Kinematics and age of the orogen-perpendicular Shkoder-Peja Normal Fault
in North Albania constrained by fault-slip data, Raman spectroscopy and
K-Ar fault-gouge dating
Abstract
The Shkoder-Peja Normal Fault (SPNF) is the largest orogen-perpendicular
fault on the Balkan Peninsula, separating the Dinarides fold-and-thrust
belt in the north from the Hellenides in the south. It has accommodated
orogen-parallel extension during clockwise oroclinal bending of the
Hellenic segment since the Eocene-Oligocene. It juxtaposes Adriatic
shelf successions in its footwall against obducted ophiolites in its
hanging wall. Despite its length of at least 100 km, it is still an
improperly understood feature. In this study, we combine results of
geological mapping of a c. 13 km swath along this fault in Northern
Albania with fault-slip data, Raman spectroscopy of carbonaceous matter
(RSCM) and K-Ar dating of fault gouges to better constrain the
kinematics and age of this fault. Our results provide evidence for
top-SSE extension across the SPNF, post-dating Eocene nappe stacking and
truncating nappe-internal folds within the footwall units. Illite
crystallinity and RSCM data suggest that anchizonal vs. diagenetic
conditions were reached in the footwall and hanging wall units,
respectively. K-Ar dates of various grain size fractions (2-6,
<2 and <0.2 µm) from fault gouges yield “mixed dates”
of authigenic and inherited illite between 47 and 106 Ma and modelled
ages of authigenic illite as young as c. 6 Ma. As minimum temperatures
of c. 110 °C are required for the formation of authigenic illite,
younger fault activity at lower temperatures cannot be excluded. In view
of a number of recent GNSS studies, we consider it likely that the
Shkoder-Peja Normal Fault is still actively accommodating deformation.