Peeling off the mantle lithosphere under the Eastern Cordillera of the Central Andes (23 S): A thermomechanical model
Abstract
The Altiplano-Puna plateau of the Central Andes was uplifted in last 20 Myr in a response to tectonic shortening caused by the Brazilian shield indenting from the east. Recent P- and S-wave tomographic images under the eastern flank of the plateau at 23 S (low-velocity mantle material at 50-80 km depth overlying east-west dipping high-velocity zone) may be interpreted as an initial stage of peeling-type delamination of the mantle part of the indenting Brazilian shield. In this work we employ internally-consistent thermomechanical modelling to explore conditions of such delamination. As a numerical tool we use 2-D explicit finite difference/finite element lagrangian code with markers tracking material properties. In our model a shallow residing astenosphere under the plateau extends laterally towards the indenting shield and intrudes into the relatively low-viscous lower crust of the shield while bending the mantle part of the shield downwards. The initiation and rate of this peeling delamination depends on a set of control parameters. Main studied parameters are: viscosity of the astenosphere, depth of its implacement under the plateau, chemical buyoancy of the indenting shield mantle, pushing rate of the shield, viscosity of its lower crust. We found that delamination process is most sensible to the chemical buyoancy of the shield and its pushing rate; without pushing of the shield or with positive buyoancy of the shield mantle of 0.03 g/cc no delamination occurs. Variations of the astenospheric viscosity by one order of magnitude influence the rate of the process but do not prevent delamination. We discuss also the roles of other model parameters.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....8773B