IRTG-StRATEGy: The Andes and their Forelands

The Andean orogen is a ~7000 km long N-S trending mountain range along the South American western continental margin. In the central part, the formation of this mountain range is driven by the subduction of the oceanic Nazca plate beneath the continental South American plate.

The DFG graduate school “IRTG-StRATEGy” comprises a set of projects that aim to study the coupling between tectonics, climate, erosion, sedimentation and hydrocarbon potential in the central Andes and their foreland basins. Funded by the DFG, the German-Argentinian graduate school is a cooperation between the University of Potsdam and the GFZ Potsdam, together with CONICET and several Argentinian universities. The project contributes to Topics 3 'Geohazards' and 8 'Georesources' in POF and comprises two phases: the first phase from 2015 to 2018 and the second one from 2018 to 2021. In each of these phases, 12 PhD students in each country have studied the Andean geology within one of four Working Packages (WP):

  • WP1: Climate-tectonic impacts on surface processes
  • WP2: Interplay between tectonics and inherited crustal inhomogeneities
  • WP3: Basin modelling and georesource formation
  • WP4: Metallogenesis of metal deposits in felsic magmas

As a part of WP3 , we aim to explore the present-day compositional, thermal and rheological configuration of the Central Andes and their adjacent forelands (21°-39°S) on a lithospheric scale. Therefore, we use data-driven 3D numerical models to understand how lithospheric structure controls the deformational behaviour. The general workflow involves data-constrained structural- and density-modelling in order to obtain models of the 3D distribution of physical properties for the Central Andes. These models are then used to predict the steady-state thermal field, which are further applied to assess the present-day rheological state in the study area.

G.3.3-I

In the first project phase of StRATEGy, our work focussed on the 3D lithosphere-scale density and thermal structure of the intracontinental Chaco-Paraná basin system in the northern Central Andes. The main results are summarized in the PhD thesis of Christian Meeßen carried out under the supervision of Magdalena Scheck-Wenderoth and Manfred Strecker and in close collaboration with Judith Bott and our Argentine partners. The main outcomes of this project are (Meeßen et al. 2018; Meeßen 2019):

  • To the north (21°S-26°S), the lithosphere of the thin-skinned foreland region of the Subandean ranges is characterised by a relatively strong crust and a weak mantle. Contrarily, the adjacent foreland basin consists of a fully coupled, very strong lithosphere. Thus, shortening in northern Argentina can only be accommodated within the weak lithosphere of the orogen and the Subandean ranges.
  • To the south (26°S-34°S), in contrast to the northern foreland, the lithosphere of the thick-skinned Sierras Pampeanas is fully coupled and characterised by a strong crust and mantle. The high overall strength prevents the generation of crustal-scale faults by tectonic stresses. Due to thermal weakening, and potentially lubrication of the inherited discontinuities, the lithosphere is locally weakened such that tectonic stresses can uplift the basement blocks.

G.3.3-II

The second project phase of the WP3 takes a closer look on the lithospheric-scale 3D configuration of the southern Central Andes and adjacent forelands (29°S-39°S). It is part of the PhD project of Constanza Rodriguez Piceda, under the supervision of Magdalena Scheck-Wenderoth and Manfred Strecker and in close collaboration with Judith Bott, Maria Laura Gomez-Dacal and Claudia Prezzi. A first-order characteristic of this area is that the subduction angle changes at latitudes 33°S-35°S from flat in the North to normal in the South. The aim of the project is to study the relationship between the characteristics of the overriding plate and the crustal deformation and dynamics of the subduction system. The first outcomes of this second phase can be summarized as follows (Rodriguez Piceda et al. under review; Rodriguez Piceda et al., in preparation):

  • There is a clear segmentation between the forearc, the orogen (i.e. main orogenic wedge and arc) and the foreland in terms of crustal thickness, density distribution and thermal state.
  • The lithosphere of the orogen is thicker, lighter and warmer than the remaining regions of the orogenic system.
  • The forearc lithosphere appears denser, thinner and colder than the adjacent orogen. Therefore, it acts as a rigid indenter that can facilitate the propagation of the deformation into the orogenic interior.
  • The foreland lithosphere is overall denser, thinner and colder than the adjacent orogen. Several lithospheric domains can be recognized from north to south in terms of variations of crustal density, thickness and temperature. The lithospheric configuration of the northern foreland (29°S-33°S; thick, dense, cold and potentially strong lithosphere) may enhance the coupling between the subducting and overriding plates and therefore could contribute to the establishment of a flat subduction setting.

For more information about IRTG StRATEGy, visit www.irtg-strategy.de

Zuwendungsgeber: DFG - Deutsche Forschungsgemeinschaft

Status: laufend

References:

  • Meeßen C, Bott [Sippel] J, Scheck-Wenderoth M, et al (2018) Crustal Structure of the Andean Foreland in Northern Argentina: Results From Data-Integrative Three-Dimensional Density Modeling. J Geophys Res Solid Earth 123:1875–1903. doi.org/10.1002/2017JB014296
  • Meeßen, C. (2019) The thermal and rheological state of the Northern Argentinian foreland basins, PhD Thesis, Potsdam : Universität Potsdam, 151 p. doi.org/10.25932/publishup-43994
  • Rodriguez Piceda, C, Scheck-Wenderoth M, Gómez Dacal ML., Bott, J, Prezzi C, and Strecker M (2020) Lithospheric density structure of the Southern Central Andes and their forelands constrained by 3D gravity modelling, EGU General Assembly 2020, Online, EGU2020-3313, doi.org/10.5194/egusphere-egu2020-3313, 2020
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