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Hydrothermal circulation in its most general sense is the circulation of hot water (
Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the diale ...
ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press. and θέρμη, ''heat'' ). Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near
volcanic A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet ar ...

volcanic
activity, but can occur in the shallow to mid crust along deeply penetrating fault irregularities or in the deep crust related to the intrusion of
granite Granite () is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cool ...

granite
, or as the result of
orogeny Orogeny is the primary mechanism by which mountains are formed on continents. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. This leads to both structural deformation Deformation ...
or
metamorphism Metamorphism is the change of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs nat ...
.


Seafloor hydrothermal circulation

Hydrothermal circulation in the
ocean The ocean (also the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
s is the passage of the water through
mid-oceanic ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of ~ and rises about two kilometers above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along ...
systems. The term includes both the circulation of the well-known, high-temperature vent waters near the ridge crests, and the much-lower-temperature,
diffuse 250px, Diffusion from a microscopic and macroscopic point of view. Initially, there are solution, solute molecules on the left side of a barrier (purple line) and none on the right. The barrier is removed, and the solute diffuses to fill the wh ...

diffuse
flow of water through sediments and buried
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

basalt
s further from the ridge crests. The former circulation type is sometimes termed "active", and the latter "passive". In both cases, the principle is the same: Cold, dense seawater sinks into the basalt of the seafloor and is heated at depth whereupon it rises back to the rock-ocean water interface due to its lesser density. The heat source for the active vents is the newly formed basalt, and, for the highest temperature vents, the underlying
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
chamber. The heat source for the passive vents is the still-cooling older basalts. Heat flow studies of the seafloor suggest that basalts within the oceanic crust take millions of years to completely cool as they continue to support passive hydrothermal circulation systems.
Hydrothermal vent A hydrothermal vent is a fissure A fissure is a long, narrow crack opening along the surface of the Earth. It is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in the Earth's crust, on ice sheets and glaciers, and ...
s are locations on the seafloor where hydrothermal fluids mix into the overlying ocean. Perhaps the best-known vent forms are the naturally occurring
chimney A chimney is an architectural ventilation structure made of masonry, clay or metal that isolates hot toxic exhaust gas Exhaust gas or flue gas Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for c ...

chimney
s referred to as
black smoker A hydrothermal vent is a fissure vent, fissure on the seafloor from which Geothermal (geology), geothermally heated water discharges. Hydrothermal vents are commonly found near volcano, volcanically active places, areas where tectonic plates are m ...
s.


Volcanic and magma related hydrothermal circulation

Hydrothermal circulation is not limited to ocean ridge environments. Hydrothermal circulating convection cells can exist in any place an anomalous source of heat, such as an intruding
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
or
volcanic A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet ar ...

volcanic
vent, comes into contact with the
groundwater Groundwater is the water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known form ...

groundwater
system where permeability allows flow. This convection can manifest as hydrothermal explosions,
geysers A geyser (, ) is a spring (hydrosphere), spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam. As a fairly rare phenomenon, the formation of geysers is due to particular hydrogeological conditio ...

geysers
, and
hot springs A hot spring, hydrothermal spring, or geothermal spring is a spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of ...

hot springs
, although this is not always the case.   Hydrothermal circulation above magma bodies has been intensively studied in the context of geothermal projects where many deep wells are drilled into the system to produce and subsequently re-inject the hydrothermal fluids. The detailed data sets available from this work show the long term persistance of these systems, the development of fluid circulation patterns, histories that can be influenced by renewed magmatism, fault movement, or changes associated with hydrothermal brecciation and eruption sometimes followed by massive cold water invasion. Less direct but as intensive study has focused on the minerals deposited especially in the upper parts of hydrothermal circulation systems. Understanding volcanic and magma-related hydrothermal circulation means studying hydrothermal explosions, geysers, hot springs, and other related systems and their interactions with associated surface water and groundwater bodies. A good environment to observe this phenomenon is in volcanogenic lakes where hot springs and geysers are commonly present. The convection systems in these lakes work through cold lake water percolating downward through the permeable lake bed, mixing with groundwater heated by magma or residual heat, and rising to form thermal springs at discharge points. The existence of hydrothermal convection cells and hot springs or geysers in these environments depends not only on the presence of a colder water body and geothermal heat but also strongly depends on a no-flow boundary at the water table. These systems can develop their own boundaries. For example the water level represents a fluid pressure condition that leads to gas exsolution or boiling that in turn causes intense mineralization that can seal cracks.


Deep crust

Hydrothermal also refers to the transport and circulation of water within the deep crust, in general from areas of hot rocks to areas of cooler rocks. The causes for this convection can be: * Intrusion of magma into the crust * Radioactive heat generated by cooled masses of granite * Heat from the mantle * Hydraulic head from mountain ranges, for example, the
Great Artesian Basin bathing thermes supplied by artesian bore water Image:ThargomindahHydro.jpg, upright=1.2, Hot water bore hole into the Great Artesian Basin in Thargomindah, Queensland, Thargomindah The Great Artesian Basin (GAB), located in Australia, is the ...

Great Artesian Basin
* Dewatering of metamorphic rocks, which liberates water * Dewatering of deeply buried sediments Hydrothermal circulation, in particular in the deep crust, is a primary cause of
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

mineral
deposit formation and a cornerstone of most theories on
ore genesis Various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust (geology), crust. Ore-genesis theories vary depending on the mineral or commodity examined. Ore-genesis theories generally involve t ...
.


Hydrothermal ore deposits

During the early 1900s, various geologists worked to classify hydrothermal ore deposits that they assumed formed from upward-flowing aqueous solutions. (1860–1939) developed a classification based on interpreted decreasing temperature and pressure conditions of the depositing fluid. His terms: "hypothermal", "mesothermal", "epithermal" and "teleothermal", expressed decreasing temperature and increasing distance from a deep source. Recent studies retain only the ''epithermal'' label. John Guilbert's 1985 revision of Lindgren's system for hydrothermal deposits includes the following:Guilbert, John M. and Charles F. Park, Jr., 1986, ''The Geology of Ore Deposits'', Freeman, p. 302 * Ascending hydrothermal fluids,
magmatic 300px, Hawaii Hawaii ( ; haw, Hawaii or ) is a U.S. state in the Western United States, in the Pacific Ocean about 2,000 miles (3,200 km) from the U.S. mainland. It is the only state outside North America, the only island state, and ...
or
meteoric waterMeteoric water is the water derived from Precipitation (meteorology), precipitation (snow and rain). This includes water from lakes, rivers, and icemelts, which all originate from precipitation indirectly. While the bulk of rainwater or meltwater fro ...
**
Porphyry copper Bingham Canyon mine in 2005. The gray rocks visible in the pit are almost all in the primary-sulfide ore zone. Porphyry copper deposits are copper Copper is a chemical element with the Symbol (chemistry), symbol Cu (from la, cuprum) and at ...
and other deposits, 200–800 °C, moderate pressure ** Igneous metamorphic, 300–800 °C, low to moderate pressure ** Cordilleran veins, intermediate to shallow depths ** Epithermal, shallow to intermediate, 50–300 °C, low pressure * Circulating heated meteoric solutions ** Mississippi Valley-type deposits, 25–200 °C, low pressure ** Western US uranium, 25–75 °C, low pressure * Circulating heated seawater ** Oceanic ridge deposits, 25–300 °C, low pressure


See also

*
Volcanogenic massive sulfide ore deposit Volcanogenic massive sulfide ore deposits, also known as VMS ore deposits, are a type of metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), o ...
*
Geothermal gradient ). Geothermal gradient is the rate of temperature change with respect to increasing depth in Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consi ...
*
Hydrothermal synthesis crystal grown by the hydrothermal method Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solution An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making ...


References

{{physical oceanography Geological processes Physical oceanography