Fluid inclusion

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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 Inclumed.gif
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 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 inclusions usually range in size from 0.01 mm to 1 mm and are only visible in detail by microscopic study, however specimens of fenster or skeletal quartz may include thin sheet-like inclusions that are many millimetres in length and breadth within their lamellar voids.

Contents

These inclusions occur in a wide variety of environments. For example, they are found within cementing minerals of sedimentary rocks, in gangue minerals such as quartz or calcite in hydrothermal circulation deposits, in fossil amber, and in deep ice cores from the Greenland and Antarctic ice caps. [1] The inclusions can provide information about the conditions existing during the formation of the enclosing mineral. Fourier transform infrared spectroscopy and Raman spectroscopy can be used to determine the composition of fluid inclusions.

Formation

Hydrothermal 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. [1] 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, sylvite, hematite or sulfides, are present in the inclusion, they provide direct clues as to the composition of the original fluid.

Fluid inclusions and mineral exploration

Photomicrographs from Pea Ridge, MO, USA of secondary fluid inclusions in apatite (image A) and quartz (images B-H). Hofstra-F10.large.jpg
Photomicrographs from Pea Ridge, MO, USA of secondary fluid inclusions in apatite (image A) and quartz (images B–H).

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, [2] and variations in other properties such as decrepitation behavior, and inclusions chemistry. [1] 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. [2] Microthermometric properties (changes in temperature during phase changes) are used to characterize and categorize areas that witnessed thermal activity during mineral formation. [2]

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 (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. [3] 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.

Extraterrestrial

[4]

Sutter's Mill meteorite [5] [6]

(162173) Ryugu [7] [8] [9]

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 rocks have provided important clues on the petrogenesis of dry granulite facies rocks through the influx of CO2-rich fluids from sub-lithospheric sources. [10] CO2-rich fluid inclusions were also recorded from a number of ultra high temperature granulite facies terranes, suggesting the involvement of CO2 in extreme crustal metamorphism. [10] Some recent studies speculate that CO2 derived by sub-solidus decarbonation reactions during extreme metamorphism has contributed to the deglaciation of the snowball Earth. [10]

Orogenic application

Fluid inclusions trapped in veins and minerals have been used as a proxy to explore the deformation history in orogenic belts. [11] 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. [12] 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. [12]

This 84-million-year-old air bubble lies trapped in amber (fossilized tree sap). Using a quadrupole mass spectrometer, scientists can learn what the atmosphere was like when the dinosaurs roamed the earth. Source: USGS Treesmed.gif
This 84-million-year-old air bubble lies trapped in amber (fossilized tree sap). Using a quadrupole mass spectrometer, scientists can learn what the atmosphere was like when the dinosaurs roamed the earth. Source: USGS

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 Period and then plummeted to near present levels during the early Tertiary. The abrupt decline corresponds to or closely follows the Cretaceous–Paleogene extinction event and may be the result of a major meteorite impact that created the Chicxulub Crater.

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. [13] Air bubbles trapped within the deep ice caps can also be analyzed for clues to ancient climate conditions.

See also

Related Research Articles

<span class="mw-page-title-main">Metamorphic rock</span> Rock that was subjected to heat and pressure

Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than 150 to 200 °C and, often, elevated pressure of 100 megapascals (1,000 bar) or more, causing profound physical or chemical changes. During this process, the rock remains mostly in the solid state, but gradually recrystallizes to a new texture or mineral composition. The protolith may be an igneous, sedimentary, or existing metamorphic rock.

<span class="mw-page-title-main">Pentlandite</span> Iron–nickel sulfide

Pentlandite is an iron–nickel sulfide with the chemical formula (Fe,Ni)9S8. Pentlandite has a narrow variation range in nickel to iron ratios (Ni:Fe), but it is usually described as 1:1. In some cases, this ratio is skewed by the presence of pyrrhotite inclusions. It also contains minor cobalt, usually at low levels as a fraction of weight.

<span class="mw-page-title-main">Metamorphism</span> Change of minerals in pre-existing rocks without melting into liquid magma

Metamorphism is the transformation of existing rock to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of 150 °C (300 °F), and often also at elevated pressure or in the presence of chemically active fluids, but the rock remains mostly solid during the transformation. Metamorphism is distinct from weathering or diagenesis, which are changes that take place at or just beneath Earth's surface.

<span class="mw-page-title-main">Hydrothermal vent</span> Fissure in a planets surface from which heated water emits

Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspots. The dispersal of hydrothermal fluids throughout the global ocean at active vent sites creates hydrothermal plumes. Hydrothermal deposits are rocks and mineral ore deposits formed by the action of hydrothermal vents.

<span class="mw-page-title-main">Skarn</span> Hard, coarse-grained, hydrothermally altered metamorphic rocks

Skarns or tactites are coarse-grained metamorphic rocks that form by replacement of carbonate-bearing rocks during regional or contact metamorphism and metasomatism. Skarns may form by metamorphic recrystallization of impure carbonate protoliths, bimetasomatic reaction of different lithologies, and infiltration metasomatism by magmatic-hydrothermal fluids. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or shear zones that commonly intrude into a carbonate layer composed of either dolomite or limestone. Skarns can form by regional or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from a variety of sources; magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on both the original composition of the hydrothermal fluid and the original composition of the protolith.

<span class="mw-page-title-main">Magnesite</span> Type of mineral

Magnesite is a mineral with the chemical formula MgCO
3. Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts.

<span class="mw-page-title-main">Eclogite</span> Metamorphic rock formed under high pressure

Eclogite is a metamorphic rock containing garnet (almandine-pyrope) hosted in a matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum and, rarely, diamond. The chemistry of primary and accessory minerals is used to classify three types of eclogite. The broad range of eclogitic compositions has led to a longstanding debate on the origin of eclogite xenoliths as subducted, altered oceanic crust.

<span class="mw-page-title-main">Metasomatism</span> Chemical alteration of a rock by hydrothermal and other fluids

Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical composition, excluding volatile components. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.

<span class="mw-page-title-main">Ultramafic rock</span> Type of igneous and meta-igneous rock

Ultramafic rocks are igneous and meta-igneous rocks with a very low silica content, generally >18% MgO, high FeO, low potassium, and are usually composed of greater than 90% mafic minerals. The Earth's mantle is composed of ultramafic rocks. Ultrabasic is a more inclusive term that includes igneous rocks with low silica content that may not be extremely enriched in Fe and Mg, such as carbonatites and ultrapotassic igneous rocks.

<span class="mw-page-title-main">Anthophyllite</span> Silicate amphibole mineral

Anthophyllite is an orthorhombic amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are classed as asbestos. The name is derived from the Latin word anthophyllum, meaning clove, an allusion to the most common color of the mineral. The Anthophyllite crystal is characterized by its perfect cleavage along directions 126 degrees and 54 degrees.

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Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.

In geology ultrahigh-temperature metamorphism (UHT) is extreme crustal metamorphism with metamorphic temperatures exceeding 900 °C. Granulite-facies rocks metamorphosed at very high temperatures were identified in the early 1980s, although it took another decade for the geoscience community to recognize UHT metamorphism as a common regional phenomenon. Petrological evidence based on characteristic mineral assemblages backed by experimental and thermodynamic relations demonstrated that Earth's crust can attain and withstand very high temperatures (900–1000 °C) with or without partial melting.

<span class="mw-page-title-main">Melt inclusion</span>

A melt inclusion is a small parcel or "blobs" of melt(s) that is entrapped by crystals growing in magma and eventually forming igneous rocks. In many respects it is analogous to a fluid inclusion within magmatic hydrothermal systems. Melt inclusions tend to be microscopic in size and can be analyzed for volatile contents that are used to interpret trapping pressures of the melt at depth.

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<span class="mw-page-title-main">Eclogitization</span> The tectonic process in which the dense, high-pressure, metamorphic rock, eclogite, is formed

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<span class="mw-page-title-main">Subduction zone metamorphism</span> Changes of rock due to pressure and heat near a subduction zone

A subduction zone is a region of the Earth's crust where one tectonic plate moves under another tectonic plate; oceanic crust gets recycled back into the mantle and continental crust gets produced by the formation of arc magmas. Arc magmas account for more than 20% of terrestrially produced magmas and are produced by the dehydration of minerals within the subducting slab as it descends into the mantle and are accreted onto the base of the overriding continental plate. Subduction zones host a unique variety of rock types formed by the high-pressure, low-temperature conditions a subducting slab encounters during its descent. The metamorphic conditions the slab passes through in this process generates and alters water bearing (hydrous) mineral phases, releasing water into the mantle. This water lowers the melting point of mantle rock, initiating melting. Understanding the timing and conditions in which these dehydration reactions occur, is key to interpreting mantle melting, volcanic arc magmatism, and the formation of continental crust.

<span class="mw-page-title-main">Sveconorwegian orogeny</span> Orogenic belt in southwestern Sweden and southern Norway

The Sveconorwegian orogeny was an orogenic system active 1140 to 960 million years ago and currently exposed as the Sveconorwegian orogenic belt in southwestern Sweden and southern Norway. In Norway the orogenic belt is exposed southeast of the front of the Caledonian nappe system and in nappe windows. The Sveconorwegian orogen is commonly grouped within the Grenvillian Mesoproterozoic orogens. Contrary to many other known orogenic belts the Sveconorwegian orogens eastern border does not have any known suture zone with ophiolites.

Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually produce metallic-rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted for a profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. The presence of a known but unexploited mineral deposit implies a lack of evidence for profitable extraction.

An orogenic gold deposit is a type of hydrothermal mineral deposit. More than 75% of the gold recovered by humans through history belongs to the class of orogenic gold deposits. Rock structure is the primary control of orogenic gold mineralization at all scales, as it controls both the transport and deposition processes of the mineralized fluids, creating structural pathways of high permeability and focusing deposition to structurally controlled locations.

References

  1. 1 2 3 Wilkinson, J. J (2001). "Fluid inclusions in hydrothermal ore deposits". Lithos. Fluid Inclusions: Phase Relationships - Methods - Applications. A Special Issue in honour of Jacques Touret. 55 (1): 229–272. Bibcode:2001Litho..55..229W. doi:10.1016/S0024-4937(00)00047-5. ISSN   0024-4937.
  2. 1 2 3 Goldstein, Robert H.; Reynolds, T. James (1994), "Fluid inclusion microthermometry", Systematics of Fluid Inclusions in Diagenetic Minerals, SEPM (Society for Sedimentary Geology), pp. 87–121, doi:10.2110/scn.94.31.0087, ISBN   1-56576-008-5 , retrieved 2021-10-31
  3. ↑ Jarmołowicz-Szulc, Katarzyna (2021). "Application of Fluid Inclusions to Petroleum Basin Recognition—A Case Study from Poland". Minerals. 11 (5): 500. Bibcode:2021Mine...11..500J. doi: 10.3390/min11050500 . ISSN   2075-163X.
  4. ↑ Roedder, E. (1984). Fluid inclusions. Mineralogical Society of America. ISBN   978-0939950-16-4.
  5. ↑ Tsuchiyama, A. Miyake A. Kawano J. (2018). Nano-Sized CO2-H2O Fluid Inclusions in Calcite Grains of the Sutter's Mill CM Meteorite. LPSC. p. 6187.
  6. ↑ Zolensky, M. E. (2021). Analysis of Fluid Inclusions in Astromaterials: Why, Where and How. MetSoc. p. 6034.
  7. ↑ Nakamura, T.; Matsumoto, M.; Amano, K.; Enokido, Y.; Zolensky, M. E. (Mar 2022). Early History of Ryugu's Parent Asteroid: Evidence From Return Sample. LPSC. p. 1753.
  8. ↑ McCain, K. A.; Matsuda, N.; Liu, M-C. (12 Jan 2023). "Early fluid activity on Ryugu inferred by isotopic analyses of". Nature. 7: 309.
  9. ↑ Zolensky, M.; Dolocan, A.; Bodnar, R.; Gearba, I.; Martinez, J.; Han, J.; Nakamura, T. (Aug 2023). Update on Measurement of The Composition of Ryugu Fluid Inclusions. Meteoritical Society Meeting. Vol. 6011.
  10. 1 2 3 Santosh, M.; Omori, S. (2008). "CO2 windows from mantle to atmosphere: Models on ultrahigh-temperature metamorphism and speculations on the link with melting of snowball Earth". Gondwana Research. Snowball Earth to Cambrian Explosion. 14 (1): 82–96. Bibcode:2008GondR..14...82S. doi:10.1016/j.gr.2007.11.001. ISSN   1342-937X.
  11. ↑ Ojha, Arun K.; Sharma, Rajesh; Srivastava, Deepak C.; Lister, Gordon S. (October 2019). "Polyphase development of chocolate-tablet boudins in the SAT zone, Kumaun Lesser Himalaya, India". Journal of Structural Geology. 127: 103863. Bibcode:2019JSG...12703863O. doi:10.1016/j.jsg.2019.103863. S2CID   199109016.
  12. 1 2 Ojha, Arun K.; Srivastava, Deepak C.; Sharma, Rajesh (July 2022). "Fluctuation in the fluid and tectonic pressures in the South Almora Thrust Zone (SATZ), Kumaun Lesser Himalaya; paleoseismic implications". Journal of Structural Geology. 160: 104631. Bibcode:2022JSG...16004631O. doi:10.1016/j.jsg.2022.104631. S2CID   248928633.
  13. ↑ Bąbel, M.; Schreiber, B.C. (2014), "Geochemistry of Evaporites and Evolution of Seawater", Treatise on Geochemistry, Elsevier, pp. 483–560, doi:10.1016/b978-0-08-095975-7.00718-x, ISBN   9780080983004
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