analogue modelling of multiple compressive phases deforming and extended margin

Abstract

Earlier extended continental margins are frequently involved into late compressive deformation during mountain building (i.e. orogenesis). This process gives rise to positive inversion of previous extensional faults, but these structures may also play different roles during late compressive phases, interacting in various ways with inherited structures from older tectonic stages.Moreover, different orientation of compression direction related to different phases affecting extended continental margins may give rise to complex structural settings whose evolution is often difficult to reconstruct. To address this problem, we performed an analogue model experimental series aiming at extending a continental margin and then imposing on the same margin differently oriented compressive phases. Models were quantitatively analyzed through particle image velocimetry (PIV) to highlight fault interaction, and by using Digital Elevation Models reconstructed with Structure from Motion (SfM) techniques. Our results show that well developed and favorably oriented normal fault systems drive the location of successive compressive structure, often through inversion processes, but they also condition the final geometrical setting without inversion. Moreover, an important role is also played by the orientation of the direction of compression (obliquity angle a varied from 0° to 90°), which gives rise to different structural patterns when is superimposed to extensional structures as a first compressive phase or is superimposed to already formed compressive structure as second compressive phase. The resultant complex structural patterns show differently oriented structures cutting each other even at high angles, a feature often seen in nature. Therefore, these experiments may be applied to a variety of natural cases, helping to decipher geological evolution of the analyzed areas basing on the geometrical relationships among structures.