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Crustal Thickness, Oceanic Lithosphere Distribution and OCT Structure for the Eastern Mediterranean from Gravity Inversion

Leanne Cowie and Nick J. Kusznir

The distribution of oceanic and continental crust in the eastern Mediterranean region is not well understood but has major implications for the tectonic evolution of this region and its petroleum systems. Gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to map Moho depth, crustal basement thickness, and continental lithosphere thinning for the eastern Mediterranean in order to determine oceancontinent transition (OCT) structure and the distribution of oceanic lithosphere. Knowledge and understanding OCT structure and the distal extent of continental crust are of critical importance in evaluating petroleum systems in deepwater frontier oil and gas exploration at continental margins and predicting heat flow.

The data used in the gravity inversion are public domain free-air gravity (Sandwell and Smith, 2009), bathymetry (Amante and Eakins, 2009) and sediment thickness (Laske and Masters, 1997). Gravity inversion results are dependent on the age of continental breakup and oceanic lithosphere because of the inclusion of the lithosphere thermal gravity correction; however, these ages are uncertain for the eastern Mediterranean. Gravity inversion sensitivities to break-up ages of 225Ma (late Triassic) and 100Ma (mid Cretaceous) have been examined.

Gravity inversion results show thin crust (5 – 8 km thickness) for the Ionian Sea and the Herodotus Basin, consistent with these basins being underlain by oceanic or highly thinned continental crust. The sharp increase in crustal thickness to the south of the very thin crust within the Herodotus Basin and eastern Ionian Sea suggests that the COB to the north-west of Egypt and eastern Libya is a transform margin. In contrast, the much broader transition from thick to thin crust in the Levantine Basin to the east of the Herodotus Basin most probably indicates that this is a rifted continental margin.

Continental lithosphere thinning and post-breakup residual thicknesses of continental crust determined from gravity inversion have been used to predict the preservation of continental crustal radiogenic heat productivity and the transient lithosphere heat-flow contribution within thermally equilibrating rifted continental margin and oceanic lithosphere. The resulting crustal radiogenic productivity and lithosphere transient heat flow components, together with base lithosphere background heat-flow, are used to produce regional maps of present-day top-basement heat-flow.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013