Structural History of the Andean Foreland, Peru, and Its Relation to Subduction Zone Dynamics*
Alex Bump1; Lorcan Kennan2; and Jessica Fallon1
Search and Discovery Article #30062 (2008)
Posted August 4, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008
1Exploration and Production Technology, BP, Houston, TX ([email protected]).
2Tectonic Analysis Ltd., West Sussex, United Kingdom ([email protected]).
The present-day Andean foreland of Peru is composed of a number of discrete, structurally controlled sub-basins. All show a complex, polyphase deformation history. Seismic mapping, construction of balanced cross-sections and integration with wells, published literature and surface maps reveals at least four generations of Phanerozoic deformation, including Early Carboniferous compression, Permian rifting, Late Triassic and Late Jurassic compression, and Cenozoic compression. Each of these deformational episodes reactivated existing basement faults in the modern Andean foreland and created additional new ones. The present-day Andes are characterized by a thin-skinned thrust belt impinging eastward on a system of foreland basement-cored uplifts, some of which offset the frontal thin-skinned thrusts. Both systems are active today.
For much of the Phanerozoic, a subduction zone bounded western South America and much of the deformation affecting the Peruvian foreland can be linked to subduction zone dynamics. These links include Carboniferous docking of the Arequipa terrane, Permian slab roll-back, Cretaceous westward movement of South America, Eocene increase in subduction rate and last, flattening of the subducting slab.
Changing subduction dynamics have had at least three important effects. 1) The complex deformation history has created widespread potential traps and widely varying trap styles. 2) The repeated episodes of deformation within the foreland have created a profoundly heterogeneous stratigraphic section, rife with local unconformities, facies variations, and areally restricted deposits. 3) Recent flattening of the subducting slab has replaced hot asthenosphere with cold oceanic lithosphere, cooling the overriding plate, deepening the seismogenic zone and promoting reactivation of ancient foreland faults.
· Peruvian foreland shows 3 key pre-Andean events:
o Eo-Hercynian orogeny.
o Jurua orgeny.
o Nevadan orogeny.
· All have a strong compressional component.
· Possible strike-slip element difficult to assess on current data.
· Mitu rifting expressed only locally in the foreland, if at all.
· Three effects on modern Andean orogeny:
o Reactivation of some foreland faults.
o Distribution of detachment horizons in thrust belt.
o Location of crustal-scale ramp at edge of Mitu rift.
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