- Melt Inclusions
Melt inclusions are small parcels or "blobs" of molten rock that are trapped within crystals that grow in the magmas that form
igneous rocks. In many respects they are analogous to fluid inclusions. Melt inclusions are generally small - most are less than 100 micrometres across (a micrometre is one thousandth of a millimeter, or about 0.00004 inches). Nevertheless they can provide an abundance of useful information. Using microscopic observations and a range of chemical microanalysistechniques geochemists and igneous petrologists can obtain a range of useful information from melt inclusions. Two of the most common uses of melt inclusions are to study the compositions of magmas present early in the history of specific magma systems. This is because inclusions can act like "fossils" - trapping and preserving these early melts before they are modified by later igneous processes. In addition, because they are trapped at high pressures many melt inclusions also provide important information about the contents of volatile elements (such as H2O, CO2,S and Cl) that drive explosive volcanic eruptions.
Sorby (1858) was the first to document microscopic melt inclusions in crystals. The study of melt inclusions has been driven more recently by the development of sophisticated chemical analysis techniques. Scientists from the former Soviet Union lead the study of melt inclusions in the decades after world war II (Sobolev and Kostyuk, 1975), and developed methods for heating melt inclusions under a microscope, so changes could be directly observed. Most recently scientists from a number of different countries are involved in the study of melt inclusions.
Although they are small, melt inclusions may contain a number of different constituents, including glass (which represents magma that has been quenched by rapid cooling), small crystals and a separate vapour-rich bubble. They occur in most of the crystals found in igneous rocks and are common in the minerals quartz, feldspar, olivine and pyroxene. The formation of melt inclusions appears to be a normal part of the crystallization of minerals within magmas, and they can be found in both
References and External Links
Jake Lowenstern's USGS melt inclusion page [http://volcanoes.usgs.gov/yvo/aboutus/jlowenstern/meltinclusions/index.php]
Phil Brown's World of Fluid and Melt inclusions at the University of Wisconsin-Madison [http://www.geology.wisc.edu/flincs/fi.html]
Sorby HC (1858) On the microscopic structures of crystals, indicating the origin of minerals and rocks. Geol Soc London Q J 14: 453-500
Sobolev VS, Kostyuk VP (1975) Magmatic crystallization based on a study of melt inclusions. Fluid Incl Res 9: 182– 235
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