olivinetowadsleyite

Olivine to wadsleyite refers to the high-pressure phase transition within the magnesium silicate system Mg2SiO4, in which olivine transforms into the denser mineral wadsleyite. Olivine (forsterite-fayalite series) is the dominant mineral in the upper mantle, and wadsleyite is its high-pressure polymorph. The transition occurs under increasing pressure at mantle temperatures and is a key feature of the mantle transition zone.

The olivine to wadsleyite transformation is typically invoked at pressures around 13 to 15 gigapascals, corresponding to depths near 410 kilometers in a representative mantle composition. This boundary is temperature dependent and marks a major change in mineral structure and density. Wadsleyite exhibits a more compact crystal framework than olivine, leading to higher density and altered elastic properties.

Geophysically, the transition provides a plausible explanation for the seismic discontinuity observed at about 410 kilometers depth, where seismic waves change velocity due to the phase change. The stability field of wadsleyite lies within the mantle transition zone, and the presence of this phase is inferred from high-pressure experiments on silicates, natural mantle xenoliths, and seismic interpretations. The olivine to wadsleyite transition is followed by further high-pressure transformations, ultimately leading to ringwoodite at greater depths.

In summary, the olivine to wadsleyite transition is a fundamental mantle process that underpins a major seismic boundary and informs our understanding of deep Earth mineralogy and mantle dynamics.