Fluid venting activity within the eastern Nankai Trough accretionary wedge; a summary of the 1989 Kaiko-Nankai results

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doi: 10.1016/0012-821X(92)90094-C
Author(s): Le Pichon, X.; Kobayashi, K.; Cadet, Jean-Paul; Ashi, J.; Boulègue, Jacques; Chamot-Rooke, Nicolas; Fiala-Médioni, Aline; Foucher, J. P.; Furuta, T.; Gamo, T.; Henry, P.; Iiyama, J. T.; Lallemand, Serge E.; Lallemant, S. J.; Ogawa, Y.; Sakai, H.; Segawa, J.; Sibuet, Myriam; Taira, A.; Takeuchi, A.; Tarits, P.; Toh, H.
Japan, Kaiko-Nankai Scientific Crew
Author Affiliation(s): Primary:
Ec. Norm. Supér., Lab. Géol., Paris, France
Ec. Norm. Supér., France
Tokyo Univ., Japan
Volume Title: Fluids in convergent margins
Volume Author(s): Kastner, M., editor; Le Pichon, Xavier
Source: Earth and Planetary Science Letters, 109(3-4), p.303-318; Fluids in subduction zones, Paris, France, Nov. 5-6, 1991, edited by M. Kastner and Xavier Le Pichon. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 36 refs.; illus. incl. sects., sketch maps
Summary: Fluid flow manifestations within the outer 20 km of the E Nankai accretionary wedge, between water depths of 4000 and 2000 m, are concentrated near the outcrop of a shallow detachment fault immediately behind the frontal thrust near a depth of 3800 m and along a probable strike-slip fault, on the top of a 2000 m deep 'pop-up' structure, 20 km inside the wedge. Using sub-bottom T measurements, the authors estimate Darcy upward flow velocities below clam colonies at the 3800 m site and show that one can associate a narrow range of velocities with the different types of colonies. Then, combining a statistical survey of the distribution of colonies with the velocity estimates, the authors compute a yearly outflow budget of 200 m3 per metre of width of the wedge in the toe area. This is 40 times larger than the amount expected from steady-state compactive dewatering, but the authors propose that 80-90% of this flow is produced by shallow sea-water convection. Because variations in sea-bottom T were too large, fluid outflow budgets in the 2000 m venting area could not be estimated. However, 20 000 and 130 000 yr-old shells fossilized within widespread carbonate concentrations indicate that fluid flow has been active in the 2000 m venting area since at least 130 000 yr ago, probably in a sporadic fashion. Chemical evidence indicates that a significant part of the fluid is coming from a depth of at least several 100 m. Sub-bottom T measurements over a period of two months in the 3800 m venting site show fluctuations of 20-30% in the venting velocity below an active colony that have an apparent period of two weeks. Although the fluid circulation appears to be controlled by active faults at least in the shallow part of the wedge, not every active fault corresponds with an aquifer. [Authors' abstract]
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Accretionary wedges; Active faults; Dehydration; Faults; Fluid phase; Leg 131; Marine sediments; Nankai Trough; North Pacific; Northwest Pacific; Ocean Drilling Program; Ocean floors; Oceanography; Pacific Ocean; Pore water; Sediments; Troughs; Vents; West Pacific
Coordinates: N333500 N335500 E1381000 E1374000
Record ID: 1992024685
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom