The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution

Arévalo, Ricardo; McDonough, William F.; Luong, M.

doi:10.1016/j.epsl.2008.12.023

Cited by 220 publications

(194 citation statements)

References 77 publications

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“…The recent estimate of 19,000 by Arevalo et al [2009] is unsubstantiated by the current study, and Figure 13. Cartoon illustrating one of the potential solutions to the paradox that the mean upper mantle composition equals the bulk silicate Earth composition proposed by Jackson and Carlson [2012].…”

Section: Discussionsupporting

confidence: 63%

The mean composition of ocean ridge basalts

Gale

Dalton

Langmuir

et al. 2013

Geochem. Geophys. Geosyst.

142

317

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[1] The mean composition of mid-ocean ridge basalts (MORB) is determined using a global data set of major elements, trace elements, and isotopes compiled from new and previously published data. A global catalog of 771 ridge segments, including their mean depth, length, and spreading rate enables calculation of average compositions for each segment. Segment averages allow weighting by segment length and spreading rate and reduce the bias introduced by uneven sampling. A bootstrapping statistical technique provides rigorous error estimates. Based on the characteristics of the data, we suggest a revised nomenclature for MORB. "ALL MORB" is the total composition of the crust apart from back-arc basins, N-MORB the most likely basalt composition encountered along the ridge >500 km from hot spots, and D-MORB the depleted end-member. ALL MORB and N-MORB are substantially more enriched than early estimates of normal ridge basalts. The mean composition of back-arc spreading centers requires higher extents of melting and greater concentrations of fluid-mobile elements, reflecting the influence of water on back-arc petrogenesis. The average data permit a re-evaluation of several problems of global geochemistry. The K/U ratio reported here (12,340 AE 840) is in accord with previous estimates, much lower than the estimate of Arevalo et al. (2009). The low Sm/Nd and 143 Nd/ 144 Nd ratio of ALL MORB and N-MORB provide constraints on the hypothesis that Earth has a non-chondritic primitive mantle. Either Earth is chondritic in Sm/Nd and the hypothesis is incorrect or MORB preferentially sample an enriched reservoir, requiring a large depleted reservoir in the deep mantle.

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Section: Discussionsupporting

confidence: 63%

The mean composition of ocean ridge basalts

Gale

Dalton

Langmuir

et al. 2013

Geochem. Geophys. Geosyst.

142

317

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“…23). Assuming extra mantle heat contributions of 3.0 TW from other isotope decays 6,24 , the convective Urey ratio deduced from the KamLAND and Borexino data is between 0.18 and 0.67 at the 68% CL, consistent with 0.3 from the BSE model. A fully radiogenic model (Urey ratio of 1) is constructed by introducing U and Th uniformly in the mantle (homogeneous hypothesis) or, alternatively, by putting all of the U and Th at the mantle-core interface (sunken-layer hypothesis).…”

Section: Radiogenic Heat Estimation and Outlooksupporting

confidence: 57%

“…The composition deduced from this model results in a radiogenic heat production of 8 TW from the 238 U decay chain, 8 TW from the 232 Th decay chain and 4 TW from 40 K (ref. 6). In this model, the radiogenic heat contribution is nearly half of the Earth's total heat flow (44.2 ± 1.0 TW, ref.…”

Section: Earth Composition Modelmentioning

confidence: 99%

Partial radiogenic heat model for Earth revealed by geoneutrino measurements

Gando¹,

Gando²,

Ichimura³

et al. 2011

Nature Geosci

201

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The Earth has cooled since its formation, yet the decay of radiogenic isotopes, and in particular uranium, thorium and potassium, in the planet's interior provides a continuing heat source. The current total heat flux from the Earth to space is 44.2 ± 1.0 TW, but the relative contributions from residual primordial heat and radiogenic decay remain uncertain. However, radiogenic decay can be estimated from the flux of geoneutrinos, electrically neutral particles that are emitted during radioactive decay and can pass through the Earth virtually unaffected. Here we combine precise measurements of the geoneutrino flux from the Kamioka Liquid-Scintillator Antineutrino Detector, Japan, with existing measurements from the Borexino detector, Italy. We find that decay of uranium-238 and thorium-232 together contribute 20.0 +8.8 −8.6 TW to Earth's heat flux. The neutrinos emitted from the decay of potassium-40 are below the limits of detection in our experiments, but are known to contribute 4 TW. Taken together, our observations indicate that heat from radioactive decay contributes about half of Earth's total heat flux. We therefore conclude that Earth's primordial heat supply has not yet been exhausted.

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“…These experiments have shown that these isotopes account for > 5 TW (probably *19 TW) of internal energy production, out of a total rate of *44 TW (Araki et al, 2005;KamLAND Collaboration, 2011;Dye, 2012). For this study, we will assume a Th/U ratio of 3.9 (Anders and Ebihara, 1982;Anders and Grevesse, 1989), similar to chondritic, and a low, but observationally permitted, K/U ratio of 12,000 (Arevalo et al, 2009), *40 times less than chondritic (Anders and Grevesse, 1989). Earth is enriched in U relative to chondrites but depleted in K. The half-lives of the 235 U, 238 U, 232 Th, and 40 K species are 0.7, 4.5, 13.9, and 1.4 Gyr, respectively.…”

Section: Internal Heating Of Terrestrial Exoplanets (Rory Barnes)mentioning

confidence: 97%

Astrobiological Stoichiometry

et al. 2014

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Chemical composition affects virtually all aspects of astrobiology, from stellar astrophysics to molecular biology. We present a synopsis of the research results presented at the ''Stellar Stoichiometry'' Workshop Without Walls hosted at Arizona State University April 11-12, 2013, under the auspices of the NASA Astrobiology Institute. The results focus on the measurement of chemical abundances and the effects of composition on processes from stellar to planetary scales. Of particular interest were the scientific connections between processes in these normally disparate fields. Measuring the abundances of elements in stars and giant and terrestrial planets poses substantial difficulties in technique and interpretation. One of the motivations for this conference was the fact that determinations of the abundance of a given element in a single star by different groups can differ by more than their quoted errors. The problems affecting the reliability of abundance estimations and their inherent limitations are discussed. When these problems are taken into consideration, self-consistent surveys of stellar abundances show that there is still substantial variation (factors of *2) in the ratios of common elements (e.g., C, O, Na, Al, Mg, Si, Ca) important in rock-forming minerals, atmospheres, and biology. We consider how abundance variations arise through injection of supernova nucleosynthesis products into star-forming material and through photoevaporation of protoplanetary disks. The effects of composition on stellar evolution are substantial, and coupled with planetary atmosphere models can result in predicted habitable zone extents that vary by many tens of percent. Variations in the bulk composition of planets can affect rates of radiogenic heating and substantially change the mineralogy of planetary interiors, affecting properties such as convection and energy transport.

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The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution

Cited by 220 publications

References 77 publications

The mean composition of ocean ridge basalts

The mean composition of ocean ridge basalts

Partial radiogenic heat model for Earth revealed by geoneutrino measurements

Astrobiological Stoichiometry

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