Abstract: Development of Continental-Slope Basins Along Convergence Zone Off South America

Stephen H. Johnson, L. D. Kulm

The rapidly converging Nazca and South American plates produce a complex geotectonic framework along the Peru continental margin. Rupture of oceanic layer 2 within segments of the Peru-Chile Trench forms large-scale basalt ridges and disturbed axial-turbidite basins adjacent to the margin. The shallow-dipping (10 to 15°) oceanic slab extends tens of kilometers beneath the continental slope as a coherent, but often faulted feature, becoming less coherent landward. The relation between this slab and a high-velocity (5.7 to 6.2 km/sec) metamorphic block which is the foundation for continental-shelf basins is unclear.

Prominent upper continental slope basins contain up to 2 km of sediment (1.6 to 3.0 km/sec). A metamorphic block forms the basement of the landward parts of the upper slope basins, whereas a thick highly diffracting section (> 3.0 km/sec) underlies the seaward part. Smaller basins may be present in the middle-slope region. Landward migration of the deposition centers in upper slope basins suggests uplift of the outer margin and therefore the accretion of trench sediments. Upper slope deposits are either complexly faulted or essentially undisturbed. Large ocean-plate features, namely the Nazca Ridge, appear to inhibit the development of slope basins.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC