Dear Umberto,
Some triangular facets form by kink-band migration that folds the
land surface. They are associated with a discontinuity in uplift
rate. There are wonderful examples near Kuche in the southern
Tianshan. They are documented in detail in a paper on "active
folding of the landscape in the southern Tianshan, China" that is
coming out in JGR this Fall with Aurelia Hubert-Ferrari as first
author. They are also briefly illustrated in pages 31-33 of a
conference field trip guidebook available at:
http://geoweb.princeton.edu/beijingconference/
I can't tell from your description whether or not your triangular
facets have anything to do with a localized discontinuity in uplift
rate, which is what is common to classic triangular facets of normal
fault scarps and to triangular facets of fold scarps. But maybe this
will help think about it.
Best wishes,
John
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