Partial melt (also: Teilschmelze , Partielle Anatexis ) describes in geosciences the product of a melting process in the earth's interior, in which the solid rock material is partially melted at a prevailing temperature.
Rocks such as granite or basalt are usually made up of several different mineral components. Plutonites , like granite, show grain sizes of several millimeters to centimeters, while volcanites , like basalt, have very small grain sizes because of the much faster cooling and thus mostly show a diffuse rock matrix.
If rocks are heated slowly, it can be observed that the material does not completely liquefy at a certain temperature, but only partially melts. This is because the various mineral components that make up a rock have different melting temperatures and are therefore not necessarily melted at the same time.
While some minerals are already completely liquefied, others may still be in a solid state. Correspondingly, rocks are not referred to as melting temperatures, but rather as melting ranges. The temperature at which the entire rock structure is still in a solid state is referred to as the solidus . The temperature at which all components of a rock are completely melted is called liquidus .
The partial melt is present within the melting range , the chemical composition of which consequently depends on the degree of melting , i.e. on the proportion of the rock that has already melted. If the partial melt is erupted by a volcano , the composition is reflected in the lava . The chemical analysis of volcanic rock thus allows conclusions to be drawn about the approximate depth of magma formation and the parent rock.
The asthenosphere represents an extensive zone with partial melt, which lies in the upper mantle below the lithosphere and was discovered by seismological methods. Due to the partial melt, the propagation speeds of seismic waves are reduced here.
- University of Alabama, Department of Geological Sciences: Volcanology II. Generation, Rise And Storage Of Magma: Partial Melting. ( Memento from March 1, 2009 in the Internet Archive )