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| Titel |
Implication for horizontally-elongated fluid flow inferred from heat flow measurements in the Iheya-North hydrothermal field, Okinawa Trough back-arc basin |
| VerfasserIn |
Yuka Masaki, Masataka Kinoshita, Yoshifumi Kawada |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037034
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| Zusammenfassung |
| The Okinawa Trough is a back-arc basin located in the southwestern part of Japan. It is
considered to be in the initial stage of rifting of continental crust, and the activity generates
volcanic edifices in this area, accompanied by hydrothermal circulation. The Iheya-North is
one of the most active hydrothermal fields among them. As a proposed drilling site for the
Integrated ocean Drilling Program, extensive geophysical surveys have been carried out
including single-channel seismic imaging, and precise side-scan sonar imaging by using
autonomous underwater vehicle “Urashima” of Japan Agency for Marine-Science and
Technology.
In the recent few years, we have measured heat flow in and around the Iheya-North
hydrothermal field to understand the spatial of hydrothermal circulation in detail. 78
measurements show that heat flow is higher than 10 W/m2 with in 0.5 km of the
hydrothermal vent complex, that it gradually decrease eastward to < 1 W/m2, and that very
low heat flow around 0.01 W/m2 is observed at 1.5 km east from the hydrothermal field. The
average heat flow outside of Iheya-North is ~0.1 W/m2.
The low heat flow to the east is most likely caused by an inward flow of seawater into the
formation. Seismic and side-scan sonar images as well as piston core samples suggest an
impermeable sediment layer to a few hundreds meters below the seafloor in this area. This
sediment layer should work as a hydrological barrier to suppress flow through the
seafloor, whereas seawater can penetrate into the formation at 1.5 km east of the
hydrothermal field, where sidescan images suggest coars sediments on the seafloor. We
infer that the hydrothermal circulation within the Iheya-North involves one with
a horizontally-elongated scale (~1.5 km horizontal vs. ~a few hundreds meters
vertical).
We performed numerical calculations of fluid flow and heat transportation to give
constraints on the depth of hydrothermal circulation, the magnitude of darcy velocity, and the
permeability at depth. The simulated results will be compared with measured heat flow
distribution and will be checked for the larger or smaller circulation scale proposed from heat
flow or fluid geochemistry data. |
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