Fractional crystallization (geology)

In the fractional crystallization is a term used in petrology related to the rock formation.

Definition

Fractional crystallization is a process that often takes place during the so-called igneous differentiation. Here, minerals such as olivine and pyroxene crystallize earlier than others and fall in Magma downwards and remain. By the crystallization of these minerals to the composition of the remaining liquid residue magma changed (so-called fluid phase ).

Compatibility

A measure of the incorporation and retention of elements in the fluid or the solid phase is the incompatibility / compatibility. In order to make statements about the conditions of crystallization of magmas, their trace element concentrations are frequently examined. Play a decisive role in the so-called mineral separation coefficient and the mass separation coefficient, indicating the concentration in the liquid, the ratio of the concentration in the mineral (whose paragenesis or ). If this ratio is greater than 1, one speaks of compatible elements, it is less than 1, of incompatible trace elements. Rubidium and zirconium are examples of highly incompatible trace elements in many magmas. Considering the extent of crystallization, so the ratio of the mass of the liquid left over after the process of mass at the start ( ' daughter ' to ' parental magma '). After the Rayleigh Fraktionierungsgleichung the compatible trace elements take the fastest of at large separation coefficient and incompatible elements take with progressive differentiation to. Different concentrations of incompatible elements, for example in MORB ( mid-ocean - ridge basalt ) and OIB ( oceanic island basalt ) can be of a similar or different genesis of basaltic taking into account the size of the melting fractions.

Causes

There are several causes for insertion of this process: