Evidência de tensão N-S intraplaca no neógeno, Complexo Atuba - região de Curitiba (PR)

Abstract

In the structural framework of the Atuba Complex, the current or recent deformation is in the brittle regime due recent or reactivated faults in a dominant strike-slip system. Aside from the master faults at the regional scale that already coincide with reactivations of existing NE-SW and NW-SE alignments, new structures were generated starting in the Neogene with extensional and shear characteristics (hybrid) that agree with the maximum compressive stress ( σ 1) direction in the horizontal. These are also oriented N-S . Associated with the N-S structures, a prominent conjugate strike-slip system oriented N20-35E and N20-35W can be found. The shear fractures of these three families are responsible for the displacement and intense fracturing of diabase and lamproites dikes. The same strike-slip system causes slikensides and steps in the gneisses and metabasic rocks, as well as sub-vertical conjugate fractures that extend out into the sedimentary cover of the Curitiba Basin. Besides the strike-slip system, major shallowly-dipping (20 o to 30 o ) reverse faults exist, oriented close to N20W/35NE and N20E/20NW; their brittle shear generates cataclastic breccia in the gneisses and displacement in diabase dikes. The brittle low-angle shear zones are cut by the strike-slip system mentioned earlier. Such structuring and kinematics allow us to better characterize the D2’ event of Salamuni (1998), whose current or recent stress field presents a main σ 1 in the N-S direction.