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21.
The Tasmanian dolerites, part of the Ferrar Province of Australia and Antarctica, have some trace‐element and isotopic compositions that suggest continental contamination of mantle‐derived magmas. The debate has centred on whether the contamination occurred during intrusion into the crust, or if the mantle source itself was contaminated. The behaviour of Sr and O isotopes suggests that the mantle source had a δ18O composition of +6‰ and an initial 87Sr/86Sr ratio of 0.709, which supports the latter contention. Recently published Re–Os data likewise dismiss upper crustal contamination: Re–Os isotopic compositions of magnetite‐rich mineral separates from seven Tasmanian dolerites yield an isochron that gives the same age, within uncertainties, as other dating techniques, namely 175 ± 5 Ma. Moreover, Re–Os data from a study of Antarctic Ferrar Province samples lie on the same isochron and the data together give an age of 177.3 ± 3.5 Ma. The initial 187Os/188Os of 0.125 ± 0.033 is the calculated mantle composition at the time. These results support previous models that attribute chemical features of the Ferrar magmas to re‐enrichment of a depleted mantle source region rather than processes involving assimilation of crust by basaltic magma. 相似文献
22.
Raúl O.C. Fonseca Guilherme Mallmann Hugh St.C.O''Neill Ian H. Campbell 《Earth and Planetary Science Letters》2007,260(3-4):537-548
Although the Re/Os isotopic system has proved to be a valuable aid in understanding the evolution of the Earth's mantle, interpretation of the data is currently hindered by limited knowledge of the high-temperature geochemical behaviour of Re. In particular, the extent to which Re in the mantle is hosted by sulphide or silicate phases is poorly known. We report the results of an experimental study of the solubility of Re in sulphide melts (called here “mattes”) coexisting with a Re-rich Re–Fe alloy in the system Fe–Re–S–O over a range of fO2, fS2 and temperatures, which allow extrapolation to conditions pertinent to the Earth's mantle. The solubility of Re in mattes increases with increasing fS2, with Re dissolving as Re4+ at high fS2 and Re0 at low fS2. The effect of fO2 is negligible except at high fO2 where O in the matte becomes important. At constant fS2, an increase in temperature leads to an increase in the solubility of Re0 in the matte, but a decrease in the solubility of Re4+. These results, coupled with data for the Re solubility in silicate melts taken from the literature, allow the calculation of Re matte/silicate–melt partition coefficients (DRematte/sil) for a range of conditions. The calculated DRematte/sil show a large dependence on fO2, and a lesser dependency on fS2, with Re behaving as a chalcophile element for relatively reduced MORB-type mantle and as a lithophile element for the oxidised sources of island-arc basalts. The sensitivity of Re to fS2 and fO2 reconciles the apparent discrepancies between previous estimates of this parameter, which can vary by more than five orders of magnitude within the range of fS2 and fO2 covered by terrestrial basaltic magmas. 相似文献
23.
Du Andao He Hongliao Yin Ningwan Zou Xiaoqiu Sun Yali Sun Dezhong Chen Shaozhen Qu Wenjun 《《地质学报》英文版》1995,8(2):171-181
Abstract This study deals with the first application of the isotope dilution-inductively coupled plasma mass spectrometry in the rhenium-osmium geochronometry in China. The chemical separation procedure included decomposition of samples by means of alkali fusion, extraction of rhenium by acetone and extraction of osmium by distillation. The recovery of both elements in the entire process was more than 90% . The blanks of analyses were 0.07 ng for rhenium and 0.01 ng for <sup>187</sup>Os. The mineralization ages of molybdenites from four molybdenum deposits in China were determined by using this method, with a precision (2σ) of about ±3% . These results agree satisfactorily with their geological backgrounds. The Re-Os method can directly determine ages of metal deposits and reflect the true ages more reliably than other dating methods that only determine the ages of country rocks from which mineralization ages are inferred. As many hydrothermal sulphide deposits usually contain molybdenites, this method has bright prospects of wide application. 相似文献
24.
Carius管溶样-负离子热表面电离质谱准确测定辉钼矿铼-锇同位素地质年龄 总被引：175，自引：30，他引：175
将样品、混合稀释剂和逆王水加入到Carius管中,于230℃溶样10h.利用蒸馏法分离Os,萃取和阴离子交换法分离Re.采用负离子热表面电离质谱精确测定了所研制的年龄标准参考物辉钼矿(HLP)的Re-Os年龄.对取自12个小瓶中17个样品所测平均年龄为221.3±0.3Ma,置信度95%.中值年龄和平均绝对偏差为221.34±0.12Ma.美国克罗拉多州立大学AIRIE小组19次单独取样所测HLP的平均年龄为221.3±1.0Ma,置信度95%.中值年龄和平均绝对偏差为221.34±0.24Ma. 相似文献
25.
铼—锇定年法中碱熔分解样品方法的改进 总被引：10，自引：4，他引：10
为改进铼锇测年的准确度 ,试验了 4种熔样和稀释剂加入方式 ,最后选择了锆埚熔样和加入混合稀释剂溶液的方法。先用NaOH溶液中和混合稀释剂溶液 ,在碱性稀释剂溶液烤干后 ,再分层加入NaOH、样品、NaOH、Na2 O2 进行高温熔融。采用同位素稀释 -等离子体质谱 (ID-ICP -MS)对所研制的Re -Os年龄参考样辉钼矿JDC的年龄进行了 4次测定 ,测定值为1 39.1 0± 0 .2 6Ma ,相对标准偏差为 0 .2 %。采用 φ =5 %的NH3·H2 O和浓H2 O2 交替清洗测量系统 ,可更有效地消除ICP -MS测量中Os的记忆效应。浓HNO3浸煮和加热烘烤可较有效地除去Teflon器皿中残留的Os。 相似文献
26.
The geochemistry of Re-Os and the recent use of Re as a non-traditional stable isotope both need accurate and precise quantification of 187 Re/185 Re ratios. This paper reports rhenium isotopic data obtained from the analysis of a standard solution and geological samples by MC-ICP-MS. We show that measured isotopic ratios are modified by matrix effects that cannot be accounted for by the standard solution bracketing technique. The bias resulting from measurements on a spiked (185 Re-enriched) sample is shown to alter the apparent Re concentration by several percent. When spiking samples and calibrators with tungsten, simultaneous measurement of tungsten and rhenium isotopes compensates for the matrix-induced modification of mass bias. Rhenium and tungsten are shown to have different fractionation factors. This may be due to the fact that the two elements fractionate in a different but systematic way, or that the reference isotopic ratios used for elemental Re and W are incoherent with one another. The consistency of fractionation through time can be used to obtain an empirical relationship between W and Re measured ratios from a standard solution to obtain a sample's fractionation-corrected 187 Re/185 Re spiked ratio on samples containing pg g−1 levels of Re, even if some matrix capable of affecting mass bias remains in the final solution. 相似文献
27.
Quantitative Separation of Molybdenum and Rhenium from Geological Materials for Isotopic Determination by MC-ICP-MS 总被引：1，自引：0，他引：1
Christopher R. Pearce Anthony S. Cohen Ian J. Parkinson 《Geostandards and Geoanalytical Research》2009,33(2):219-229
We have developed a new chemical procedure for the quantitative separation of molybdenum (Mo) and rhenium (Re) from a wide variety of geological samples. A single pass anion exchange separation provided complete recovery of pure Mo and Re in a form that was ideal for subsequent isotope and abundance determination by multi-collector inductively coupled plasma-mass spectroscopy (MC-ICP-MS). An enriched 100 Mo-97 Mo solution, mixed with the sample before digestion, enabled natural mass-dependant isotopic fractionation of Mo to be determined with an external reproducibility of < 0.12‰ (δ98 Mo/95 Mo, 2 s ). Determination of the concentration of Mo and Re in the same sample was achieved by isotope dilution, with instrumental mass-fractionation of Re being corrected by the simultaneous measurement of the 191 Ir/193 Ir ratio. We have applied the new procedure to a variety of samples, including seawater, basalt and organic-rich mudrock. The procedure is ideally suited to palaeoredox studies requiring the precise determination of the Mo isotope composition and the Re/Mo ratio from the same sample. 相似文献
28.
电感耦合等离子体发射光谱法测定钼矿石和铜矿石中的铼 总被引：3，自引：0，他引：3
采用氧化镁-硝酸钠-过氧化氢处理试样,不需分离富集,电感耦合等离子体发射光谱法直接测定钼矿石及铜矿石中的铼,筛选了不同溶矿方法和仪器参数条件。方法检出限为0.014μg/g,相对标准偏差(RSD,n=11)小于5.00%,经国家一级钼矿石及铜矿石标准物质分析验证,结果与标准值吻合。 相似文献
29.
30.
LA-ICP-MS analysis of molybdenite from the Sar Cheshmeh porphyry Cu-Mo deposit(PCD), Iran, shows moderate concentration of Re(average ～207 ppm) and low concentration of chalcogenides(average of Pb + Te + Bi, ～31 ppm) as well as metalloids(average of As + Sb + Ge, ～4.5 ppm). The early-formed quartz–molybdenites associated with potassic alteration are characterized by moderately low concentration of Re(21–215 ppm with an average of 83 ppm), whereas the transitional quartz–molybdenite veins related to the sericitic stage of mineralization contain more Re(62–465 ppm, with an average of 207 ppm). In contrast, the late-formed quartz–molybdenite veins associated with phyllic alteration show the highest concentration of Re(up to 1273 ppm with an average of 395 ppm). Gradual increase in Re content of molybdenites deposited throughout the evolution of the porphyry system is probably related to elevated ?O2 and acidic conditions of the ore fluids governing the transitional and late stage of mineralization, when compared to the moderately low ?O2 and basic conditions of the ore fluids precipitating the low-Re molybdenites associated with potassic alteration. The mixed mantle/crustal source of the ore-related magma and its fractionated composition in Sar Cheshmeh are consistent with magmatic conditions for the formation of Mo-rich and Re-poor PCDs in the world. 相似文献