scholarly journals Leaky at the Core

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Jon Kelvey
Keyword(s):  
Lower Mantle ◽  
Outer Core ◽  
Mantle Plumes ◽  
The Core ◽  
Deep Mantle ◽  
New Evidence

New evidence from deep mantle plumes suggests that Earth’s liquid outer core might be leaking tungsten isotopes into the lower mantle.

scholarly journals Mantle plumes and mantle dynamics in the Wilson cycle

2019 ◽  
Vol 470 (1) ◽  
pp. 87-103 ◽  
Author(s):  
Philip J. Heron
Keyword(s):  
Mantle Convection ◽  
Large Scale ◽  
Thermal Evolution ◽  
Mantle Flow ◽  
Mantle Plumes ◽  
Mantle Dynamics ◽  
The Core ◽  
Deep Mantle ◽  
Igneous Provinces ◽  
Wilson Cycle

AbstractThis review discusses the thermal evolution of the mantle following large-scale tectonic activities such as continental collision and continental rifting. About 300 myr ago, continental material amalgamated through the large-scale subduction of oceanic seafloor, marking the termination of one or more oceanic basins (e.g. Wilson cycles) and the formation of the supercontinent Pangaea. The present day location of the continents is due to the rifting apart of Pangaea, with the dispersal of the supercontinent being characterized by increased volcanic activity linked to the generation of deep mantle plumes. The discussion presented here investigates theories regarding the thermal evolution of the mantle (e.g. mantle temperatures and sub-continental plumes) following the formation of a supercontinent. Rifting, orogenesis and mass eruptions from large igneous provinces change the landscape of the lithosphere, whereas processes related to the initiation and termination of oceanic subduction have a profound impact on deep mantle reservoirs and thermal upwelling through the modification of mantle flow. Upwelling and downwelling in mantle convection are dynamically linked and can influence processes from the crust to the core, placing the Wilson cycle and the evolution of oceans at the forefront of our dynamic Earth.

scholarly journals Geochemical constraints on the structure of the Earth’s deep mantle and the origin of the LLSVPs

2021 ◽  
Author(s):  
Matthew Gleeson ◽  
Caroline Soderman ◽  
Simon Matthews ◽  
Sanne Cottaar ◽  
Sally Gibson
Keyword(s):  
Mantle Source ◽  
Lower Mantle ◽  
Source Region ◽  
Shear Velocity ◽  
Mantle Plumes ◽  
The North ◽  
Deep Mantle ◽  
The Pacific ◽  
Heterogeneous Mantle ◽  
Low Shear

Geophysical analysis of the Earth’s lower mantle has revealed the presence of two superstructures characterized by low shear wave velocities on the core-mantle boundary. These Large Low Shear Velocity Provinces (LLSVPs) play a crucial role in the dynamics of the lower mantle and act as the source region for deep-seated mantle plumes. However, their origin, and the characteristics of the surrounding deep mantle, remain enigmatic. Mantle plumes located above the margins of the LLSVPs display evidence for the presence of this deep-seated, thermally and/or chemically heterogeneous mantle material ascending into the melting region. As a result, analysis of the spatial geochemical heterogeneity in OIBs provides constraints on the structure of the Earth’s lower mantle and the origin of the LLSVPs. In this study, we focus on the Galápagos Archipelago in the eastern Pacific, where bilateral asymmetry in the radiogenic isotopic composition of erupted basalts has been linked to the presence of LLSVP material in the underlying plume. We show, using spatial variations in the major element contents of high-MgO basalts, that the isotopically enriched south-western region of the Galápagos mantle – assigned to melting of LLSVP material – displays no evidence for lithological heterogeneity in the mantle source. As such, it is unlikely that the Pacific LLSVP represents a pile of subducted oceanic crust. Clear evidence for a lithologically heterogeneous mantle source is, however, found in the north-central Galápagos, indicating that a recycled crustal component is present near the eastern margin of the Pacific LLSVP, consistent with seismic observations.

scholarly journals Cyclicity and Connectivity in Nez Perce Relative Clauses

2016 ◽  
Vol 47 (3) ◽  
pp. 427-470 ◽  
Author(s):  
Amy Rose Deal
Keyword(s):  
Word Order ◽  
Relative Clause ◽  
Crucial Role ◽  
Relative Clauses ◽  
Head Noun ◽  
Intermediate Position ◽  
Nez Perce ◽  
The Core ◽  
New Evidence ◽  
Relative Pronouns

This article studies two aspects of movement in relative clauses, focusing on evidence from Nez Perce. First, I argue that relativization involves cyclic Ā-movement, even in monoclausal relatives: the relative operator moves to Spec,CP via an intermediate position in an Ā outer specifier of TP. The core arguments draw on word order, complementizer choice, and a pattern of case attraction for relative pronouns. Ā cyclicity of this type suggests that the TP sister of relative C constitutes a phase—a result whose implications extend to an ill-understood corner of the English that-trace effect. Second, I argue that Nez Perce relativization provides new evidence for an ambiguity thesis for relative clauses, according to which some but not all relatives are derived by head raising. The argument comes from connectivity and anticonnectivity in morphological case. A crucial role is played by a pattern of inverse case attraction, wherein the head noun surfaces in a case determined internal to the relative clause. These new data complement the range of existing arguments concerning head raising, which draw primarily on connectivity effects at the syntax-semantics interface.

Multiple inner core reflections from a Novaya Zemlya explosion

1972 ◽  
Vol 62 (4) ◽  
pp. 1063-1071 ◽  
Author(s):  
R. D. Adams
Keyword(s):  
Lower Bound ◽  
Inner Core ◽  
Nuclear Explosion ◽  
Outer Core ◽  
Low Velocity ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Novaya Zemlya ◽  
The Core ◽  
Velocity Channel

Abstract The phases P2KP, P3KP, and P4KP are well recorded from the Novaya Zemlya nuclear explosion of October 14, 1970, with the branch AB at distances of up to 20° beyond the theoretical end point A. This extension is attributed to diffraction around the core-mantle boundary. A slowness dT/dΔ = 4.56±0.02 sec/deg is determined for the AB branch of P4KP, in excellent agreement with recent determinations of the slowness of diffracted P. This slowness implies a velocity of 13.29±0.06 km/sec at the base of the mantle, and confirms recent suggestions of a low-velocity channel above the core-mantle boundary. There is evidence that arrivals recorded before the AB branch of P2KP may lie on two branches, with different slownesses. The ratio of amplitudes of successive orders of multiple inner core reflections gives a lower bound of about 2200 for Q in the outer core.

Mantle plumes at the boundary of the upper and lower mantle

2014 ◽  
Vol 459 (1) ◽  
pp. 1397-1399 ◽  
Author(s):  
V. P. Trubitsyn ◽  
M. N. Evseev
Keyword(s):  
Lower Mantle ◽  
Mantle Plumes

scholarly journals Ancient subducted oceans controlling the positioning of deep mantle plumes

2019 ◽  
Author(s):  
Philip Heron ◽  
Juliane Dannberg ◽  
Rene Gassmöller ◽  
Grace Shephard ◽  
Jeroen van Hunen ◽  
...  
Keyword(s):  
Mantle Plumes ◽  
Deep Mantle

scholarly journals Nonlinear quenching of current fluctuations in a self-exciting homopolar dynamo

1997 ◽  
Vol 4 (4) ◽  
pp. 201-205 ◽  
Author(s):  
R. Hide
Keyword(s):  
Boundary Conditions ◽  
Outer Core ◽  
Angular Speed ◽  
Current Fluctuations ◽  
Geological Time ◽  
Dynamo Action ◽  
Lorentz Forces ◽  
In Series ◽  
Geomagnetic Polarity ◽  
New Evidence

Abstract. In the interpretation of geomagnetic polarity reversals with their highly variable frequency over geological time it is necessary, as with other irregularly fluctuating geophysical phenomena, to consider the relative importance of forced contributions associated with changing boundary conditions and of free contributions characteristic of the behaviour of nonlinear systems operating under fixed boundary conditions.  New evidence -albeit indirect- in favour of the likely predominance of forced contributions is provided by the discovery reported here of the possibility of complete quenching by nonlineax effects of current fluctuations in a self-exciting homopolar dynamo with its single Faraday disk driven into rotation with angular speed y(τ) (where τ denotes time) by a steady applied couple.  The armature of an electric motor connected in series with the coil of the dynamo is driven into rotation' with angular speed z(τ) by a torque xf (x) due to Lorentz forces associated with the electric current x(τ) in the system (just as certain parts of the spectrum of eddies within the liquid outer core are generated largely by Lorentz forces associated with currents generated by the self-exciting magnetohydrodynamic (MHD) geodynamo).   The discovery is based on bifurcation analysis supported by computational studies of the following (mathematically novel) autonomous set of nonlinear ordinary differential equations: dx/dt = x(y - 1) - βzf(x), dy/dt = α(1 - x²) - κy, dz/dt = xf (x) -λz,          where f (x) = 1 - ε + εσx, in cases when the dimensionless parameters (α, β, κ, λ, σ) are all positive and 0 ≤ ε ≤ 1. Within those regions of (α, β, κ, λ, σ) parameter space where the applied couple, as measured by α, is strong enough for persistent dynamo action (i.e. x ≠ 0) to occur at all, there are in general extensive regions where x(τ) exhibits large amplitude regular or irregular (chaotic) fluctuations.  But these fluctuating régimes shrink in size as increases from zero, and they disappear altogether when ε = 1, leaving only steady régimes of dynamo action.

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