Mathematics – Logic
Scientific paper
Apr 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992e%26psl.109..463m&link_type=abstract
Earth and Planetary Science Letters, Volume 109, Issue 3-4, p. 463-468.
Mathematics
Logic
4
Scientific paper
The fluid flow regime of accretionary prisms influences their morphology and dynamics, and is closely interrelated with deformation. For example, the Lesser Antilles prism shows drainage principally along channels provided by tectonic structures such as thrusts and the basal decollement. A similar behaviour has been suggested for the Nankai prism, and this was investigated during ODP Leg 131. Coring at site 808 penetrated the entire prism and underthrust sediments, and allowed detailed documentation of structures seen in the cores. However, neither the frontal thrust nor the decollement show any visible sign of channelised fluid flow. No veins, mineralised surfaces or clastic dykes were observed. The single clastic dyke seen within the prism appears unrelated to a deformation zone. On the other hand, small-scale structures such as faults and deformation bands are unusually numerous in the Nankai prism, and colour and diagenetic changes within them suggest that they may have acted as micro-conduits for drainage. Further contrasts with other prisms are shown by the sequence of deformation at Nankai and the relative paucity of deformation in the underthrust material.
Therefore, the tectonic and fluid flow regime at site 808 differs from the expected pattern. Marked increase in porosity immediately below the decollement hints at overpressuring in this zone, but the structures show no record of localised fluid activity. The structural geological observations throughout the Nankai prism are more consistent with bulk, pervasive dewatering, perhaps utilising the abundant deformation microstructures.
Byrne Tim
Karig Dan
Lallemant Siegfried
Maltman Alex
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