dc.description.abstract
This doctoral thesis presents new thermochronological and thermometric data, cross-sections, and plate reconstructions on the kinematics and age of orogen-parallel extension and arc formation, as well as studies of basin and landscape evolution at the junction of the Dinaric and Hellenic orogens.
The Dinaric-Hellenic mountain belt bends some 30° where two fault systems transect the orogen: (1) the Shkoder-Peja Normal Fault system (SPNF); (2) the Shkoder Peja Transfer Zone (SPTZ) that dextrally offsets the Dinaric-Hellenic nappes by ~75 km. The SPNF is a composite structure that cuts Dinaric folds and nappe contacts. It comprises four segments that were active under ductile-brittle conditions and downthrow the West Vardar Ophiolite in the hanging wall while exhuming two domes with anchizonal-to-lower greenschist-facies metamorphism in the footwall.
Peak-metamorphic temperatures of ~280°C from RSCM (Raman spectroscopy of carbonaceous matter) analysis of the mélange of the ophiolite nappe atop the Dinaric nappe stack were attained during obduction in latest Jurassic-Early Cretaceous time, followed by cooling of the ophiolithic mélange to <180°C ((U/Th)-He zircon ages; ZHe) in Cretaceous (~125-100 Ma) time. The offset of the ophiolite front along the SPTZ is attributed to re-activation of an Early Mesozoic rift transfer zone in the Adriatic margin during Eocene subduction of the Pindos Ocean. This subduction involved a clockwise rotation of the Hellenides with respect to the Dinarides around a pole at the NW end of the then-existing Krasta-Cukali basin.
Stratigraphic criteria indicate that thrusting and nappe stacking beneath the emplaced ophiolite in the Internal Dinarides initiated in Late Cretaceous time. Contours of peak temperature in the nappe stack cross the thrust contacts, with a maximum temperature of ~460°C reached in the Decani Dome, in the footwall of the SPNF. The arcuate peak-temperature contours around the perimeter of the dome indicate that the attainment of peak-temperatures pre-dates Decani doming. There, the nappes underwent extensional mylonitic shearing (~300-350°C) and cooling to < 240°C at ~70 Ma (zircon fission track ages; ZFT) at temperatures somewhat less than those attained in the dome itself. This suggests that doming and extensional mylonitic shearing were broadly coeval. This attributes to extension in a back-arc setting to the east of the then-active accretion-subduction front. This first pulse of doming and extension at the Dinaric-Hellenic junction in the Late Cretaceous (80-70 Ma) occurred in the upper plate of the SW-propagating orogenic front.
Nappe stacking in the External Dinarides continued throughout Middle Eocene to Early Oligocene time according to stratigraphic criteria. Peak-temperatures in the External Dinaric nappes were lower (~180-280°C) than in the Internal Dinarides and correspond to a burial depth of ~6-10 km. Peak temperatures were attained after nappe stacking and the formation of the Cukali Dome in the SW footwall of the SPNF, as contours here transect both the nappe contacts and the Cukali Dome. Cooling below ~180°C (57-43 Ma, ZHe) and ~110°C (35-21 Ma, apatite fission track ages) suggests that the Dinaric nappes cooled slowly after Early Eocene time.
The two prominent Decani and Cukali Domes locate in the SPNF footwall and are accompanied by their segments: the Cukali-Tropoja Fault and the Decani Shear Zone, whereas the latter represents the oldest SPNF part that hosts the aforementioned Decani Dome in its footwall. The Cukali-Tropoja Fault and a late ductile-brittle phase of the Decani Shear Zone formed during a post-nappe stacking phase of orogen-parallel extension and clockwise rotation, with a minimum of ~2500 m vertical offset. Extension north of the SPNF is attributed to detachment of part of the Adriatic slab beneath the internal Dinarides that triggered magmatism, core complex formation and uplift.
The second pulse of SPNF doming and extension occurred sometime between 32 and 16 Ma, and is attributed to rollback subduction of the untorn part of the Adriatic slab beneath the Hellenides towards the SW. This phase involved localized subsidence of Neogene basins at the Dinaric-Hellenic junction coupled with accelerated post-Paleogene clockwise oroclinal bending. However slower cooling (3.0-3.2°C/Ma) in vicinity to the Dinaric-Hellenic junction after Eocene time corresponds to an average denudation rate of 0.1-0.2 mm/yr, equivalent to removal of ~1.6–3.2 km of overburden since ~16 Ma. Faster, tectonically induced cooling and denudation at shorter timescales is possible, but beyond the detectability of our applied methods.
The Dukagjini Fault, with about ~1000 m vertical throw, now covered by Pliocene sediments, represents the youngest segment of the SPNF and is largely responsible for the formation of the Western Kosovo Basin, as evidenced by the oldest Middle Miocene syntectonic sediments in the basin.
To bridge the gap between the Neogene uplift, exhumation and deformation history of the Dinaric-Hellenic junction and the influence of the SPNF on the recent landscape evolution, the sediments of the sedimentary basins preserved today and the present-day geomorphology were analyzed. Analysis of fluvial morphology of the Drin River system reveals higher values of river slope indices (ksn) and χ (Chi) between the SPNF and the Drin drainage divide. The drainage divide is predicted to be migrating away from the SPNF, except at its NE end. The Western Kosovo Basin and Tropoja Basin contain flat-lying late Pliocene-to-Holocene sedimentary rocks deposited well after the main fault activity and immediately after the LGM. These layers document an early Pleistocene transition from lacustrine to fluvial conditions that reflects a sudden change from internal to external drainage of paleo-lakes. In the Tropoja Basin these layers were incised to form three generations of river terraces, interpreted to reflect episodic downstream incision during re-organization of the paleo-Drin River drainage system. 36Cl-cosmogenic-nuclide depth-profile ages of the two youngest of these terraces (~12 and ~8 ka) correlate with periods of wetter climate and increased sediment transport in post-LGM time. The incision rate (~12 mm/yr) is significantly greater than reported in central and southern Albania. Thus, glacial/interglacial climatic variability, hinterland erosion and baselevel changes appear to have regulated basin filling and excavation cycles when the rivers draining the basins became part of the river network emptying into the Adriatic Sea. These dramatic morphological changes occurred long after SPNF related normal faulting. However, the SPNF provided a structural and erosional template upon which climate-induced erosion in Holocene time effected reorganization of the regional drainage pattern. The arc of the main drainage divide around the SPNF deviates from the general coincidence of this divide with the NW-SE trend of the Dinaric-Hellenic mountain chain. This arc encompasses the morphological imprint left by the rollback subduction of the Adriatic plate beneath the northwestern Hellenides, and thus represents a witness to the structural evolution of the Dinaric-Hellenic junction, which began over 100 million years ago and is still evident in the landscape today.
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