Evidence for dynamic coupling of surface processes with isostatic compensation in the lower crust during active extension of western Turkey

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Abstract
Western Turkey, in the eastern part of the Aegean region, is extending slowly, with extension no faster than ∼0.5 mm yr−1 across any individual active normal fault. Up to 15 km of southward extension has occurred in the most active ∼100 km wide part of this region since ∼15 Ma, indicating a typical strain rate of ∼3×10−16 s−1. Rivers carry a sediment flux of ∼4×106 m3 yr−1 westward to the Aegean Sea coast, with offshore sedimentation at ∼1 mm yr−1. Sediment loading causes coastal areas to subside much faster than would be expected from the extension alone. Most of this sediment is derived from regional erosion of inland areas to the east at a typical rate of ∼0.1 mm yr−1, this erosion being isostatically compensated by uplift. It is suggested that the lower crustal material displaced by sediment loading near the coast flows east to isostatically compensate the erosion. The average eastward velocity of this lower crustal channel flow beneath the Aegean coast is estimated as ∼1 mm yr−1; the maximum velocity is >∼2 mm yr−1. This case study thus indicates the general point that isostatically compensated erosion and lower crustal channel flow can affect the evolution of sedimentary basins that are surrounded by eroding landmasses, factors that are often neglected.