HR: 08:45h
AN: T41F-04    [Abstracts]
TI: Thermal regime from bottom simulating reflectors along the N Ecuador - S Colombia margin: relation between tectonic segmentation, thermal variation and the limit of the seismic rupture zones.
AU: * Marcaillou, B
EM: marcaill@obs-vlfr.fr
AF: University of Victoria, School of Earth and Ocean Sciences, Victoria, BC V8W 2Y2 Canada
AU: Spence, G
EM: gspence@uvic.ca
AF: University of Victoria, School of Earth and Ocean Sciences, Victoria, BC V8W 2Y2 Canada
AU: Collot, J
EM: collot@obs-vlfr.fr
AF: IRD / UMR Géosciences Azur, Observatoire océanologique de Villefranche sur mer - BP48, Villefranche sur mer, 06235 France
AU: Wang, K
EM: KWang@NRCan.gc.ca
AF: Pacific Geosciences Center, P.O. Box 6000, Sydney, BC V8L 4B2 Canada
AU: Ribodetti, A
EM: ribodeti@obs-vlfr.fr
AF: IRD / UMR Géosciences Azur, Observatoire océanologique de Villefranche sur mer - BP48, Villefranche sur mer, 06235 France
AB: In the North Ecuador South Columbian (NESC) convergent margin (0°N) three megathrust events, in 1942, 1958 and 1979, present rupture zones that abut one another. Multichannel seismic (MCS) reflection and bathymetric data acquired during the SISTEUR (2000) and AMADEUS (2005) cruises highlighted that the margin comprises four transverse segments (called, from south to north, the Esmeraldas, Manglares, Tumaco and Patia segments), each with clearly different tectonic and structural patterns. The central Manglares and Tumaco segments are separated by the newly discovered NW trending Manglares fault that matches the boundary between the 1958 and 1979 rupture zones. North of the fault, the fore-arc basin is shortened deformed and uplifted, while to the south the fore-arc basin, located landward of a prominent Outer Basement High (OBH), is widely subsiding and undeformed. Moreover, to the north of the Manglares fault, the underthrusting Nazca plate present an intense normal faulting is absent to the south. To investigate the relationships between seismogenesis and thermal structure along the plate boundary, we conducted thermal modelling constrained by sediment heat flow measurements and by heat flow derived from Bottom Simulating Reflectors (BSRs) on MCS lines collected during the SISTEUR and AMADEUS cruises. Just landward of the deformation front in the region of the Tumaco segment, a zone of anomalously low heat flow values is present and results in a thermal segmentation of the margin consistent with the tectonic segmentation. Finite-element thermal models carried out for each thermal segment show that: The along-strike heat flow variations are produced by changes in the age of the oceanic plate, the dip of the decollement and hydrothermal cooling due to the subduction of the strongly faulted part of the Nazca crust. The hypocenters for both the 1958 and 1979 earthquakes occurred at a depth on the interface where the temperature is ~160°C. For the seismogenic zone estimated from the aftershock area, its updip limit, for the 1942 and 1979 earthquakes, reaches the deformation front where our thermal models indicate temperatures from 50 to 60°C. Nevertheless, in between, the seismogenic zone of the 1958 event is restricted to a region landward of the prominent Outer Basement High where temperature appears to be ~100°C. This suggests that on the NESC margin the updip limit of the seismogenic zone may be controlled by very low temperature processes, except for the 1958 event for which the seismogenic updip limit appears to be related to the frontal OBH. In the vicinity of the Manglares fault the boundaries between thermal segments, tectonic segments and rupture zone are intriguingly consistent. A previous seismic rupture model proposed that the seismic coupling conditions beneath the OBH and an associated splay fault partially controlled the seaward rupture limit of the 1958 event landward of the OBH. We propose that normal faulting of the downgoing crust to the north of the fault and the absence of normal faulting to the south also contribute to differences in mechanical conditions near the deformation front. Thus, with the change occurring at the Manglares fault, these interplate mechanical variations may be associated with along-strike thermal variations and with the abrupt change in the fore-arc basin tectonics.
DE: 3004 Gas and hydrate systems
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8104 Continental margins: convergent
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8123 Dynamics: seismotectonics
SC: Tectonophysics [T]
MN: Fall Meeting 2005