Temperatures, Heat and Energy in the Mantle of the Earth

Jaupart, Claude; Labrosse, S.; Mareschal, Jean‐Claude

doi:10.1016/b978-044452748-6.00114-0

Cited by 168 publications

(228 citation statements)

References 164 publications

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“…These remain a subject of significant debate and have been arguably 'the most controversial subject in solid Earth sciences for the last few decades' (Korenaga 2008c). Without doubt, mantle convection is a requirement of a secularly cooling Earth (see Jaupart et al 2007;Ogawa 2008 for recent reviews) but establishing the nature of modern convection in the modern Earth has proved difficult and is more so in its extrapolation to the geological past (Schubert et al 2001).…”

Section: Mantle Evolutionmentioning

confidence: 99%

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

Reddy

Evans

2009

115

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The Palaeoproterozoic era was a time of profound change in Earth evolution and represented perhaps the first supercontinent cycle, from the amalgamation and dispersal of a possible Neoarchaean supercontinent to the formation of the 1.9-1.8 Ga supercontinent Nuna. This supercontinent cycle, although currently lacking in palaeogeographic detail, can in principle provide a contextual framework to investigate the relationships between deep-Earth and surface processes. In this article, we graphically summarize secular evolution from the Earth's core to its atmosphere, from the Neoarchaean to the Mesoproterozoic eras (specifically 3.0-1.2 Ga), to reveal intriguing temporal relationships across the various 'spheres' of the Earth system. At the broadest level our compilation confirms an important deep-Earth event at c. 2.7 Ga that is manifested in an abrupt increase in geodynamo palaeointensity, a peak in the global record of large igneous provinces, and a broad maximum in several mantle-depletion proxies. Temporal coincidence with juvenile continental crust production and orogenic gold, massive-sulphide and porphyry copper deposits, indicate enhanced mantle convection linked to a series of mantle plumes and/or slab avalanches. The subsequent stabilization of cratonic lithosphere, the possible development of Earth's first supercontinent and the emergence of the continents led to a changing surface environment in which voluminous banded iron-formations could accumulate on the continental margins and photosynthetic life could flourish. This in turn led to irreversible atmospheric oxidation at 2.4-2.3 Ga, extreme events in global carbon cycling, and the possible dissipation of a former methane greenhouse atmosphere that resulted in extensive Palaeoproterozoic ice ages. Following the great oxidation event, shallow marine sulphate levels rose, sediment-hosted and iron-oxide-rich metal deposits became abundant, and the transition to sulphide-stratified oceans provided the environment for early eukaryotic evolution. Recent advances in the geochronology of the global stratigraphic record have made these inferences possible. Frontiers for future research include more refined modelling of Earth's thermal and geodynamic evolution, palaeomagnetic studies of geodynamo intensity and continental motions, further geochronology and tectonic syntheses at regional levels, development of new isotopic systems to constrain geochemical cycles, and continued innovation in the search for records of early life in relation to changing palaeoenvironments.

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Section: Mantle Evolutionmentioning

confidence: 99%

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

Reddy

Evans

2009

115

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“…In addition, Hutnak and Fisher (2007) show that rapid sedimentation and conductive thermal rebound following the cessation of hydrothermal activity can jointly account for a downward bias in heatflow measurements of ∼5-30%. More generally, Jaupart et al (2007) argue that "heat flux measurements require sedimentary cover and hence are systematically biased towards anomalously low heat flux areas" (see also Harris and Chapman, 2004). Accordingly, the global heatflow estimate presented here should be viewed as a lower bound, to be refined in a future study.…”

Section: A Global Heatflow Dataset For Ocean Studiesmentioning

confidence: 99%

Geothermal heating, diapycnal mixing and the abyssal circulation

Emile‐Geay

Madec

2009

Ocean Sci.

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Abstract. The dynamical role of geothermal heating in abyssal circulation is reconsidered using three independent arguments. First, we show that a uniform geothermal heat flux close to the observed average (86.4 mW m −2 ) supplies as much heat to near-bottom water as a diapycnal mixing rate of ∼10 −4 m 2 s −1 -the canonical value thought to be responsible for the magnitude of the present-day abyssal circulation. This parity raises the possibility that geothermal heating could have a dynamical impact of the same order. Second, we estimate the magnitude of geothermally-induced circulation with the density-binning method (Walin, 1982), applied to the observed thermohaline structure of Levitus (1998). The method also allows to investigate the effect of realistic spatial variations of the flux obtained from heatflow measurements and classical theories of lithospheric cooling. It is found that a uniform heatflow forces a transformation of ∼6 Sv at σ 4 =45.90, which is of the same order as current best estimates of AABW circulation. This transformation can be thought of as the geothermal circulation in the absence of mixing and is very similar for a realistic heatflow, albeit shifted towards slightly lighter density classes. Third, we use a general ocean circulation model in global configuration to perform three sets of experiments: (1) a thermally homogenous abyssal ocean with and without uniform geothermal heating; (2) a more stratified abyssal ocean subject to (i) no geothermal heating, (ii) a constant heat flux of 86.4 mW m −2 , (iii) a realistic, spatially varying heat flux of identical global average; (3) experiments (i) and (iii) with enhanced vertical mixing at depth. Geothermal heating and diapycnal mixing are found to interact non-linearly through the density field, with geothermal heating eroding the deep stratification supporting a downward diffusive flux, while diapycnal mixing acts to map near-surface temperature gradientsCorrespondence to: J. Emile-Geay (julieneg@usc.edu) onto the bottom, thereby altering the density structure that supports a geothermal circulation. For strong vertical mixing rates, geothermal heating enhances the AABW cell by about 15% (2.5 Sv) and heats up the last 2000 m by ∼0.15 • C, reaching a maximum of by 0.3 • C in the deep North Pacific. Prescribing a realistic spatial distribution of the heat flux acts to enhance this temperature rise at mid-depth and reduce it at great depth, producing a more modest increase in overturning than in the uniform case. In all cases, however, poleward heat transport increases by ∼10% in the Southern Ocean. The three approaches converge to the conclusion that geothermal heating is an important actor of abyssal dynamics, and should no longer be neglected in oceanographic studies.

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“…Approximately 70% of Earth's total heat loss of ϳ46 TW occurs through oceanic lithosphere (ref. 2, referred to hereafter as J07) because it is the only part of the surface that actively participates in mantle convection. This component is also subject to the tectonic evolution of the ocean basins: the geometry of these basins and the organization of the plates within them change over the course of the Wilson cycle (e.g., refs.…”

mentioning

confidence: 99%

Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

Loyd

Becker²,

Conrad³

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ϳ0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.global heat flow ͉ mantle convection ͉ plate reconstructions ͉ seafloor spreading E arth's heat loss is fueled by two dominant sources: (i) decay of radioactive elements within the planet's interior and (ii) secular cooling of the mantle (see reviews in refs. 1 and 2). Approximately 70% of Earth's total heat loss of ϳ46 TW occurs through oceanic lithosphere (ref. 2, referred to hereafter as J07) because it is the only part of the surface that actively participates in mantle convection. This component is also subject to the tectonic evolution of the ocean basins: the geometry of these basins and the organization of the plates within them change over the course of the Wilson cycle (e.g., refs. 3 and 4). If oceanic heat flow is sensitive to these changes, then global heat flow might have been different in the recent past. Temporal variations in Earth's heat flow have important implications for mantle dynamics and can influence parameterized models of Earth's thermal evolution (e.g., ref. 5, referred to hereafter as G05). New tectonic reconstructions of seafloor age (e.g., ref. 6, referred to hereafter as X06; see also refs. 7 and 8) present an opportunity to constrain the time variability of mantle heat flow directly and so provide new insights into the relationship between plate tectonics and Earth's thermal evolution.Global heat flow is dominated by young oceanic crust, with minor contributions from older oceanic crust, plume activity, and continental radiation (see, e.g., discussion in J07). Recently erupted mid-ocean ridge basalt conducts hea...

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Temperatures, Heat and Energy in the Mantle of the Earth

Cited by 168 publications

References 164 publications

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

Palaeoproterozoic supercontinents and global evolution: correlations from core to atmosphere

Geothermal heating, diapycnal mixing and the abyssal circulation

Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

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