Mechanisms for tectonic erosion of an accretionary complex in the d'Entrecasteaux Zone-New Hebrides Island arc collision zone

Conference · Fri Jun 01 04:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6266337

Collot, J Y ^[1]; Fisher, M A ^[2]

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1. Orstom, Villefranche-sur-mer (France)
2. Geological Survey, Menlo Park, CA (USA)

In the southwest Pacific Ocean the d'Entrecasteaux Zone (DEZ) is an arcuate submarine mountain chain that collides with the central part of the New Hebrides island arc. The collision zone moves slowly (2.5 cm/yr) northward along the trench, owing to the small oblique angle between the DEZ and the azimuth of convergence. Extensive Seabeam bathymetry as well as single- and multichannel seismic reflection data were collected over both the collision zone and the accretionary wedge that lies south of this zone. These data indicate that the accretionary complex underwent considerable tectonic erosion in response to oblique subduction of the DEZ during the past 8 Ma. Simplified calculation indicates that the mean erosional rate of this complex is 800-900 km{sup 3}/Ma. The main mechanisms for tectonic erosion of the accretionary complex involve mass wasting and extensional tectonics. First, mobilization and mass wasting of accreted rocks result in overlapping slump masses that blanket the arc slope. Second, block sliding along an extensional detachment within accreted rocks strips off the upper (about 1 km) part of the accretionary complex. Third, as the DEZ moves northward, the accreted rocks in the wake of the DEZ lose support and collapse along large normal faults that trend oblique to the arc slope. An additional errosive mechanism involves the formation of a deep subcircular reentrant into the accretionary complex; the reentrant is believed to be a scar caused by the collision and subduction of a seamount. The reentrant cuts downward through the accreted rocks almost to the depth of the abyssal oceanic plain.

• OSTI ID: 6266337
• Report Number(s): CONF-900702--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:6
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
EROSION
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
ISLANDS
NEW HEBRIDES ISLANDS
PACIFIC OCEAN
SEAS
SURFACE WATERS
TECTONICS