Describe the crystallisation of a bi-component magma with the help of solid-solution series.
Answers
The minerals that make up igneous rocks crystallize at a range of different temperatures. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series (Figure 3.10 and Who was Bowen).
Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300°C. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals react (combine) with some of the silica in the magma (see Box 3.1) to form pyroxene. As long as there is silica remaining and the rate of cooling is slow, this process continues down the discontinuous branch: olivine to pyroxene, pyroxene to amphibole, and (under the right conditions) amphibole to biotite.
At about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize. At that temperature, the plagioclase is calcium-rich (anorthite) (see Figure 2.15). As the temperature drops, and providing that there is sodium left in the magma, the plagioclase that forms is a more sodium-rich variety.
Answer:
The crystallization of a bi-component magma with the help of solid-solution series has been explained.
Explanation:
As per the given data,
Bowen's reaction series is based on observations and tests of natural rocks; as basaltic magmas cool, their crystallisation patterns alter. It is a tool for classifying materials based on the temperature at which common magmatic silicate minerals form.
The temperatures at which many common silicate minerals transition from the liquid to solid phase are described by Bowen's Reaction Series (or solid to liquid). Years of melting tests were carried out by petrologist Norman Bowen (1887–1956) to support the granite theory in the early 1900s. He discovered that a basaltic meltdown gradually cooled and that minerals crystallised in a specific order.
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