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Volcano No. 19, Tonga

Latitude: 24°48'S
Longitude: 177°1'E
Volcano 19 is a large stratovolcano located in the southernmost part of the Tonga arc. The volcano has a basal dimension of 14 x 12 km and rises from a water depth of 1400 m to 385 m. It has smooth flanks that rise to a complex summit peaking at 450 mbsl. The summit is dominated by an old caldera, an infilling cone, and a younger western caldera, all elongated in a NW–SE direction.

PISCES identified two large hydrothermal fields on Volcano 19. One is situated near the summit of the central cone between 385 and 540 m water depth. This is the biggest and hottest field which is known along the Tonga-Kermadec arc. The upper part of the central cone (an area of 800 x 800 m) is almost completely covered by Fe-oxyhydroxide crusts, formed from diffusely venting low temperature fluids. Chimneys composed of Feoxyhydroxides have formed where the venting fluids reach temperatures of 70°C. More focused, high temperature venting occurs along the narrow, NE-SW–trending ridge at the top of the cone complex. Here, clusters of large barite and anhydrite chimneys occur along a series of vertical dikes and faults. At slightly greater water depths (420–435 m) at the southern end of the ridge, large high-temperature chimneys show vigorous flow. Focused high-temperature venting also occurs at a water depth of 540 m in one of the shallow pit craters on the central cone. Here, small chimneys and low-relief mounds of barite and anhydrite protrude from the sediment in the pit. Clear two-phase venting occurs from the orifices of several chimneys.

A second, large area of low-temperature venting occurs among a swarm of dikes in the south wall of the western caldera. Here, Fe-oxyhydroxide crusts extend for more than 900 m along the base of the caldera wall and over a depth range of 985–850 m. Diffuse venting of warm fluids and mats of Fe-stained filamentous bacteria occur throughout this field. At the center of the field, large clusters of Fe-oxyhydroxide and silica chimneys cover an area of 200 x 300 m.

Mineral List

Anhydrite
Baryte
Chalcopyrite
Ferrihydrite
Galena
Goethite
Opal
Sphalerite
Sulphur
Wurtzite


10 entries listed. 10 valid minerals.

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References

Schwarz-Schampera, U., et al. (2007), Cruise Report SONNE 192/2, MANGO. Marine Geoscientific Research on Input and Output in the Tonga-Kermadec Subduction Zone.

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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