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Titolo:
The rates of accretion, core formation and volatile loss in the early Solar System
Autore:
Halliday, AN; Lee, DC; Porcelli, D; Wiechert, U; Schonbachler, M; Rehkamper, M;
Indirizzi:
ETH Zentrum, Dept Earth Sci, CH-8092 Zurich, Switzerland ETH Zentrum Zurich Switzerland CH-8092 Sci, CH-8092 Zurich, Switzerland
Titolo Testata:
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY OF LONDON SERIES A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES
fascicolo: 1787, volume: 359, anno: 2001,
pagine: 2111 - 2134
SICI:
1364-503X(20011015)359:1787<2111:TROACF>2.0.ZU;2-9
Fonte:
ISI
Lingua:
ENG
Soggetto:
W ISOTOPIC EVIDENCE; MARTIAN ATMOSPHERE; TERRESTRIAL ACCRETION; EARLY DIFFERENTIATION; CHEMICAL-COMPOSITION; ORDINARY CHONDRITES; TUNGSTEN ISOTOPES; RAPID ACCRETION; SNC METEORITES; EARTHS MANTLE;
Keywords:
planetary accretion; isotopes; geochemistry;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
95
Recensione:
Indirizzi per estratti:
Indirizzo: Halliday, AN ETH Zentrum, Dept Earth Sci, Sonneggstr 5, CH-8092 Zurich, Switzerland ETH Zentrum Sonneggstr 5 Zurich Switzerland CH-8092 tzerland
Citazione:
A.N. Halliday et al., "The rates of accretion, core formation and volatile loss in the early Solar System", PHI T ROY A, 359(1787), 2001, pp. 2111-2134

Abstract

Nuclides with half-lives of 10(5)-10(8) yr permit the elucidation of nebula time-scales and the rates of accretion of planetesimals. However, the Hf-182-W-182 system with a half-life of 9 +/-2 Myr also provides new and very useful constraints on the formation of the terrestrial planets. This technique allows one to address the timing of metal-silicate equilibration in objects as different as chondrites and the Earth. With improvements in sensitivity and precision, very small time differences in metal segregation in asteroids should be resolvable from measuring iron meteorites. It is already clear that the formation and differentiation of some asteroidal-sized objects was completed in less than 10 Myr. Accretion and core formation were protracted in the case of the Earth (greater than 50 Myr) relative to Mars (probably less than 20 Myr). Indeed, the Martian mantle appears to retain both chemical and isotopic heterogeneities that are residual from the process ofcore formation. Such early features appear to have been eliminated from the Earth's mantle presumably because of 4.5 Gyr of relatively efficient convective mixing. Tungsten isotope data provide compelling support for the 'giant impact' theory of lunar origin. The Moon is a high Hf/W object that contains a major component of chondritic W. This is consistent with a time of formation of greater than 50 Myr after the start of the Solar System. New highly precise oxygen isotope data are unable to resolve any difference between the source of components in the Earth and Moon. Therefore, the giant impact itself may have produced some of the differences in moderately volatile element budgets between these objects. This finds support in precise Sr isotopic data for early lunar samples. The data are consistent with the proto-Earth and Theia (the impactor) having Rb/Sr ratios that were not very different from that of present day Mars. Therefore, the extended history of accretion, rather than nebular phenomena, may be responsible for some of the major differences between the terrestrial planets.

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Documento generato il 04/04/20 alle ore 13:37:57