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The Persistent Mantle Plume Myth D This article was downloaded by: [217.44.161.233] On: 09 October 2013, At: 03:09 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/taje20 The persistent mantle plume myth D. L. ANDERSON a a Seismological Laboratory , California Institute of Technology , Pasadena , CA , 91125 , USA Published online: 26 Sep 2013. To cite this article: D. L. ANDERSON , Australian Journal of Earth Sciences (2013): The persistent mantle plume myth, Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia, DOI: 10.1080/08120099.2013.835283 To link to this article: http://dx.doi.org/10.1080/08120099.2013.835283 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and- conditions TAJE_A_835283.3d (TAJE) 24-09-2013 23:37 Australian Journal of Earth Sciences (2013) http://dx.doi.org/10.1080/08120099.2013.835283 The persistent mantle plume myth D. L. ANDERSON* Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA Seismology, thermodynamics and classical physics—the physics associated with the names of Fourier, Debye, Born, Gruneisen,€ Kelvin, Rayleigh, Rutherford, Ramberg and Birch—show that ambient shallow mantle under large long-lived plates is hundreds of degrees hotter than in the passive upwellings that fuel the global spreading ridge system, that potential temperatures in mantle below about 200 km gen- erally decrease with depth and that deep mantle low shear wave-speed features are broad, sluggish and dome-like rather than narrow and mantle-plume-like. The surface boundary layer of the mantle is more voluminous and potentially hotter than regions usually considered as sources for intraplate volca- noes. This means that the ‘mantle plume’ explanation for Hawaii and large igneous provinces is unnec- essary. In isolated systems, heated from within and cooled from above, upwellings are passive and large, which suggests that tomographic features, and upwellings, are responses to plate tectonics, spreading and subduction, at least until melting introduces a small intrinsic buoyancy at shallow depths. Melting anomalies, or ‘hotspots,’ are side-effects of plate tectonics and are fed primarily by shear- driven processes in the boundary layer (BL), not by deep buoyant upwellings. A dense basal melange (BAM) component further stabilises the lower boundary layer of the mantle. Mid-ocean ridges and asso- ciated broad passive depleted mantle (DM) upwellings probably originate in the transition region. Deeper mantle upwellings are broad domes that stay in the lower mantle. KEYWORDS: mantle geochemistry, plumes, perisphere, LLAMA, boundary layers, classical physics, tomography. The law that entropy always increases holds the supreme seldom appreciated that it is without a sound logical position among the laws of Nature. If someone points out (see Appendix 1) or physical foundation (Appendix 2). to you that your pet theory of the universe is in disagree- Any logical basis was extinguished as it was amended ’ — ment with Maxwell s equations then so much the worse and modified. Physics and logic are routinely violated in for Maxwell’s equations. If it is found to be contradicted the underlying assumptions and arguments (Tozer 1973; by observation—well, these experimentalists do bungle Larsen & Yuen 1997; Anderson 2007a, 2012a, b; Anderson things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you & Natland 2007). Crust and volatile recycling, shallow no hope; there is nothing for it but to collapse in deepest melting, lithospheric extension, volcanism and shear- humiliation. and plate-driven upwellings are now accepted as unavoid- —Sir Arthur Stanley Eddington, able consequences of plate tectonics. Nevertheless the The Nature of the Physical World (1929) myth persists and has distorted thinking about the Earth for decades. In science this is an old story, likely to be Downloaded by [217.44.161.233] at 03:09 09 October 2013 Prelude (motivated by and adapted, paraphrased and repeated, as defenders of common wisdom, e.g. an estab- updated from a 1991 article in this journal entitled lished paradigm or belief system, are seldom treated ‘The persistent myth of crustal growth’ by Richard with the same scepticism as challengers of the status quo. Armstrong) The conclusion is inescapable that terrestrial planets A myth is a tale invented to explain some natural phe- underwent essentially immediate—mostly irreversible— nomenon. It cannot be falsified by any observation or the- differentiation into relatively constant volume core, ory.The mantle plume idea originated as a testable, albeit enriched crust and fluid reservoirs, and refractory speculative, scientific hypothesis. As modified to explain degassed residual mantle that the Earth, on average, is compositions and volumes of island and continental cooling down and is periodically assembling and destroy- basalts, and subjective correlations with lower mantle ing supercontinents, and growing or shrinking its crust. features, and as paradoxes accumulated and were Planets are not homogenised by self-driven convection. ignored, it became a myth (e.g. Armstrong 1991; Dickin- Potential temperatures, on average, in an isolated planet, son 2003) or a just-so story. In philosophy, a just-so story, decrease with time and with depth below the convective or ad hoc fallacy, is an unverifiable unfalsifiable explana- sublayer. tion of some natural process. ‘Mantle plume,’ as cur- The geochemical basis of the cold Earth and plume rently used, has acquired the status of dogma, but it is ideas can be traced to Harold Urey and his Chicago *[email protected] Ó 2013 Geological Society of Australia TAJE_A_835283.3d (TAJE) 24-09-2013 23:37 2 D. L. Anderson colleagues and former students, and their students, who convection. These concepts have been replaced by a advocated a cold origin for the planets, and a terrestrial dense basal melange (BAM) consisting of crust, primi- crust that grew slowly over time from a primordial tive matter and recycled slabs that rises to the surface as undifferentiated undegassed interior. Urey viewed plan- it traps core heat. Recycling has now been accepted but, etary accretion as a gentle drawn-out process, involving in current versions of the plume paradigm, recycled accumulation of small planetesimals; he predicted pri- fragments are mixed with undegassed lower mantle, or mordial undegassed interiors for planets and a primor- gases from the core, before they return to the surface. dial basalt-free surface for the Moon. Cold accretion Some numerical versions enforce whole mantle convec- models predicted that planets should be little affected by tion, a constant temperature core or injections of exter- igneous processing and degassing. However, physical nal energy or fluid, none of which are allowed in natural considerations show that the history, internal structure systems. These assumptions are modern versions of and dynamics of the Earth are inexorably linked to the Maxwell’s demon hypothesis, which was an early enormous energy of Earth and core formation and the attempt to circumvent the second law by forcing desired subsequent cooling (Birch 1952, 1965; Arkani-Hamed behaviour on natural systems. 1994; Carlson & Boyet 2008). Richard Armstrong asked a series of questions, which The viewpoint advocated here challenges what has I update. How can proto-planets and Earth not become become accepted wisdom over the past 15 years, and this degassed and differentiated before, during and soon paper is polemical because it highlights the logical falla- after accretion; how can Earth rapidly differentiate a cies used by acolytes and the implications of the neglect crust, core and atmosphere, yet retain an undifferenti- of physics. The mantle plume myth has been repeated, ated, undegassed homogeneous mantle? In the presence amended and defended with assertions, selective data, of enormous gradients in pressure and viscosity, how ad hoc rationalisations,
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