21 October 2016

Friday fold: a miniature ramp and flat

Posted by Callan Bentley

This is kind of fun – a folded and faulted block of chert (lens cap for scale) as seen along R40 in Barberton Mountain Land, South Africa. This is likely the Archean-aged Msauli Chert (~3.3 Ga). This block shows a nice “ramp and flat” fold/fault structure, a common “structural ingredient” in many fold and thrust belts, including the Appalachian Valley & Ridge province.


The harsh sunlight made me take a second photo, where the entire sample was in even shadow. I’m not sure, however, which image I prefer.


Here’s an annotated copy, with bedding highlighted in yellow, and faults in black. White arrows show the kinematics on the main fault. Minor back-thrusts on the trailing edge of this “proto-nappe” may


A miniature ramp and thrust… Too bad it wasn’t a wee bit smaller – I could have brought it home with me!