STREFY ŚCINANIA PODATNEGO NA OBSZARZE WAREŃSKIEJ STREFY RUDNEJ, POŁUDNIOWO-ZACHODNIA LITWA

Abstract

DUCTILE SHEAR ZONES FROM THE REGION OF VARENA ORE DEPOSITS, SOUTHWESTERN LITHUANIA

Abstract. Detailed structural analysis with kinematic elements from the region of Varena ore deposits region (VSR, southwestern Lithuania) is presented. The region occurs in the Middle Lithuanian Suture Zone between the West and East Lithuanian terranes. Based upon analysis of 5650 m of drill-cores from 68 boreholes, ductile shear zones, kinematic indicators, direction and sense of tectonic transport and deformation regimes were established for the first time. Rocks from the region show signs of dynamic metamorphism with variably developed mylonitic rocks. Mylonitic S/M foliation, locally forming complex foliation S/0+S/M, dips mostly at about 50-60 degrees. Using analysis of geophysical measurements of axis curvature in 21 boreholes and 30 oriented cores it was possible to define the dominant strike of S/M foliation in a direction approaching to the NW-SE with a dip mostly to the NE. The structural analysis with kinematic elements from the Varena ore region revealed the predominance of thrusting processes with the development of numerous ductile thrust sheets, imbrications and/or duplexes. These structures formed with a hanging-wall-to-the-top of boreholes i.e. towards SW. In this new tectonic interpretation, the Middle Lithuanian Suture Zone is a wide belt characterized by a transpressional deformation regime, which caused, which has caused SW ward displacements of numerous thrust sheets of the East Lithuanian terranes. This transpressional deformation with a dextral strike-slip component occurred during the collision of Fennoscandia with Sarmatia after the Svecofennian orogeny, approximately 1.70-1.62 Ga ago. Assuming such tectonic interpretation of the Middle Lithuanian Suture Zone altogether with the Varena ore region it seems possible that numerous magnetite ore deposits occur mainly in frontal domains of the thrust sheets. These domains are ranging in size from a few to a few tens km2 and were commonly thrusted to the SW. Skarns with magnetite ore deposits and mafic rocks form separate sheets or their sequences. More localized and younger were deformations connected with ductile-brittle and brittle faulting.