Tertiary tectonic evolution of the external East Carpathians (Romania)

Paleostress calculation and analysis of mesoscopic structures are integrate d with depth interpreted geological profiles based on seismic studies and w ell correlation to derive a Tertiary tectonic model for the East Carpathian s. Following Early Miocene and older orogenic phases, the first tectonic ev ent that affected the studied area is characterised by a WSW-ENE-oriented s hortening of Middle Miocene (Late Burdigalian) in age. Resulting deformatio ns induced ENE-ward thrusting of Tarcau and Marginal units, as well as the internal part of the Subcarpathian nappe. A second shortening event with an E-W to WSW-ENE contraction direction took place in the Late Miocene (Sarma tian) characterised by further foreland thrusting of the Subcarpathian napp e and out-of-sequence deformation in the Tarcau and Marginal Folds nappes. Along strike, differences in deformation mechanisms are controlled by the f riction coefficients along the main detachment layers, by the lateral varia tions in the wedge thickness and by the involvement in the northern part of the thrusting system of the thick, competent East European platform. Tear faulting occurred in both tectonic events, the main resulting structure bei ng the triangle zone developed south of the Trotus valley. The Latest Mioce ne (Latest Sarmatian)-Early Pliocene is characterised by a strike-slip stre ss field with NNE-SSW compression and WNW-ESE tension axis, left-lateral fa ults being dominant. The last deformation which affected the studied area i s characterised by NNW-SSE shortening during the Pliocene, major deformatio ns taking place mainly in the SW-most bending zone. (C) 2000 Elsevier Scien ce B.V. All rights reserved.