Long-lived mega fault-scarps and related breccias at distal rifted margins: insights from present-day and fossil analogues

Abstract

Thinning of the continental crust during rifting is accommodated by a number of major faults, only a few of which produce long-lived mega fault-scarps. In this paper, we investigate mega fault-scarps and the sedimentary system located at their toe across magma-poor rifted margins. Our approach combines observations from subsurface examples along present-day margins and field analysis of fossil examples exposed in the Alpine Tethys margins. Whereas present-day examples of rifted margins imaged by seismic techniques provide details about the architecture of the top basement and the relationship between faults and sediments, outcrops give access to the sedimentary features of rocks related to mega fault-scarps. Our study shows that (1) mega fault-scarps are preferentially located at rift domain boundaries, implying a topographic escarpment that juxtaposes rift domains of different crustal thickness, and (2) mega fault-scarps are long-lived local sources for syn- and post-tectonic breccia, respectively produced during and after fault activity.