全部 标题 作者
关键词 摘要

OALib Journal期刊
ISSN: 2333-9721
费用:99美元

查看量下载量

相关文章

更多...

洋中脊和洋岛玄武岩过剩230Th成因:全球铀系同位素数据库、常量和稀土元素地球化学制约

, PP. 1389-1398

Keywords: 过剩230Th,单斜辉石,石榴子石,尖晶石-二辉橄榄岩,洋中脊,洋岛

Full-Text   Cite this paper   Add to My Lib

Abstract:

?通过洋中脊和洋岛玄武岩230Th-238U不平衡和常量元素数据,进行地幔熔融参数计算,并分析了过剩230Th的成因.快速和慢速洋中脊玄武岩(230Th/238U)在整体上与初始熔融深度(Fe8,P0)和平均熔融程度(Na8,Fmelt)明显呈正相关;洋岛玄武岩过剩230Th与地幔初始熔融深度和平均熔融程度没有明显的相关性,且与洋中脊玄武岩相比,其较高的(230Th/238U)反而对应更低的部分熔融程度.这表明洋中脊玄武岩过剩230Th受地幔熔融条件的控制,洋岛玄武岩过剩230Th更像是受深部难熔石榴子石相的控制,而不直接受控于地幔熔融条件.计算获得绝大多数230Th过剩的洋中脊玄武岩初始熔融压力介于1.0~2.5GPa之间,与近年来实验在压力>1.0GPa时单斜辉石相中出现DU>DTh的结论相符;洋岛玄武岩的初始熔融压力多介于2.2~3.5GPa,大约在尖晶石-石榴子石转换带附近,其相对洋中脊玄武岩较低的过剩226Ra也暗示更深的地幔源区.据此,洋中脊和洋岛玄武岩过剩230Th可能分别形成于尖晶石-和石榴子石-二辉橄榄岩源区.另外,洋中脊玄武岩的K2O/TiO2与(230Th/238U)和初始熔融压力(P0)相关性不明显,因此形成过剩230Th的地幔深度范围内不存在明显的尖晶石-石榴子石相转换.洋岛与洋中脊玄武岩在(230Th/238U)-K2O/TiO2和(230Th/238U)-P0图解上位于两个明显分割的区域内,说明控制洋岛和洋中脊玄武岩过剩230Th的矿物相不同.快速和慢速扩张洋中脊Ce/Yb-Ce曲线相似,甚至快速扩张洋中脊的Ce/Yb比值略低,相比之下,洋岛玄武岩Ce/Yb-Ce曲线显示其受石榴子石影响较为明显.因此,洋中脊与洋岛玄武岩过剩230Th的控制因素存在明显的差异性,而过剩230Th形成于石榴子石源区的机制只适合于洋岛而不适合于洋中脊玄武岩.

References

[1]  12 Blundy J D, Wood B J. Prediction of crystal-melt partition coefficients from elastic moduli. Nature, 1994, 372: 452—454
[2]  13 Spiegelman M, Elliott T. Consequences of melt transport for uranium series disequilibrium in young lavas. Earth Planet Sci Lett, 1993, 118: 1—20
[3]  14 Van Orman J A, Grove T L, Shimizu N. Uranium and thorium diffusion in diopside. Earth Planet Sci Lett, 1998, 160: 505—519
[4]  15 Bourdon B, Zindler A, Elliott T, et al. Constraints on mantle melting at mid-ocean ridges from global 238U-230Th disequilibrium data. Nature, 1996, 384: 231—235
[5]  16 Elkins L J, Gaetani G A, Sims K W W. Partitioning of U and Th during garnet pyroxenite partial melting: Constraints on the source of alkaline ocean island basalts. Earth Planet Sci Lett, 2008, 265: 270—286
[6]  17 Pertermann M, Hirschmann M M, Hametner K, et al. Experimental determination of trace element partitioning between garnet and silica-rich liquid during anhydrous partial melting of MORB-like eclogite. Geochem Geophys Geosyst, 2004, 5, doi: 10.1029/2003GC000638
[7]  18 Hawkesworth C, Scherstén A. Mantle plumes and geochemistry. Chem Geol, 2007, 241: 319—331
[8]  19 Prytulak J, Elliott T. Determining melt productivity of mantle sources from 238U-230Th and 235U-231Pa disequilibria: An example from Pico Island, Azores. Geochim Cosmochim Acta, 2009, 73: 2103—2122
[9]  20 Russo C J, Rubin K H, Graham D W. Mantle melting and magma supply to the Southeast Indian Ridge: The roles of lithology and melting conditions from U-series disequilibria. Earth Planet Sci Lett, 2009, 278: 55—66
[10]  21 Salters V J M, Hart S R. The hafnium paradox and the role of garnet in the source of mid-ocean ridge basalts. Nature, 1989, 342: 420—422
[11]  23 Blundy J D, Robinson J A C, Wood B J. Heavy REE are compatible in clinopyroxene on the spinel lherzolite solidus. Earth Planet Sci Lett, 1998, 160: 493—504
[12]  24 Landwehr D, Blundy J, Chamorro-Perez E M, et al. U-series disequilibria generated by partial melting of spinel lherzolite. Earth Planet Sci Lett, 2001, 188: 329—348
[13]  25 Iyer S D, Ray D. Structure, tectonic and petrology of mid-oceanic ridges and the Indian scenario. Curr Sci, 2003, 85: 277—289
[14]  26 Herzberg C. Partial crystallization of mid-ocean ridge basalts in the crust and mantle. J Petrol, 2004, 45: 2389—2405
[15]  27 Shaw C S J, Dingwell D B. Experimental peridotite-melt reaction at one atmosphere: A textural and chemical study. Contrib Mineral Petrol, 2008, 155: 199—214
[16]  28 Le Roux P J, Le Roex A P, Schilling J G. Crystallization processes beneath the southern Mid-Atlantic Ridge (40o—55oS), evidence for high-pressure initiation of crystallization. Contrib Mineral Petrol, 2002, 142: 582—602
[17]  29 Zhang G L, Zeng Z G, Yin X B, et al. Deep fractionation of clinopyroxene in the East Pacific Rise 13oN: Evidence from high MgO MORB and melt inclusions. Acta Geol Sin, 2009, 83: 266—277
[18]  30 Kokfelt T F, Hoernle K, Lundstrom C, et al. Time-scales for magmatic differentiation at the Snaefellsj?kull central volcano, western Iceland: Constraints from U-Th-Pa-Ra disequilibria in post-glacial lavas. Geochim Cosmochim Acta, 2009, 73: 1120—1144
[19]  31 Claude-Ivanaj C, Joron J L, Allegre C J. 238U-230Th-226Ra fractionation in historical lavas from the Azores: Long-lived source heterogeneity vs. metasomatism fingerprints. Chem Geol, 2001, 176: 295—310
[20]  32 Turner S, Hawkesworth C, Rogers N, et al. U-Th isotope disequilibria and ocean island basalt generation in the Azores. Chem Geol, 1997, 139: 145—164
[21]  33 Lundstrom C C, Hoernle K, Gill J. U-series disequilibria in volcanic rocks from the Canary islands: Plume versus lithospheric melting. Geochim Cosmochim Acta, 2003, 67: 4153—4177
[22]  34 Rogers N W, Thomas L E, Macdonald R, et al. 238U-230Th disequilibrium in recent basalts and dynamic melting beneath the Kenya rift. Chem Geol, 2006, 234: 148—168
[23]  35 Rubin K H, Macdougall J D. 226Ra excesses in mid-ocean-ridge basalts and mantle melting. Nature, 1988, 335: 158—161
[24]  36 Rubin K H, Van Der Zander I, Smith M C, et al. Minimum speed limit for ocean ridge magmatism from 210Pb-226Ra-230Th disequilibria. Nature, 2005, 437: 534—538
[25]  37 Tepley III F J, Lundstrom C C, Sims K W W, et al. U-series disequilibria in MORB from the Garrett transform and implications for mantle melting. Earth Planet Sci Lett, 2004, 223: 79—97
[26]  38 Cooper K M, Goldstein S J, Sims K W W, et al. Uranium-series chronology of Gorda ridge volcanism: New evidence from the 1996 eruption. Earth Planet Sci Lett, 2003, 206: 459—475
[27]  39 Bourdon B, Turner S P, Ribe N M. Partial melting and upwelling rates beneath the Azores from a U-series isotope perspective. Earth Planet Sci Lett, 2005, 239: 42—56
[28]  40 Peate D W, Hawkesworth C J, Van Calsteren P W, et al. 238U-230Th constraints on mantle upwelling and plume-ridge interaction along the Reykjanes ridge. Earth Planet Sci Lett, 2001, 187: 259—272
[29]  41 Pietruszka A J, Rubin K H, Garcia M O. 226Ra-230Th-238U disequilibria of historical Kilauea lavas (1790—1982) and the dynamics of mantle melting within the Hawaiian plume. Earth Planet Sci Lett, 2001, 186: 15—31
[30]  42 Bourdon B, Joron J L, Claude-Ivanaj C, et al. U-Th-Pa-Ra systematics for the Grande Comore volcanics: Melting processes in an upwelling plume. Earth Planet Sci Lett, 1998, 164: 119—133
[31]  43 Niu Y L, Batiza R. An empirical method for calculating melt compositions produced beneath mid-ocean ridges: Application for axis and off-axis (seamounts) melting. J Geophys Res, 1991, 96: 21753—21777
[32]  44 Hirose K, Kushiro I. Partial melting of dry peridotites at high pressures: Determination of compositions of melts segregated from peridotite using aggregates of diamond. Earth Planet Sci Lett, 1993, 114: 477—489
[33]  45 Klein E M, Langmuir C H. Global correlation of ocean ridge basalt chemistry with axial depth and crustal thickness. J Geophys Res, 1987, 92: 8089—8115
[34]  1 Tepley F J, Lundstromb C C, Sims K W W, et al. U-series disequilibria in MORB from the Garrett Transform and implications for mantle melting. Earth Planet Sci Lett, 2004, 223: 79—97
[35]  2 McKenzie D. Constraints on melt generation and transport from U-series activity ratios. Chem Geol, 2000, 162: 81—94
[36]  3 Sims K W W, Goldstein S J, Blichert-Toft J, et al. Chemical and isotopic constrains on the generation and transport of magma beneath the East Pacific Rise. Geochim Cosmochim Acta, 2002, 66: 3481—3504
[37]  4 Sims K W W, Depaolo D J, Murrell D M, et al. Mechanisms of magma generation beneath Hawaii and mid-ocean ridges: Uranium/thorium and samarium/neodymium isotopic evidence. Science, 1995, 267: 508—511
[38]  5 Richardson C, McKenzie D. Radioactive disequilibria from models of melt generation by plumes and ridges. Earth Planet Sci Lett, 1994, 128: 425—437
[39]  6 Spiegelman M, Reynolds J R. Combined dynamic and geochemical evidence for convergent melt flow beneath the East Pacific Rise. Nature, 1999, 402: 282—285
[40]  7 Williams R W, Gill J B. Effects of partial melting on the uranium decay series. Geochim Cosmochim Acta, 1989, 53: 1607—1619
[41]  8 Turner S, Blundy J, Wood B, et al. Large 230Th-excesses in basalts produced by partial melting of spinel lherzolite. Chem Geol, 2000, 162: 127—136
[42]  22 Salters V J M. The generation of mid-ocean ridge basalts from the Hf and Nd isotope perspective. Earth Planet Sci Lett, 1996, 141: 109—123
[43]  49 Shen Y, Forsyth D W. Geochemical constraints on initial and final depths of melting beneath mid-ocean ridges. J Geophys Res, 1995, 100: 2211—2237
[44]  50 Longhi J. Some phase equilibrium systematics of lherzolite melting: I. Geochem Geophys Geosyst, 2002, 3, doi: 10.1029/2001GC000204
[45]  51 Tenner T J, Hirschmann M M, Withers A C, et al. Hydrogen partitioning between nominally anhydrous upper mantle minerals and melt between 3 and 5 GPa and applications to hydrous peridotite partial melting. Chem Geol, 2009, 262: 42—56
[46]  52 O’Hara M J, Richardson S W, Wilson G. Garnet-peridotite stability and occurrence in crust and mantle. Contrib Mineral Petrol, 1971, 32: 48—68
[47]  57 Robinson J A C, Wood B J. The depth of the spinel to garnet transition at the peridotite solidus. Earth Planet Sci Lett, 1998, 164: 277—284
[48]  58 Toomey D R, Wilcock W S, Solomon S C, et al. Mantle seismic structure beneath the MELT region of the East Pacific Rise from P and S wave tomography. Science, 1998, 280: 1224—1227
[49]  59 Saltzer R L, Humphreys E D. Upper mantle P wave velocity structure of the eastern Snake River Plain and its relationship to geodynamic models of the region. J Geophys Res, 1997, 102: 11829—11841
[50]  46 Hekiniana R, Francheteaub J, Armijoc R, et al. Petrology of the Easter microplate region in the South Pacific. J Volcanol Geotherm Res, 1996, 72: 259—289
[51]  47 Niu Y L, Waggoner D G, Sinton J M, et al. Mantle source heterogeneity and melting processes beneath seafloor spreading centres: The East Pacific Rise, 18°—19°S. J Geophys Res, 1996, 101: 27711—27733
[52]  48 Taylor B, Martinez F. Back-arc basin basalt systematics. Earth Planet Sci Lett, 2003, 210: 481—497
[53]  53 Jenkins D M, Newton R C. Experimental determination of the spinel peridotite to garnet peridotite inversion at 900°C and 1000°C in the system CaO-MgO-Al2O3-SiO2, and at 900°C with natural garnet and olivine. Contrib Mineral Petrol, 1979, 68: 407—419
[54]  54 Makenzie D, O’Nions R K. Partial melt distributions from inversion of rare earth element concentrations. J Petrol, 1991, 32: 1021—1091
[55]  55 Hirschmann M M, Stolper E M. A possible role for garnet pyroxenite in the origin of the ‘‘garnet signature’’ in MORB. Contrib Mineral Petrol, 1996, 124: 185—208
[56]  56 Klemme S, O’Neill H S. The near-solidus transition from garnet lherzolite to spinel lherzolite. Contrib Mineral Petrol, 2000, 138: 237—248
[57]  9 Wood B J, Blundy J D, Robinson J A C. The role of clinopyroxene in generating U-series disequilibrium during mantle melting: Implications for uranium series disequilibria in basalts. Geochim Cosmochim Acta, 1999, 63: 1613—1620
[58]  10 Beattiea P. The generation of uranium series disequilibria by partial melting of spinel peridotite: Constraints from partitioning studies. Earth Planet Sci Lett, 1993, 117: 379—391
[59]  11 Koh K M, Tay E G, Lundstrom C C, et al. Investigating solid mantle upwelling rates beneath mid-ocean ridges using U-series disequilibria, 1: A global approach. Earth Planet Sci Lett, 1998, 157: 151—165

Full-Text

Contact Us

service@oalib.com

QQ:3279437679

WhatsApp +8615387084133