Tectonics, structure, and sedimentary framework of the Peru-Chile Trench

Abstract

A comprehensive data set of more than 200 profiles across the Peru-Chile Trench between 4° and 45° S is used to describe the morphology and shallow structure of the trench axis and the downbending oceanic plate just prior to subduction. Five morphotectonic provinces (4°-I2°, 12°-17°, 17°-28°, 28°-45°S) show distinct changes in trench depth, axial sediment thickness, oceanic plate fault structures, and dip of the seaward trench slope. In general, the northern and southern regions are characterized by relatively shallow axial depths, moderate to thick trench axis turbidites, and a gently dipping seaward trench slope that exhibits minor normal faults. The deeper central area is almost barren of axial sediments and bends downward more steeply prior to subduction; bending has developed an extensive network of major faults with up to 1,000 m vertical offset on the seaward slope.Two systems of faulting occur in conjunction with subduction. Bending of the oceanic plate causes extensional stress and brittle failure of the upper oceanic crust, resulting in step faults, grabens, and tilted fault blocks on the seaward trench slope. Extensional faulting begins near the outer edge of the trench and develops progressively toward the trench axis. Basaltic ridges and tilted, uplifted trench fill at several locales along the trench can both be explained by thrust faulting. Compressional stress due to plate convergence occasionally can be transmitted seaward from beneath the continental margin through the oceanic plate, emerging as thrust faults within the oceanic crust near the trench axis. Axial turbidites are commonly tilted landward as they are uplifted, probably as a result of downward curving of the underlying thrust fault. Faulting of the oceanic crust prior to and during subduction may have important implications for evolution of convergent continental margins.

The relationship between plate curvature and elastic plate thickness: A study of the Peru‐Chile Trench

“…The rise reaches peaks of over 1200 m, far larger than most outer rises, which are rarely larger than 600 m [Caldwell et al, 1976;Turcotte et al, 1978;Jones et al, 1978;Carey and Dubois, 1981]. The bulge also has a gravity high of 80 mgal associated with it, which is larger than those observed over any other Pacific trench [Schweller et al, 1981].…”

“…However, geologic evidence of faulting in and near the trench also supports the existence of yielding due to the curvature of the plate. Faulting on the outer trench wall is not well resolved on the 5-minute grid of the data used in this study, but is apparent in profiles taken along ship tracks across the Peru-Chile Trench [Fisher and Raitt, 1962;Schweller et al, 1981]. These show numerous step faults and some graben structures.…”

“…However, this model requires that the flexural rigidity of the plate increase from the peak of the bulge to the trench wall, an area where the curvature is increasing and where it would be expected that flexural rigidity would decrease. Several observations, including the presence of thrust faulting near the base of the trench wall [Schweller et al, 1981] and a thickening of the plate approaching the trench axis [Hussong et al, 1976], may help explain the appearance of a stronger plate here. The 50 spacing of the bathymetric data makes resolution of faults impossible, and since the data is interpolated onto this spacing from ship track data sharp features such as faults are smoothed in the process.…”

“…The 50 spacing of the bathymetric data makes resolution of faults impossible, and since the data is interpolated onto this spacing from ship track data sharp features such as faults are smoothed in the process. Another possible explanation for this steepening, the accumulation of a wedge of sediments on the plate near the trench axis, appears to be ruled out by seismic cross-sections of the trench wall which indicate that sediment thickness remains constant from the outer rise nearly to the trench axis [Schweller et al, 1981]. Tables 1 and 3.…”

Constricción neógena en la Cordillera de la Costa, norte de Chile: neotectónica y datación de superficies con 21Ne cosmogónico

“…Las líneas continuas blancas exponen las trazas principales del Sistema de fallas de Atacama (SFA). La línea segmentada blanca en la fosa indica la zona con ausencia de sedimento según Schweller et al (1981). La diferencia de tonalidad de grises en la Placa Oceánica de Nazca indica el contorno de edad del fondo oceánico según Müller et al (1997).…”