Progradation of the Alpidic Central Western Carpathians orogenic wedge related to two subductions: constrained by Ar-40/Ar-39 ages of white micas

摘要

To reveal a model of the polystage evolution of an orogenic wedge subsequent to two subduction S, Ar-40/Ar-39 dating of white micas (Wmca) across the shear zones in the Central Western Carpathians (CWC) has been carried out. This wedge is limited by the two suture zones, as a remnant after subducted oceanic crust of the Neotethyan Meliatic (in the S) and South-Penninic (in the N) oceans. It is composed of a system of basement and cover nappes, separated by major shear zones. Wmca aggregates from different microstructural and grain-size domains of lower- to medium-grade blastomylonites were dated by the Ar-40/Ar-39 method. The minimum age of NW-ward thrusting of the Gemeric and Meliatic nappes over the South-Veporic nappes in the southern part of this wedge was detected around 100 Ma. The NE-SW trending sinistral transpression, combined with a top-to-the SE extensional exhumation was dated at 90 - 85 Ma in the South-Veporic unit. Collision continued at ca. 95-90 Ma in the central part of the North-Veporic unit, while in the frontal part and in the Tatric and Infratatric units it was identified at 80 - 70 Ma. Lateral extrusion of the Tatric unit towards the NE occurred in Early Eocene, at ca. 50 Ma, indicating a final evolutionary stage of this wedge. The younging of ages from S to N revealed that footwall-propagating thrust-faults were responsible for the growth of the orogenic wedge.