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Evolution of U–Pb and Sm–Nd systems in numerical models of mantle convection andplate tectonics. J.Geophys (2004)
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@TECHREPORT{Xie04evolutionof,
author = {Shunxing Xie and Paul J. Tackley},
title = {Evolution of U–Pb and Sm–Nd systems in numerical models of mantle convection andplate tectonics. J.Geophys},
institution = {},
year = {2004}
}
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Abstract
[1] The development of U-Th-Pb and Sm-Nd isotopic signatures in a convecting mantle is studied using a numerical convection model with melting-induced differentiation and tracking of major and trace elements. The models include secular cooling and the decay of heat-producing elements, a rudimentary ‘‘self-consistent’ ’ treatment of plate tectonics, and both olivine system and garnet-pyroxene system phase transitions. The system self-consistently evolves regions with a high m(=U/Pb) (HIMU)-like Pb signature and regions with low 143Nd/144Nd. However, the isotopic ‘‘age’ ’ determined from the slope in (207Pb/204Pb)–(206Pb/204Pb) space is much larger than observed. Several hypotheses are examined to explain this discrepancy. Sampling length scale has a minimal effect on age. The extent of crustal settling above the core-mantle boundary makes some difference but not enough. More frequent remelting is a possible explanation but requires the rate of crustal production to have been much higher in the past. Not introducing HIMU into the mantle prior to 2.0–2.5 Gyr before present, because of a change in the surface oxidization environment or subduction zone processes, can account for the difference, but its effect on other isotope systems needs to be evaluated. Improved
Keyphrases
numerical model sm nd system j.g eophys mantle convection andplate tectonics system self-consistently evolves region length scale crustal production surface oxidization environment plate tectonics minimal effect several hypothesis trace element isotope system isotopic age sm-nd isotopic signature crustal settling olivine system numerical convection model pb signature rudimentary self-consistent treatment possible explanation garnet-pyroxene system phase transition convecting mantle subduction zone heat-producing element core-mantle boundary frequent remelting melting-induced differentiation secular cooling
