Editing Hydrothermal circulation

{{redirect|Hydrothermal|use in geochemistry/mineralogy|Hydrothermal synthesis}}
{{short description|Circulation of water driven by heat exchange}}
'''Hydrothermal circulation''' in its most general sense is the circulation of hot water ([[Ancient Greek]] ὕδωρ, ''water'',<ref name="Liddell & Scott">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.</ref> and θέρμη, ''heat'' <ref name="Liddell & Scott"/>). Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's [[Crust (geology)|crust]]. In general, this occurs near [[volcanic]] activity,<ref>{{Cite journal|date=2008-10-15|title=Low-temperature hydrothermal alteration of intra-caldera tuffs, Miocene Tejeda caldera, Gran Canaria, Canary Islands|url=https://www.sciencedirect.com/science/article/abs/pii/S0377027308002163|journal=Journal of Volcanology and Geothermal Research|language=en|volume=176|issue=4|pages=551–564|doi=10.1016/j.jvolgeores.2008.05.002|issn=0377-0273|last1=Donoghue|first1=Eleanor|last2=Troll|first2=Valentin R.|last3=Harris|first3=Chris|last4=O'Halloran|first4=Aoife|last5=Walter|first5=Thomas R.|last6=Pérez Torrado|first6=Francisco J.|bibcode=2008JVGR..176..551D|url-access=subscription}}</ref> 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]], or as the result of [[orogeny]] or [[metamorphism]]. Hydrothermal circulation often results in [[Hydrothermal mineral deposit|hydrothermal mineral deposits]].

==Seafloor hydrothermal circulation==
Hydrothermal circulation in the [[ocean|oceans]] is the passage of the water through [[mid-oceanic ridge]] systems.

The term includes both the circulation of the well-known, high-temperature vent waters near the ridge crests, and the much-lower-temperature, [[diffusion|diffuse]] flow of water through sediments and buried [[basalt]]s further from the ridge crests.<ref>{{Citation|last1=Wright|first1=John|title=Hydrothermal circulation in oceanic crust|date=1998|url=https://linkinghub.elsevier.com/retrieve/pii/B9780750639835500060|work=The Ocean Basins: Their Structure and Evolution|pages=96–123|publisher=Elsevier|language=en|doi=10.1016/b978-075063983-5/50006-0|isbn=978-0-7506-3983-5|access-date=2021-02-11|last2=Rothery|first2=David A.|url-access=subscription}}</ref>  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]] 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]]s are locations on the seafloor where hydrothermal fluids mix into the overlying ocean.<ref name="German-2014">{{Citation|last1=German|first1=C.R.|title=Hydrothermal Processes|date=2014|url=https://linkinghub.elsevier.com/retrieve/pii/B9780080959757006070|work=Treatise on Geochemistry|pages=191–233|publisher=Elsevier|language=en|doi=10.1016/b978-0-08-095975-7.00607-0|isbn=978-0-08-098300-4|access-date=2021-02-11|last2=Seyfried|first2=W.E.|url-access=subscription}}</ref> Perhaps the best-known vent forms are the naturally occurring [[chimney]]s referred to as [[black smoker]]s.<ref name="German-2014" />

==Volcanic and magma related hydrothermal circulation==
[[File:Taal Crater Lake (39228545370).jpg|thumb|[[Taal Volcano Main Crater Lake]], where hydrothermal circulating convection cells exist]]
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]] or [[volcanic]] vent, comes into contact with the [[groundwater]] system where permeability allows flow.<ref name="Cardenas-2012">{{Cite journal|last1=Bayani Cardenas|first1=M.|last2=Lagmay|first2=Alfredo Mahar F. |author-link2= Mahar Lagmay |last3=Andrews|first3=Benjamin J.|last4=Rodolfo|first4=Raymond S.|last5=Cabria|first5=Hillel B.|last6=Zamora|first6=Peter B.|last7=Lapus|first7=Mark R.|date=January 2012|title=Terrestrial smokers: Thermal springs due to hydrothermal convection of groundwater connected to surface water: SPRINGS DUE TO HYDROTHERMAL CONVECTION|journal=Geophysical Research Letters|language=en|volume=39|issue=2|pages=n/a|doi=10.1029/2011GL050475|doi-access=free}}</ref><ref>{{Cite journal|last1=Donoghue|first1=Eleanor|last2=Troll|first2=Valentin R.|last3=Harris|first3=Chris|last4=O'Halloran|first4=Aoife|last5=Walter|first5=Thomas R.|last6=Pérez Torrado|first6=Francisco J.|date=October 2008|title=Low-temperature hydrothermal alteration of intra-caldera tuffs, Miocene Tejeda caldera, Gran Canaria, Canary Islands|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027308002163|journal=Journal of Volcanology and Geothermal Research|language=en|volume=176|issue=4|pages=551–564|doi=10.1016/j.jvolgeores.2008.05.002|bibcode=2008JVGR..176..551D|url-access=subscription}}</ref> This convection can manifest as [[Hydrothermal explosion|hydrothermal explosions]], [[Geyser|geysers]], and [[Hot spring|hot springs]], although this is not always the case.<ref name="Cardenas-2012" />  

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 persistence 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.<ref name="Cardenas-2012" /> A good environment to observe this phenomenon is in [[Volcanogenic lake|volcanogenic lakes]] where hot springs and geysers are commonly present.<ref name="Cardenas-2012" /> 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.<ref name="Cardenas-2012" />

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.<ref name="Cardenas-2012" />  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]]
* 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]] deposit formation and a cornerstone of most theories on [[ore genesis]].

===Hydrothermal ore deposits===
During the early 1900s, various geologists worked to classify hydrothermal ore deposits that they assumed formed from upward-flowing aqueous solutions. [[Waldemar Lindgren]] (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.<ref>W. Lindgren, 1933, ''Mineral Deposits'', McGraw Hill, 4th ed.</ref> Recent studies retain only the ''epithermal'' label.  John Guilbert's 1985 revision of Lindgren's system for hydrothermal deposits includes the following:<ref>Guilbert, John M. and Charles F. Park, Jr., 1986, ''The Geology of Ore Deposits'', Freeman, p. 302 {{ISBN|0-7167-1456-6}}</ref>

* Ascending hydrothermal fluids, [[Magmatic water|magmatic]] or [[meteoric water]]
** [[Porphyry copper]] and other deposits, 200–800&nbsp;°C, moderate pressure
** Igneous metamorphic, 300–800&nbsp;°C, low to moderate pressure
** Cordilleran veins, intermediate to shallow depths
** Epithermal, shallow to intermediate, 50–300&nbsp;°C, low pressure
* Circulating heated meteoric solutions
** [[Carbonate hosted lead zinc ore deposits|Mississippi Valley-type deposits]], 25–200&nbsp;°C, low pressure
** [[Uranium ore deposits|Western US uranium]], 25–75&nbsp;°C, low pressure
* Circulating heated seawater
** [[Volcanogenic massive sulfide ore deposit|Oceanic ridge deposits]], 25–300&nbsp;°C, low pressure

==See also==
*[[Volcanogenic massive sulfide ore deposit]]
*[[Geothermal gradient]]
*[[Hydrothermal synthesis]]

==References==
{{Reflist}}

{{physical oceanography}}

[[Category:Geological processes]]
[[Category:Physical oceanography]]