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In order to develop Ca isotopes as a tracer for biogeochemical Ca cycling in terrestrial environments and for Ca utilisation in plants, stable calcium isotope ratios were measured in various species of alpine plants, including woody species, grasses and herbs. Analysis of plant parts (root, stem, leaf and flower samples) provided information on Ca isotope fractionation within plants and seasonal sampling of leaves revealed temporal variation in leaf Ca isotopic composition. There was significant Ca isotope fractionation between soil and root tissue $$\Updelta^{44/42}\hbox{Ca}_{\rm root-soil} \approx -0.40\,\permille$$ in all investigated species, whereas Ca isotope fractionation between roots and leaves was species dependent. Samples of leaf tissue collected throughout the growing season also highlighted species differences: Ca isotope ratios increased with leaf age in woody species but remained constant in herbs and grasses. The Ca isotope fractionation between roots and soils can be explained by a preferential binding of light Ca isotopes to root adsorption sites. The observed differences in whole plant Ca isotopic compositions both within and between species may be attributed to several potential factors including root cation exchange capacity, the presence of a woody stem, the presence of Ca oxalate, and the levels of mycorrhizal infection. Thus, the impact of plants on the Ca biogeochemical cycle in soils, and ultimately the Ca isotope signature of the weathering flux from terrestrial environments, will depend on the species present and the stage of vegetation succession. [ABSTRACT FROM AUTHOR]

The Moon is thought to have formed from debris ejected by a giant impact with the early ‘proto’-Earth and, as a result of the high energies involved, the Moon would have melted to form a magma ocean. The timescales for formation and solidification of the Moon can be quantified by using 182Hf–182W and 146Sm–142Nd chronometry, but these methods have yielded contradicting results. In earlier studies, 182W anomalies in lunar rocks were attributed to decay of 182Hf within the lunar mantle and were used to infer that the Moon solidified within the first ∼60 million years of the Solar System. However, the dominant 182W component in most lunar rocks reflects cosmogenic production mainly by neutron capture of 181Ta during cosmic-ray exposure of the lunar surface, compromising a reliable interpretation in terms of 182Hf–182W chronometry. Here we present tungsten isotope data for lunar metals that do not contain any measurable Ta-derived 182W. All metals have identical 182W/184W ratios, indicating that the lunar magma ocean did not crystallize within the first ∼60 Myr of the Solar System, which is no longer inconsistent with Sm–Nd chronometry. Our new data reveal that the lunar and terrestrial mantles have identical 182W/184W. This, in conjunction with 147Sm–143Nd ages for the oldest lunar rocks, constrains the age of the Moon and Earth to Myr after formation of the Solar System. The identical 182W/184W ratios of the lunar and terrestrial mantles require either that the Moon is derived mainly from terrestrial material or that tungsten isotopes in the Moon and Earth’s mantle equilibrated in the aftermath of the giant impact, as has been proposed to account for identical oxygen isotope compositions of the Earth and Moon. [ABSTRACT FROM AUTHOR]

Presents a study which examined the crustal involvement and magma residence times in the petrogenesis of volcanic rocks from the Nevados de Payachata volcano which erupted in the Central Volcanic Zone of the Andes. Analysis of lavas and mineral separates; Geochemical observations; Details on time constraints on magma differentiation.

Discusses observations of radioactive disequilibrium between 238U and the product 230Th in mid-ocean-ridge basalts (MORB). The availability of constraints for modelling melt generation at mid-ocean ridges; Quantitative treatment of the thermal model; The two types of source enrichment; Origin of the garnet signature in MORBs.

Replying to: D. L. Anderson & J. H. Natland 450, doi: 10.1038/nature06376 (2007)Anderson and Natland’scomment does not question our results regarding the velocity structure of mantle upwellings based on uranium-series. We stated clearly that our results do not provide direct measurements of the depth from which hotspot volcanism starts; we have not made unjustified claims by saying we have identified deep mantle plumes. However, our results do shed light on the still incompletely understood causes of hotspot volcanism. [ABSTRACT FROM AUTHOR]