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Here it is shown that the ratio of zinc to total iron content constrains the valence state of iron in primary arc basalts and their mantle sources. Primitive arc magmas have identical Zn/Fe_T ratios (Fe_T = Fe²⁺ + Fe³⁺) as mid-ocean-ridge basalts, indicating a similar iron oxidation state of primary mantle melts in arcs and ridges and that the subduction of oxidized crustal material may not significantly alter the redox state of the mantle wedge. It is concluded that the observed higher oxidation states of arc lavas must therefore be, in part, a consequence of shallow-level differentiation processes.

For the first billion years or so of the Earth's history, there may have been whole-mantle convection, but after this period differentiation of the Earth's mantle has been controlled by solid-state convection. Many trace elements — known as 'incompatible elements' — preferentially partition into low-density melts and are concentrated into the crust, but half of these incompatible elements should be hidden in the Earth's interior. It is now suggested that a by-product of whole-mantle convection is deep and hot melting, resulting in the generation of dense liquids that sank into the lower mantle.

The exact origin of lithium enrichment in arc magmatic systems is unclear. Here the authors conduct a global systematics of lithium, explaining why volcanic arcs built on thickened crust are most lithium-enriched, which sheds light on the future exploration of lithium resources.

The metal content of magmas erupted at subduction zone arcs is thought to be derived from the mantle. A correlation between crustal thickness and copper content in arc magmas worldwide, however, reveals an important role for the crust in the upper plate.

The continents are archives of Earth's evolution. Analysis of the isotopic signature of continental crust globally suggests that buoyant, silicic continents began to form 3 billion years ago, possibly linked to the onset of plate tectonics.

The origin of volcanic activity occurring far from tectonic-plate boundaries has been a subject of contention. The latest geodynamic model offers a fresh take on the matter. See Letter p.386

A case study of migmatites indicates that the juvenile arc crust underwent a rapid self-recycling process from arc magmatism to erosion and weathering at the surface, then to burial and remelting. Intra-arc thrust fault systems might efficiently promote endogenous recycling.

Correlation between large igneous province activity and iron formation ages suggests that subducted iron formations may have facilitated mantle plume upwelling in the Archaean and Proterozoic Earth.

The timing and mechanism of uplift of the Tibetan plateau continues to be a source of debate. Here, the authors present a new tomographic model revealing a T-shaped high wave speed structure beneath South-Central Tibet and interpret this an upper-mantle remnant from lithospheric foundering.

It is unclear why the crust among many arcs is so silica rich when there is a missing mafic component. Here the authors compile a global evaluation of Nb/Ta and examine xenoliths from Arizona to derive a model of why Nb/Ta fractionation is favored in the crust.

Pegmatite crystals are thought to grow rapidly, yet their growth rates and conditions are not well constrained. Here, the authors find that the trace element distributions of pegmatitic quartz crystals indicate rapid growth in highly dynamic environments, suggesting that large meter-scale crystals can be formed within days.

The magmatic processes required to form economic-grade porphyry Cu deposits are still poorly understood. This Review discusses the magmatic, redox and hydrothermal processes required for porphyry ore formation, revealing that both crustal thickness and depth of ore body emplacement can influence metal endowment.

Atmospheric oxygen levels increased in two stages. This two-step rise of oxygen may be a natural consequence of lowered oxidative capacity caused by the emergence of felsic continents and the growth of a continental carbon reservoir.