History of subduction and back-arc extension in the Central Mediterranean.pdf

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History of subduction and back-arc extension in the Central Mediterranean.pdf

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History of subduction and back-arc extension in the Central Mediterranean

History of subduction and back-arc extension in the Central Mediterranean Claudio Faccenna,1 Thorsten W. Becker,2 Francesco Pio Lucente,3 Laurent Jolivet4 and Federico Rossetti1 1 Dipartimento di Scienze Geologiche, Universita? Roma TRE, Largo S. L. Murialdo 1, 00146, Rome, Italy. E-mail: faccenna@uniroma3.it 2 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA 3 Istituto Nazionale di Geofisica, Roma, Italy 4 Department de Ge?oTectonique, Universite? Paris VI, Paris, France Accepted 2001 January 19. Received 2001 January 15; in original form 2000 June 16 SUMMARY Geological and geophysical constraints to reconstruct the evolution of the Central Mediterranean subduction zone are presented. Geological observations such as upper plate stratigraphy, HP–LT metamorphic assemblages, foredeep/trench stratigraphy, arc volcanism and the back-arc extension process are used to define the infant stage of the subduction zone and its latest, back-arc phase. Based on this data set, the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross-sections from the northern Apennines and from Calabria to the Gulf of Lyon can be derived. Further, the reconstruction is used to unravel the main evolutionary trends of the subduction process. Results of this analysis indicate that (1) subduction in the Central Mediterranean is as old as 80 Myr, (2) the slab descended slowly into the mantle during the first 20–30 Myr (subduction speeds were probably less than 1 cm yearx1), (3) subduction accelerated afterwards, producing arc volcanism and back-arc extension and (4) the slab reached the 660 km transition zone after 60–70 Myr. This time-dependent scenario, where a slow initiation is followed by a roughly exponential increase in the subduction speed, can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic litho- sphere to the rate of change of potential