DYNAMICS and ACTIVE PROCESSES - International Lithosphere ...

ILP TASK FORCE on SEDIMENTARY BASINS
2010 International Workshop
November 7-12, 2010, Tirana (Albania)
Strength and weakness of the World lithosphere
Magdala Tesauro (1), Mikhail K. Kaban (1), Sierd A.P.L Cloetingh (2)
(1) GeoForschungsZentrum Potsdam (GFZ), Germany (2) VU University, The Netherlands,
magdala@gfz-potsdam.de, kaban@gfz.potsdam.de, sierd.cloetingh@falw.vu.nl
Rheology and strength of the Earth’s lithosphere have been debated since the beginning of the
last century, when the concept of a strong lithosphere overlying viscous asthenosphere was
introduced. The issue of strength of the lithospheric plates and their spatial and temporal
variations is important for many geodynamic applications. For rocks with given mineralogical
composition and microstructure, temperature is one of the most important parameters
controlling rheology. We present the first world strength map obtained from global crustal
(Fig.1a) and thermal models (Fig. 1b). Temperature estimates for the deeper horizons of the
lithosphere, where the heat transport is mostly conductive, requires a precise knowledge of
many crustal parameters (mainly thermal conductivity and heat production), which are
extremely uncertain. Therefore, we use a combination of indirect approaches, such as seismic
tomography and geothermal analysis (Ritsema and Van Hejist, 2004 ; � ermák, 1993).
Furthermore, we implement a global crustal model by assembling the most recent
compilations (e.g. Mooney and Kaban, 2010 ; Tesauro et al., 2008). Rheology of the upper
and lower crust (Fig.1c) was classified based on a tectonic maps of the World (Mooney,
2009). The results show a good correspondence between strength values and geological
features (Fig. 2). Pronounced strength contrasts exist between old cratons and areas affected
by the Tertiary volcanism, which are mostly coincident with the boundaries of seimogenic
zones. The Te in the continents (Fig. 3) demonstrates a bimodal distribution around two peaks
at ~25 km, which is the representative value for the continental areas outside of the cratons,
and at ~70 km, which is a common value for the cratons. This clustering is probably related to
influence of the plate structure: depending on the ductile strength of the lower crust, the
continental crust can be mechanically coupled or decoupled with the mantle resulting in
highly different Te values. The largest changes of Te occur at sutures that separate different
provinces characterized by major changes in the lithospheric strength. The lithosphere
strength appears to be primary controlled by the crust in the young (Phanerozoic) geological
provinces characterized by low Te (~25 km), high topography (>1000m) and seismicity. By
contrast, the old (Achaean and Proterozoic) cratons of the continental plates show high Te
(over 100 km), low topography (