Tomographic and geological constraints on subduction along the eastern Sundaland continental margin (South-East Asia)

The SE Asian region is characterised by the active subduction of Cenozoic m arginal basins. A new tomographic model interpreted in the light of geologi cal data, provides details on the geometry of the oceanic lithospheric slab s subducted along the eastern margin of Sundaland. We present first evidenc es for a relatively continuous active margin which have extended from Taiwa n to Java before the collision of the Banda bloc with Sundaland during the Miocene. The north dipping slab below Timor is interpreted as the result of the new subduction zone following this collision and connecting westward w ith thr present Java-Sumatra trench. We also try to estimate the amount of shortening within the Sunda block, which was mainly accommodated by subduct ion of the SE Asia marginal basins, formerly opened within this part of Eur asia during the Palaeogene. Closure of the Sulu and Celebes basins is recen t, whereas the subduction of the Proto-South China Sea is marked by a 300 k m long slab below Borneo, but also eastward by a large velocity anomaly int erpreted as a. detached slab fragment of this basin sunk into the mantle.