How do rocks melt and migrate beneath the seafloor?
The WHOI ion microprobe is helping researchers shed light on a fundamental, but still largely unknown process that shapes our planet—how rock deep beneath mid-ocean ridges melts to form magmas, and how the melted rock then migrates toward Earth’s surface at the ridges. The instrument has provided the first unequivocal evidence that a type of melting called “near-fractional melting” is occurring deep beneath ridges. In near-fractional melting, solid and melted rock do not stay together. The melt finds pathways and immediately escapes the not-yet-melted rock. We deduced the occurrence of this type of melting by examining compositions of the solid rocks found at mid-ocean ridges. The work is based on our knowledge that when rocks melt, elements are distributed between solid and liquid phases in a particular way. Evidence for near-fractional melting was first found by determining abundance patterns of particular trace elements (the rare earths, or lanthanides) found in a mineral (diopside)
