A slab tear between the Hellenic and Cyprus arcs : toward a better understanding of the contribution of mantle flow to regional surface dynamics
Abstract
This study provides constraints of the present-day shape of the subducted African lithosphere. We focus on the Aegean-Anatolian region, which is the most tectonically active area of Europe and an excellent laboratory to test competing hypothesis on the relationship between surface kinematics and mantle flow. A major role in the evolution and the dynamics of the system is played by the fast retreat of the Hellenic slab towards the South. We used the seismic data set compiled from the SIMBAAD 2-year experiment and added data from permanent stations to obtain a dense (60-80 km) and homogeneous coverage of broadband stations in the area [35-42°N; 20-35°E]. We bring constraints on the morphology of subducted slabs from long period Rayleigh wave tomography and on mantle flow from SKS splitting measurements. A high resolution 3D S-velocity model of the mantle is computed by inversion of phase velocity maps for periods between 20 and 200s. Our new tomographic results clearly show a vertical slab tear, with a narrow horizontal extent (~160 km), between the eastern termination of the concave Hellenic slab and the Cyprus slab. This corridor (located beneath SW Anatolia) of low velocity is exactly correlated in space with a sudden change in the orientation of the fast velocity directions (from 30°N to -40°N) measured from split SKS phases. Indeed, below the entire region, the anisotropy is fairly uniform with a gradual change in orientation from 45°N, in Eastern and Central Anatolia, to 0°N in central Aegea and large time-lags (≥1s) everywhere which points towards an astenospheric origin of the anisotropy. The slab tear beneath SW-Anatolia is likely to be responsible for the acceleration of the retreat of the Hellenic subduction that started at ~30-35Ma. The imaged slab tear beneath SW Anatolia well explains the change in mantle flow that we believe is related to toroidal flow at the edge of the Hellenic slab. Our results supply a precise framework for future modelling of small scale mantle flow that would help establishing the contribution of mantle circulation to surface tectonics [see e.g. Faccenna & Becker, 2010] at the scale of the Eastern Mediterranean region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMDI31A1956S
- Keywords:
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- 7240 SEISMOLOGY / Subduction zones;
- 8120 TECTONOPHYSICS / Dynamics of lithosphere and mantle: general;
- 8180 TECTONOPHYSICS / Tomography