Depleted melt inclusions in MORB plagioclase: messages from the mantle or mirages from the magma chamber?

被引:36
|
作者
Michael, PJ
McDonough, WF
Nielsen, RL
Cornell, WC
机构
[1] Univ Tulsa, Dept Geosci, Tulsa, OK 74104 USA
[2] Univ Maryland, Dept Geol, College Pk, MD 20742 USA
[3] Oregon State Univ, Coll Oceanog & Atmospher Sci, Corvallis, OR 97331 USA
基金
美国国家科学基金会;
关键词
melt inclusion; high field strength elements; MORB plagioclase;
D O I
10.1016/S0009-2541(01)00371-0
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Melt inclusions that are depleted in high field strength elements (HFSE; Ti, Zr, Nb), relative to other incompatible elements, were found in a plagioclase phyric normal mid-ocean ridge basalt (N-MORB) from the southern Mid-Atlantic Ridge. Similar inclusions are present in many other phyric NMORB. HFSE-depleted inclusions constitute only a few percent of all melt inclusions in this sample, and inclusions within individual crystals display a limited range of HFSE-depletion. Relative to host glass, they are depleted in the order: Nb<Zr <Tiapproximate toHREEzapproximate toTh<LREE<U. Concentrations of Si, Al, Fe, Mg and Ca are similar to the host glass. Large ion lithophile elements (LILE) are enriched relative to the host glass in the order: Rb>Ba>K>Pb>Na>Sr. La/Sm is higher than in the host glass. Cl is enriched but not to the level observed in HFSE-depleted inclusions by Nielsen et al. [Geochem. Geophys. Geosyst. (2000) 1], who deemed similar inclusions in other MORB as "Clenriched". HFSE depletion is not related to inclusion size, plagioclase host composition, or inclusions' Mg#s. Because of the disparate behavior of elements with similar bulk crystal-liquid partition coefficients, the depletion trends cannot be modeled by any process that involves crystal liquid equilibrium, such as melting or crystallization. Nielsen et al. proposed that similar inclusions represent liquids that were formed by melting of hydrothermally altered depleted peridotite. An alternative explanation is that the inclusions' compositions were controlled by diffusional processes. There is a good correlation of the elements' abundance relative to the host with Z(2)r(i), a quantity that is highly correlated with diffusion in silicate liquids ([Hofmann, A.W., 1980. Diffusion in natural silicate melts: a critical review. Physics of Magmatic Processes, Princeton Univ. Press, pp. 385-417]; Z=atomic radius and r(i) = ionic radius) and possibly in plagioclase. The depletions are consistent with a model in which plagioclase rapidly dissolves to form a plagioclase-like melt, while diffusion through liquid channels or solid plagioclase transports elements from the host liquid to the inclusion. Plagioclase dissolution may have been aided by increased Cl + H2O in the enclosing magma, which might have been ultimately derived from hydrothermal activity. A second diffusion-related model starts with the entrapment of ultradepleted melt inclusions such as those found in olivine. Subsequent diffusion from a less depleted host melt through solid plagioclase into the inclusion would control the inclusion's incompatible element abundances. Comparison of elements with similar Z(2)r(i) (e.g., LREE vs. HREE) suggests that the host liquid of the analyzed sample was enriched in incompatible elements despite the inclusions' depletion in Nb, Zr and REE. Compositions of inclusions that are not HFSE-depleted also suggest that the host melt was enriched. Ultradepleted inclusions in MORB olivine [Nature 363 (1993) 151] are not like those in plagioclase: they are depleted in all incompatible elements, and their compositions are consistent with progressive fractional melts of the mantle (ibid). However, the possibility of a diffusion relationship should also be examined. (C) 2002 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:43 / 61
页数:19
相关论文
共 50 条
  • [1] Magma mixing in a compositionally layered silicic magma chamber:: Inferences from silicate melt inclusions
    Harangi, S
    Czuppon, G
    Lukács, R
    Ntaflos, T
    [J]. GEOCHIMICA ET COSMOCHIMICA ACTA, 2004, 68 (11) : A651 - A651
  • [2] MELT INCLUSIONS IN HIGH-AN PLAGIOCLASE FROM THE GORDA RIDGE - AN EXAMPLE OF THE LOCAL DIVERSITY OF MORB PARENT MAGMAS
    NIELSEN, RL
    CRUM, J
    BOURGEOIS, R
    HASCALL, K
    FORSYTHE, LM
    FISK, MR
    CHRISTIE, DM
    [J]. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1995, 122 (1-2) : 34 - 50
  • [3] Evidence of primitive melt heterogeneities preserved in plagioclase-hosted melt inclusions of South Atlantic MORB
    Magnani, Marco
    Fujii, Toshitsugu
    Orihashi, Yuji
    Yasuda, Atsushi
    Hirata, Takafumi
    Santo, Alba P.
    Vaggelli, Gloria
    [J]. GEOCHEMICAL JOURNAL, 2006, 40 (03) : 277 - 290
  • [4] Melt inclusions from the Galapagos plume: Mirrors and mirages of the deep
    Koleszar, A. M.
    Saal, A. E.
    Hauri, E. H.
    Kurz, M. D.
    [J]. GEOCHIMICA ET COSMOCHIMICA ACTA, 2007, 71 (15) : A508 - A508
  • [5] Crustal origin for coupled 'ultra-depleted' and 'plagioclase' signatures in MORB olivine-hosted melt inclusions: evidence from the Siqueiros Transform Fault, East Pacific Rise
    Leonid V. Danyushevsky
    Michael R. Perfit
    Stephen M. Eggins
    Trevor J. Falloon
    [J]. Contributions to Mineralogy and Petrology, 2003, 144 : 619 - 637
  • [6] Crustal origin for coupled 'ultra-depleted' and 'plagioclase' signatures in MORB olivine-hosted melt inclusions: evidence from the Siqueiros Transform Fault, East Pacific Rise
    Danyushevsky, LV
    Perfit, MR
    Eggins, SM
    Falloon, TJ
    [J]. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 2003, 144 (05) : 619 - 637
  • [7] The ridge filter: How melt supply and magma chambers modulate mantle compositions in MORB
    Rubin, K. H.
    Sinton, J. M.
    [J]. GEOCHIMICA ET COSMOCHIMICA ACTA, 2008, 72 (12) : A810 - A810
  • [8] Highly Unradiogenic Pb Isotopes Revealed by Plagioclase-Hosted Melt Inclusions in E-MORB From the South China Sea
    Wu, Tao
    Zhang, Wen
    Wilde, Simon A.
    Lu, Jianggu
    Zhang, Guoliang
    Li, Chunfeng
    Chen, Xuegang
    Chen, Shuangshuang
    [J]. JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 2023, 128 (04)
  • [9] Experimental Constraints on Homogenization of Plagioclase-Hosted Melt Inclusions From Plagioclase Ultraphyric Basalts
    Lewis, Kristen R.
    Ustunisik, Gokce K.
    Nielsen, Roger L.
    [J]. FRONTIERS IN EARTH SCIENCE, 2021, 8
  • [10] Reequilibration Processes Occurring in Plagioclase-Hosted Melt Inclusions From Plagioclase Ultraphyric Basalts
    Drignon, Melissa J.
    Nielsen, Roger L.
    Tepley, Frank J., III
    Bodnar, Robert J.
    [J]. GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, 2019, 20 (01) : 109 - 119