The Northern Calcareous Alps revisited: Formation of a hyperextended margin and mantle exhumation in the Northern Calcareous Alps sector of the Neo-Tethys (Eastern Alps, Austria)

Abstract

The Neo-Tethys margin evolution is preserved in the Northern Calcareous Alps (Eastern Alps), from Late Permian crustal stretching to Late Triassic oceanization. The Northern Calcareous Alps represent the salt-floored fold-and-thrust belt developed from the salt-influenced Triassic carbonate sedimentary cover of the ancestral European margin of the Neo-Tethys Ocean. A crustal scale model for the margin has been obtained by restoration of regional cross-sections of the Northern Calcareous Alps carbonate platforms. Lithospheric break-up was investigated from remnants of exhumed mantle found within an evaporitic melange, suggesting hyperextended crust underneath the distal Triassic platforms of the Northern Calcareous Alps preceding breakup. By modelling the thermal evolution of the margin in combination with excellent stratigraphic control, a detailed timeline has been established for the evolution of the Neo-Tethys margin, especially around the period of rapid mantle exhumation. Our study indicates that salt-floored carbonate shelfs can be used as a proxy to characterize the margins evolution, from crustal stretching to continental breakup. Diagnostic stratigraphic records are preserved in the carbonate platforms: pre- mantle exhumation carbonates are represented by aggrading isolated carbonate platforms first, followed by expanding and margin wide prograding carbonate shelfs once thermal subsidence dominates. In addition, a distinct clastic sequence is deposited as an immediate response to mantle exhumation, in between the pre- and post-mantle exhumation carbonate factory. Our study proposes a new refined model for the formation of the Neo-Tethys margin and provides new insights for the dynamic coupling of salt-controlled carbonate shelfs and the underlying lithosphere during continental breakup.