Photogeological interpretation – an efficient tool for tectonic analysis. Study case – the Oas-Gutai Mts. (NW Romania)

Besides the detailed photogeological and volcanological maps, the geological photointerpretation on the Oas and Gutai Mountains (OGM) led to the detailed deciphering of the fractural elements which affected the area following the lower Miocene obduction of the Pienidic Units from the Central-East Carpathians. The photogeological interpretation reveals the nappe units disposal of the Pienides system (Botiza, the Wildflysh and some other already mentioned units in the area like Magura, Babesti-Tiacovo, Kricevo, with different spatial and structural disposal from author to author). The slides structure composed by imbricate entities WSW/ENE oriented, with maximal development on 300-400 m width and 1-2 km length within an entity with frequent sequences of discordance is revealed. This image closely fits to the structural model of the frontal Nappes of the Botiza Unit as outlined in the area of maximum outcropping and is extended upon the entire Botiza and Wildflysch Units (conformable to the main entity of the nappe units upon which sporadic outcropping and consistent Upper Miocen sedimentary cover are observed). The development of the crystalline rocks assigned to the Internal Dacides Units vs. Tisia-Dacia as well as of the Cretaceous, Paleogene and Upper Miocene deposits and mostly of the Badenian-Pannonian volcanics have defined a crustal puzzle difficult to decipher, which favored different cartographic and structural interpretations. Based on the photogeologic image, the tectonic interpretation evidenced the major fractures in OGM area: 1. NE Gutai Fault, 2. Dragos Voda-Bogdan Voda Fault, 3. Suior-Baia Sprie Fault (the last two ones being frequently taken one for another), all sinistral strike-slips. We designed also the corresponding sintetic/antitetic faults, as well as other minor faults with considerable structural effects.
   The statistic analyses of all fractural alignments quantified by discordant measurable segments (considered proportionally with the value of the fractural amplitude) led to the vectorial representation of the major fractures and their associated syntetic/antitetic secondary faults (1., 2., 3.) advancing the cinematic model (translational and rotational) of the analyzed tectonic block (OGM). The model indicates northeastward movement and counterclockwise rotation (45°-60°) as compensation (retreating) effect of the convergence generated by the oblique collision of the major tectonic plates (East European Plate/African Plate). This cinematic hypothesis (collision at open angle to WSW) seems to infirm the closing sense of the oceanic basin, illustrated by the migration of the foreland basin depocenter in front of the Carpathian arc from W to SE and can be explained only by a specific oblique collision of this tectonic area. The reconciliatory advanced solution of the two interpretative scenarios regarding the Miocene kinematics of the area is a NE peninsula part of the Tisia-Dacia block or of a distinct crustal entity with its own kinematics (Zemplin), at northern joint of the Alcapa/Tisia-Dacia Units. A detailed evaluation of each fractural entity including compressive/distenssive associated assembles (pull apart, positive flower structure, double compressive bands, bypass bends, distenssive and compressive bends etc.) has been performed.