Bowen’s Reaction Series: A Comprehensive Guide for Science Students

Bowen’s Reaction Series is a fundamental concept in the study of igneous rocks, providing a quantifiable framework to understand the mineral composition and crystallization temperatures of these rocks. The series describes the sequence of mineral crystallization as magma cools, with minerals crystallizing at specific temperature ranges.

Understanding the Temperature Ranges

The Bowen’s Reaction Series spans a temperature range from approximately 700°C (1,292°F) to 1,250°C (2,282°F) at standard sea-level pressure (1 bar). This temperature range can be further divided into two distinct branches:

1. Continuous Reaction Series: This branch involves solid solutions between minerals, where the composition of the minerals changes gradually as the temperature decreases. The minerals in this series include olivine, pyroxene, and plagioclase feldspar.

2. Discontinuous Reaction Series: This branch involves the incongruent melting of minerals, where the mineral composition changes abruptly as the temperature decreases. The minerals in this series include amphibole, biotite, and quartz.

The minerals near the top of the Bowen’s Reaction Series, such as olivine and anorthite, crystallize at higher temperatures, while the minerals near the bottom, such as quartz and muscovite, crystallize at lower temperatures.

Mineral Composition and Crystallization Behavior

The Bowen’s Reaction Series includes a variety of minerals, each with specific temperature ranges and crystallization behaviors. These minerals can be categorized into the following groups:

1. Olivine: Olivine is a magnesium-iron silicate mineral that crystallizes at the highest temperatures in the Bowen’s Reaction Series, typically between 1,200°C (2,192°F) and 1,250°C (2,282°F).

2. Pyroxene: Pyroxene is a group of silicate minerals that crystallize at temperatures ranging from 1,100°C (2,012°F) to 1,200°C (2,192°F).

3. Amphibole: Amphibole is a group of silicate minerals that crystallize at temperatures ranging from 900°C (1,652°F) to 1,100°C (2,012°F).

4. Biotite: Biotite is a sheet silicate mineral that crystallizes at temperatures ranging from 800°C (1,472°F) to 900°C (1,652°F).

5. Plagioclase Feldspar: Plagioclase feldspar is a group of aluminosilicate minerals that crystallize at temperatures ranging from 1,100°C (2,012°F) to 800°C (1,472°F).

6. Quartz: Quartz is a silicon dioxide mineral that crystallizes at the lowest temperatures in the Bowen’s Reaction Series, typically between 700°C (1,292°F) and 800°C (1,472°F).

The specific temperature ranges and crystallization behaviors of these minerals are crucial in understanding the formation and composition of igneous rocks.

Igneous Rock Classification

Bowen’s Reaction Series is used to classify igneous rocks based on their mineral composition and crystallization temperatures. The series is divided into four groups of igneous rocks:

1. Ultramafic Rocks: These rocks are composed primarily of olivine and pyroxene, with little to no quartz or feldspar. They crystallize at the highest temperatures in the Bowen’s Reaction Series, typically between 1,200°C (2,192°F) and 1,250°C (2,282°F).

2. Mafic Rocks: These rocks are composed primarily of pyroxene and plagioclase feldspar, with minor amounts of olivine and amphibole. They crystallize at temperatures ranging from 1,100°C (2,012°F) to 1,200°C (2,192°F).

3. Intermediate Rocks: These rocks are composed of a mixture of plagioclase feldspar, amphibole, and biotite, with minor amounts of quartz. They crystallize at temperatures ranging from 900°C (1,652°F) to 1,100°C (2,012°F).

4. Felsic Rocks: These rocks are composed primarily of quartz and alkali feldspar, with minor amounts of biotite and muscovite. They crystallize at the lowest temperatures in the Bowen’s Reaction Series, typically between 700°C (1,292°F) and 800°C (1,472°F).

Understanding the classification of igneous rocks based on the Bowen’s Reaction Series is crucial for geologists and petrologists in interpreting the formation and composition of these rocks.

Experimental Data and Quantifiable Measurements

Bowen’s Reaction Series is based on extensive experimental data obtained by grinding combinations of rocks into powder, sealing the powders into metal capsules, heating them to various temperatures, and then cooling them. These experiments provide quantifiable data on the crystallization temperatures and mineral assemblages of igneous rocks.

Some key quantifiable measurements and data points related to Bowen’s Reaction Series include:

1. Mineral Composition: The precise mineral compositions of the various igneous rock groups, including the percentages of olivine, pyroxene, amphibole, biotite, plagioclase feldspar, and quartz.

2. Crystallization Temperatures: The specific temperature ranges at which each mineral in the series crystallizes, as well as the overall temperature range of the series.

3. Pressure Dependence: The effect of pressure on the crystallization temperatures and mineral assemblages, as the series is primarily based on experiments conducted at standard sea-level pressure (1 bar).

4. Cooling Rates: The influence of cooling rates on the mineral compositions and textures of the resulting igneous rocks, as faster cooling can lead to the formation of more fine-grained or glassy textures.

5. Solid Solution Compositions: The specific compositions of the solid solutions that form in the continuous reaction series, such as the iron-magnesium ratio in olivine and the calcium-sodium ratio in plagioclase feldspar.

These quantifiable data points and measurements are essential for understanding the formation and evolution of igneous rocks, as well as for interpreting the geological history of various regions.

Practical Applications of Bowen’s Reaction Series

Bowen’s Reaction Series has numerous practical applications in the field of geology and related sciences:

1. Igneous Rock Identification: The series provides a framework for identifying and classifying igneous rocks based on their mineral composition and crystallization temperatures.

2. Magma Differentiation: The series helps explain the process of magma differentiation, where the composition of the magma changes as minerals crystallize and are removed from the melt.

3. Volcanic Eruption Prediction: Understanding the Bowen’s Reaction Series can aid in predicting the composition and behavior of volcanic eruptions, as the series provides insights into the crystallization and cooling of magma.

4. Ore Deposit Formation: The series can help explain the formation of certain ore deposits, as the crystallization of specific minerals can concentrate valuable elements in the remaining melt.

5. Metamorphic Reactions: The series can be used to understand the reactions that occur during metamorphism, as the stability of minerals is influenced by temperature and pressure changes.

6. Planetary Geology: Bowen’s Reaction Series has been applied to the study of igneous rocks on other planetary bodies, such as the Moon and Mars, to understand their formation and evolution.

By understanding the quantifiable data and practical applications of Bowen’s Reaction Series, science students can gain a deeper appreciation for the complexity and importance of igneous rock formation and evolution.

References:

1. Bowen, N.L. (1928). The Evolution of the Igneous Rocks. Princeton University Press.
2. Philpotts, A.R. (1990). Principles of Igneous and Metamorphic Petrology. Prentice-Hall.
3. Blatt, H., Tracy, R.J., & Owens, B.E. (2006). Petrology: Igneous, Sedimentary, and Metamorphic. W.H. Freeman.
4. Hess, P.C. (1989). Origins of Igneous Rocks. Harvard University Press.
5. Frost, B.R., & Frost, C.D. (2014). Essentials of Igneous and Metamorphic Petrology. Cambridge University Press.