Magmaevolusjon

Magmaevolusjon, or magma evolution, refers to the changes in chemical and mineralogical composition of a magmatic system over time as a magma body cools, crystallizes, and interacts with surrounding rocks. It encompasses how a single magmatic chamber can give rise to distinct rock types through differentiation and contamination, shaping the diversity of igneous rocks observed in the crust.

The primary processes involved are fractional crystallization, where early-formed crystals are separated from the melt and progressively alter its composition; assimilation or crustal contamination, in which surrounding or intruded crustal rocks are melted and incorporated into the magma; and magma mixing and mingling, where magmas of different compositions exchange heat and material. Combined processes, such as assimilation coupled with fractional crystallization (AFC), can drive complex evolutionary paths. Volatile exsolution, pressure changes, and temperature shifts further influence mineral stability and melt composition.

Geochemical and petrological evidence used to study magma evolution includes major and trace element compositions, isotope ratios (such as Sr-Nd-Pb), and rare earth element patterns, as well as zoning in minerals and cross-cutting relationships among rocks. By reconstructing these signals, scientists infer the history of chamber processes, magma recharge events, and the timing of differentiation. Magma evolution is central to understanding crust formation, volcanic arc magmatism, and ore-genesis, and it informs models of how diverse igneous rocks develop from common parental magmas over timescales ranging from thousands to millions of years.