Igneous differentiation
The term magmatic differentiation refers to the emergence of different partial magmas from a so -called parent magma by changing the chemical composition. This concept originates from a branch of geology, Endogenous dynamics that deals with the magmatic processes in the Earth's interior. It describes the phenomenon that from a liquid molten rock ( magma ) with a specific chemical and mineralogical composition (parent magma ), not just have to crystallize a particular igneous rock of the same composition, as would be expected, but that it is a whole series of different rocks can with different compositions, ie different mineral components arise.
Separation by gravity and crystallization
Already in the molten state, immiscible components, such as sulfidic and oxidic phases of a melt can separate from each other, similar to how oil separates from vinegar ( Liquident mixture or liquation ). More often, however, the separation of early crystallized minerals from the remaining partial melt (also called residual ) in which the minerals under its own specific weight on the bottom of the magma chamber sink ( Schwereseigerung, or Gravitationsdifferentiation ). Even Charles Darwin had in 1844 suggested that the partial magmas thus produced can be pressed and separated by tectonic movements. In the 1920s, Paul Niggli and Hans Cloos developed the idea that the solid and liquid, or immiscible components of a melt particularly during the ascent of magma to the surface separating ( Bewegungsdifferentiation ).
The concept of magmatic differentiation by fractional crystallization was developed especially by Norman Bowen and is based on the fact that molten rock or magma or multi-component or multi-component systems whose individual components have different melting points. Upon cooling of a magma therefore crystallized first from the component with the highest melting point and sinks into the magma chamber due to higher density down. From the remaining part of the melt, the residue, crystallized upon further cooling and release the individual component with the next highest melting point, which in turn falls downwards; thus the residual melt is constantly changing their chemical composition during continuous cooling.
Basaltic melts
In basaltic melts, a distinction the continuous series of the discontinuous series.
In the continuous differentiation series begins with a calcium-rich plagioclase feldspar end member of the solid solution system anorthite. The further cools the magma or the more anorthite is deposited, the further shifts the mixed crystal system for sodium-rich end member albite. At the end of differentiation albite is only deposited. The discontinuous series refers to the differentiation of various minerals according to their melting point. First, olivine is the highest melting point, pyroxenes, amphiboles, and then finally biotite with the lowest melting point deposited. These two lines run parallel next to each other and describe the differentiation of a mafic ( basic ) melt towards a felsic (acidic) residue, last crystallize out of the minerals quartz, feldspar and muscovite.
General take in the course of magmatic differentiation, the levels of magnesium, iron and calcium in the residual magma from and to the silicon, sodium, and potassium. This means that from basaltic melts initially crystallize the mafic and intermediate felsic minerals and a residual magma is generated, which ultimately solidifies to a granitic rock.
Example: Bushveld complex in South Africa
The most prominent example for Differentiationsvorgänge is located in South Africa 's Bushveld Complex. This basaltic intrusive rock has a variation of ultrabasic to granitic composition and is characterized by a very well-defined position texture that looks amazingly similar to the layering of sedimentary rocks. It reflects the different Differentiationszyklen of the Bushveld. The basic to ultrabasic shares resulting from differentiation of a tholeiitic magma, which are regarded as Granite melted and contaminated crustal material.