HR: 0800h
AN: T31A-1282    [Abstracts]
TI: The Long-Term Strength of Europe and its Implications for Plate Forming Processes
AU: * Perez-Gussinye, M
EM: martap@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences Parks road, Oxford, OX1 3PR United Kingdom
AU: Watts, T
EM: Tony.Watts@earth.ox.ac.uk
AF: University of Oxford, Department of Earth Sciences Parks road, Oxford, OX1 3PR United Kingdom
AB: There is considerable debate on the methods to measure the effective elastic thickness, $T_e$, and its significance for the rheology of continental lithosphere. While some authors obtain both low and high $T_e$ from the Bouguer coherence and suggest that high values indicate a strong mantle, others only obtain estimates of $< 25$ km using the free-air admittance and suggest that the mantle is weak everywhere and the strength resides in the crust. We have used topography, free-air and Bouguer gravity anomaly data to estimate $T_e$ in Europe using both spectral techniques. We show that when both techniques are consistently formulated, the $T_e$ structure is equivalent: the old Archean and early Proterozoic terranes have large $T_e$ values ($> 60$ km), indicating that the mantle is strong, whereas young Phanerozoic terranes have low $T_e$ values and hence a comparatively weaker mantle. This strength contrast cannot be explained by a single thermal boundary layer cooling model. Rather, we suggest that it is related to differences in the plate forming processes through Earth's history. During Archean and early Proterozoic a higher mantle temperature and/or volatile content led to a greater degree of melting producing thick, highly depleted lithosphere which strengthened with time as it cooled. However, during the Phanerozoic, partial melting of a cooler and dryer sub-lithospheric mantle led to the formation of plates which are thinner and intrinsically weaker, due to thermal and compositional effects. This fundamental strength contrast has probably contributed to the concentration of deformation in Phanerozoic terranes. These terranes act as stress buffers for the strong Archean and early Proterozoic plates which remain undeformed.
DE: 8110 Continental tectonics--general (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8122 Dynamics, gravity and tectonics
DE: 8159 Rheology--crust and lithosphere
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting