Initial Tectonic Deformation of Hemipelagic Sediment at the Leading Edge of the Japan Convergent Margin.

Arthur, M. A., Carson, B. and von Huene, Roland (1980) Initial Tectonic Deformation of Hemipelagic Sediment at the Leading Edge of the Japan Convergent Margin. Open Access Initial Reports of The Deep Sea Drilling Project, 56/57 . pp. 521-568. DOI 10.2973/dsdp.proc.5657.115.1980.

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Diatomaceous mudstones at depth under the deep sea terrace and
the trench inner slope off Japan have been variably affected by tectonic
stress. Veins, healed fractures, and microfaults occur at all sites
except the shallow Site 435 on the upper trench inner slope and Site
436 on the Pacific Plate. Veins, fractures, and faults occur in cores
from below 620 meters (lower to middle Miocene) in the landward
sites (438 and 439) on the deep sea terrace, and are probably related
to normal faulting seen in seismic records. The depth to "consolidated"
sediment and to the first occurrence of veins and healed fractures
shallows progressively toward the trench. The intensity of deformation
also appears to increase seaward. However, no sediments
younger than upper Pliocene are deformed. Open fractures may exist
in situ at Sites 434 and 441 at levels between about 150 and 500 meters
The Japan Transect sediments—in contrast to deposits in the zone
of initial deformation at other convergent margins—though highly
deformed, are not highly overconsolidated. However, sediment at
depth in the trench inner slope sites is overconsolidated relative to
that at the same depth in the landward reference site. None of the deformed
Japan margin sediments recovered at Legs 56 and 57 sites
originated by accretion of oceanic plate material—also in contrast to
sediments at some of the margins previously studied. We suggest that
tectonic stress related to convergence has been communicated to the
slope sediments on the trench inner slope, either continuously or periodically,
causing rapid tectonic dewatering and inducing fracturing
and faulting. If episodic, the latest of these deformational periods
may have occurred during the late Pliocene. The faults and fractures
are either rehealed by continued overburden pressure (sediment loading)
or may remain open at shallower levels. Fracturing and dewatering
of semiconsolidated sediment beneath an unconsolidated but impermeable
mud veneer may cause overpressured zones at depths of
200 to 500 meters. These overpressured zones possibly locally reduce
shear strength and cause downslope mass movement of sediment,
even on low-angle slopes on the trench inner slope.

Document Type: Article
Keywords: Japan Convergent Margin, Tectonic deformation, Hemipelagic Sediments
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.2973/dsdp.proc.5657.115.1980
Projects: DSDP
Date Deposited: 10 Oct 2016 13:14
Last Modified: 10 Oct 2016 13:14

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