Hydrothermal circulation
Hydrothermal circulation in its most general sense is the circulation of hot water; 'hydros' in the Greek meaning water and 'thermos' meaning heat. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust
Crust (geology)
In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle...

. This generally occurs near volcanic activity, but can occur in the deep crust related to the intrusion of granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

, or as the result of orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

 or metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...


Seafloor hydrothermal circulation

Hydrothermal circulation in the ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s 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, diffuse
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 flow of water through sediments and buried basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

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 a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 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
Hydrothermal vent
A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

s are locations on the seafloor where hydrothermal fluids mix into the overlying ocean. Perhaps the best known vent forms are the chimney
A chimney is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. Chimneys are typically vertical, or as near as possible to vertical, to ensure that the gases flow smoothly, drawing air into the combustion in what is known as the...

s referred to as black smokers.

Volcanic and magma related hydrothermal circulation

Hydrothermal circulation is not limited to ocean ridge environments. The source water for hydrothermal explosion
Hydrothermal explosion
Hydrothermal explosions occur when superheated water trapped below the surface of the earth rapidly converts from liquid to steam, violently disrupting the confining rock. Boiling water, steam, mud, and rock fragments called breccia are ejected over an area of a few meters up to several kilometers...

s, geyser
A geyser is a spring characterized by intermittent discharge of water ejected turbulently and accompanied by a vapour phase . The word geyser comes from Geysir, the name of an erupting spring at Haukadalur, Iceland; that name, in turn, comes from the Icelandic verb geysa, "to gush", the verb...

s and hot spring
Hot spring
A hot spring is a spring that is produced by the emergence of geothermally heated groundwater from the Earth's crust. There are geothermal hot springs in many locations all over the crust of the earth.-Definitions:...

s is heated groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 convecting below and lateral to the hot water vent. Hydrothermal circulating convection cells exist any place an anomalous source of heat, such as an intruding magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...

 or volcanic vent, comes into contact with the groundwater system.

Deep crust

Hydrothermal also refers to the transport and circulation of water within the deep crust, generally 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
    Great Artesian Basin
    The Great Artesian Basin provides the only reliable source of freshwater through much of inland Australia. The basin is the largest and deepest artesian basin in the world, stretching over a total of , with temperatures measured ranging from 30°C to 100°C...

  • Dewatering of metamorphic rocks which liberates water
  • Dewatering of deeply buried sediments

Hydrothermal circulation, particularly in the deep crust, is a primary cause of mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 deposit formation and a cornerstone of most theories on ore genesis
Ore genesis
The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....


Hydrothermal ore deposits

During the early 1900s various geologists worked to classify hydrothermal ore deposits which were assumed to have formed from upward flowing aqueous solutions. Waldemar Lindgren
Waldemar Lindgren
Waldemar Lindgren was a Swedish-American geologist. Lindgren was one of the founders of modern Economic geology.-Biography:...

 developed a classification based on interpreted decreasing temperature and pressure conditions of the depositing fluid. His terms: hypothermal, mesothermal, epithermal and teleothermal were based on decreasing temperature and increasing distance from a deep source. Only the epithermal has been used in recent works. John Guilbert's 1985 redo of Lindgren's system for hydrothermal deposits includes the following:
  • Ascending hydrothermal fluids, magmatic
    Magmatic water
    Magmatic water or juvenile water is water which exists within and in equilibrium with a magma or water rich volatile fluids which are derived from a magma. This magmatic water is released to the atmosphere during a volcanic eruption...

     or meteoric water
    Meteoric water
    Meteoric water is a hydrologic term of long standing for water in the ground which originates from precipitation. This includes water from lakes, rivers, and icemelts, which all originate from precipitation indirectly.- Overview :...

    • Porphyry copper and other deposits, 200 - 800 °C, moderate pressure
    • Igneous metamorphic, 300 - 800 °C, low - 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
      Carbonate hosted lead zinc ore deposits
      Carbonate-hosted lead-zinc ore deposits are important and highly valuable concentrations of lead and zinc sulfide ores hosted within carbonate formations and which share a common genetic origin....

      , 25 - 200 °C, low pressure
    • Western US uranium, 25 - 75 °C, low pressure
  • Circulating heated seawater
    • Oceanic ridge deposits
      Volcanogenic massive sulfide ore deposit
      Volcanogenic massive sulfide ore deposits are a type of metal sulfide ore deposit, mainly Cu-Zn-Pb which are associated with and created by volcanic-associated hydrothermal events in submarine environments....

      , 25 - 300 °C, low pressure

See also

  • convection
    Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

  • ocean current
    Ocean current
    An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...

  • thermohaline circulation
    Thermohaline circulation
    The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

  • metamorphic rocks
  • volcanogenic massive sulfide ore deposit
    Volcanogenic massive sulfide ore deposit
    Volcanogenic massive sulfide ore deposits are a type of metal sulfide ore deposit, mainly Cu-Zn-Pb which are associated with and created by volcanic-associated hydrothermal events in submarine environments....

  • volcanic gas
    Volcanic gas
    |250px|thumb|right|Image of the [[rhyolitic]] [[lava dome]] of [[Chaitén Volcano]] during its 2008-2010 eruption.Volcanic gases include a variety of substances given off by active volcanoes...

  • geothermal
  • hydrothermal synthesis
    Hydrothermal synthesis
    Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". The term "hydrothermal" is of geologic origin. Geochemists and mineralogists have studied hydrothermal phase...

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