Charakterystyka mioceńskiej strefy subdukcji Karpat Polskich na podstawie wyników modelowań ugięcia litosfery

Abstract

CHARACTERISTICS OF THE MIOCENE SUBDUCTION ZONE OF THE POLISH CARPATHIANS: RESULTS OF FLEXURAL MODELLING Summary Flexural modelling technique was applied in order to characterise Miocene subduction zone of the Polish Carpathians. This technique relies on assumption that continental collision zone and related subduction of lower lithospheric plate can be adequately approximated by flexure of thin, elastic plate of uniform thickness (lithosphere) floating on the fluid half-space of zero viscosity (asthenosphere). Flexure of the lithosphere can be due to two types of loads: topographic loads related to the weight of the orogenic belt and sediments of the foredeep basin, and subsurface loads acting on the end of subducted lithospheric. Obtained results showed that along the Carpathians elastic properties of the lower (foreland) lithospheric plate change significantly. Effective elastic thickness EET was estimated to be in range of 8-16 km in the western Polish Carpathians, and 20-25 km in their eastern part. This can be attributed to the fact that in the western Polis h Carpathians foreland plate belongs to the Western European Platform (younger age of consolidation and lower flexural rigidity) while in the eastern segment of the thrust belt to the Teisseyre-Tornquist zone and Eastern European Platform (older age of consolidation and higher flexural rigidity). AIso, it was proved that for all the profiles subsurface loads were most important for the observed present-day flexure ofthe foreland lithospheric plate. This fact, combined with other features of the Carpathians, Carpathian Foredeep Basin and Pannonian Basin can serve as a proof that the Carpathian Miocene collision zone developed in relation to retreating subduction zone. Slab-pull mechanism can be postulated as the main subduction-driving mechanism for the Miocene evolution of the Polish Carpathians. This mechanism can possibly be caused by negative buoyancy of the subducted oceanic or thinned continental crust. It can also be concluded that development of the Carpathian Foredeep basin was mainly controlled by deep tectonic processes active within the subduction zone that also controlled thrusting of the Outer Carpathian flysch nappes.