Search

Author(s): Remco C. Hin (corresponding author) [1]; Christopher D. Coath [1]; Philip J. Carter [2]; Francis Nimmo [3]; Yi-Jen Lai [1]; Philip A. E. Pogge von Strandmann [1, 4]; Matthias [...]

Interactions between crustal and mantle reservoirs dominate the surface inventory of volatile elements over geological time, moderating atmospheric composition and maintaining a lifesupporting planet (1). While volcanoes expel volatile components into surface reservoirs, subduction of oceanic crust is responsible for replenishment of mantle reservoirs (2,3). Many natural, 'superdeep' diamonds originating in the deep upper mantle and transition zone host mineral inclusions, indicating an affinity to subducted oceanic crust (4-7). Here we show that the majority of slab geotherms will intersect a deep depression along the melting curve of carbonated oceanic crust at depths of approximately 300 to 700 kilometres, creating a barrier to direct carbonate recycling into the deep mantle. Low-degree partial melts are alkaline carbonatites that are highly reactive with reduced ambient mantle, producing diamond. Many inclusions in superdeep diamonds are best explained by carbonate melt-peridotite reaction. A deep carbon barrier may dominate the recycling of carbon in the mantle and contribute to chemical and isotopic heterogeneity of the mantle reservoir., Altered oceanic crust incorporates appreciable carbon, which is added by magmatic and hydrothermal processes (8), and by addition of C[O.sub.2] during interaction of basalt with sea water (9). Together, these [...]

Author(s): Bernard J. Wood (corresponding author) [1]; Michael J. Walter [2]; Jonathan Wade [2] From observations of newly formed stars it appears that the Sun's planetary system formed from a [...]

Author(s): Takashi Yoshino (corresponding author); Michael J. Walter; Tomoo Katsura The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar [...]

Magmas that have erupted at Earth's surface reveal a potential new mantle source. This source, which is rich in nickel and has a primordial helium isotopic content, may have originated at great depth in the mantle. See Letter p.393 Nickel-rich peridotites in the deep mantle Claude Herzberg and co-authors examine lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona, and Fernandina in the Galapagos Islands. The basalts at these locations, thought to have derived from deep mantle (mantle plume) sources, are shown to have formed from peridotite with a nickel content about 20% higher than those that form modern oceanic crust at mid-ocean ridges. The authors propose that such nickel-rich mantle plumes may be sampling a less-degassed nickel-rich source formed by core-mantle interaction., Author(s): Michael J. Walter [sup.1] Author Affiliations: (1) Michael J. Walter is in the Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK., Melting of source rocks in [...]

New experimental data for partitioning of Co and Ni in Earth's upper mantle between metal and Mg-perovsite, the most abundant mineral in the lower mantle, suggest that metal-silicate equilibration would lead to an enrichment of these elements in the lower mantle in relation to the upper mantle. This finding may prompt some changes to the core-formation model that indicates a magma ocean. This research indicates the need for continued investigation of metal-silicate partitioning under lower-mantle conditions.

The analysis of nickel (Ni) and cobalt (Co) in mantle rocks shows that their relative and absolute concentration may have been formed by equilibrium between metallic and silicate melts at 280,000 atmospheres and 2,200 kelvin. The formation of the core and accretion of Earth can be determined by the mantle metal content and partitioning of metals into the metallic phase over a range of pressure, temperature and compositions. The results of the study indicate that equilibration during the formation of Earth occurred in a liquid magma.