Tectonic evolution of the Lake Ohrid and Prespa Basins (FYROM/Albania)

The region of the Lake Ohrid and Prespa Basins is located at the Greek/ FYROM (Former Yugoslav Republic of Macedonia)/Albanian border. The neotectonic and landscape evolution of the southern Albanian fold-and-thrust belt and the Albanian-FYROM extensional back-arc area (basin and range type) are directly linked to subduction and subduction rollback within the Hellenic trench system. The initiation of the Ohrid Basin is estimated between 2 and 8 million years. The deformation can be divided in three major deformation phases (1) NW-SE shortening from Late Cretaceous to Miocene with compression, thrusting and uplift; (2) uplift and diminishing compression during Messinian - Pliocene; (3) vertical uplift and (N)E-(S)W extension from Pliocene to recent associated with (half-) graben formation. This latter phase of an orogenic collapse is related with a seismogenic landscape with linear steplike fault scarps on land and offshore, wineglass shaped valleys and triangular facets. The geomorphology also points to rotated and tilted blocks. Seismic and hydroacoustic data of Lake Ohrid show that the faults and fault scarps, in general, are getting progressively younger towards the basin centre. A tectonic multi-proxy approach (palaeostress analysis, remote sensing) has been made to reveal the stress history of the region. Furthermore, apatite fissiontrack (A-FT) analysis and t-T-paths modelling was performed to constrain the thermal history, and the exhumation rates.
   For fission-track analysis apatites were separated from a suite of granitoid rocks from basement units and from flysch- and molasse-type deposits of Paleogene to Neogene age. Apatites show a range of the apparent ages from 56.5±3.1 to 10.5±0.9 Ma. The spatial distribution of ages suggests different blocks with a variable exhumation and rock uplift history. Fission-track ages from molasse and flysch sediments of the basin fillings show distinctly younger ages. Generally, the Prespa Basin reveals A-FT-ages around 10 Ma close to normal faults, whereas modelling results of the Ohrid Basin suggest a rapid uplift initiated around 1.4 Ma associated with uplift rates (? rock uplift rates or surface uplift rates?) on the order of 1 mm/a. As a conclusion we observe a westward migration of the extensional basin formation, i.e. the initiation of the Prespa Basin occurred well before the formation of the Ohrid Basin.