RATES OF TECTONIC UPLIFT IN THE CORINTH AND MEGARA BASINS, CENTRAL GREECE

We present evidence of the rates of late Quaternary tectonic uplift that have affected parts of central Greece during this period of active extension and basin formation. Dual lines of evidence indicate upper Pleistocene to Holocene uplift rates of the order of 0.3 mm yr-1 for the Corinth and Megara basins. First, U-series disequilibrium ages of Acropora sp. corals from uplifted marine sediments are used to derive minimum average rates of vertical displacement since deposition. Second, the geometries of cyclical transgressive sequences and of erosional terraces are consistent with the radiometric evidence and the known history of late Quaternary sea level fluctuations. Two types of uplift are distinguished on the basis of structural relationships: (1) fault block rotation about a horizontal axis (tilting) in response to footwall uplift on the active normal fault bounding the Alkyonides Gulf and (2) a more regional uplift which affects the Corinth Basin and Peloponnesos to the south. The results of U-series dating are discussed in the light of initial U-234/U-238 activity ratios, derived from the coral samples, which are higher than for average marine waters (1.17-1.31 compared to 1.14). These values may be related to a variable freshwater input to the structurally confined Gulf of Corinth or, alternatively, they may reflect a previously higher global U-234/U-238 activity ratio in marine waters, or post-mortem enrichment in U-234, although the mechanism of the latter is not yet understood.