HR: 11:20h
AN: GP42A-05    [Abstracts]
TI: Linking Ridge Subduction to Paleomagnetic Rotations in the Andes
AU: Torres, V
EM: vtorres@ingemmet.gob.pe
AF: Instituto Geologico, Minero y Metalurgico, 1470 Avenida Canada, Lima, 41 Peru
AU: Rousse, S
EM: rousse@mag.ig.erdw.ethz.ch
AF: ETH-Honggerberg, Ramistrasse 101, Zurich, 8092 Switzerland
AU: * Gilder, S
EM: gilder@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 5, 75252 France
AU: Farber, D
EM: farber2@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234 United States
AU: McNulty, B
EM: bamcnulty1@comcast.net
AF: California State University Dominguez Hills, 1000 E. Victoria St., Carson, 90747 United States
AU: Sempere, T
EM: thierry.sempere@lmtg.obs-mip.fr
AF: Institut de Recherche pour le Developpement, 14 avenue Edouard-Belin, Toulouse, 31400 France
AU: Patriat, P
EM: patriat@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 place Jussieu, Paris cedex 5, 75252 France
AB: Paleomagnetic data from 104 sites of upper Oligocene to Pliocene rocks from the coastal and Western Cordillera regions of central and northern Peru record a coherent pattern of counterclockwise rotations generated in the last 10 Ma. Based on the time-space relationship of deformation, magmatism and Nazca-South America plate convergence, the pattern of rotations can best be explained by a punctual and widespread tectonic event linked to subduction of the Nazca Ridge. If correct, slab coupling and concomitant mountain building are most pronounced at the beginning stages of ridge subduction, when down dip motion is inhibited. The system likely then evolves to a more normal subduction regime, probably when it becomes more energetically favorable to renew significant down dip motion rather than transfer convergent motion into building topography through tectonic shortening. As the ridge continues to subduct, significant changes in ridge-trench convergence angle, or possibly major changes in ridge topography, can increase or decrease coupling, and thus modulate compressive deformation. Ridge collisions may have lasting effects on the continental margin by weakening the crust to a level where deformation can proceed with lower levels of differential stress. This may for instance explain why the Subandean Zone (in this model initiated in times of increased coupling between the slab and overriding continental plate) remains tectonically active. It is possible that a succession of buoyant ridge subduction events played an important role in producing the paleomagnetic rotations recorded along the entire Andean chain. In this way, the modern Andes would be composed of distinct parts, with the Juan Fernandez ridge being partly responsible for shaping the Bolivian Orocline at circa 25 Ma, the Nazca ridge for the Peruvian Andes north of the Abancay deflection (15.5 S) until about 7 S at circa 8 to 4 Ma, and the Carnegie ridge for the recent deformation seen in the Northern Andes.
DE: 8102 Continental contractional orogenic belts
DE: 8150 Plate boundary--general (3040)
DE: 8157 Plate motions--past (3040)
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1527 Paleomagnetism applied to geologic processes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting