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Disclinations provide the missing mechanism for deforming olivine-rich rocks in the mantle
Using electron backscattering diffraction maps of deformed olivine to resolve the disclinations at grain boundaries, combined with a disclination-based model of a high-angle tilt boundary in olivine, reveals the missing mechanism for describing plastic flow in polycrystalline olivine: an applied shear induces grain-boundary migration through disclination motion.
- Patrick Cordier
- , Sylvie Demouchy
- & Claude Fressengeas
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Letter |
Foundering of lower island-arc crust as an explanation for the origin of the continental Moho
The calculated density and seismic structure of the two best-exposed island arc sections (Kohistan and Talkeetna) reveals that the foundering of the lower arc crust produces a sharp seismic discontinuity characteristic of the continental Mohorovičić discontinuity.
- Oliver Jagoutz
- & Mark D. Behn
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Brief Communications Arising |
Conrad et al. reply
- Clinton P. Conrad
- , Bernhard Steinberger
- & Trond H. Torsvik
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Brief Communications Arising |
Does quadrupole stability imply LLSVP fixity?
- Maxwell L. Rudolph
- & Shijie Zhong
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Article |
Olivine crystals align during diffusion creep of Earth’s upper mantle
In Earth’s mantle, the shape change of olivine grains depending on temperature and the presence of melt can result in the development of olivine crystallographic preferred orientation during diffusion creep, meaning that the process may be the principal mechanism of mantle flow.
- Tomonori Miyazaki
- , Kenta Sueyoshi
- & Takehiko Hiraga
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Letter |
Bottom-up control of geomagnetic secular variation by the Earth’s inner core
The pattern of geomagnetic secular variation observed on the Earth’s surface is shown to be reproduced by two mechanisms relying on the inner core; this bottom-up heterogeneous driving of outer-core convection dominates top-down driving from mantle thermal heterogeneities.
- Julien Aubert
- , Christopher C. Finlay
- & Alexandre Fournier
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Article |
Heat-pipe Earth
A heat-pipe model of Earth, whereby interior heat is brought to the surface through localized channels, yields predictions that agree with craton data and the detrital zircon record, and offers a global geodynamic framework in which to explore Earth’s evolution before the onset of plate tectonics.
- William B. Moore
- & A. Alexander G. Webb
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Letter |
Feeding andesitic eruptions with a high-speed connection from the mantle
Diffusion modelling of nickel in mantle melts beneath a volcano reveals the short timescales of magma movement from the base of the crust to the surface in the months to years before an eruption.
- Philipp Ruprecht
- & Terry Plank
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Letter |
Characterization and implications of intradecadal variations in length of day
Variations in Earth's rotation show clear signals of a 5.9-year oscillation and jumps in Earth’s moment of inertia; correlation with the geomagnetic field suggests an origin in Earth’s core and constrains the conductivity and thus the composition and mineralogy of the deep mantle.
- R. Holme
- & O. de Viron
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Letter |
Stability of active mantle upwelling revealed by net characteristics of plate tectonics
Global-scale mantle flow patterns can be deduced from the net behaviour (convergence and divergence) of surface plate motions; persistent quadrupole divergence in central Africa and the central Pacific suggest sustained stationary upwelling beneath these locations in the mantle.
- Clinton P. Conrad
- , Bernhard Steinberger
- & Trond H. Torsvik
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Letter |
Small effect of water on upper-mantle rheology based on silicon self-diffusion coefficients
Measurements of the silicon self-diffusion coefficients in olivine at high temperature show that the effect of water content on rock deformation is actually very small, not large as was previously thought.
- Hongzhan Fei
- , Michael Wiedenbeck
- & Tomoo Katsura
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Letter |
Argon isotopic composition of Archaean atmosphere probes early Earth geodynamics
The analysis of the isotopic signature of argon in 3.5-billion-year-old hydrothermal quartz suggests an early development of the continental crust, with implications for climate variability at that time.
- Magali Pujol
- , Bernard Marty
- & Pascal Philippot
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Article |
Intra-oceanic subduction shaped the assembly of Cordilleran North America
A new explanation for the origin of the accreted terranes that form the mountainous Cordillera of western North America is proposed and tested: stationary, intra-oceanic subduction deposited massive slab walls in the mantle and grew volcanic archipelagos at the surface, which were overridden by and accreted to North America during Cretaceous times.
- Karin Sigloch
- & Mitchell G. Mihalynuk
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Letter |
Electrical image of passive mantle upwelling beneath the northern East Pacific Rise
Sea-floor magnetotelluric soundings along a portion of the East Pacific Rise reveal a symmetric, high-conductivity triangular region at depths of 20–90 kilometres that is consistent with partial melting of passively upwelling mantle.
- Kerry Key
- , Steven Constable
- & Anne Pommier
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Letter |
Melt-rich channel observed at the lithosphere–asthenosphere boundary
Sea-floor magnetotelluric data are used to image the electrical conductivity of the lithosphere–asthenosphere boundary offshore of Nicaragua; a high-conductivity layer confined to depths of 45–70 kilometres is found, interpreted to be a partially molten channel of low viscosity.
- S. Naif
- , K. Key
- & R. L. Evans
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Letter |
Glaciations in response to climate variations preconditioned by evolving topography
Previously glaciated landscapes tend to have large areas concentrated at the same elevation; here it is shown that small climate changes can trigger massive glacial expansions for these landscapes, explaining long-term patterns of erosion in the Quaternary period.
- Vivi Kathrine Pedersen
- & David Lundbek Egholm
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Letter |
Laboratory measurements of the viscous anisotropy of olivine aggregates
Measurements of the viscous anisotropy of highly deformed polycrystalline olivine find it to be approximately an order of magnitude larger than that predicted by grain-scale simulations; the maximum degree of anisotropy is reached at geologically low shear strain, such that deforming regions of the Earth’s upper mantle should exhibit significant viscous anisotropy.
- L. N. Hansen
- , M. E. Zimmerman
- & D. L. Kohlstedt
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Letter |
Deep penetration of molten iron into the mantle caused by a morphological instability
A morphological instability causing blobs of iron-rich liquid to penetrate iron oxides is described, providing a mechanism for the iron-rich regions in the mantle.
- Kazuhiko Otsuka
- & Shun-ichiro Karato
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Letter |
Mechanisms for oscillatory true polar wander
Stabilization of the Earth’s rotation axis by a combination of long-term excess ellipticity and elastic stresses in the broken lithosphere provides an explanation for oscillatory true polar wander events spanning the past few billion years of Earth history.
- J. R. Creveling
- , J. X. Mitrovica
- & I. Matsuyama
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Letter |
April 2012 intra-oceanic seismicity off Sumatra boosted by the Banda-Aceh megathrust
The two earthquakes of respective magnitudes 8.6 and 8.2 that occurred off the coast of the Sumatra subduction zone on 11 April 2012 are shown to be part of a continuing boost of the intraplate deformation between India and Australia that followed the Aceh 2004 and Nias 2005 megathrust earthquakes.
- Matthias Delescluse
- , Nicolas Chamot-Rooke
- & Christophe Vigny
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Letter |
The 11 April 2012 east Indian Ocean earthquake triggered large aftershocks worldwide
Although strong remote aftershocks are exceedingly rare, their rate increased fivefold during the six days following the 2012 east Indian Ocean earthquake, perhaps as a result of the strike-slip nature of the 2012 event or a build up of close-to-failure nucleation sites.
- Fred F. Pollitz
- , Ross S. Stein
- & Roland Bürgmann
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Letter |
En échelon and orthogonal fault ruptures of the 11 April 2012 great intraplate earthquakes
The magnitude 8.7 earthquake that occurred off the coast of the Sumatra subduction zone on 11 April 2012 is shown to have had an extraordinarily complex four-fault rupture; these great ruptures represent large lithospheric deformation that may eventually lead to a localized boundary between the Indian and Australian plates.
- Han Yue
- , Thorne Lay
- & Keith D. Koper
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Letter |
‘Melt welt’ mechanism of extreme weakening of gabbro at seismic slip rates
A laboratory study of the frictional properties of the igneous rock gabbro at seismically relevant slip rates suggests that the initial weakening of a fault surface during earthquake rupture may be associated with hotspots and macroscopic streaks of melt, which partially unload the rest of the slip interface.
- Kevin M. Brown
- & Yuri Fialko
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Letter |
Solid–liquid iron partitioning in Earth’s deep mantle
Iron in partially molten rocks under deep-mantle conditions partitions into the melt phase less than previously reported, suggesting that melt generated near the core–mantle boundary should segregate upwards.
- Denis Andrault
- , Sylvain Petitgirard
- & Mohamed Mezouar
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Books & Arts |
Geoscience: Depth charge
Cecily Wolfe welcomes a life of cartographer Marie Tharp, revealing her part in the plate-tectonics revolution.
- Cecily Wolfe
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News & Views |
A dash of deep nebula on the rocks
The cocktail of noble-gas isotopes in an Icelandic rock suggests that the upper mantle does not, and never did, receive gas from a deeper mantle reservoir. This challenges ideas of deep Earth's behaviour and formation. See Letter p.101
- Chris J. Ballentine
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Letter |
Hafnium isotope evidence for a transition in the dynamics of continental growth 3.2 Gyr ago
Hafnium isotope ratios obtained from zircons in southern West Greenland suggest that Earth’s ancient crustal growth changed around 3.2 Gyr ago to a modern geodynamic regime involving juvenile crust generation by plate tectonic processes.
- T. Næraa
- , A. Scherstén
- & M. J. Whitehouse
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Letter |
Deposition of 1.88-billion-year-old iron formations as a consequence of rapid crustal growth
The reappearance of major iron formations at 1.88 billion years ago (after the rise in atmospheric oxygen) is puzzling because their deposition requires anoxic and iron-rich sea water, but is here explained as a consequence of major mantle activity and rapid crustal growth at that time.
- Birger Rasmussen
- , Ian R. Fletcher
- & Alan M. Thorne
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News |
Satellite system will speed up tsunami warnings
GPS networks could cut time needed for accurate alerts by a factor of ten.
- Richard A. Lovett
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Letter |
Formation of the ‘Great Unconformity’ as a trigger for the Cambrian explosion
Changes in ocean chemistry promoted during the formation of the Great Unconformity, a stratigraphic surface that separates continental basement rock from younger marine sedimentary deposits, are proposed as the cause of the Cambrian explosion of marine animals.
- Shanan E. Peters
- & Robert R. Gaines
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Letter |
Origin of Columbia River flood basalt controlled by propagating rupture of the Farallon slab
A model of subduction that reveals a long tear under Oregon and Nevada provides a new mechanism for the origin of Columbia River flood basalt, resolving previous hypotheses.
- Lijun Liu
- & Dave R. Stegman
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Research Highlights |
Explosion in Death Valley
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Letter |
Kimberlite ascent by assimilation-fuelled buoyancy
Assimilation of mantle minerals is proposed as a cause of deep-seated exsolution of dissolved volatiles and the driver of kimberlite magma ascent.
- James K. Russell
- , Lucy A. Porritt
- & Donald B. Dingwell
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Letter |
Modelling the rheology of MgO under Earth’s mantle pressure, temperature and strain rates
Numerical modelling of the rheology of MgO at the pressure, temperature and strain rates of Earth's mantle shows that extremely low strain rates counteract the influence of pressure, so that MgO is generally a very weak phase in the mantle.
- Patrick Cordier
- , Jonathan Amodeo
- & Philippe Carrez
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Letter |
Forcing of wet phases in southeast Africa over the past 17,000 years
A continuous record of hydrologic variability for the past 17,000 years at the mouth of the Zambezi River shows that hydrologic conditions in southeast Africa were controlled by variations in local insolation and migrations of the Intertropical Convergence Zone, rather than by Indian Ocean temperature.
- Enno Schefuß
- , Holger Kuhlmann
- & Jürgen Pätzold
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Letter |
Frictional ageing from interfacial bonding and the origins of rate and state friction
- Qunyang Li
- , Terry E. Tullis
- & Robert W. Carpick
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Letter |
The oxidation state of Hadean magmas and implications for early Earth’s atmosphere
Earth's mantle is likely to have reached its present-day oxidation state before 4 billion years ago, according to a determination of the oxidation state of Hadean magmatic melts.
- Dustin Trail
- , E. Bruce Watson
- & Nicholas D. Tailby
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Review Article |
The case against climate regulation via oceanic phytoplankton sulphur emissions
- P. K. Quinn
- & T. S. Bates
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Letter |
Correlation between deep fluids, tremor and creep along the central San Andreas fault
- Michael Becken
- , Oliver Ritter
- & Ute Weckmann
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Letter |
Evidence for an oxygen-depleted liquid outer core of the Earth
- Haijun Huang
- , Yingwei Fei
- & Zizheng Gong
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Letter |
Subduction dynamics and the origin of Andean orogeny and the Bolivian orocline
- F. A. Capitanio
- , C. Faccenna
- & D. R. Stegman
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Letter |
Active formation of ‘chaos terrain’ over shallow subsurface water on Europa
- B. E. Schmidt
- , D. D. Blankenship
- & P. M. Schenk
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Letter |
A long-lived lunar dynamo driven by continuous mechanical stirring
- C. A. Dwyer
- , D. J. Stevenson
- & F. Nimmo
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Review Article |
Subsurface water and clay mineral formation during the early history of Mars
- Bethany L. Ehlmann
- , John F. Mustard
- & Yves Langevin
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News & Views |
Sea change for the rise of oxygen
A model proposes that falling sea levels shifted the make-up of volcanic gases on the early Earth, triggering a chain of events that may have allowed photosynthesis in the ocean to oxygenate the atmosphere. See Letter p.229
- Timothy W. Lyons
- & Christopher T. Reinhard
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Research Highlights |
Why the Atlantic is so hot
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News |
Mantle plume propelled India towards Asia
Ancient hotspot is linked to the motions of African and Indian plates.
- Sid Perkins
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News & Views |
Plate motion and mantle plumes
A model based on geophysical data from the Indian Ocean suggests that a mantle-plume head may once have coupled the motions of the African and Indian tectonic plates, and determined their respective speeds. See Article p.47
- R. Dietmar Müller
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Article |
Indian and African plate motions driven by the push force of the Réunion plume head
- Steven C. Cande
- & Dave R. Stegman
Dynamics of continental accretion