Development of Continental Slope Basins Along the Convergence Zone Off South America
Stephen H. Johnson, L. D. Kulm, 1977. "Development of Continental Slope Basins Along the Convergence Zone Off South America", Geology of Continental Margins, Joseph R. Curray, William R. Dickinson, Wallace G. Dow, Kenneth O. Emery, Donald R. Seely, Peter R. Vail, Hunter Yarborough
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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 (10–15°) 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 (5.7–6.2 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 (1.6–3.0 km/sec). A metamorphic block forms the basement of the landward portions of the upper slope basins, whereas a thick highly diffracting section (>3.0 km/sec) underlies the seaward part. Smaller basins may occur 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.
Although there is no clear indication of imbricate thrust sheets within the continental slope seismic reflection sections, the ruptured oceanic slab, the migrating basins, and the thick diffracting section are suggestive of the imbricate thrust model. Continual movement along new and older imbricate thrusts within the continental slope may produce the ubiquitous diffracting section sandwiched between the oceanic slab and slope basins and may disturb existing basin deposits in some areas.
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Written in 1977 the publication presents interpretations of then-new data bearing on the geology and geophysics of continental margins. The book includes a discussion of plate tectonics and evolution of continental margins; presentations on the stratigraphy and structure of pull-apart and compressional margin;, prospective petroleum source rocks, their organic content, rate of burial, and distribution on slopes and rises of different margin types; prospective reservoir rock patterns in relation to depositional processes and to the sedimentary and structural histories for different types of continental margins; and seismic recognition of depositional facies on slopes and rises for different margin types with varying rates of sediment supply during eustatic sea-level changes.