HR: 1400h
AN: T43A-07 [Abstracts]
TI: The Close Connection Between the Subduction Processes, the Morphology of the Continental
Margin and the Marine Basins on the accretionary segment of the Chilean Margin
AU: * Contardo, X J
EM: xcontardo@ucn.cl
AF: Programa de Doctorado en Ciencias,mención Geología.
Depto. Cs. Geológicas
Universidad Católica del Norte, Avenida Angamos 0610
Casilla 1280, Antofagasta, 2 , Chile
AU: Cembrano, J M
EM: jcembrano@ucn.cl
AF: Programa de Doctorado en Ciencias,mención Geología.
Depto. Cs. Geológicas
Universidad Católica del Norte, Avenida Angamos 0610
Casilla 1280, Antofagasta, 2 , Chile
AB:
The differences observed in the morphology of the accretionary segment of the Chilean margin and the
architecture of the associated marine basins, are indicative of variations in the degree of erosion-accretion and
uplift of the prism at different latitudes of the margin.
The geometry of the slope basins as wedge-shaped half graben basins is controlled by differential subsidence
and uplift of the upper levels of the slope. The dynamics of the deposition and deformation of the sequences
suggest alternating tectonic events of extension, compression (or transpression) and relative stability. The main
geodynamic elements controlling the tectonic evolution of the Chilean margin can be grouped into factors
associated with the subducting oceanic Nazca Plate and those related to mass transfer processes. They
influence the geometry and deformation of slope basins.
Accretionary and non-accretionary or erosional episodes are linked to temporal variations in sediment thickness
of the trench, which is mainly associated with climatic fluctuations. Glacial material flux contributed significantly
to the trench infill, and has also likely increased accretion rates. In some cases an accelerated sediment supply
to the trench may cause unsustainable rates. This can induce subsidence in the trench and sediment
subduction to the base of the prism, which drives more basal underplating and strong uplift localized near
surface extension in the entire convergent system.
The examination of the seismic lines acquired during a Chilean expedition in the RV Vidal Gormaz suggests
differential subsidence controlled by displacement on flanking faults as well as pre-kinematic, syn-kinematic and
post-kinematic deposition.
The thickness of basins also will influence the amount of sediment which is either distributed from the shelf to
the trench, or trapped on the slope basins. The analyzed slope basins, between 33°30' - 36°50' S,
exhibit variations along the margin. The deepest basin is observed near the Juan Fernandez Ridge (JFR)
intersection with the margin, on seismic line VG02-18 (~1 km). While thinner sequences are observed to
the south, along VG02-10 (~0,27 km and ~0,45 km) and VGO2-5 (~0 4 km and ~0,5 km).
In proximity to the JFR, the high subsidence rate on a slope basin of the seismic line VG02-18, is influenced by
the tectonic erosion at the base of the accretionary wedge linked with the progressive positions of subducting
seamounts.
The alternation between syn-tectonic and pre-post tectonic deposition documents cyclic tectonic events which
can be associated with the accretionary and the non-accretionary, or erosive episodes for the development of the
south Chile margin. The most probable mass transfer mode in the South Chilean accretive system is partly
frontal accretion and partly underthrusting of sediment entering the trench with potential underplating. Frontal and
basal accretion leads to characteristic growth patterns of the forearc area.
In this study, episodes of frontal accretion can be associated with pre-post tectonic sequences along the slope,
which evidences episodes of stability without deformation of sequences and parallel continuous deposition of
sediment. The basal accretion of large volumes of underplated sediment beneath the buttress undergoes
deformation and tilting and can be associated with the syn-tectonic units.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4558 Sediment transport (1862)
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Joint Assembly