On the observation of 92Nb and 94Nb in nature

Radioactivity measurements have shown evidence for long-lived ⁹²Nb and $\text{2.03 × 10}{}^4\text{yr}{}^{94}\text{Nb}$ in natural niobium. The specific activity of ⁹⁴Nb was observed to be 0.32 ± 0.03 dis/min. kg Nb and that of ⁹²Nb to be 0.058 ± 0.035 dis/min. kg Nb. With $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ taken as ≈ 1.7 × 10⁸yr, the isotopic abundance of ⁹⁸Nb is 1.2 × 10^?10 per cent.     

Littoral '92

Reports

Littoral '92     

Nb/Zr fractionation on the Moon and the search for extinct Nb

A comprehensive Zr isotopic study was conducted on eleven lunar basalts and highland rocks to search for evidence of the extinct nuclide ⁹²Nb, which decays to ⁹²Zr with a half-life of 36 Ma. Internal isochrons were determined for two early highland rocks, 77215 and 60025. No resolvable Zr isotopic variations were detected in this wide range of lunar samples and thus there is no evidence for the former existence of live ⁹²Nb on the Moon. The Nb/Zr ratios of lunar ilmenites and bulk rock samples vary by only a factor of two to three relative to the chondritic Nb/Zr ratio. No evidence for larger Nb/Zr fractionation was found. This limited fractionation and late isotopic closure of the source region prevents the formation of measurable ⁹²Zr anomalies in high-Ti mare basalts. As a consequence, it is not possible to draw conclusions from the ⁹²Nb-⁹²Zr chronometer about the timing of early lunar differentiation and to constrain the role of ilmenite in the source region of high-Ti mare basalts. However, the fractionation is still sufficient to deduce an upper limit for the initial ⁹²Nb/⁹³Nb ratio of the solar system of <5 × 10⁻⁴.     

Implications of εNd—La／Nb,Ba／Nb,Nb／Th Diagrams to Mantle Heterogeneity—Classification of Island—arc Basalts and Decomposition of EMII Component

A group of εNd/Nb,Ba/Nb,Nb/Th diagrams are used to study mantle heterogeneity.Island-arc basalts(IAB) are distributed in a triangle of these diagrams. Three end-member components (the MORB-type depleted mantle, the fluid released from subducted oceanic crust and the sediments from the continental crust) of the source of IAB may be displayed in these diagrams. Two types of IAB are identified .They are of the two-component type (with little continental sediments), such as the basalts from Aletians and New Britain ,and the three-compeonent type, such as those from Sunda, Lesser Antilles and Andes. In addition ,the EMII type mantle-derived rocks may also be divided into two groups. One is exemplified by continental flood basalts and some peridotite xenoliths, similar to IAB, with high La/Nb and Ba/Nb and low Nb/Th ratios, The other includes the Samoa-type oceanic island basalts, with low La/Nb and Ba/Nb and high Nb/Th ratios. The corresponding two sub-components of EMII are EMIIM, which is related to the metasomatism of lithosphere mantle by fluids released from the subducted oceanic crust, and EMIISR, related to the intervention of recycling continental sediments into the convective mantle.     

微量铌快速测定

采用氧氟酸溶矿-酒石酸浸取-醋酸乙脂萃取,干扰杂质可通过盐酸反萃取除去,方便快速,与经典分析方法结果相符,特别适用于铌含量在0．000X-0．001％的样品分析。     

THE EUROPEAN MACROSEISMIC SCALE (MSK-92)

A new updated version of the MSK macroseismic intensity scale has been prepared by a Working Group of the European Seismological Commission and has been published in April 1993 (European Macroseismic Scale 1992: updated MSK scale, 1993, ed. by G. Grünthal, Cahiers du Centre Européen de Geodynamique et de Séismologie, no. 7).     

鄂西北碱性火山岩型铌矿床榍石矿物学及对铌富集机理的指示

位于南秦岭武当地区的天宝铌矿床是我国典型的碱性火山岩型铌矿床,但其岩浆成因、演化及成矿机理等方面的研究十分薄弱.天宝碱性火山岩主要分为粗面质岩石和碱性玄武岩两大类,两者在空间上紧密共生.在详细的岩(矿)相学及榍石显微结构研究的基础上,利用LA-ICP-MS分析技术对天宝粗面质火山岩中的榍石进行原位U-Pb定年,并利用E...     

铌与钽的某些地球化学问题

针对地球圈层之间Nb、Ta质量不平衡的难题,较系统收集分析了我国基性岩墙(脉)群、太古宙基性火山岩、碱性岩、大火成岩省火山岩,俯冲带中富Nb玄武岩、高压变质岩、花岗岩类的Nb、Ta含量、比值、相关同位素组成以及Nb、Ta实验地球化学资料.这些资料表明,Nb、Ta在这些岩类中的分布呈现非常不均匀变化,除花岗岩外,上述岩石的Nb/Ta比值均高于或近于球粒陨石值17.5.花岗岩中的幔源斜长花岗岩及与裂谷、热点环境有关的碱性花岗岩Nb/Ta比值近于地球平均值,而普通S型及I型花岗岩,特别是高演化花岗岩,Nb/Ta比值均明显低于球粒陨石(<10),甚至呈现Nb/Ta≤1.这些资料表明,在不均匀的地幔中可能存在呈布丁状分布的Nb/Ta比值高于球粒陨石的储源.金红石的稳定性及Nb、Ta分配系数实验资料不支持地球深部存在高Nb/Ta比值的含金红石榴辉岩.     

铌掺杂对硅化石墨的增强效应

按硅粉的1％，5％，6％，10％将铌粉加入硅粉中，用“液硅渗透法”制备出四种掺铌硅化石墨样品。力学性能测试结果表明：6％铌掺杂增强效果最好，可使硅化石墨抗折、抗拉强度达178．5MPa,94.2%MPa,XRD、SEM、EPMA测试分析表明铌掺杂增强硅化石墨的机理是：碳化铌相的生成使原材料平直表面界面锯齿化，并平衡晶界附近不饱和价键，降低了晶界能；同时掺杂行为使晶粒细化，晶粒尺寸减小、气孔均匀分布，从而减弱应力集中，抑制裂纹扩展，提高材料强度。铌掺杂硅化石墨是改善材料性能的有效方式。     

SAF—CTMAB荧光猝灭法测定痕量铌

本文研究了铌对水杨基荧光酮(SAF)-OTMAB体系荧光的熄灭效应,建立了痕量铌的荧光测定新方法。经纸色层分离,用于矿样中痕量铌的测定,结果满意。     

Constancy of Nb/U in the mantle revisited

It has long been proposed that MORB and OIB have constant supra-primitive mantle (PM) Nb/U values identical to each other. This fact together with complementary sub-PM values for the continental crust (CC), are taken as fundamental evidence, linking the mantle sources of MORB and OIB to the formation of the CC. Given that plate subduction at convergent margins is the major known process that dramatically fractionates Nb from U, and consequently that subducted oceanic slabs are the main primary carriers of supra-PM Nb/U, a constant supra-PM Nb/U in MORB mantle implies that the mixing of subducted oceanic crust is essentially finished or the newly recycled oceanic crust has Nb/U close to that of the mantle. The similarity between Nb and U as well as the constancy of Nb/U in MORB are revisited here based on MORB glass data obtained using laser ablation ICP-MS. The result shows that Nb/U is not correlated with Nb/Hf, supporting that Nb and U are similarly incompatible. Further investigation shows that Nb is not perfectly identical to, but is faintly more incompatible than U as indicated by the good correlation between log(U) and log(Nb) with a slope of 0.954, very close to 1. Nonetheless, the similarity between Nb and U is high enough, such that the average Nb/U value of MORB glasses should be very close to that of the MORB mantle. By contrast, the difference between Ce and Pb is more obvious. Ce is more incompatible than Pb with a slope of 1.13 in a log(Pb) versus log(Ce) diagram. Therefore, the Ce/Pb of MORB should be a little bit higher than that of the mantle source. The Nb/U value is not as uniform as expected for the similar incompatibility in studied MORB glasses, but varies by a factor of ∼2, suggesting that MORB mantle source is not yet homogenized in term of Nb/U. This indicates that the mixing back of subducted oceanic crust is still an ongoing process, i.e., subducted oceanic crust is recycling back after staying in the lower mantle for billions of years.     

Partitioning of Nb and Ta between rutile and felsic melt and the fractionation of Nb/Ta during partial melting of hydrous metabasalt

In order to fully assess the role of rutile in fractionation of Nb/Ta during partial melting of hydrous metabasalt, we have measured rutile - felsic melt partition coefficients (D values) for Nb and Ta with tonalitic to trondhjemitic compositions at 1.5-3.5 GPa, 900-1350 °C and ∼5.0-20 wt% H₂O. D_Nb, D_Ta and D_Nb/D_Ta range from 17 ± 1 to 246 ± 13, 34 ± 2 to 232 ± 25 and 0.51 ± 0.04 to 1.06 ± 0.13, respectively. For the compositions investigated, melt composition appears to have no observable effect on the partitioning; the effect of pressure is also slight; whereas temperature and H₂O have marked effects. D_Nb, D_Ta and D_Nb/D_Ta increase with decreasing temperature and H₂O content, showing a reversal of D_Nb/D_Ta from <1.0 to >1.0. Using the data that approached equilibrium and obeyed Henry’s law, expressions describing the dependences of D_Nb, D_Ta and D_Nb/D_Ta on temperature, pressure and melt H₂O content were obtained:

(1)     

X92井长裸眼井段钻井液技术措施

X92井是胜利油田在某地区布置的一口预探井。为节约投资,二开睨15．90mm井眼段采用长裸眼钻井施工,裸眼长度达3771m。该井地质条件复杂,除具有一般长裸眼井钻进的难度外,还具有多压力层系并存并且对地层压力系数不明确等难点,如果处理不好容易造成钻井事故。通过合理的控制钻井液性能,再加上钻井液维护和处理等配套技术,较好地解决了该井技术难题,形成了一套适合该井的优快钻井技术及施工措施。该井的顺利完成,为以后在该地区进行长裸眼钻井优化设计及施工提供了相关经验。