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respectively). The recycling rate inferred from the F(t) constraint is too small to explain the discrepancy between the observed and inferred Sm/Nd ratios in each reservoir. Therefore, Nd isotopic evolution of the upper mantle is controlled not only by recycling of continental crust but also by exchange of material with a different reservoir (21) with a low(More)
Noble-gas geochemistry is an important tool for understanding planetary processes from accretion to mantle dynamics and atmospheric formation. Central to much of the modelling of such processes is the crystal-melt partitioning of noble gases during mantle melting, magma ascent and near-surface degassing. Geochemists have traditionally considered the 'inert'(More)
This note is concerned with the efficiency of the Top-to-Bottom parsing algorithm as used in connection with programming language grammars. It is shown, for instance, that retracing of unprofitable paths can often be eliminated by a suitable rearrangement of the productions defining the grammar. The essential weakness of the method is in dealing with(More)
Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a life-supporting planet. While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs. Many(More)
The Ethiopian Rift Valley hosts the longest record of human co-existence with volcanoes on Earth, however, current understanding of the magnitude and timing of large explosive eruptions in this region is poor. Detailed records of volcanism are essential for interpreting the palaeoenvironments occupied by our hominin ancestors; and also for evaluating the(More)
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