Bowen's reaction series
The ordered sequence in which minerals crystallize from cooling magma, with continuous plagioclase evolution and discrete mafic mineral replacements.
Continuous reaction series: Plagioclase feldspar that steadily changes from calcium-rich anorthite to sodium-rich albite as magma cools. The continuous branch: each plagioclase composition reacts with the melt to become more sodium-rich.
Norman L. Bowen: Petrologist at the Geophysical Laboratories who experimentally established the reaction series, 1912–1930s. He ran the quenching experiments on melts that produced the series now bearing his name.
Magma: Molten silicate rock with dissolved volatiles and suspended crystals, the raw material of igneous rocks. The cooling liquid whose changing chemistry the series tracks.
Assimilation: Melt chemistry changed by dissolving surrounding country rock rather than by crystal removal. Rivals fractionation as the driver of compositional variation in many intrusions.
Ore genesis: The process by which metal deposits form, often from late residual liquids of crystallizing magma. Chromium, nickel and platinum ores form exactly where early-series minerals settle out.
Discontinuous reaction series: The stepwise replacement of one ferromagnesian mineral by another: olivine, pyroxene, amphibole, biotite. The other branch, where each mineral becomes unstable and is replaced at discrete temperatures.
Geophysical Laboratory: Carnegie Institution lab in Washington, D.C., founded 1903 for experimental high-temperature geochemistry. Where Bowen performed the furnace experiments that turned igneous petrology quantitative.
Silicate minerals: Minerals built from linked silicon-oxygen tetrahedra, forming nearly all igneous rock minerals. Every mineral in the series is a silicate with a different polymerized structure.
Magma mixing: Blending of two magmas of different composition, producing intermediate melts and disequilibrium textures. An independent path to intermediate compositions the series alone cannot produce.
Layered intrusion: A pluton with planar mineral layers deposited sequentially from an evolving magma chamber. Layer sequences match the series order, letting geologists read chamber history.