Thin Section Interpretation and Incompatible Elements
Terms you will need
- thin sectionA thin section is a very thin slice of rock that is used to study the minerals and textures of the rock under a microscope.
- polarized lightPolarized light is light that has been filtered so that its waves all vibrate in the same direction, which helps in identifying minerals in thin sections.
- birefringenceBirefringence is the property of some minerals to split light into two rays that travel at different speeds, causing them to appear colorful under polarized light.
- cleavage planesCleavage planes are the surfaces along which a mineral tends to break, determined by the arrangement of atoms in the mineral.
- extinctionExtinction is when a mineral in a thin section appears dark when viewed under polarized light that is rotated 90 degrees.
- twinningTwinning is when two or more crystals of the same mineral grow together in a symmetrical pattern, often visible under a microscope.
How this topic runs
Thin section interpretation is a crucial technique in geology that allows scientists to examine the microscopic structure of rocks and minerals. By slicing a rock into a very thin section and viewing it under a microscope, geologists can identify the minerals present, understand the rock's texture, and infer its history and origin. This method is particularly important in the study of igneous, sedimentary, and metamorphic rocks, as it provides detailed information about the composition and formation processes of these rocks. Incompatible elements, on the other hand, are chemical elements that do not easily fit into the crystal structures of common minerals. Their presence and distribution in rocks can provide valuable insights into the geological processes that formed the rock, such as magma evolution and metamorphism. Understanding these elements and their behavior is essential for interpreting the geological history of a rock and for various applications in resource exploration and environmental studies.
Figures (10)
Incompatible elements are those that do not easily fit into the crystal structures of common minerals due to their ionic size and charge. During the formation of igneous rocks, these elements are excluded from the growing mineral crystals and tend to concentrate in the remaining melt. This exclusion is governed by the partition coefficients, which quantify how much an element prefers to be in the melt versus in the solid mineral.
As the magma cools and crystallizes, incompatible elements become increasingly enriched in the residual liquid. This process is influenced by the temperature and pressure conditions, as well as the chemical composition of the magma. The enrichment of incompatible elements in the melt can lead to the formation of late-stage minerals or fluid phases that incorporate these elements.
By examining thin sections, geologists can observe the textures and mineral assemblages that reflect the history of incompatible element behavior, providing insights into the magma's evolution and the geological processes that formed the rock.
Key Points
- A thin section is a very thin slice of rock that is prepared for examination under a microscope to study its mineral composition and texture.
- Cleavage planes are the specific planes along which a mineral tends to break due to the arrangement of atoms in its crystal lattice.
Terms
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Sources & licensing(4)
- Steven Earle, Physical Geology – 2nd Edition, BCcampus Open Education — opentextbc.ca/physicalgeology2ed/ (Creative Commons Attribution 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Thin_section (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Polarized_light_microscopy (Creative Commons Attribution-ShareAlike 4.0)
- Wikipedia contributors — en.wikipedia.org/wiki/Birefringence (Creative Commons Attribution-ShareAlike 4.0)