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Abstract: Structural Styles of the Foldbelt Associated to the Maranon-Oriete-Putumayo (MOP) Foreland Basins

Jerome J. Kendall, Antenor M. Aleman, Jaime Guerra

Along strike variations in structural style of the foldbelt associated with the MOP basins reflect changes in mechano-stratigraphy and cross sectional taper in space and time. Oblique convergence of the Farallon/Nazca and South America plates accounts for strain partitioning along the foldbelt and significant orogen parallel strike slip faulting. Inversion of Jurassic grabens was coeval with compressional deformation along the entire foldbelt. In the Colombia-Ecuador segment, the late Senonian Peruvian phase of the Andean Orogeny was dominated by thin-skinned deformation coeval with collision of allochthonous terranes along the Peltetec Fault. The buttressing effect of the Jurassic plutons along the Cosanga/Mendez Fault accounts for changes in deformation to thick-skinned style from Middle Eocene (Incaic Phase) onward (Quechua Phase).

Near the Peru-Ecuador border the margin changed southward to an arc-trench system. Deformation also changed from basement involved near and along the "Maranon Geanticline" during Late Cretaceous and Paleogene to a salt related fold and thrust belt from Late Miocene onward. Seismic data in the Santiago and Huallaga foldbelts documents outward and lateral salt movement since Mesozoic enhanced by Jurassic extension and by Late Cretaceous to Paleogene molasse deposition. Late Miocene/Pliocene compressional deformation partially overprinted these early salt structures. Folding is characterized by anticlinal thickening and synclinal thinning of the salt, and faulting is dominated by back thrusts with diffuse forward-vergent thrusts. Salt piercement accounts for narrow periclinal structures nd enlargement of preexisting broad synclines. The frontal thrust is characterized by box-folds, overturned folds and upright folds above a major salt core. There is a lack of a preferred structural vergence of ramps and folds.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela