HR: 1330h
AN: OS22A-1146    [PDF]
TI: The Matakaoa Margin Multiple Mudflows, North-East New Zealand
AU: * Lamarche, G
EM: g.lamarche@niwa.co.nz
AF: NIWA, PO Box 14901, Wellington, 6003 New Zealand
AU: Carter, L
EM: l.carter@niwa.co.nz
AF: NIWA, PO Box 14901, Wellington, 6003 New Zealand
AU: Migeon, S
EM: migeon@obs-vlfr.fr
AF: Geosciences Azur, BP 48, Villefranche/mer, 06235 France
AU: Collot, J
EM: collot@obs-vlfr.fr
AF: Geosciences Azur, BP 48, Villefranche/mer, 06235 France
AB: The 45 km-long, ~30 km-wide Matakaoa re-entrant near the collisional Australian-Pacific plate boundary off New Zealand, has incised the at least 1000 m-thick, seaward dipping sedimentary section of the East Cape margin. Swath bathymetry and seismic reflection data provide clear insights into the margin's evolution, and in particular the mechanisms associated with submarine debris avalanches and flows. The re-entrant morphology suggests active erosion at its head, as shown by pervasive gully formation, large slump blocks in the process of collapse, and an active, fan/channel system. Blocks up to 2.8 km across scatter the area north of the re-entrant, and indicate the large Matakaoa debris avalanche. North of the re-entrant, three major debris flows are identified within the first kilometres beneath seafloor. (1) The oldest flow is ~60 km wide and extends ~70 km north from a large basement anticline at the re-entrant mouth. At the base of the flow, coherent reflections indicate numerous imbricated thrusts and faults over a distance of at least 50 km. This may indicate viscous behaviour possibly due to dewatering during flow emplacement. (2) The second flow overlies the first over its entire ~70 km-length. Its western flank is eroded into a conspicuous 200 m-high NNE-trending scarp, outlined by numerous kilometre-scale angular blocks detached from the main body of the debris flow. The scarp forms the eastern limit of the major channel that guides turbidity currents descending from the re-rentrant. (3) The youngest flow, the Matakaoa debris flow, fills the major channel, and extends 200 km north. It appears contemporaneous with the Matakaoa avalanche. First estimates give debris flow volumes ranging 500-1000 km3. The eastern re-entrant is filled by an estimated 15 km3 of material slumped from the margin either contemporaneous with or post-dating the Matakaoa debris flow. Rapid sediment accumulation, from high discharge rivers draining the rapidly uplifting East Cape region, may provide enough material to generate ~20 km3 debris flows every 500-2000 yrs. Deposition of thick sediment piles about the faulted headward scarp of the re-entrant, coupled with the region's high seismicity, are prime factors controlling the multiple margin failures.
DE: 3022 Marine sediments--processes and transport
DE: 3045 Seafloor morphology and bottom photography
DE: 8015 Local crustal structure
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting