Gravity anomalies of the Cyprus Arc and their tectonic implications

Continental crust forms from structurally thickened remnants of oceanic crust and overlying sediments, which are then invaded by arc magmatism. Understanding this process is a first order problem of lithospheric dynamics. The transition in young mountain belts, from ocean crust through the agglomeration of arc systems with long histories of oceanic closures, to a continental hinterland is well exemplified by the plate margin in the eastern Mediterranean. The boundary between the African plate and the Aegean/Anatolian microplate is in the process of transition from subduction to collision along the Cyprus Arc. In the west, north of the oceanic Herodotus Basin, subduction may be continuing; in the east, microcontinental blocks such as the Eratosthenes Seamount are already colliding with Cyprus to the north of the suture. The changes in crustal structure along and across this convergent zone are not known except by inference from bathymetry, and from a couple of deep-penetrating wide-angle seismic transects on the African plate margin. In this contribution we model four Bouguer gravity profiles across the Cyprus Arc. The profiles are similar in showing a gravity low over the plate boundary suture attributed to thick sediments, with Bouguer highs over oceanic or transitional crust to the south, and over ophiolites and thinner sediments, on thin continental crust to the north. Bouguer lows at the northern ends of the profiles are characteristic of elevated continental crust. Well-sedimented oceanic or transitional crust on the African plate margin is replaced north of the suture by variably sedimented basement, in which continental crustal thickness increases from 10 km to 30 km over the forearc region. The models involve assumptions about characteristic densities and trade-offs between sediment and crustal thicknesses, but they do provide well-defined targets for future wide-angle seismic tests.