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Komatiites and the structure of the Archaean mantle

Nisbet, Euan G. and Walker, David (1982) Komatiites and the structure of the Archaean mantle. Earth and Planetary Science Letters, 60 (1). pp. 105-113. ISSN 0012-821X. doi:10.1016/0012-821X(82)90025-5.

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The existence of Archaean komatiites with eruption temperatures greater than 1650°C requires that the mantle be vertically differentiated by the time of komatiite eruption. If in the unlikely event that undifferentiated mantle had survived primordial planetary differentiation and had been hot enough to deliver 1650°C komatiite, it would have been extensively molten to depths of ∼250 km, resulting in rapid, profound, vertical differentiation anyway. During primordial differentiation (or Archaean komatiite petrogenesis) the high density and compressibility of ultrabasic melt allowed storage of a global melt layer beneath a buoyant residue of dunite and/or harzburgite. This refractory cap segregated by extraction of melt both upwards and downwards from the depth at which the density contrast between crystals and liquid vanishes. Eruption of komatiite from the melt layer by corrosion of the cap was the Archaean earth's principal means of dissipating excess heat. This subterranean magma ocean precluded vertical homogenization of the Archaean mantle by convection but effectively absorbed lateral mantle heterogeneities and imposed the relative uniformity of maximum eruption temperature and MgO contents (∼32%) seen in primitive Archaean komatiites on all continents. Verification of the postulated density relations of liquids and crystals to 100 kbar becomes a pressing concern in view of the expected consequences these relations may have had.

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Additional Information:© 1982 Elsevier B.V. Received 17 August 1981, Revised 26 May 1982. We thank the various people who have criticized or added a bit to this model, and in particular N.T. Amdt, M.J. Bickle, C.T. Herzberg, T.J.B. Holland, B.D. Marsh, D.P. McKenzie, R.K. O’Nions, A. Putnis, R.S.J. Sparks, and at a later stage, D.L. Anderson, B.H. Hager, A.M. Hofmeister, and E.M. Stolper. We especially thank M.J. O’Hara, R.W. Nesbit and A. Cattell for their detailed and helpful review and in particular for their comments on our models of the emunctory processes of the LLLAMA. Parts of the research were supported by N.E.R.C. grant GR3/4407 and NSF grants OCE79-09699 and EAR79-23977 (J.F. Hays, P.I.), and the Committee on Experimental Geology and Geophysics of Harvard University. D.W. thanks the California Institute of Technology for a Fairchild Fellowship during which this work was completed. California Institute of Technology, Division of Geological and Planetary Sciences Contribution Number 3764.
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Natural Environment Research Council (NERC)GR3/4407
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Caltech Division of Geological and Planetary Sciences3764
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Official Citation:Euan G. Nisbet, David Walker, Komatiites and the structure of the Archaean mantle, In Earth and Planetary Science Letters, Volume 60, Issue 1, 1982, Pages 105-113, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83040
Deposited By: Tony Diaz
Deposited On:07 Nov 2017 23:10
Last Modified:15 Nov 2021 19:54

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