锂同位素实验方法及其在西藏驱龙花岗岩中的应用
详细信息    本馆镜像全文|  推荐本文 |  |   获取CNKI官网全文
摘要
本文采用MC-ICP-MS分析测试技术,在国内实验室建立了有效的Li同位素实验方法。条件实验的工作溶液由纯碳酸锂和标准岩石样品(AGV-2、BHVO-2和NKT)混合而成,采用三根阳离子交换树脂(AG 50W-X8)填充的聚丙烯交换柱和石英交换柱对Li进行分离提纯,淋洗液分别为2.8 M HCl、0.15 M HCl以及0.5 M HCl和30%乙醇,接收区间分别是6ml、23ml和9ml。整个实验流程中Li的回收率大于97.6%。
     利用本文建立的Li同位素实验方法,测定了国际标样AGV-2、BHVO-2、NTK(相对于IRMM016)和IRMM016(相对于L-SVEC)的δ7Li值,分别为7.08±0.6%o、4.11±0.6‰、9.80±0.7‰和+0.34±0.7‰,与前人分析结果吻合,实现了标准样品的稳定重现。
     本文尝试将锂同位素技术运用于岩浆成因研究中,首次获得了西藏驱龙巨型斑岩铜矿区一批岩石和矿物的锂同位素分析数据,进一步限定了岩浆来源。本次共分析了27个样品的Li同位素组成,其中14个花岗闪长岩全岩样品,8个闪长质包体的全岩样品,以及5个包体中角闪石样品。CIA(chemical index of alteration)指数显示,花岗闪长岩和闪长质包体都没有受到蚀变的影响。花岗闪长岩的Li含量和δ7Li的变化都不大,Li含量为4.5×10-6-8.1×10-6,δ7Li的变化范围是-2.68%o-+6.55%o。闪长质包体的Li含量变化大,最低为4.9×10-6,最高为9.4×10-6。8个闪长质包体样品中,δ7Li最低为-8.89%o,最高位+1.73%o。角闪石是主要的富锂矿物之一,最高Li含量为6.8×10-6,平均为4.5±2×10-6(1σ),δ7Li为-5.03‰~+1.02‰。由于部分闪长质包体不仅存在矿化现象,而且有可能在被携带至地表的过程中发生了动力分馏,因此分析认为花岗闪长岩和闪长质包体真实有效的Li同位素组成范围分别是十2.51‰~+6.55‰和-3.69‰~+1.02‰。
     根据Li同位素研究结果,结合Sr-Nd同位素体系,本文认为驱龙铜矿区花岗闪长岩可能是由俯冲板片脱出的流体交代地幔楔形成。而闪长质包体的δ7Li明显较低,有3种可能:一是包体在被携带运移的过程中与围岩之间发生了扩散分馏,使包体中富集6Li;二是底侵的岩浆与包体所代表的源区之间发生了同位素的动力分馏,使其源区的Li同位素变轻;再者就是包体反应的是真实的Li同位素组成,推测这种低δ7Li的特征可能源自残余板片的部分熔融。
A high-yield lithium separation technique for roch samples has been established together with precise Li isotope analysis based on MC-ICP-MS.Three separate stages of ion-exchange chromatography were carried out using organic cation exchange resin(AG50W-X8,200-400 mesh). Eluants used for lithium separation in different stages were 2.8mol/L HCl,0.5 mol/L HCl and 0.5 mol/L HCl in 30% ethamol, and the volume of the eluants collected for each column were 6ml,23ml and 9ml, respectively.The recovery is more than 97.6%. International standard materials were analyzed, including AGV-2、BHVO-2、NTK and IRMM016, the in-run precise and reproducibility of measured standard materials were 7.08±0.6‰,4.11±0.6‰, 9.80±0.7%o and+0.34±0.7%o, respectively.The results are consistent with other laboratory abroad.
     Researches have been carried out to solve the origin of the Miocene igneous rock in Qulong, but it is still controvertible. In order to constrain the problem using lithium isotope,27 samples were analyzed, including 14 granodiorite (whole roch),8 diorite enclaves (whole roch) and 5 amphibole minerals. Neither 57Li nor Li concentration in granodiorite varies largely,-2.68%o~+6.55‰and 4.5×10-6~8.1×10-6, correspondingly. Li in diorite enclaves varies from 4.9×10-6 to 9.4×10-6, andδ7Li varies dramaticly from-8.89‰to+1.73‰. As a Li enriched mineral, Li in amphibole is up to 6.8×10-6, and the avrage is 4.5±2×10-6 (1σ), the range ofδ7Li is -5.03‰~+1.02‰. Considering the influence of mineralization and Li fractionation induced by diffusion between diorite enclaves and wall rock, thus the lithium isotope compositions for granodiorite and diorite enclaves are +2.51‰~+6.55‰and -3.69‰~+1.02‰, respectively.
     Based on the Li isotope data, combined Sr-Nd system, we consider granodiorite derives from partial melting of mantle wedge caused by fluid released from Tethys slab subduction.87Li of diorite is lower than that of granodiorite, we interpret that:(1) fractionation of Li duffusion was happened when enclavse were migrated to the surface; (2) duffusion fractionation was induced by under plating of magmas,which can lead to the source region where the enclaves are from has a lighterδ7Li; (3) if the data can represent the truth, we infer that diorite enclaves derives from partial melting of residual subducted-slab.
引文
[1]肖应凯,祁海平,王蕴慧等.青海柴达木湖卤水、沉积物和水源中锂同位素组成.地球化学,1994(4):329-338.
    [2]Elliott T, Jeffcoate A and Kasemann S. Li isotopic evidence for subduction induced mantle heterogeneity. Goldschmidt Conference Abstracts,2006.
    [3]Brenan J M, Ryerson F J and Shaw H. The role of aqueous fluids in the slab-to-mantle transfer of boron, beryllium, and lithium during subduction:Experiments and models. Geochimica et Cosmochimica Acta,1998,6:19-20.
    [4]Leeman W P, Tonarini S, Chan L H, et al. Boron and lithium isotopic variations in a hot subduction zone-the southern Washington Cascades. Chemical Geology,2004,212:101-124.
    [5]Seyfried W E J, Janecky D R and Mottl M J. Alteration of the oceanic crust:Implications for geochemical cycles of lithium and boron. Geochimica et Cosmochimica Acta,1983,48:557-569.
    [6]Chan L H, Edmond J M, Thompson G, et al. Lithium isotope composition of submarine basalts: implications for the lithium cycle in the oceans. Earth and Planetary Science letters,1992,108: 151-160.
    [7]Rudnick R L, Tomascak P B, Njo H B, et al. Extreme lithium isotopic fractionation during continental weathering revealed in saprolites from South Carolina. Chemical Geology,2004, 212 (1-2):45-57.
    [8]Teng F Z, MCdonough W F, Rudnick R L, et al. Lithium isotopic composition and concen-tration of the upper continental crust. Geochimica et Cosmochimica Acta,2004,68(20): 4167-4178.
    [9]Teng F Z, McDonough WF, Rudnick RL, et al. Diffusion-driven extreme lithium isotopic fractionation in country rocks of the Tin Mountain pegmatite. Earth and Planetary Science Letters,2006a,243 (3-4):701-710.
    [10]Teng F Z, McDonough W F, Rudnick R L, et al. Limited lithium isotopic fractionation during progressive dehydration in metapelites:a case study from the Onawa contact aureole. Maine. Chemical Geology,2007,239 (1-2):1-12.
    [11]Teng F Z, McDonough W F, Rudnick R L, et al. Lithium isotopic systematics of granites and pegmatites from the Black Hills. South Dakota. Am. Mineral,2006b,91 (10):1488-1498.
    [12]Svec H J, Anderson A R. The absolute abundances of the lithium isotopes in natural sources. Geochimica et Cosmochimica Acta,1965,29:633-641.
    [13]Isakov Y A, Plyushin G S, Brandt S B. Natural fractionation of lithium isotopes. Geochem Int, 1969,6:598-600
    [14]Tomascak P B. Developments in the understanding and application of lithium isotopes in the earth and planetary sciences.Reviews in Mineralogy and Geochemistry,2004,55:153-195.
    [15]Chan L H. Variation of lithium isotope composition in the marine environment:A preliminary report. Geochimica et Cosmochimica Acta,1988,52:1711-1717.
    [16]Tomascak P B, Carlson R W and Shirey S B. Accurate and precise determination of Li isotopic compositions by multi-collector sector ICP-MS. Chemical Geology,1999a,158:145-154.
    [17]Brooker R A, James R H and Blundy J D.Trace elements and Li isotope systematics in Zabargad peridotites:evidence of ancient subduction processes in the Red Sea mantle. Chemical Geology, 2004,212:179-204.
    [18]David R B, Richard L H, Peter R B, et al. Lithium isotope analysis of olivine by SIMS: Calibration of a matrix effect and application to magmatic phenocrysts. Chemical Geology,2009, 258:5-16.
    [19]汤艳杰,张宏福,英基丰.锂同位素分馏机制讨论.地球科学—中国地质大学学报,2009,34(1):43-55
    [20]Moriguti Takuya and Nakamura Eizo. Across-arc variation of Li isotopes in lavasand implications for crust-mantle recycling at subduction zones. Earth and Planetary Science Letters,1998,163: 167-174.
    [21]苏嫒娜,李真真,田世洪等.锂同位素方法及其在大陆裂谷环境碳酸岩研究中的应用.矿床地质,2010,29(5):827~842.
    [22]Plyushin G S, Posokhov V F, Sandimirova G P.Magmatic differentiation and the relationship of7Li/6Li ratio to fluorine content. Doklady,1979,248:223-225.
    [23]Richter F M, Davis A M, DePaolo D J, et al. Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochimica et Cosmochimica Acta,2003,67:3905-3923.
    [24]Elliott T, Thomas A, Jeffcoate A B, et al. Li isotope composition of the upper mantle. EOS Trans, Am Geophys Union,2003,84:1608.
    [25]Benton L D, Savov I, Ryan J G.Recycling of subducted lithium in forearcs:Insights from a serpentine seamount. EOS Trans, Am Geophys Union,1999,80:S349.
    [26]Chan L H and Frey F A. Lithium isotope geochemistry of the Hawaiian plume:Results from the Hawaiian Scientific Drilling Project and Koolau Volcano. Geochem Geophys Geosyst,2003,4: 8707.
    [27]Chan L H, Leeman W P, You C F.Lithium isotopic composition of Central American volcanic arc lavas:implications for modifi cation of subarc mantle by slab-derived fluids:Correction. Chemical Geology,2002,182:293-300.
    [28]Bouman C, Elliott T R, Vroon P Z, Pearson D G. Li isotope evolution of the mantle from analyses of mantle xenoliths. J Conf Abst,2000,5:239.
    [29]李真真,田世洪,侯增谦等.俯冲带的锂同位素特征.矿物岩石学杂志,2010,29(4):431-438.
    [30]Tang Y J, Zhang H F and Ying J F. A brief review of isotopically light Li-a feature of the enriched mantle? International Geology Review,2009, DOI:10.1080/00206810903211385.
    [31]Magna T, Wiechert U H, Grove T L, et al. Lithium isotope composition of arc volcanics from the Mt. Shasta region, N California. Geochimica et Cosmochimica Acta,2003,67:A267
    [32]Benton LD, Tera F. Lithium isotope systematics of the Marianas revisited. J Conf Abst,2000, 5:210
    [33]Moriguti Takuya, Shibata Tomoyuki and Nakamura Eizo. Lithium, boron and lead isotope and trace element systematics of Quaternary basaltic volcanic rocks in northeastern Japan: mineralogical controls on slab-derived fluid composition. Chemical Geology,2004,212:81-100.
    [34]Tomascak P B, Widom E, Benton L D, et al. The control of lithium budgets in island arcs. Earth and Planetary Science Letters,2002,196:227-238.
    [35]Tomascak P B, Ryan J G and Defant M J. Lithium isotope evidence for light element decoupling in the Panama subarc mantle.Geology,2000,28(6):507-510.
    [36]Agostini S, Ryan J G, Tonarini S, et al. Drying and dying of a subducted slab:Coupled Li and B isotope variations in Western Anatolia Cenozoic Volcanism. Earth and Planetary Science Letters,2008,272:139-147.
    [37]Marschall H R, Pogge von Strandmann P A E, Seitz H M, et al. The lithium isotopic composition of orogenic eclogites and deep subducted slabs. Earth and Planetary Science Letters,2007a,262: 563-580.
    [38]Hanrahan M, Brey G, Woodland A, et al. Li as a barometer for bimineralic eclogites:Experiments in natural systems. Lithos,2009,112(2):992-1001
    [39]Magna T, Uwe W, Grove T L, et al. Lithium isotope fractionation in the southern Cascadia subduction zone. Earth and Planetary Science Letters,2006,250:428-443.
    [40]Marschall H R, Altherr R, Ludwig T, et al. Partitioning and budget of Li, Be and B in high-pressure metamorphic rocks. Geochimica et Cosmochimica Acta,2006,70:4750-4769.
    [41]Marschall H R, Altherr R and Rupke L. Squeezing out the slab-modelling the release of Li, Be and B during progressive high-pressure metamorphism. Chemical Geology,2007b,239:323-335.
    [42]Teng F Z, Rudnick R L, McDonough W F, et al. Lithium isotopic composition and concentration of the deep continental crust. Chemical Geology,2008,255:47-59.
    [43]Bryant C J, Chappell B W, Bennett V C, et al. Li isotopic variations in Eastern Australian granites. Geochimica et Cosmochimica Acta,2003b,67:A47.
    [44]Teng F Z, Rudnick R L, McDonough W F, et al. Lithium isotopic systematics of A-type granites and their mafic enclaves:further constraints on the Li isotopic composition of the continental crust. Chemical Geology,2009,262 (3-4):370-379.
    [45]Huh Y, Chan L H and Edmond J M. Lithium isotopes as a probe of weathering processes:Orinoco river. Earth and Planetary Science Letters,2001,194:189-199.
    [46]Bottomley D J, Chan L H, Katz A, et al. Lithium isotope geochemistry and origin of Canadian Shield brines. Groundwater,2003,41:847-856.
    [47]Divis A Fand Clark J R.Geochemical Exploration 1978:Proceedings of the Seventh International Geochemical Exploration Symposium, Golden, Colorado. Assoc Exploration Geochemists,1978,233-241.
    [48]Olsher U, Izatt R M, Bradshaw J S, et al. Coordination chemistry of lithium ion:a crystal and molecular structure review. Chem. Rev.,1991,91:137-164.
    [49]Wenger M and Armbruster T. Crystal chemistry of lithium:oxygen coordination and bonding. Eur J Mineral,1991,3:387-399.
    [50]O'Neil JR. Theoretical and experimental aspects of isotopic fractionation. Rev Mineral,1986,16:1-40.
    [51]James R H,and Palmer M R. Marine geochemical cycles of the alkali elements and boron:The role of sediments. Geochimica et Cosmochimica Acta,2000,64:3111-3122.
    [52]Pistiner J and Henderson G M. Lithium isotope fractionation during continental weathering processes. Earth and Planetary Science Letters,2003,214:327-339.
    [53]Parkinson I J, Hammond S J, James R H, et al. High-temperature lithium isotope fractionation: Insights from lithium isotope diffusion in magmatic systems. Earth and Planetary Science Letters, 2007,257:609-621.
    [54]Marks M A W, Rudnick R L, McCammon C, et al. Arrested kinetic Li isotope fractionation at the margin of the Ilimaussaq complex, South Greenland:Evidence for open-system processes during final cooling of peralkaline igneous rocks. Chemical Geology,2007,246:207-230.
    [55]Moriguti T and Nakamura E. High-yield lithium separation and the precise isotopic analysis for natural rock and aqueous samples. Chemical Geology,1998,145:91-104.
    [56]Croudace I W. A possible error source in silicate wet chemistry caused by insoluble fluorides. Chemical Geology,1980,31:153-155.
    [57]Ryan J G and Langmuir C H. The systematics of lithium abundances in young volcanic rocks. Geochimica et Cosmochimica Acta,1987,51:1727-1741.
    [58]Bouman C, Elliott T and Vroon P Z. Lithium inputs to subduction zones. Chemical Geology,2004,212(1/2):59-79.
    [59]Meier A L. Determination of lithium isotopes at natural abundance levels by atomic absorption spectrometry. Anal. Chem.,1982,54:2158-2161.
    [60]Chaussidon M and Robert F.7Li/6Li and "B/10B variations in chondrules from the Semarkona unequilibrated chondrite. Earth and Planetary Science Letters,1998,164:577-589.
    [61]Decitre S and Deloule E. Determination of Li contents and isotopic compositions in various oceanic basalts by ion microprobe:implication for the Li geochemical cycle. EUG-10 Jour. Conference Abstract,1999,4(1):814.
    [62]Gregoire D C, Acheson B M and Taylor R P. Measurement of lithium isotope ratios by inductively coupled plasma mass spectrometry:application to geological materials. J. Anal. Atom. Spectrom.,1996,11:765-772.
    [63]Xiao Y K and Beary E S. High-precision isotopic measurement of liuthium by thermal ionization mass spectrometry. International Journal of Mass Spectrometer and Ion Processes, 1989,94:101-114.
    [64]Hoefs J and Sywall M. Lithium isotope composition of Quaternary and Tertiary biogene carbonates and a global lithium isotope balance. Geochimica et Cosmochimica Acta,1997,61: 2679-2690.
    [65]Tomascak P B, Tera F, Helz R T and Walker R J. The absence of lithium isotope fractionation during basalt differentiation:new measurements by multicollector sector ICP-MS. Geochimica et Cosmochimica Acta,1999b,63:907-910
    [66]Tomascak P B, Carlson R W and Shirey S B. Accurate and precise determination of Li isotopic compositions by multi-collector sector ICP-MS. Chemical Geology,1999c,158:145-154.
    [67]汪齐连,赵志琦,刘丛强等.天然样品中锂的分离及其同位素比值的测定.分析化学,2006,34(6):764-768.
    [68]Millot R, Guerrot C, Vigier N. Accurate and high-precision measurement of lithium isotopes in two reference materials by MC-ICP-MS. Geostandards and Geoanalytical Research,2004,28: 153-159.
    [69]侯可军,李延河,邹天人等LA-MC-ICP-MS锆石Hf同位素的分析方法及地质应用.岩石学报,2007,23(10):2595-2604.
    [70]侯可军,李延河,田有荣等MC-ICP-MS高精度Cu、Zn同位素测试技术.矿床地质,2008,27(6):774-781.
    [71]Magna T, Wiechert U H, and Halliday A N.Low-blank isotope ratio measurement of small samples of lithium using multiple-collector ICPMS. International Journal of Mass Spectrometry, 2004,239:67-76
    [72]Kosle J, Magna T, Mlcoch B, et al. Combined Sr, Nd, Pb and Li isotope geochemistry of alkaline lavas from northern James Ross Island (Antarctic Peninsula) and implications for back-arc magma formation. Chemical Geology,2008, doi:10.1016/j.chemgeo.2008.10.006.
    [73]Zack T, Tomascak P B, Rudnick R L, et al. Extremely light Li in orogenic eclogites:The role of isotope fractionation during dehydration in subducted oceanic crust. Earth and Planetary Science Letters,2003,208:279-290.
    [74]Yin A and Harrison T M.2000. Geologic evolution of the Himalayan-Tibetan orogen. Annu. Rev. Earth and Planetary Science Letters,28:211-280.
    [75]侯增谦,孟祥金,曲晓明等.西藏冈底斯斑岩铜矿带埃达克质斑岩含矿性:源岩相变及深部过程约束.矿床地质,2005,24:108-121.
    [76]Harrison T M, Copeland P, Kidd W S F, et al. Raising Tibet. Science,1992,255:1663-1670.
    [77]Williams H, Turner S, Kelley S, et al. Age and composition of dikes in Southern Tibet:new constraints on the timing of east-west extension ans It's relationship to post-collisional volcanism. Geology,2001,29:339-342.
    [78]Ding L, Kapp P, Zhong D, et al. Cenozoic volcanism in Tibet:evidence for a a transition frome oceanic to continental subduction. Journal of Petrology,2003,44:1833-1865.
    [79]Klootwijk C T, Gee J S, Peirce J W, et al. An early India-Asia contact:paleomagnetic constraints from Nineyeast Ridge, ODP Leg 121. Geology,1992,20:395-398.
    [80]莫宣学,赵志丹,邓晋福等.印度-亚洲大陆主碰撞过程与火山作用响应.地学前缘,2003,10:135-148.
    [81]董方浏,侯增谦,高永丰等.滇西腾冲新生代花岗岩:成因类型与构造应用.岩石学报,2006,22:927-937.
    [82]侯增谦,莫宣学,杨志明等.青藏高原碰撞造山带成矿作用:构造背景、时空分布和主要类型.中国地质,2006a,33:348~359.
    [83]侯增谦,杨竹森,徐文艺等.青藏高原碰撞造山带:Ⅰ.主碰撞造山成矿作用.矿床地质,2006b,25:337-358.
    [84]侯增谦,潘桂棠,王安建等.青藏高原碰撞造山带:Ⅱ.晚碰撞转换成矿作用.矿床地质,2006c,25:521-543.
    [85]侯增谦,曲晓明,杨竹森等.青藏高原碰撞造山带:Ⅲ.后碰撞伸展成矿作用.矿床地质,2006d,25:629~651.
    [86]杨志明.西藏驱龙超大型斑岩铜矿床——岩浆作用及矿床成因:[博士论文].北京:中国地质科学院,2008.
    [87]江万,莫宣学,赵崇贺等.青藏高原冈底斯带中段花岗岩类及其中铁镁质微粒包体地球化学特征.岩石学报,1999,15:89~97.
    [88]Debon F, Le Fort P, Sheppard S M F, et al. The four plutonic belts of the trans-Himalaya:A chemical, mineralogical, isotopic and chronological synthesis along a Tibet-Nepal section. Journal of Petrology,1986,27:219-250.
    [89]Harris N B W, Inger S and Xu R. Cretaceous plutonism in Central Tibet:An example of post-collision magmatism?. Journal of Volcanology and Geothermal Research,1990,44:21-32.
    [90]Chu M F, Chung S L, Song B, et al. Zircon U-Pb and Hf isotope constranints on the Mesozoic tectonics and crustal evolution of southern Tibet. Geology,2006,34:745-748.
    [91]赵志丹,莫宣学,Nomade S等.青藏高原拉萨地块碰撞后超钾质岩石的时空分布及其意义.岩石学报,2006,22:787-794.
    [92]Hou Z Q, Gao Y F, Qu X M,et al. Origin of adakitic intrusives generated during mid-Miocene east-west extension in southern Tibet. Earth and Planetary Science Letters,2004,220:139-155.
    [93]侯增谦,莫宣学,高永丰等.埃达克岩:斑岩铜矿的重要含矿母岩-以西藏和智利斑岩铜矿为例.矿床地质,2003a,21:1-12.
    [94]董彦辉,许继峰,曾庆高等.存在比桑日群弧火山岩更早的新特提斯洋俯冲记录吗.岩石学报,2006,22:661~668.
    [95]郑有业,薛迎喜,程力军等.西藏驱龙超大型斑岩铜(钼)矿床:发现、特征及意义.地球科学——中国地质大学学报,2004,29:103-108.
    [96]Nesbitt H W and Young G M. Early Proterozoic climates and plate motions inferred from major element chemistry of lutites. Nature,1982,299 (21);715-717.
    [97]Ryan J G and Kyle P R. Lithium abundance and lithium isotope variations in mantle sources: insights from intraplate volcanic rocks from Ross Island and Marie Byrd Land (Antarctica) and other oceanic islands. Chemical Geology,2004,212:125-142.
    [98]Richter F M, Davis A M, DePaolo D J, et al. Isotope fractionation by chemical diffusion between molten basalt and rhyolite. Geochim. Cosmochim. Acta,2003,67(20):3905-3923.
    [99]Magna T, Janousek V, Kohut M, et al. Fingerprinting sources of orogenic plutonic rocks from Variscan belt with lithium isotopes and possible link to subduction-related origin of some A-type granites. Chemical Geology,2010,274:94-107.
    [100]刘红涛,翟明国,刘建明等.华北克拉通北缘中生代花岗岩:从碰撞后到非造山.岩石学报,2002,18(4):433-448
    [101]Brown M. The generation, segregation, ascent and emplacement of granite magma:the migmatite-to-rustallyderived granite connection in th ickened orogens. Earth Science Reviews, 1994,36:83-30

© 2004-2018 中国地质图书馆版权所有 京ICP备05064691号 京公网安备11010802017129号

地址:北京市海淀区学院路29号 邮编:100083

电话:办公室:(+86 10)66554848;文献借阅、咨询服务、科技查新:66554700