Abstract
The Hellenic arc, where the African (Nubian) slab subducts beneath the
Aegean and Anatolian microplates, has emerged as a type-locality for
understanding subduction dynamics, including slab tear, slab fragments,
drips, and transfer zones. Based on field evidence and geophysical,
tectonics, and geochemical studies, it has been recognized that the
subducting African slab is a primary driver for extension in the Aegean
and Anatolian microplates and plays a significant role in accommodating
present-day westward extrusion of the Anatolian microplate. Thus,
understanding the Hellenic arc subduction zone initiation (SZI) age is
critical in deciphering ancient mantle flow, how plate tectonics is
maintained, and the mechanisms involved in triggering the onset of
subduction. The SZI for the Hellenic arc has two disparate ages based on
different lines of evidence. A Late Cenozoic (Eocene-Pliocene) SZI is
proposed using the analysis of topography combined with estimates of
slab age and depth, paleomagnetism, the timing of metamorphism, and
volcanic activity, and timing of sedimentation within its accretionary
wedge, the Mediterranean Ridge. This age follows an induced-transference
SZI model, where a new subduction zone initiates following the jamming
of an older subduction zone by buoyant crust due to regional
compression, uplift, and underthrusting. A Late Cretaceous-Jurassic SZI
age has also been proposed using reconstructions of images of subducted
slabs seen using tomography and timing of obducted ophiolite fragments
thought to be related to the system. In this case, the
induced-transference SZI model fails, and a single subduction zone
persists. As a result, continental lithospheric fragments and the
ancient oceans between them become incorporated into the overall system
without creating a new subduction zone. The presence of a long-lived
subduction zone has implications for understanding Earth’s mantle
dynamics and how plate tectonics operates. This paper describes and
summarizes the evidence for both models in the Aegean-Western Anatolia
region.