Geophysical analysis of fault geometry and volcanic activity in the Erzincan Basin, Central Turkey: Complex evolution of a mature pull-apart basin

• The Erzincan Basin has a Plio-Quaternary history comprising at least two phases.
• Gravity and magnetic studies and surface mapping define a complex fracture system.
• Basin cross faulting with variable thick infill define a mature pull-apart advancing to extinction.

The Erzincan Basin is one of several Neogene sedimentary basins developed by prolonged right-lateral strike-slip along the North Anatolian Fault Zone (NAFZ), the intracontinental transform defining the present boundary between the Eurasian Plate to the north and accreted Anatolian terranes to the south. The basin has a strong asymmetry and young (<780 ka) volcanic centers with widespread development of cross faults defining an advanced phase of pull-apart basin evolution. To isolate faults with no surface geomorphic or morphotectonic signatures in the young sedimentary cover, continuous magnetic profiles were conducted together with detailed interpretation of the regional Bouguer gravity map. This geophysical approach combined with surface mapping defines a fault geometry highlighting a series of buried structures including a fracture system 0.2–2.35 km wide which conforms to the volcanic lineaments seen at the surface. A model is developed for the evolution of the Erzincan Basin with a history commencing as a simple pull-apart by right-lateral strike-slip on the developing NAFZ, probably in Early Pliocene times. Subsequent interaction with a major left-lateral (Ovacık) fault (OF) caused the focus of motion on the NAFZ to shift to the southwest and develop a complex fishbone fracture system. This became the focus of volcanic activity on three lineaments which migrated progressively southwards toward the axis of the basin. Continuing motion on the OF transformed the south east margin of the basin into an extensional zone and the tectonic history of the basin has been further complicated by its proximity to a major transform intersection between the NAFZ and OF. The signatures of recent volcanism and the development of cross faults on which much activity is now concentrated define a mature pull-apart advancing toward extinction.