HR: 09:00h
AN: T51D-05    [Abstracts]
TI: Successive Shortening and Extensional Faulting on the Southern Margin of the Puna Plateau and Fiambala Basin, Northwest Argentina
AU: * Schoenbohm, L
EM: lindsays@geo.uni-potsdam.de
AF: University of Potsdam, Inst. for Geosciences, Postfach 601553, Potsdam, 14415 Germany
AU: Strecker, M
EM: strecker@geo.uni-potsdam.de
AF: University of Potsdam, Inst. for Geosciences, Postfach 601553, Potsdam, 14415 Germany
AU: Carrapa, B
EM: carrapa@geo.uni-potsdam.de
AF: University of Potsdam, Inst. for Geosciences, Postfach 601553, Potsdam, 14415 Germany
AU: Barbieri, C
EM: chiara.barbieri@manhattan.unipv.it
AF: University of Pavia, Dept. of Earth Sciences, Via Ferrata, 1, Pavia, 27100 Italy
AU: Wulf, H
EM: henne.wu@gmx.de
AF: University of Potsdam, Inst. for Geosciences, Postfach 601553, Potsdam, 14415 Germany
AB: On the southern margin of the Puna Plateau, active normal and strike-slip faults accommodate N-S extension, overprinting earlier NW-SE and NE-SW shortening. These relationships, noted elsewhere by other researchers, can be seen north of the Fiambala Basin at the intersection of the plateau, the Cordillera Principal and the northwestern Sierras Pampeanas structural provinces. Here, N-S striking thrust faults place basement over Tertiary strata and late Pliocene-Quaternary Punaschotter Conglomerate (PSC), in a NE-SW direction. Structural, geomorphic and provenance data show deformation began before and continued during deposition of the PSC, initiating intramontane basin conditions, and ended before re-incision of the Fiambala basin began. The thrust faults are superseded by a NE striking, steeply NW dipping normal fault with a minimum vertical displacement of 200 m. The fault terminates against a N-S thrust fault. Tilted ignimbrites in the hanging wall and recent, unconsolidated volcanic ashes indicate the fault is active and has been a depocenter since faulting began. This area thus experienced a kinematic shift from Plio-Quaternary NW-SE directed shortening to active N-S extension. Similar relationships are observed elsewhere on the southern Puna margin, where active E-W, NE-SW or NW-SE normal and strike-slip faults accommodate N-S extension. These faults are oblique to and often terminate against older, N-S thrust faults. This relationship may be a result of (1) delamination of the mantle lithosphere beneath the Puna Plateau, (2) the structural interaction at intersection of the plateau to the north, the Sierras Pampeanas to the south and the Cordillera Principal to the west, (3) changes in absolute plate motion, (4) N-S extensional collapse of the Puna Plateau, or (5) a combination of these factors. Regardless, the change in extension and shortening directions in this region reflects important aspects of plateau development and may herald a new stage in the evolution of the world's second largest plateau.
DE: 8102 Continental contractional orogenic belts
DE: 8105 Continental margins and sedimentary basins
DE: 8107 Continental neotectonics
DE: 8109 Continental tectonics--extensional (0905)
DE: 8122 Dynamics, gravity and tectonics
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting