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The influence of potassium on core and geodynamo evolution.
- Geophys. J. Int.
, 2004
"... Abstract Recently there has been renewed interest in the evolution of the inner core and in the possibility that radioactive potassium might be found in significant quantities in the core. The arguments for core potassium come from considerations of the age of the inner core and the energy required ..."
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Abstract Recently there has been renewed interest in the evolution of the inner core and in the possibility that radioactive potassium might be found in significant quantities in the core. The arguments for core potassium come from considerations of the age of the inner core and the energy required to sustain the geodynamo [Nimmo, F., Price, G.D., Brodholt, J., Gubbins, D., 2004. The influence of potassium on core and geodynamo evolution. Geophys. J. Int. 156, 363-376; Labrosse, S., Poirier, J. Lett. 200,[63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78]. The Earth's core is also located at the lower boundary of the convecting mantle and the presence of radioactive heat sources in the core will affect the flux of heat between these two regions and will, as a result, have a significant impact on the Earth's thermal history. In this paper, we present Earth thermal history simulations in which we calculate fluid flow in a spherical shell representing the mantle, coupled with a core of a given heat capacity with varying degrees of internal heating in the form of 40 K and varying initial core temperatures. The mantle model includes the effects of the temperature dependence of viscosity, decaying radioactive heat sources, and mantle phase transitions. The core model includes the thermal effects of inner core solidification and we present models for which the final size of the inner core is the same that for the present-day Earth. We compare the results of simulations with and without the effects of inner core solidification and we compare the results of the numerical model with those of a parameterized model. Models with concentrations of potassium in the core of roughly 600 ppm best satisfy the present-day surface heat flow constraint; however, the core temperatures in these models are somewhat high. In addition, we find that models with lesser degrees of heating in the core can also satisfy the surface heat flow constraint provided that the mantle is in a particularly active state. Our models predict a relatively young inner core with the greatest age being 1756 Ma. We demonstrate that models with high core temperatures * Corresponding author. in the latter part of simulations result in high CMB heat flows which lead to predictions of young inner cores. For fixed initial core temperatures, this leads to a slight decrease in the predicted age of the inner core with increasing concentration of radioactive elements in the core.
this volume), Implications of lower-mantle structural heterogeneity for existence and nature of wholemantle plumes
- in Foulger, G.R., and Jurdy, D.M., Plates, plumes, and planImplications of
, 2007
"... Recent seismological studies demonstrate the presence of strong deep-mantle elas-tic heterogeneity and anisotropy, consistent with a dynamic environment having chem-ical anomalies, phase changes, and partially molten material. The implications for deep-mantle plume genesis are discussed in the light ..."
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Cited by 12 (1 self)
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Recent seismological studies demonstrate the presence of strong deep-mantle elas-tic heterogeneity and anisotropy, consistent with a dynamic environment having chem-ical anomalies, phase changes, and partially molten material. The implications for deep-mantle plume genesis are discussed in the light of the seismological findings. Nearly antipodal large low–shear velocity provinces (LLSVPs) in the lowermost man-tle beneath the Pacific Ocean and Africa are circumscribed by high-velocity regions that tend to underlie upper-mantle downwellings. The LLSVPs have sharp bound-aries, low VS/VP ratios, and high densities; thus, they appear to be chemically distinct structures. Elevated temperature in LLSVPs may result in partial melting, possibly accounting for the presence of ultra-low-velocity zones detected at the base of some re-gions of LLSVPs. Patterns in deep-mantle fast shear wave polarization directions within the LLSVP beneath the Pacific are consistent with strong lateral gradients in the flow direction. The thermal boundary layer at the base of the mantle is a likely lo-cation for thermal instabilities that form plumes, but geodynamical studies show that
Metamorphic patterns in orogenic systems and the geological record. In
- Geological Society, London, Special Publications
"... Abstract: Regional metamorphism occurs in plate boundary zones. Accretionary orogenic systems form at subduction boundaries in the absence of continent collision, whereas collisional orogenic systems form where ocean basins close and subduction steps back and flips (arc collisions), simply steps bac ..."
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Cited by 5 (1 self)
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Abstract: Regional metamorphism occurs in plate boundary zones. Accretionary orogenic systems form at subduction boundaries in the absence of continent collision, whereas collisional orogenic systems form where ocean basins close and subduction steps back and flips (arc collisions), simply steps back and continues with the same polarity (block and terrane collisions) or ultimately ceases (continental collisions). As a result, collisional orogenic systems may be superimposed on accretionary orogenic systems. Metamorphism associated with orogenesis pro-vides a mineral record that may be inverted to yield apparent thermal gradients for different meta-morphic belts, which in turn may be used to infer tectonic setting. Potentially, peak mineral assemblages are robust recorders of metamorphic P and T, particularly at high P–T conditions, because prograde dehydration and melting with melt loss produce nominally anhydrous mineral assemblages that are difficult to retrogress or overprint without fluid influx. Currently on Earth, lower thermal gradients are associated with subduction (and early stages of collision) whereas higher thermal gradients are characteristic of back-arcs and orogenic hinterlands. This duality of thermal regimes is the hallmark of asymmetric or one-sided subduction and plate tectonics on modern Earth, and a duality of metamorphic belts will be the characteristic imprint of asymmetric
Invited review Plate tectonics, flood basalts and the evolution of Earth’s oceans
- Terra Nova
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Thermal evolution of the Earth: Secular changes and
"... This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author’s institution, sharing with colleagues and providing to institution administration. Other uses, including reproductio ..."
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This article was published in an Elsevier journal. The attached copy is furnished to the author for non-commercial research and education use, including for instruction at the author’s institution, sharing with colleagues and providing to institution administration. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit:
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"... eo dy na m ic s an d te ct on ic s Temperature and heat flux scalings for isoviscous thermal convection in spherical geometry ..."
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eo dy na m ic s an d te ct on ic s Temperature and heat flux scalings for isoviscous thermal convection in spherical geometry
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"... eo dy na m ic s an d te ct on ic s Temperature and heat flux scalings for isoviscous thermal convection in spherical geometry ..."
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eo dy na m ic s an d te ct on ic s Temperature and heat flux scalings for isoviscous thermal convection in spherical geometry
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"... frequency scattered energy or the pulse distortion of short-period body waves, preferably in situations where the scattered energy precedes, rather than follows, the main seismic arrival, so that it is not obliterated by the coda. (This is possible for seismic phases, such as PKKP, which follow a ma ..."
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frequency scattered energy or the pulse distortion of short-period body waves, preferably in situations where the scattered energy precedes, rather than follows, the main seismic arrival, so that it is not obliterated by the coda. (This is possible for seismic phases, such as PKKP, which follow a maximum-time path.) By studying precursors to PKKP it has been possible to infer the existence of CMB topography with root mean square amplitude a few hundred meters with a correlation length of 7–10 km (Earle and Shearer, 1997). Seismic imaging of the core-mantle boundary topography is in prin-ciple quite straightforward, but it is in reality complicated by a number of practical issues. The scanty and irregular global sampling of the CMB, the imperfect account of mantle and core structure, the simpli-fied theoretical modelling of wave propagation, all concur with the small signal to noise ratio to limit the imaging potential of seismic core data. As a result, the different studies on the topic have not quite gone beyond a qualitative agreement, and often disagree. However, the qua-litative correspondence found among different models, the stochastic analyses of travel times, and the accordance with inferences from man-tle dynamic modeling, point towards the existence of kilometric topo-graphy at the CMB. Better knowledge of the seismic structure of the Earth’s mantle, including the still elusive D00 layer, and perhaps a better modeling of the full effects of such three-dimensional structures on seismic waves, are still needed to wipe our glasses and clarify our vision.
Editor: R.D. van der Hilst
, 2008
"... Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean Heat flow variations may arise, for example, from changes in the aspect ..."
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Variations in Earth's rates of seafloor generation and recycling have far-reaching consequences for sea level, ocean Heat flow variations may arise, for example, from changes in the aspect
