Chemical composition of Earth's primitive mantle and its variance: 1. Method and results

Abstract

[1] We present a new statistical method to construct a model for the chemical composition of Earth's primitive mantle along with its variance. Earth's primitive mantle is located on the melting trend exhibited by the global compilation of mantle peridotites, using cosmochemical constraints on the relative abundances of refractory lithophile elements (RLE). This so-called pyrolite approach involves the least amount of assumptions, thereby being probably most satisfactory compared to other approaches. Its previous implementations, however, suffer from questionable statistical treatment of noisy geochemical data, leaving the uncertainty of model composition poorly quantified. In order to properly take into account how scatters in peridotite data affect this geochemical inference, we combine the following statistical techniques: (1) modeling a nonlinear melting trend in the multidimensional compositional space through the principal component analysis, (2) determining the primitive mantle composition on the melting trend by simultaneously imposing all of cosmochemical constraints with least squares, and (3) mapping scatters in original data into the variance of the final model through the bootstrap resampling technique. Whereas our model is similar to previous models in terms of Mg, Si, and Fe abundances, the RLE contents are at $2.16 ± 0.37 times the CI chondrite concentration, which is lower than most of previous estimates. The new model is depleted by >20% in a number of incompatible elements including heat-producing elements, U, Th, and K, and this depleted nature is further amplified (up to 60%) in terms of predicted composition for the present-day mantle.

Composition of the Oceanic Crust

“…The explanation in the case of copper may be the small amounts of a sulfide phase that has fractionated; in the case of Zn, the problem most likely lies in the partition coefficients used. Figure 23 illustrates MORB, N-MORB, and bulk oceanic crust trace element compositions from Tables 2 and 8, along with previous estimates of MORB composition in a 'spider' or 'extended rare earth' plot in which concentrations are normalized to the estimated bulk silicate Earth composition of Lyubetskaya and Korenaga (2007). All show some degree of increasing depletion with increasing incompatibility.…”

Lower mantle hydrogen partitioning between periclase and perovskite: A quantum chemical modelling

“…McDonough and Sun, 1995;Zindler and Hart, 1986;Lyubetskaya and Korenaga, 2007;Javoy et al, 2010), and it is extended to the whole silicate Earth; 2) The heterogeneous mantle model (LM = layered mantle), which is based on geophysical data and cosmochemical constraints; it proposes a lower mantle which is chemically distinct from the upper mantle (e.g. Anderson, 1989;Stixrude and Bukowinski, 1992;Cammarano and Romanowicz, 2007;Matas et al, 2007;Javoy et al, 2010).…”

The next-generation liquid-scintillator neutrino observatory LENA

“…A significant contributor to this heat flux comes from the heat producing elements, K, Th and U, with its flux proportion dependent upon their absolute abundance inside the Earth. The many models that describe the composition of the Earth come from cosmochemical, geochemical and geophysical observations and predict a range of abundances and distributions of these elements [228][229][230][231].…”