Os水吸收液ICP-MS测量信号强度衰减原因研究     

周利敏  李超  李欣尉  赵鸿  屈文俊  杜安道 《岩矿测试》2018,37(4):431-438

蒸馏法能从样品中有效分离出OsO_4,吸收液直接用于ICP-MS测定,是辉钼矿Re-Os定年的关键技术环节。但实验发现,长时间放置的吸收液中Os信号强度显著降低。根据OsO_4化学性质推测原因在于一是挥发使吸收液Os含量减少,二是还原使+8价Os变成低价态,气态比例降低,若雾化效率不变,进入质谱仪的Os减少,两者都会导致信号降低,但具体影响情况不明,需深入研究。本文利用辉钼矿标准物质制备不同放置时间、酸度和温度的吸收液,对比上述条件对ICP-MS信号强度的影响。实验时将残余吸收液与稀释剂、氧化剂封入Carius管加热蒸馏,测定Os含量。结果表明:吸收液放置时间越长,酸度越低,温度越高,信号降幅越大,幅度达到3.2%~68.6%。室温下放置相同时间,低酸度吸收液的Os保存率高于高酸度吸收液,但Os信号强度低于后者,证明了挥发和还原共同导致信号衰减,且还原是主导原因。本文提出,冷冻(-18℃)可抑制OsO_4挥发,提高酸度(约3.5 mol/L)可减弱OsO_4还原,两者结合抑制信号衰减,提高了蒸馏法的灵活性和适用性。  相似文献   

Isotope stratigraphy and U-Pb dating of detrital zircons from the Vendian-Cambrian deposits of the North Muya block     

I.A. Vishnevskaya  E.F. Letnikova  N.A. Kanygina  A.I. Proshenkin  N.G. Soloshenko  E.V. Vetrov  V.Yu. Kiseleva 《Russian Geology and Geophysics》2018,59(11):1433-1449

U-Pb dating of detrital zircons from the sandstones of the Mamakan Formation has been made. Geochemical and isotope parameters of the carbonate deposits of the Yanguda Formation in the Vendian-Cambrian cover of the North Muya continental block have been estimated. It has been established that only the Neoproterozoic (630-915 Ma) rocks of the North Muya block were the provenances of terrigenous material. In the least altered carbonate rocks of the Yanguda Formation, the ⁸⁷Sr/⁸⁶Sr ratio is within 0.70814-0.70879 and δ¹³C varies from -0.4 to + 1.9‰. Comparison of the evaluated isotope parameters with those of carbonate rocks of typical Vendian-Cambrian sections shows that the carbonate deposits of the Yanguda Formation accumulated in the Early Cambrian, about 520 Ma. Sedimentation of the Mamakan and Yanguda Formations took place in the local sedimentary basin in the Vendian-Early Cambrian, in the absence of tectonic activity within the North Muya block. Detrital material that formed during the destruction of the rocks of the Siberian Platform basement and cover was not supplied into the basin.  相似文献   

The oldest (~ 1.9 Ga) metadolerites of the southern Siberian craton: age,petrogenesis, and tectonic setting     

T.V. Donskaya  D.P. Gladkochub  A.M. Mazukabzov  S. Denyszyn  S.A. Pisarevsky  Z.L. Motova  E.I. Demonterova 《Russian Geology and Geophysics》2018,59(12):1548-1559

Geological, geochronological, and isotope-geochemical studies of the metadolerites of the Angaul complex, widespread in the Urik-Iya graben of the southern Siberian craton, were carried out. The metadolerites forming separate conformal bodies (sills) among the metasandstones of the Ingash Formation were studied in detail. U-Pb zircon (SHRIMP) dating of metadolerites yielded an age of 1913 ± 24 Ma, and U-Pb baddeleyite (ID-TIMS) dating of these rocks yielded an age of 1914.0 ± 1.7 Ma. Thus, the date of 1914 ± 2 Ma can be taken as the most precise age estimate for the studied rocks. The metadolerites of the Angaul complex correspond in chemical composition to the normal-alkaline tholeiitic basalts. Metadolerites are differentiated rocks with mg# of 36 to 58. They show fractionated REE patterns: (La/Yb)_n = 1.2-3.5. All metadolerites, independently of their mg# value, have low contents of Nb (1.6-10.2 ppm) and show well-pronounced negative Nb-Ta anomalies in multielement patterns (Nb/Nb* = 0.19-0.54). The metadolerites are characterized by positive ε_Nd(T) values ranging from 0.4 to 5.2, which correlate well with their SiO₂ content and mg# value. The isotope-geochemical parameters of the metadolerites of the Angaul complex indicate that fractional crystallization, along with the assimilation of the host rocks (AFC), might have been the main process during the formation of the most differentiated metadolerites. The geochemical characteristics of metadolerites with the maximum mg# values of 57-58 and ε_Nd(T) = 5.2 suggest that the parental mantle source of the metadolerites resulted from mixing of predominant depleted mantle material with the subcontinental-lithosphere material. Intrusion of the dolerites of the Angaul complex, as well as the deposition of the sedimentary strata of the Ingash Group, took place at the Paleoproterozoic stage of intracontinental extension caused by the collapse of the orogen resulted from the collision of the Biryusa block with the Tunguska superterrane in the southern Siberian craton.  相似文献   

The source of sulfur in sulfide deposits in the Siberian Platform traps (from isotope data)     

V.V. Ryabov  O.N. Simonov  S.G. Snisar  A.A. Borovikov 《Russian Geology and Geophysics》2018,59(8):945-961

The source of sulfur in giant Norilsk-type sulfide deposits is discussed. A review of the state of the problem and a critical analysis of existing hypotheses are made. The distribution of δ³⁴S in sulfides of ore occurrences and small and large deposits and in normal sedimentary, metamorphogenic, and hypogene sulfates is considered. A large number of new δ³⁴S data for sulfides and sulfates in various deposits, volcanic and terrigenous rocks, coals, graphites, and metasomatites are presented. The main attention is focused on the objects of the Norilsk and Kureika ore districts. The δ³⁴S value varies from -14 to + 22.5‰ in sulfides of rocks and ores and from 15.3 to 33‰ in anhydrites. In sulfide-sulfate intergrowths and assemblages, δ³⁴S is within 4.2-14.6‰ in sulfides and within 15.3-21.3‰ in anhydrites. The most isotopically heavy sulfur was found in pyrrhotite veins in basalts (δ³⁴S = 21.6‰), in sulfate veins cutting dolomites (δ³⁴S = 33‰), and in subsidence caldera sulfates in basalts (δ³⁴S = 23.2-25.2‰). Sulfide ores of the Tsentral’naya Shilki intrusion have a heavy sulfur isotope composition (δ³⁴S = + 17.7‰ (n = 15)). Thermobarogeochemical studies of anhydrites have revealed inclusions of different types with homogenization temperatures ranging from 685 °C to 80 °C. Metamorphogenic and hypogene anhydrites are associated with a carbonaceous substance, and hypogene anhydrites have inclusions of chloride-containing salt melts. We assume that sulfur in the trap sulfide deposits was introduced with sulfates of sedimentary rocks (δ³⁴S = 22-24‰). No assimilation of sulfates by basaltic melt took place. The sedimentary anhydrites were “steamed” by hydrocarbons, which led to sulfate reduction and δ³⁴S fractionation. As a result, isotopically light sulfur accumulated in sulfides and hydrogen sulfide, isotopically heavy sulfur was removed by aqueous calcium sulfate solution, and “residual” metamorphogenic anhydrite acquired a lighter sulfur isotope composition as compared with the sedimentary one. The wide variations in δ³⁴S in sulfides and sulfates are due to changes in the physicochemical parameters of the ore-forming system (first of all, temperature and P_ch4) during the sulfate reduction. The regional hydrocarbon resources were sufficient for large-scale ore formation.  相似文献   

南秦岭小茅岭复式岩体地球化学特征及其构造意义     

刘仁燕  李清山  牛宝贵  和政军  任纪舜 《地球学报》2018,39(2):201-215

南秦岭北缘小茅岭复式岩体主要由宋家屋场基性辉绿(辉长)岩,迷魂阵、磨沟峡和叶家湾中性-偏酸性闪长岩组成,形成于新元古代早期870~840 Ma。岩石地球化学研究显示,宋家屋场基性岩属亚碱性系列岩石,富集轻稀土元素及大离子亲石元素,Nb、Ta、Ti、P等具有弱的负异常,Zr、Hf等高场强元素的含量较高,Zr/Y、Ta/Yb比值较高,Zr/Nb比值较低,与岛弧玄武岩的地球化学特征相似,在构造环境判别图解中投于火山弧岩石区域,一些元素的富集特征可能来源于受俯冲块体流体交代的岩石圈地幔。迷魂阵、磨沟峡及叶家湾闪长岩体均属准铝质亚碱性系列岩石,具有岛弧火成岩的地球化学特征。Sr-Nd-Hf同位素地球化学分析显示,宋家屋场岩体主要来自亏损地幔源区,磨沟峡和叶家湾岩体主要为新生基性下地壳的部分熔融,而迷魂阵岩体主要为古老地壳物质的部分熔融。上述特征表明小茅岭复式岩体各组成部分可能形成于870~840 Ma俯冲相关的岛弧构造背景,俯冲块体脱水形成的流体交代上覆地幔楔,这种地幔部分熔融形成了宋家屋场角闪辉绿(辉长)岩,由于基性岩浆的加热,诱发新生基性下地壳及原古老地壳物质部分熔融,岩浆上升、侵位,形成磨沟峡、叶家湾及迷魂阵岩体。结合陡岭地区~850–780 Ma变质作用及岩浆事件相关报导,在南秦岭北缘小茅岭—陡岭隆起带上,新元古代早期存在一期构造-岩浆-变质事件,该事件的区域大地构造属性则有待进一步研究。  相似文献   

内蒙古西乌旗罕乌拉地区下二叠统寿山沟组碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义   总被引：2，自引：2，他引：0  

张晓飞  王必任  张华川  周毅  冯俊岭  曹军  滕超  刘俊来 《地质通报》2018,37(5):863-880

中亚造山带南缘二叠纪的构造背景一直存在争议。以内蒙古西乌旗罕乌拉地区发育的寿山沟组为研究对象,开展了野外地质、岩石学、碎屑锆石LA-ICP-MS U-Pb年龄研究。2个样品锆石阴极发光图像和Th/U值指示,锆石为岩浆成因锆石。103颗碎屑锆石年龄测试结果显示,年龄信息可划分为5组:285~328Ma,峰期年龄302Ma;338~361Ma;455~490Ma;757Ma;1278Ma、2380Ma。最年轻的年龄为285Ma,结合侵入其中的花岗岩同位素年龄,指示西乌旗罕乌拉地区寿山沟组沉积时限介于285~280Ma之间,主体沉积时代应为早二叠世Sakmarian期—Artinskian期。寿山沟组碎屑锆石反映出近源、快速沉积的特点,沉积物源中含有较多的火山碎屑物,可能代表弧后盆地沉积,为早二叠世古亚洲洋闭合前洋壳俯冲消减作用的沉积响应。结合区域资料,寿山沟组碎屑锆石的年龄对应于东北地区的变质基底及其后的构造岩浆事件,物源区物质主要来自于苏尼特左旗—锡林浩特—西乌旗一带早石炭世末—晚石炭世岩浆弧及贺根山—东乌旗一带,并进一步限制了华北与西伯利亚两大板块的缝合线应位于寿山沟组发育地区的南部,即索伦缝合带,拼合时代最可能为晚二叠世—早三叠世。  相似文献   

新疆东准噶尔拉伊克勒克斑岩铜(钼)矿床成岩成矿年龄、地球化学特征及其意义     

李高峰  孟贵祥  张丽婷  吴建  严加永  杨岳清 《地质通报》2018,37(6):1113-1124

拉伊克勒克矿床是在第四系覆盖区新发现的隐伏斑岩铜(钼)矿床。采用LA-ICP-MS技术,对赋矿岩体英云闪长岩中的锆石和矿石中的辉钼矿分别进行锆石U-Pb同位素、Re-Os同位素和锆石Hf同位素测定及相应的研究。测得锆石U-Pb年龄为421.8±2.5Ma,辉钼矿Re-Os模式年龄为409.1±2.6Ma,表明拉伊克勒克斑岩铜(钼)矿床形成于晚志留世—早泥盆世,与琼河坝地区主要斑岩矿床大规模成矿时间一致。英云闪长岩属过铝质-钙碱性系列花岗岩类,岩体具有较高的铝钙含量,K_2O/Na_2O值普遍偏低,介于0.16~0.29之间;稀土元素配分曲线呈现右倾特征,稀土元素总量较低,轻稀土元素相对富集,负Eu异常不明显。在微量元素原始地幔标准化蛛网图上,高场强元素Th、Nb、Ta、P、Ti等相对亏损,大离子亲石元素Rb、Ba、U、K、Sr等相对富集。同时岩体具有高的正ε_(Hf)(t)值(10.98~15.01)和年轻的模式年龄(451~708Ma),暗示英云闪长岩体是大陆边缘弧环境下大洋板片熔融的产物,对进一步明确琼河坝地区斑岩型矿床的成矿环境和找矿方向具有重要意义。  相似文献   

Late Quaternary tephrostratigraphy and pollen stratigraphy of Uwa Formation,Shikoku Island,SW Japan: Reconsidering the MIS 11 super-interglacial horizon     

《Quaternary Geochronology》2022

We investigated a late Quaternary terrestrial sedimentary sequence (Uwa Formation) in core IC2, from a site adjacent to that of the reported core IC on NW Shikoku Island, SW Japan, and developed its tephra and pollen stratigraphy to refine the age model of the formation. First, we identified 19 horizons with high glass shard concentrations in the IC2 core sediments as possible tephras or cryptotephras, and correlated them with reported tephras on the basis of the major- and trace-element compositions of their glass shards. All correlated widespread tephras and cryptotephras were products of volcanoes in the Kyushu volcanic zone (Aso, Kakuto, Aira, Ata, and Kikai calderas). Second, we confirmed the presence in core IC2 of two pollen zones dominated by Quercus subgen. Cyclobalanopsis, which is an indicator of very warm interglacial vegetation. In the Japanese Islands, these two vegetation zones have usually been considered to characterize marine isotopic stages (MISs) 1 and 11. A previous study of the Uwa Formation correlated the upper pollen zone to MIS 1, but the lower zone was not correlated to MIS 11; rather, it was inferred to be older than MIS 12 because it was stratigraphically below the “Oda” tephra (equivalent to a distal Kasamori 5 [Ks5] tephra [MIS 12]). In this study, however, noting that the Naruohama-IV tephra (Nh-IV; MIS 10d) and Ks5 cannot be distinguished by their shard chemistries, we inferred that the suggested “Oda” tephra actually correlates to Nh-IV, rather than to the Ks5 tephra. By re-assigning the “Oda” tephra to Nh-IV, we could correlate the underlying Quercus subgen. Cyclobalanopsis-abundant zone to MIS 11 and, consequently, a pair of pollen zones indicating cool and warm conditions below the MIS 11 pollen zone to MISs 12 and 13, respectively. The resulting age model whereby tephra and pollen constraints are integrated showed a roughly constant sedimentation rate from MIS 13, without any long-term gaps; further, our MIS 13 horizon in core IC2 corresponds to the reported 1 Ma tephra horizon in core IC. Therefore, these findings represent a dramatic change in the Uwa Formation age model and validate the Uwa Formation as one of the most useful terrestrial archives of Quaternary tephrostratigraphy and paleoclimatic fluctuation in SW Japan.  相似文献   

粤东铁坑坳铁锡多金属矿床锆石及锡石U-Pb年代学、Nd-Hf同位素特征及其意义     

张志涛  柯昌辉  徐林刚  马收先  陈懋弘  叶会寿  潘玉峰 《矿床地质》2022,41(3):543-566

铁坑坳铁锡多金属矿床位于粤东莲花山断裂带西部,矿区出露的花岗岩类主要有粗粒二长花岗岩和花岗闪长斑岩,花岗质岩石与碳酸盐岩的接触带中发育铁锡多金属矿化。该矿区的成岩成矿时代尚不明确,成矿与哪一种岩体具有成因上的联系也不清楚。文章选择与铁锡多金属矿体相关的花岗岩类的锆石和块状矿石中的锡石,首次开展LA-ICP-MS U-Pb定年和Nd-Hf同位素研究。结果表明：粗粒二长花岗岩和花岗闪长斑岩的锆石U-Pb年龄分别为（132±1） Ma （n=24,MSWD=0.78）和（94±1） Ma （n=25,MSWD=1.80）;块状矿石中锡石U-Pb年龄为（130±3） Ma （n=36,MSWD=0.62）,成矿时代与粗粒二长花岗岩形成时代基本一致,均形成于早白垩世;粗粒二长花岗岩的锆石ε_Hf （t）变化于-4.9~-0.1,平均值为-2.8,地壳Hf模式年龄T_DMC=1192~1497 Ma,平均值为1366 Ma,全岩ε_Nd （t）值介于-8.8~-8.7,Nd同位素二阶段模式年龄T_DM2变化于1630~1642 Ma;花岗闪长斑岩的锆石ε_Hf （t）变化于-5.7~-2.9,平均值为-4.4,地壳Hf模式年龄T_DMC=1342~1523 Ma,平均值为1440 Ma,全岩ε_Nd （t）值介于-5.4~-4.9,Nd同位素二阶段模式年龄T_DM2变化于1291~1332 Ma。Nd-Hf同位素综合研究表明,粗粒二长花岗岩的源区物质主要来自于中元古代地壳,有少量幔源组分或新生地壳的加入,花岗闪长斑岩的源区物质中幔源组分或新生地壳的混入比例高于粗粒二长花岗岩。  相似文献   

甘肃厂坝-李家沟超大型铅锌矿床成矿金属来源——来自闪锌矿原位S-Pb和Zn同位素证据     

魏然  王义天  胡乔青  黄诗康  窦平  胡文荣 《矿床地质》2022,41(4):722-740

甘肃厂坝-李家沟铅锌矿床位于西秦岭多金属成矿带内的西成矿集区,为矿集区内重要的超大型铅锌矿床。矿体赋存在中泥盆统安家岔组的白云石化大理岩及石英片岩中,其成因认识一直存在争议,主要分歧集中在是同生还是后生。文章对不同成矿阶段的闪锌矿,采用多接收电感耦合等离子体质谱(MC-ICP-MS)测定Zn同位素组成、采用激光剥蚀-多接收电感耦合等离子体质谱(LA-MC-ICP-MS)原位微区分析技术测定S、Pb同位素组成,示踪成矿物质来源,并分析矿物沉淀机制,为深入理解矿床成因提供新的精细证据。研究结果显示,Ⅰ、Ⅱ、Ⅲ三个成矿阶段闪锌矿的δ⁶⁶Zn分别为0.08‰~0.29‰,平均0.20‰;0.19‰~0.37‰,平均0.30‰;0.36‰~0.37‰,平均0.37‰。其中,Ⅰ阶段的闪锌矿δ³⁴S_Ⅰ值为20.9‰~26.1‰,平均24.4‰;Ⅱ阶段的闪锌矿δ³⁴S_Ⅱ值为12.2‰~21.9‰,平均19.1‰;Ⅲ阶段的闪锌矿δ³⁴S_Ⅲ值为18.2‰~24.7‰,平均21.5‰。3个阶段的矿石矿物Pb同位素组成变化不大,²⁰⁶Pb/²⁰⁴Pb为17.922~18.013,²⁰⁷Pb/²⁰⁴Pb为15.567~15.647,²⁰⁸Pb/²⁰⁴Pb为37.990~38.266。δ⁶⁶Zn同位素值显示,成矿金属早期来源于围岩海相碳酸盐岩,由于混合了岩浆热液或者是瑞利分馏作用,在成矿作用中后期δ⁶⁶Zn同位素逐渐上升。δ³⁴S同位素值显示,早期硫源主要为地层中的硫酸盐,中后期的δ³⁴S同位素值降低,可能是成矿流体中岩浆热液中的S^2-成分逐渐增多导致,闪锌矿为硫酸盐通过TSR反应沉淀成矿。Pb同位素指示成矿物质来源于上地壳,并混入了部分古老的变质基底的成分。笔者研究发现,厂坝-李家沟铅锌矿的成矿机制为不同来源的流体混合,随着pH值、成矿流体的温度发生变化而沉淀成矿。  相似文献