Slab in the wrong place: Lower lithospheric mantle delamination in the last stage of the Eastern Carpathian subduction retreat

Abstract

A model with a new type of delamination of the lower lithospheric mantle is proposed to explain the Pliocene to recent tectonic evolution of the Eastern Carpathians. We suggest that, after the continental collision in middle Miocene time, break-off of the west-dipping subducting slab occurred at a depth of 70 km. Slab break-off propagated horizontally toward the east, inducing lithospheric delamination and movement of the Vrancea slab into its present position. Delamination was followed by rapid asthenospheric rise, resulting in magma generation and the explosive alkaline basaltic magmatism of the Persani Mountains. Contamination of the former subduction-related magmatic reservoirs with the alkalic basaltic material and differentiation processes produced the Harghita calc-alkaline and shoshonitic rocks. The asthenospheric rise induced crustal uplift, which is the triggering mechanism for extension and formation of the Brasov-Gheorghieni hinterland basins. The extension was accommodated by shortening and folding in the foreland. The vertical Vrancea slab appears in our model as a segment of delaminated lower lithospheric mantle that is seismically active due to the ongoing pull of the eclogitized oceanic crust. The model explains the displaced and shallow position of the slab relative to the Eastern Carpathian suture zone.