Folds and folding - description

[@tarfaalajmi8162]

very useful , thank you.

[@tarfaalajmi8162]

May I ask : What's the relationship btw. thickness and wavelength ?

[@robbutler2095]

Thanks for the question. In the Biot-Ramberg theory for buckle folds... thicker layers fold on longer wavelengths than thinner layers. This assumes that the layers have the same viscosity contrast with the medium within which they are embedded - and that they behave as single layers. Check out the "How do rocks fold" video... and the images of the folded aplite veins embedded in granodiorite - from Ticino, Swiss Alps.

[@袁大神]

thank you so much！！！！

[@robbutler2095]

Glad you found it useful!

[@张宏远-z8t]

It is the first time for me to know parasitic fold. Can this type of fold is just taken as softer asymmetric folds which are geometrically appearing like the signal S,M,Z in different part of the larger folds ?

[@robbutler2095]

Yes indeed - parasitic folds can give the vergence - the relationship to larger-scale fold structures. While I'm writing - I'll just ay - I'm not a fan of the use of s and z-shaped fold usage... it depends upon which side of an outcrop you observe the parasitic folds. One approach is always to look down-plunge... which is fine as long as the folds don't change plunge (i.e. are curvilinear).... better to report vergence towards a geographic direction...

[@张宏远-z8t]

@@robbutler2095 Thanks a lot for the answer. Then that vergence usage of parasitic folds can be similar to "top to some direction" of a thrust.