区典中组火山岩年代学、地球化学特征及其构造意义

广泛分布于拉萨地块南部的林子宗群火山岩被认为是新特提斯洋北向俯冲消减到陆陆碰撞构造背景转化过程中的岩浆作用产物，记录了从新特提斯洋俯冲到印度-欧亚板块碰撞、后碰撞的丰富信息.对狮泉河地区的林子宗群典中组火山岩样品进行了详细的年代学、元素及同位素地球化学研究.结果显示典中组火山岩样品LA-ICP-MS锆石U-Pb年龄集中在67.1±1.7 Ma至70.8±1.1 Ma，表明其形成于白垩纪晚期.火山岩岩性主要包括玄武安山岩、安山岩、流纹岩等，其中，中基性火山岩为一套低钾拉斑-钙碱性系列岩石，具有低TiO₂（平均值< 1%），高Al₂O₃（平均值>15%），均富集K、Rb、Th、U等大离子亲石元素（LILE），亏损Nb、Ta、Zr、Ti等高场强元素（HFSE），具有弧岩浆岩的地球化学特征.两件中基性岩样品（87Sr/86Sr）_i比值分别为0.707 437、0.707 672，ε_Nd（t）值分别为-5.06和-4.31.酸性火山岩为一套高钾钙碱性岩石，具有高的SiO₂（76.01%~76.77%）、高K₂O（4.93%~4.98%）、高K₂O/Na₂O（1.41%~1.45%）以及相对高的Mg#（平均值为45.38），富集K、Rb、Th、U等大离子亲石元素（LILE），亏损Nb、Ta、Zr、Ti等高场强元素（HFSE），具有明显的Eu和Sr负异常.以上特征暗示典中组中基性火山岩可能是新特提斯洋北向俯冲消减过程中板片流体引起上覆地幔楔部分熔融的产物，且在上升过程中受到地壳混染的影响，酸性岩则可能来源于上覆地壳的部分熔融，且受到少量幔源物质的影响.此外，年代学及地球化学特征均表明本研究样品不属于前人认为的则弄群火山岩，而应重新厘定为林子宗群典中组火山岩.      

重庆石柱二叠纪栖霞组地球化学特征及其环境意义

在对重庆市石柱县二叠纪栖霞组地层野外露头沉积特征研究的基础上,结合室内薄片观察,根据碳酸盐岩样品的元素含量、比值及相关性,探讨了栖霞组沉积地球化学特征与古环境意义.用于古环境分析的10件栖霞组样品SiO₂、MgO含量低,且两者具有较好的正相关性,Sr含量高,平均为1 751×10-6,Mn/Sr<0.1,Fe/Sr<1,δ18O_PDB>-10‰,表明成岩过程中样品几乎不受硅化及白云岩化作用的影响,未发生化学性质上的改变,可作为古环境分析的可靠对象.栖霞组碳酸盐岩CaO含量高,平均为53.81%,接近纯灰岩的理论化学组成,陆源元素Al₂O₃、TiO₂含量很低,平均值分别为0.17%与0.012%,表明其形成于陆源碎屑影响微弱的稳定古海洋环境.古气候指标MgO/CaO比值极低,平均为0.026,古盐度指标100×(MgO/Al₂O₃)比值高,平均为1 241,古水深判别指标Sr/Ba、1000×(Sr/Ca)比值高,平均值分别为286和4.54,指示了栖霞组碳酸盐岩为潮湿气候下的陆表海(远岸)沉积.古氧相地球化学指标U/Al、V/Al、Mo/Al、Cr/Al、Co/Al、V/(V+Ni)和U/Th特征一致表明栖霞组碳酸盐岩沉积于贫氧—缺氧环境.垂向上,陆源元素∑(Al₂O₃+TiO₂)含量逐渐降低,古水深指标Sr/Ba、1000×(Sr/Ca)比值逐渐增大,表明栖霞组沉积过程中离岸渐远、陆源供给逐步减少、水体持续加深.     

中国东北软流圈地幔中的原始橄榄岩质地幔:来自大兴安岭地区新生代玄武岩的地球化学证据

为了进一步了解中国东北新生代玄武岩地幔源区的物质属性,报道了大兴安岭哈拉哈河-柴河地区新生代玄武岩的全岩主量、微量元素和Sr、Nd、Pb、Hf同位素组成.哈拉哈河-柴河玄武岩属钠质碱性系列,具有与洋岛玄武岩相似的微量元素特征,如富集大离子亲石元素（LILEs）、明显的Nb、Ta正异常等.它们具有中等亏损的Sr-Nd-Hf同位素组成（87Sr/86Sr=0.703 5~0.703 9、ε_Nd=5.21~6.55、ε_Hf=10.00~11.25）,接近中国东部新生代玄武岩的亏损端元.这些玄武岩具有中等的放射成因Pb同位素组成（206Pb/204Pb=18.37~18.57、207Pb/204Pb=15.52~15.54和208Pb/204Pb=38.24~38.43）,在206Pb/204Pb-207Pb/204Pb相关图上位于4.42~4.45 Ga的地球等时线之间.它们在Sr-Nd-Pb同位素相关图中均落入地幔柱来源的、高3He/4He比（>30R_a）的洋岛玄武岩范围内,暗示其源区可能存在来自深部地幔的古老原始地幔物质.此外,这些玄武岩具有高MgO（8.49%~11.58%）、高Ni（174×10-6~362×10-6）和高Mg#（59.1~66.9）的特征,表明它们接近于原始岩浆的成分.反演的哈拉哈河-柴河玄武岩的原始岩浆组成具有中等的SiO₂、低Al₂O₃以及高CaO/Al₂O₃比的特征,与石榴子石橄榄岩高压（>2.5 GPa）实验熔体的成分相当,暗示玄武岩的源区岩性最可能为橄榄岩.对以原始地幔（而不是亏损地幔）的微量元素为初始成分的饱满石榴子石二辉橄榄岩进行低程度（1%~2%）部分熔融的模拟计算,产生的熔体与哈拉哈河-柴河玄武岩具有一致的微量元素特征,这进一步支持了上述推断.综上所述,认为大兴安岭地区哈拉哈河-柴河玄武岩的源区含有来自深部地幔的古老的橄榄岩质原始地幔组分.      

Preliminary Investigation into the Use of a High Resolution Inductively Coupled Plasma-Mass Spectrometer with Laser Ablation for Bulk Analysis of Geological Materials Fused with Li2B4O7

The paper presents preliminary results of the use of a high resolution double-focussing, magnetic sector inductively coupled plasma-mass spectrometer (HR-ICP-MS) with ultraviolet laser ablation (LA) for the bulk analysis of geological materials fused with Li₂B₄O₇. Detection limits are based on data from precision measurements of a fused SiO₂ sample of high purity, and sensitivity data (cps/μg g^-1) obtained on the Reference Material (RM) Syenite SY-2. For many trace elements, the detection limits are better than 0.05 μg g^-1 using a sample to flux weight ratio of 1:7.
Calibration curves, which are based entirely on RMs, are established for Hf, Ta, Tb, Tm and Lu. They indicate that, even at this early stage in the development of the technique, data accurate to ˜ 25% can be collected. It is concluded that the method may prove to be a valuable supplement to XRF for low level element concentration measurements; it is also very practical, as the same sample discs can be used for both XRF and LA-ICP-MS analyses.