HR: 0830h
AN: T31C-0851    [PDF]
TI: Tectonic and Climatic Control of Landscape Evolution in the Northern Sierras Pampeanas, Argentina
AU: * Sobel, E R
EM: sobel@rz.uni-potsdam.de
AF: Institut fuer Geowissenschaften, Universitaet Potsdam, Postfach 601553, Potsdam, 14415 Germany
AU: Strecker, M R
EM: strecker@rz.uni-potsdam.de
AF: Institut fuer Geowissenschaften, Universitaet Potsdam, Postfach 601553, Potsdam, 14415 Germany
AB: Rock uplift, surface uplift and exhumation can be constrained if thermochronologic data can be converted to exhumation and if geological relations provide a datum. In the northern Sierras Pampeanas of Argentina, the Cenozoic Santa Mar\'{\i}a basin, which overlay resistant crystalline basement prior to rapid exhumation, provides an ideal setting to examine the effect of contrasting thermal and erosional regimes. There, tectonically active reverse-fault bounded blocks partly preserve a basement peneplain at elevations $>$4500 m. Prior to exhumation, the study area was covered by 1 to 1.6 km of ca. 12-6 Ma sediments; this sequence begins with shallow marine deposits immediately overlying the regional erosion surface which are superseded by sandstones and conglomerates. These rapidly deposited sediments have low thermal conductivity and are readily eroded, in contrast to underlying resistant basement. Apatite fission-track data were obtained from two vertical transects in the Calchaqu\'{\i}es and Aconquija ranges bounding the basin. At Cumbres Calchaqu\'{\i}es, erosion leading to the development of the peneplain commenced in the Cretaceous; limited late Neogene cooling is documented by track-length modeling. In contrast, Sierra Aconquija cooled rapidly between 5.5 and 4.5 My. At the onset of this rapid exhumation, sediment was quickly removed, causing fast cooling, but relatively slow rates of surface uplift. Syntectonic conglomerates could only be produced when faulting exposed resistant bedrock; this change in rock erodability lead to enhanced surface uplift rates but decreased exhumation rates. The creation of an orographic barrier after the range had attained sufficient elevation further decreased exhumation rates on the leeward side and increased surface uplift rates. This imbalance cannot be sustained for extended periods of time; either crustal strength or bedrock fluvial incision will ultimately limit the magnitude of relief which can be created before tectonism, and hence rock uplift, migrates to other locations. Differences in the magnitude of exhumation at the two transects are related to both differences in the thickness of the sedimentary basin prior to exhumation and differences in effective precipitation due to an orographic barrier in the foreland.
DE: 1035 Geochronology
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting