On the evolution of Subduction-Transform Edge Propagators (STEPs): consequences for the Calabrian arc

Abstract:

Passive margins are first order strength contrasts between ocean and continents, and they may therefore play a critical role in steering the propagation direction of STEPs. Subduction history potentially is also relevant because it is a decisive factor for the forces that drive continued subduction. In this study we explore these factors with mechanical models.

Results show that a STEP will follow a passive margin as long as variations in strike remain within 20 degrees. A change in strike of the passive margin ahead of the STEP of less than 15 degrees results in propagation along the passive margin. If the change in strike of the margin is greater than 15 degrees, the STEP will propagate into the direction that it had before reaching the change in margin strike. Surprisingly, subduction history and strength contrast are less relevant.

The results shed light on the evolution of the Calabrian arc (central Mediterranean) after the Miocene: slab rollback towards the ESE was facilitated by a roughly W-E oriented STEP that followed the Africa-Ionian passive margin along the north coast of Sicily. The geology of NE Sicily suggests that this passive margin changed orientation here and was parallel to the present-day Sisifo fault. Given that this corresponds to a moderate orientation change, the active STEP continued to follow the margin. The next orientation change of the passive margin, to the one that is bounded by the Malta Escarpment, was approximately 50 degrees. Based on our model results, we therefore predict that the STEP propagated into the Ionian basin in a direction that was approximately parallel to the Sisifo fault. Interestingly, the predicted location of the present-day STEP fault in the basement at the SW termination of the Calabrian trench appears to correspond with a significant discontinuity within the accretionary wedge.