Abstract
Off northwest Libya the Cyrenaica foreland basin domain and its Pan-African continental crust, which constitute the African promontory, are overthrusted by the Mediterranean Ridge Complex. The thrust belt contact and its seismic stratigraphy have been analysed using pre-stack depth-migrated multichannel seismic (MCS) lines recorded during the MEDISIS survey (2002). The geometry and sedimentary distribution analysis through the wedge-top depocentres allow reconstruction of schematic cross-sections of the tectono-sedimentary wedge that includes two major thrust sequences separated by an apparently poorly deformed transition zone. Based on time–space variation of several piggyback basins, we propose that these thrust sequences relate to distinct phases of shortening. (1) A first event, which probably occurred just prior to the Messinian crisis in latest Miocene (Tortonian times?) and (2) A second event, that has finally led to the present-day overthrusting of the Mediterranean Ridge over the Libyan continental slope.
Highlights
Extending off Libya, the north Cyrenaica foreland basin (Fig. 1) results from a diachronous geological evolution including a passive margin stage and its subsequent tectonic inversion, which originated from a still ongoing convergence between the African and Eurasian plates
While considered for a long time as enigmatic, the geology of the Central Mediterranean Ridge has recently been clarified through the use of detailed swath bathymetric data (Huguen & Mascle 2005; Huguen et al 2005), various academic seismic reflection data (Cita et al 1989; Camerlenghi et al 1992, 1995; De Voogd et al 1992; Zitter 2004; Chamot-Rooke et al 2005) including several multichannel seismic (MCS) lines (Finetti 1982; Chaumillon 1995; Kopf et al 1998; Mascle & Chaumillon 1998; Costa et al 2004) and ODP leg 160 drilling results (Emeis et al 1996)
According to Huguen & Mascle (2005), the wedge can be divided into three different morphostructural provinces: (1) a southern front overthrusting the passive African continental margin, (2) a central, rather flat, domain and (3) a northern province in backthrust contact to the North with the Hellenic active margin
Summary
Extending off Libya, the north Cyrenaica foreland basin (Fig. 1) results from a diachronous geological evolution including a passive margin stage and its subsequent tectonic inversion (and uplift), which originated from a still ongoing convergence between the African and Eurasian plates. According to Huguen & Mascle (2005), the wedge can be divided into three different morphostructural provinces: (1) a southern front overthrusting the passive African continental margin, (2) a central, rather flat, domain and (3) a northern province in backthrust contact to the North with the Hellenic active margin Whether this morphologic feature expresses only relatively shallow thrusted sequences within the wedge-top depozone, or deeply rooted structures of the subducting African crust, remains an open debate. How this shortening is expressed and what its timing is are questions we are tentatively trying to answer
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