Volume 5 Issue 4, April 2012

Earth's crust is formed where tectonic plates rift apart and upwelling magma solidifies. Disparate observations from rifts beneath the oceans and on land provide insights into the dynamics of rifting and opportunities for synthesis.

The plausibility of the high end of global warming projections in recent assessments is a subject of debate. A study of multi-model climate simulations argues that we need to take the possibility of strong warming seriously.

The supply of magma to Kīlauea Volcano was relatively stable for 50 years. But between 2003 and 2007, the volcano experienced a surge in the supply of magma from the mantle that implies short-term changes in the underlying Hawaiian hotspot.

A giant impact on the young proto-Earth is thought to explain the formation of the Moon. High-precision analysis of titanium isotopes in lunar rocks suggests that the Moon and Earth's mantle are more similar than existing models permit.

Most of Earth's crust is created at mid-ocean ridges that are submerged deep beneath the oceans. Analyses of geodetic and seismic data from rare sections of ridges that are exposed on land in Iceland and the Afar region in east Africa demonstrate that rifting episodes at these sites operate with remarkably similar mechanisms.

Geochemical evidence continues to challenge giant impact models, which predict that the Moon formed from both proto-Earth and impactor material. Analyses of lunar samples reveal isotopic homogeneity in titanium, a highly refractory element, suggesting lunar material was derived predominantly from the mantle of the proto-Earth.

The global-mean temperature evolution over the course of the twenty-first century is uncertain. Simulations with an ensemble of thousands of climate models that reproduce observed warming over the past 50 years suggest that a mid-range greenhouse-gas emissions scenario without mitigation could lead to a warming of between 1.4 and 3 K by 2050, relative to 1961–1990.

The atmospheric nitrous oxide concentration has increased by 20% since 1750. Analyses of Antarctic firn and archived air samples reveal seasonal cycles in the isotopic signature of nitrous oxide, which can help to disentangle the contribution of surface sources.

Latitudinal variations in the location of the southern westerly wind belt have been associated with millennial-scale climate variations during the last glacial period. A reconstruction of sea-surface temperatures off the southern coast of Australia suggests that these climate variations also drove changes in the location of the oceanic subtropical front.

Iron is often a limiting nutrient in ocean regions that have a constant supply of other macro-nutrients, and changes in iron supply over time have been linked to fluctuations in primary productivity. Marine sediments from the equatorial Pacific Ocean show that over the past million years, iron input was linked to the export and burial of biogenic silica.

Rates of crust formation at mid-ocean ridges are expected to vary with rates of plate spreading. U–Pb dating of zircon minerals from the fast-spreading East Pacific Rise reveals protracted formation of gabbroic rocks over timescales comparable with slow-spreading mid-ocean ridges, suggesting similar timescales of magmatic processes at slow- and fast-spreading ridges.

At faster-spreading mid-ocean ridges, the creation of new oceanic crust through magmatism usually occurs within a narrow zone on the ridge axis. Three-dimensional seismic images of the fast-spreading East Pacific Rise reveal a network of magmatic bodies 4–8 km away from the ridge axis that seem to be connected to the axial magma chamber.

Thermal models predict that spreading velocity at mid-ocean rifts should influence the geometry of the underlying magma chamber. InSAR data from the slow-spreading Ethiopian Rift identify a shallow, elongated magma chamber—a feature usually associated with fast-spreading rifts—beneath the Erta Ale segment, implying that spreading velocity may not be so important after all.

Rifting of the eastern part of the East African Rift System was thought to have begun several million years before its western counterpart. Reconstructions of drainage development, combined with dating of rift-related volcanic activity, suggest that rifting in the western branch may instead have begun at the same time as in the eastern branch.

The supply of magma to Kīlauea Volcano, Hawai‘i, was thought to have been steady over the past decades. Measurements of deformation, gas emissions, seismicity and lava composition and temperatures show that instead magma supply from the mantle doubled in 2003–2007, implying that hotspots can provide varying amounts of magma over just a few years.

Where continents rift apart, new crust is formed from upwelling magma. Eventually, a new ocean basin forms. In this web focus we present opinion pieces, along with research and overview articles that explore the dynamic processes that occur during plate rifting. Case studies include both rifting on land, in east Africa and Iceland, and at the mid-ocean ridges that divide the oceanic crust.