image:Inclumed.gif, 250px, Trapped in a time capsule the same size as the diameter of a human hair, the ore-forming liquid in this inclusion was so hot and contained so much dissolved solids that when it cooled, crystals of halite, sylvite, gypsum, and hematite formed. As the samples cooled, the fluid shrank more than the surrounding mineral, and created a vapor bubble. Source: USGS A fluid inclusion is a microscopic bubble of liquid and/or gas that is trapped within a crystal. As minerals often form from a liquid or aqueous medium, tiny bubbles of that liquid can become trapped within the crystal, or along healed crystal fractures. These small inclusions range in size from 0.01 mm to 1 mm and are usually only visible in detail by microscopic study. These inclusions occur in a wide variety of environments. For example, they are found within cementing minerals of

sedimentary rocks Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particle ...

, in

gangue In mining, gangue () is the commercially worthless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. It is thus distinct from overburden, which is the waste rock or materials overlying an ore or mineral body ...

minerals such as

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

in hydrothermal circulation deposits, in fossil

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In M ...

, and in deep

ice cores An ice core is a core sample that is typically removed from an ice sheet or a high mountain glacier. Since the ice forms from the incremental buildup of annual layers of snow, lower layers are older than upper ones, and an ice core contains i ...

from the

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...

and

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and othe ...

ice caps. The inclusions can provide information about the conditions existing during the formation of the enclosing mineral.

Fourier transform infrared spectroscopy Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectra ...

and

Raman spectroscopy Raman spectroscopy () (named after Indian physicist C. V. Raman) is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman ...

can be used to determine the composition of fluid inclusions.

Formation

Hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

ore minerals, which typically form from high temperature aqueous solutions, trap tiny bubbles of liquids or gases when cooling and forming solid rock. The trapped fluid in an inclusion preserves a record of the composition, temperature and pressure of the mineralizing environment. An inclusion often contains two or more phases. If a vapor bubble is present in the inclusion along with a liquid phase, simple heating of the inclusion to the point of resorption of the vapor bubble gives a likely temperature of the original fluid. If minute crystals, such as

halite Halite (), commonly known as rock salt, is a type of salt, the mineral (natural) form of sodium chloride ( Na Cl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, p ...

sylvite Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite ( NaCl). The two are, in fact, isomorphous. Sylvite is colorless to white with shades o ...

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

sulfides Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to chemical compounds la ...

, are present in the inclusion, they provide direct clues as to the composition of the original fluid.

Fluid inclusions and mineral exploration

Fluid inclusions can provide useful data in mineral exploration, as their characteristics depend on the mineralization process. The methods of using fluid inclusions to identify mineral deposits include assessing the abundance of a specific inclusion type, looking into variations in the inclusions' temperatures of phase changes during heating and cooling, and variations in other properties such as

decrepitation Decrepitation is the noise produced when certain chemical compounds are heated, or it refers to the cracking, or breaking-up of lumps of limestone during heating.Oates, J.A.H. (1998) 'Lime and Limestone' Wiley-VCH pp 406. Such compounds include le ...

behavior, and inclusions chemistry. Observation and point-counting of thin-sections of samples is used to identify the occurrence of specific inclusion types. If an abundance of similar fluid inclusions are found in close geographic proximity, one can conclude that the surrounding rock types are similar if not the same. Microthermometric properties (changes in temperature during phase changes) are used to characterize and categorize areas that witnessed thermal activity during mineral formation. Fluid inclusions have been used to identify deposits of oil and gas. Drilling cuts, cores, and/or outcrop materials are preserved for their pore-fluids, and the chemistry of the fluid is analyzed with Fluid Inclusion

Stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

(FIS). FIS analysis takes the spectrometric reading of a fluid inclusion's volatile species; these are indicative of a natural gas or oil deposit nearby. The abundance of similar fluid inclusions could, however, be attributed to hydrocarbon migration and accumulation, so other techniques are used to confirm the presence of the oil deposit after initial detection of fluid inclusions.

Metamorphic signatures

In the recent years, fluid inclusion research has been extensively applied to understand the role of fluids in the deep crust and crust-mantle interface. Fluid inclusions trapped within granulite

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with specified characteristics, which can be any observable attribute of rocks (such as their overall appearance, composition, or condition of formatio ...

rocks have provided important clues on the petrogenesis of dry granulite facies rocks through the influx of CO₂-rich fluids from sub-lithospheric sources. CO₂-rich fluid inclusions were also recorded from a number of ultra high temperature granulite facies

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its ow ...

s, suggesting the involvement of CO₂ in extreme crustal metamorphism. Some recent studies speculate that CO₂ derived by sub-solidus decarbonation reactions during extreme metamorphism has contributed to the

deglaciation Deglaciation is the transition from full glacial conditions during ice ages, to warm interglacials, characterized by global warming and sea level rise due to change in continental ice volume. Thus, it refers to the retreat of a glacier, an ice shee ...

of the

snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 M.Y.A. (million years ago) du ...

Orogenic application

Fluid inclusions trapped in veins and minerals have been used as a proxy to explore the deformation history in orogenic belts. As fluid activities are considerably more in shear zones in an orogenic belt, the fluid inclusions in a shear zone have been also used to explore the seismic activities during the evolution of the shear zone. In orogenic belts the earthquakes sometimes attributed to be linked with fluid activity at depth. Indirect geophysical evidence points out the role of fluid in earthquakes in many shear zones, however a few studies provide geological evidence for the role of fluid in earthquakes. Treesmed

Paleoclimate applications

Trapped bubbles of air and water within fossil amber can be analyzed to provide direct evidence of the climate conditions existing when the resin or tree sap formed. The analysis of these trapped air bubbles provides a record of atmosphere composition going back 140 million years. The data indicate that the oxygen content of the atmosphere reached a high of nearly 35% during the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Period and then plummeted to near present levels during the early

Tertiary Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago. The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...

. The abrupt decline corresponds to or closely follows the

Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...

and may be the result of a major

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...

impact that created the

Chicxulub Crater The Chicxulub crater () is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore near the community of Chicxulub, after which it is named. It was formed slightly over 66 million years ago when a large a ...

. In paleoceanography studies, fluid inclusions can inform about the chemical composition of seawater. The trapped seawater in sediments evaporates and leaves behind the salt content. The depth at which these evaporites are found relative to the composition of the trapped salt allows oceanographers to reconstruct seawater evolution.{{Citation, last1=Bąbel, first1=M., title=Geochemistry of Evaporites and Evolution of Seawater, date=2014, url=http://dx.doi.org/10.1016/b978-0-08-095975-7.00718-x, work=Treatise on Geochemistry, pages=483–560, publisher=Elsevier, access-date=, last2=Schreiber, first2=B.C., doi=10.1016/b978-0-08-095975-7.00718-x , isbn=9780080983004 Air bubbles trapped within the deep ice caps can also be analyzed for clues to ancient climate conditions.

References

External links

Fluid inclusions - USGS

Geochemistry Mineralogy Petrology