[related scientific publication Garcia-Castellanos, 2007, EPSL]
Computer simulations combining tectonic convergence, isostasy, erosion/sedimentation, and climate, suggest that the formation of high plateaus within orogens is determined not only by the structure of the crust but also by how dry the weather was during the early stages of orogenesis.
Further details in this article. Calculations have been performed using the tAo software. You can freely download the program version used for this paper and the corresponding scripts and parameter files (tar-gzipped).
The two model evolutions shown below are examples of a cross-section computer model of orogen growth (time shown in million years) differing only in climatic parameters (tectonic and lithological parameters and kept constant). The numerical model simultaneously computes the dynamics of fault generation, precipitation, erosion and sediment transport carried out by rivers. The two evolutions below differ only in the chosen climatic parameters, but they result in very different orogenic structures, one of them (to the left) developing a high plateau isolated between two cordilleras. They have been calculated using a modified version of the software tAo using a minimum work fault criterion, a shortening rate of 5 mm/yr during 18 million years, and a river transport capacity proportional to water discharge and slope.
The horizontal axis corresponds to distance across the orogen. From top to bottom: Time in millions of years; Precipitation (plain blue line) and evaportation (dashed blue line); River sedimet load (brown) and water discharge (blue); Erosion rate (red) and total erosion (dashed brown); Model geometry (1:7 vertically exaggerated and 1:1): Crustal bedrock in brown, sediments in yellow, water in blue, vertical bars are plot as markers of shortening.Schematic diagram of processes and aproximations implemented in the numerical model. See details in the paper linked above.
Schematic diagram of processes and aproximations implemented in the numerical model. See details in the paper linked above.
Summary of the proposed mechanism of climatic control of high plateau growth. Dry climate induces the accumulation of sediment in closed intraorogenic basins, leading to higher pressure along the main tectonic faults that widen the orogen.
Abstract. High plateaus are generally thought to result from tectonic compression interfering with pre-existing structural heterogeneities of the crust and in association with tectonic processes promoting uplift such as viscous lower-crustal flow or mantle delamination. Instead, results from a novel computer modeling technique integrating climatic, erosional and tectonic processes suggest that dry climate prior to the uplift of the Andean Altiplano was a first order process controlling orogenic deformation and the eventual formation of a high-plateau. According to these numerical modelling results, dry climatic parameters (particularly if imposed at the early stages of tectonic shortening) favor sediment trapping within the orogen transferring the accommodation of tectonic shortening towards the external parts of the orogen and eventually leading to the formation of a high plateau. This feedback operates in the following steps: 1) Dry climatic conditions at the early stages of orogenesis favor the tectonic defeat of rivers draining the orogen, promoting lake formation, intramountain sediment trapping, and the eventual formation of an internally-drained (endorheic) basin; 2) Endorheism extends the life of intramountain basins thus increasing dramatically the mass trapped within the orogen and expelling deformation towards the external parts of it; and 3) This propagation of tectonism further isolates the central parts of the orogen from incoming precipitation, reinforcing intramountain sediment trapping and flattening. This feedback phenomenon predicts basic topographic, drainage, and tectonic differences between orogens lacking a high-plateau, such as the Alps, and orogens with a well-developed high plateau like the Andes, without invoking tectonic controls or inherited weaknesses in the crust. It also suggests that internal drainage and high-plateaus might be a natural stage of orogeneses starting under dry climatic conditions and/or rapid tectonic shortening rates.
Comparison of erosion, precipitation, and tectonic structural profiles across the Andes (left panels) and the Alps (right). (a) Symbols indicate long and short-term erosion rate measurements in mm/yr; grey bands indicate cumulative erosion/sedimentation in km for the Central Andes (syn- and post-uplift) and the Alps (post-collisional). (b) Precipitation as compiled by the Center for Climatic Research. (c) Topography and drainage divides. (d) Schematic structural sections. Error bars in (b) and (c) represent standard deviations within the 100 km-wide data projections, whereas in (a) the represent an estimation of measurement error. Note that data in (a) are projected along a wider region than (b) and (c), due to the scarcity of erosion data.The westwards dominant wind in the Andes induces maximum orographic precipitation in the East and a marked orographic rain shadow in the western side of the Andes (Peruvian Coast), whereas in the Alps these features are missing due to more variable wind directions. The up to 3.5 km-thick syn-orogenic sedimentation in the Altiplano contrasts with the maximum exhumation values along the axis of the Alps.
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