Segmentation and linkage of the Lessini Mountains normal faults, Southern Alps, Italy

The Lessini Mountains on the southern margin of the Italian Southern Alps exhibit two Tertiary graben systems at an angle of about 40°. The NNW-trending system is orthogonal to the ENE-trending Tertiary extension direction. The NNE-trending system parallels the neighbouring Jurassic western margin of the Trento Platform and experienced sinistral transtension during the Paleogene. The interaction between the two normal fault trends defines a ca. 8 km long and 6 km wide rhomb-shaped structure containing igneous intrusions and dolomitized rock bodies, suggesting that the structure controlled syn-extensional fluid migration. At a smaller scale, fault segments of the NNE-trending set show two basic types of transfer zones, i.e. conjugate and synthetic. Due to the sinistral and normal oblique-slip on these faults, left steps of en e´chelon segments had a kinematics similar to that of pull-apart structures. The location of intrusion-centres within such transfer zones led to the collapse of the roof of the magma chambers and consequent deep basins development. In contrast, right-stepping synthetic en e´chelon normal-oblique fault segments developed relay ramps. © 2000 Elsevier Science B.V. All rights reserved.