OFFSHORE CYRENAICA SUBDUCTION; NEW BATHYMETRY DATA, NORTHEAST LIBYA

The offshore area of northeast Libya has a poor history of bathymetry analysis as a result of insufficient offshore oil and gas exploration. The structural high onshore the northeast flank of the country is known as Al Jabal al Akhdar (The Green Mountain) and is composed of carbonate formations ranging in age from Cretaceous up to Late Miocene. By now, the geological framework of the surface geology is under constant research and is largely understood. However subsurface data is scarce, and offshore bathymetry data is almost not available.

This lack of data led to a search in all the different public and private domains to have a detailed view on the offshore bathymetry of Al Jabal al Akhdar and to relate any of the geological features observed to its development. The data collected and processed utilizes sonar data collected from the 1940s to recent years. This data was compiled with the help of different software packages to produce a detailed bathymetric 3D map. The bathymetry map is the first in this region and was quality checked against neighboring countries bathymetry calculations and seafloor seismic maps. The submarine features revealed by this map gave birth to new geological observations that can help further understand Al Jabal al Akhdar development. The main features are submarine canyons and a submarine trench. The maximum depth of this trench reaches approximately -4096mss 152 km north of Benghazi City, Libya. The bathymetry produced shows magmatic bodies 150 km north of the city and south of the trench, helping identify its polarity. The analysis of this data suggests that the trench is a subduction zone plunging towards Al Jabal al Akhdar structure, indicating that this mountain range is overriding the subducting plate, leading to the uplift and formation of the relief. The axis of the trench diverts to the north toward Italy once it approaches the magmatic rocks and continues until it merges with the Apennines thrust belt. The interpreted trench (subduction zone) was named the Cyrenaica Trench.

Analysis of satellite images over the area suggest that the tectonic plate movement at the uplift has different vectorial angles, resulting in a dextral strike-slip movement across the Cyrenaica trench combined with subduction. Using high-resolution 3D bathymetries, satellite images, and field work, a general investigation of the structural setting of the onshore and offshore area of this mountain range and its structural extensions unravels its complex tectonic history.