Transtensional Basin Forming Processes in the Quaternary of Northern Greece: The Mygdonia Pull-Apart Basin

Abstract:

The geodynamic setting of the northern Aegean is governed by the superimposition of NE-SW strike-slip deformation, associated with the propagation of the North Anatolian fault zone towards the west, and N-S extension, caused by the suction of the Aegean realm towards the south due to deep seated processes of trench retreat and slab rollback. The Mygdonia basin sits at the westernmost termination of the Kavala-Xanthi-Komotini fault zone, a structure that is considered the northernmost splay of the North Anatolian fault system in the northern Aegean. It is one of the most seismically active regions in continental northern Greece, and it is herein interpreted, for the first time, as a transtensional pull-apart structure that has been progressively established since the Early Pleistocene by westward directed rupture of NW-SE and NE-SW trending oblique slip normal faults and E-W trending normal faults. The interaction of the two, separate, stress regimes in the basin demands decreasing accumulated displacement from west to east to accommodate clockwise rotation. The close correspondence between analogue models of transtensional basins and the observed spatial distribution of faulting in the Mygdonia basin attests to the importance of oblique deformation in the basin-forming processes. Detailed topographic profiles across the fault-bounded ranges confirm the decreasing trend of accrued displacement from east to west. Furthermore, topographic swaths reveal the scaling of faulting into discrete segments along the basin-bounding ranges, while calcrete maturity on abandoned hanging wall fans reveals a towards-the-west diachronous faulting with associated fan sedimentation. The Early Pleistocene age of the initial fill of the basin complex and fault displacements on the order of many hundreds of meters point to dramatic and rapid landscape forming processes in this tectonically active region. The increasing appreciation of the interaction of both strike-slip deformation and extension better refines our understanding of basin forming events in this region, in contrast to a simplistic, end-member, pure extensional basin model.