Cenozoic landforms and post-orogenic landscape evolution of the Balkanide orogen: Evidence for alternatives to the tectonic denudation narrative in the southern Bulgaria
Résumé
Continental denudation is the mass transfer of rock fromsource areas to sedimentary depocentres, and is typically
the result of Earth surface processes. However, a process known as tectonic denudation is also understood to
expose deep-seated rocks in short periods of geological timeby displacing largemasses of continental crust along
shallow-angle faults, and without requiring major contributions from surface erosion. Some parts of the world,
such as the Basin and Range in theUSA or the Aegean province in Europe, have been showcased for their Cenozoic
tectonic denudation features, commonly described as metamorphic core-complexes or as supradetachment
faults. Based on 22 new apatite fission-track (AFT) and 21 helium (AHe) cooling ages among rock samples collectedwidely
from plateau summits and their adjacent valley floors, and elaborating on inconsistencies between
the regional stratigraphic, topographic and denudational records, this study frames a revised perspective on the
prevailing tectonic denudation narrative for southern Bulgaria.We conclude that conspicuous landforms in this
region, such as erosion surfaces on basement-cored mountain ranges, are not primarily the result of Paleogene to
Neogene core-complex formation. They result instead from “ordinary” erosion-driven, subaerial denudation.
Rock cooling, each time suggesting at least 2 km of crustal denudation, has exposed shallow Paleogene granitic
plutons and documents a 3-stage wave of erosional denudation which progressed from north to south during
theMiddle Eocene, Oligocene, Early toMiddleMiocene, and Late Miocene. Denudation initially prevailed during
the Paleogene under a syn-orogenic compressional regime involving piggyback extensional basins (Phase 1), but
subsequently migrated southward in response to post-orogenic upper-plate extension driven by trench rollback
of the Hellenic subduction slab (Phase 2). Rare insight given by the denudation pattern indicates that trench rollback
progressed at amean velocity of 3 to 4 km/Ma. The Neogene horst-and-grabenmosaic that defines the modern
landscape (Phase 3) has completely overprinted the earlier fabrics of Phases 1 and 2, and has been the prime
focus of tectonic geomorphologists working in the region. The new narrative proposed here for linking the
geodynamic evolution of SE Europe with surface landform assemblages raises issues in favour of better
documenting the regional sedimentary record of existing Paleogene basins,which constitute a poorly documented
missing link to the thermochronological evidence presented here.