summit that inject volatiles into the overlying water
column at a depth of B130 m. Loihi Seamount,
situated on the south-eastern flank of the island of
Hawaii, also has active ventsnear its summit at a
depth of B1000 m. Loihi is of considerable importance because it is thought to be the current locus of
the Hawaiian hot spot. Loihi lavas and hydrothermal
fluids contain helium with a very primitive signature
ofR=R A ¼ 25230, indicating a deep mantle origin.
It has been known for some time that hydrothermal venting on Loihi Seamount produces water
column plumes that can bedetected with tracers such
as temperature, manganese, iron, and methane.
However, these tracers are not useful for far-field
studies of the Loihi plume because they are either
rapidly removed from the water column or arepresent in low concentrations. Because helium is a
stable, conservative tracerthat is highly enriched in
Loihi vent fluids, the helium signal from Loihi is
detectable at considerable distances from the Hawaiian Islands. As shown in Figure 6, a map of
dð
3 HeÞ on a surface at 1100 m depth reveals a
3
Herich plume that extends eastward from the Hawaiian
Islands for several thousand kilometers, reaching the
coast of Mexico at its greatest extent. This far-field
plume produced by the Hawaiian hot spot clearly
defines an eastward transport at B1000 m depth in
this region ofthe north Pacific. Furthermore, because
the end-member helium introduced at Loihi has a
3 He/
4 He ratio three times higher than mid-ocean
ridge helium, it should be possible to distinguish the
Loihihelium from mid-ocean ridge helium with accurate measurements of
3 He and
4 He concentrations.
The ability to distinguish hot spot helium from midocean ridge helium has been demonstrated for the
Loihi helium plume near Hawaii but not yet in the
far-field.
Subduction Zone Helium
Submarine volcanism also occurs alongconvergent
margins, particularly in regions where two oceanic
plates are converging. However, very little is known
about the incidence of submarine hydrothermal activity associated with this type of volcanism. Studies
of subaerial volcanoes at convergent margins have
shown that these volcanoes emit mantle helium with
an isotopic ratio of R=R A ¼ 327, lower than in midocean ridges. Thus the volcanic helium from subduction zones represents a third type of mantle helium that isisotopically distinct from mid-ocean ridge
and hot spot helium.
One clear example of oceanic helium plumesfrom
subduction zone volcanism is shown in Figure 7,
which shows the results of a survey along the
southern end of the Kermadec Arc northeast of New
Zealand. The Kermadec Arc consists of a series of
discrete volcanoes generated by the subduction of the
Pacific plate beneath the Australian plate. At the
southern end of the arcthese volcanoes are submarine, while farther north some of them are subaerial volcanoes, including Curtis Island, Macauley
Island, and Raoul Island. The survey shown in
Figure 7 consisted of a series of hydrographic casts
along the arc, and many of the casts were lowered
directly over the summits of these arc volcanoes. The
section shown in Figure 7B shows a series of
3
Herich found at a variety of depths between 150 m for
Rumble III volcano down to 1400 m for Brothers
volcano. A plot of
3 He versus
4 He concentration for
these samples (notshown), indicated an average
3 He/
4
He ratio of R=R A ¼ 6, in agreement with previous studies of helium from subaerial subduction
zone volcanoes. Although the lateral extent of the
helium plumes from the Kermadec Arc is not known,
this survey confirms that subduction zone volcanoes
do produce helium plumes that can be used to trace
ocean currents. Furthermore, these subduction zone
plumes are potentially quite valuable for tracer
studies, since they occur at a wide variety of depths
and are generally much shallower than plumes produced at mid-ocean ridges (Figure 7B).
See also
Hydrothermal Vent Deposits. Hydrothermal Vent
Fluids,
Chemistry
of.
Mid-Ocean
Ridge
Geochemistry and Petrology. Noble Gases and
the Cryosphere. Tritium–Helium Dating.
Further Reading
Clarke WB, Beg MA, and Craig H (1969) Excess
3 He in
the sea: evidence for terrestrial primordial helium.
Earth and Planetary Science Letters 6: 213--220.
Craig H, Clarke WB, and Beg MA (1975) Excess
3 He in
deep water on the East Pacific Rise. Earth and Planetary
Science Letters 26: 125--132.
Craig H and Lupton JE (1981) Helium-3 and mantle
volatiles in the ocean and the oceanic crust. In: Emiliani
C (ed.) The Sea, vol. 7, pp. 391–428. New York: Wiley.
Krylov A Ya, Mamyrin BA, Khabarin L, Maxina TI, and
Silin Yu I (1974) Helium isotopes in ocean floor
bedrock. Geokhimiya 8: 1220--1225.
Lupton JE (1983) Terrestrial inert gases: isotope tracer
studies and clues to primordial components in the
mantle. Annual Review of Earth and Planetary Science
11: 371--414.
VOLCANIC HELIUM 153
column at a depth of B130 m. Loihi Seamount,
situated on the south-eastern flank of the island of
Hawaii, also has active ventsnear its summit at a
depth of B1000 m. Loihi is of considerable importance because it is thought to be the current locus of
the Hawaiian hot spot. Loihi lavas and hydrothermal
fluids contain helium with a very primitive signature
ofR=R A ¼ 25230, indicating a deep mantle origin.
It has been known for some time that hydrothermal venting on Loihi Seamount produces water
column plumes that can bedetected with tracers such
as temperature, manganese, iron, and methane.
However, these tracers are not useful for far-field
studies of the Loihi plume because they are either
rapidly removed from the water column or arepresent in low concentrations. Because helium is a
stable, conservative tracerthat is highly enriched in
Loihi vent fluids, the helium signal from Loihi is
detectable at considerable distances from the Hawaiian Islands. As shown in Figure 6, a map of
dð
3 HeÞ on a surface at 1100 m depth reveals a
3
Herich plume that extends eastward from the Hawaiian
Islands for several thousand kilometers, reaching the
coast of Mexico at its greatest extent. This far-field
plume produced by the Hawaiian hot spot clearly
defines an eastward transport at B1000 m depth in
this region ofthe north Pacific. Furthermore, because
the end-member helium introduced at Loihi has a
3 He/
4 He ratio three times higher than mid-ocean
ridge helium, it should be possible to distinguish the
Loihihelium from mid-ocean ridge helium with accurate measurements of
3 He and
4 He concentrations.
The ability to distinguish hot spot helium from midocean ridge helium has been demonstrated for the
Loihi helium plume near Hawaii but not yet in the
far-field.
Subduction Zone Helium
Submarine volcanism also occurs alongconvergent
margins, particularly in regions where two oceanic
plates are converging. However, very little is known
about the incidence of submarine hydrothermal activity associated with this type of volcanism. Studies
of subaerial volcanoes at convergent margins have
shown that these volcanoes emit mantle helium with
an isotopic ratio of R=R A ¼ 327, lower than in midocean ridges. Thus the volcanic helium from subduction zones represents a third type of mantle helium that isisotopically distinct from mid-ocean ridge
and hot spot helium.
One clear example of oceanic helium plumesfrom
subduction zone volcanism is shown in Figure 7,
which shows the results of a survey along the
southern end of the Kermadec Arc northeast of New
Zealand. The Kermadec Arc consists of a series of
discrete volcanoes generated by the subduction of the
Pacific plate beneath the Australian plate. At the
southern end of the arcthese volcanoes are submarine, while farther north some of them are subaerial volcanoes, including Curtis Island, Macauley
Island, and Raoul Island. The survey shown in
Figure 7 consisted of a series of hydrographic casts
along the arc, and many of the casts were lowered
directly over the summits of these arc volcanoes. The
section shown in Figure 7B shows a series of
3
Herich found at a variety of depths between 150 m for
Rumble III volcano down to 1400 m for Brothers
volcano. A plot of
3 He versus
4 He concentration for
these samples (notshown), indicated an average
3 He/
4
He ratio of R=R A ¼ 6, in agreement with previous studies of helium from subaerial subduction
zone volcanoes. Although the lateral extent of the
helium plumes from the Kermadec Arc is not known,
this survey confirms that subduction zone volcanoes
do produce helium plumes that can be used to trace
ocean currents. Furthermore, these subduction zone
plumes are potentially quite valuable for tracer
studies, since they occur at a wide variety of depths
and are generally much shallower than plumes produced at mid-ocean ridges (Figure 7B).
See also
Hydrothermal Vent Deposits. Hydrothermal Vent
Fluids,
Chemistry
of.
Mid-Ocean
Ridge
Geochemistry and Petrology. Noble Gases and
the Cryosphere. Tritium–Helium Dating.
Further Reading
Clarke WB, Beg MA, and Craig H (1969) Excess
3 He in
the sea: evidence for terrestrial primordial helium.
Earth and Planetary Science Letters 6: 213--220.
Craig H, Clarke WB, and Beg MA (1975) Excess
3 He in
deep water on the East Pacific Rise. Earth and Planetary
Science Letters 26: 125--132.
Craig H and Lupton JE (1981) Helium-3 and mantle
volatiles in the ocean and the oceanic crust. In: Emiliani
C (ed.) The Sea, vol. 7, pp. 391–428. New York: Wiley.
Krylov A Ya, Mamyrin BA, Khabarin L, Maxina TI, and
Silin Yu I (1974) Helium isotopes in ocean floor
bedrock. Geokhimiya 8: 1220--1225.
Lupton JE (1983) Terrestrial inert gases: isotope tracer
studies and clues to primordial components in the
mantle. Annual Review of Earth and Planetary Science
11: 371--414.
VOLCANIC HELIUM 153