Hi Umberto,
crestal collapse is a term commonly referred to normal faulting active during or immediately after the growth of a tectonic-related or diapir- (salt, mud)related fold. In compression crestal faults trending near-parallel to the fold axis are located both in the forelimb or backlimb of a thrust-related anticline or are radial and concentric in the crestal zone of diapirs.
Post-orogenic collapse is an extensional phase that occurs after the mountain building and commonly but not necessarily by back-limb collapse of thrust-related anticlines.
Cheers,
Vittorio
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Dr. Vittorio Scisciani, PhD
Associate Professor in Structural Geology
and Seismic interpretation
Engineering and Geology Dept
University of Chieti
Campus Universitario Madonna delle Piane
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-----Messaggio originale-----
Da: Tectonics & structural geology discussion list [mailto:[log in to unmask]] Per conto di Umberto Fracassi
Inviato: giovedì 27 aprile 2017 11:33
A: [log in to unmask]
Oggetto: Crestal collapse: only a salt-related phenomenon?
Dear all,
while defining post-orogenic collapse during the inception of extensional phases, I am faced with a puzzling definition issue which I’d like to submit to the group.
Time and again, I have (improperly?) referred to major normal faulting that affects/disrupts major anticlines and fossilized thrust fronts as a “crestal collapse”. The cases of such “collapse” that I have in mind mostly refer to normal faulting affecting the back-limb of high-relief anticlines.
But my memory, it turns out, didn’t apparently serve me well enough, as it seems I have been using the wrong definition throughout. When I double checked to make sure I wasn’t out of track, the only field examples/natural analogs associated with crestal collapse seem to occur only when mobile units are involved. The oldest reference that I could find for such definition is a paper by Jaritz
Jaritz, W., 1973. Zur Entstehung der Salzstrukturen Nordwestdeutschlands. Geologisches Jahrbuch, A 10, 1–77.
Although I can’t speak german, “Salzstrukturen” must clearly have a lot to do with salt-related structural geology. It does make sense, of course, although I am unfamiliar with the complexities of salt tectonics and can thus appreciate the phenomenon but not fully describe it.
However, my point is: is the definition of crestal collapse solely to be related to that mechanism associated with salt tectonics? Or is this definition apt for back-limb collapse mechanism ensuing the slow-down of thust-belt mountain building? Or, in fact, would you just and simply define it a back-limb collapse fault, without the quest for an uncertain definition..?
Many thanks!
Umberto
Umberto Fracassi, Ph.D.
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