Talk:Nappe

Folding origin

The lead section uses the phrase "when folds are sheared so much that they fold back over on themselves and break apart" to describe how nappes are formed. This sounds too restrictive in that it seems to require folding plus inversion of layers and fragmentation of the sheared material. See the Structure section which seems much more encompassing and which I read as allowing an unfolded, unfragmented, sheared layer to also be a nappe.

Can someone with some geological background look at this and try to bring the lead and the Structure section into consistency and provide references. Thanks,
SBaker43 (talk) 23:32, 27 April 2013 (UTC)[reply]

Reworded the lead to remove the rather garbled bit (been there since 2006). Did it off the top o me head :) then followed up by finding a supporting ref in Twiss' Structural Geology. Need to find a supporting ref for the structure section and maybe tweak it a bit ... but, another day. Vsmith (talk) 02:32, 28 April 2013 (UTC)[reply]

I've added "thrust sheet" as an alternative, because the term "nappe" tends to be mainly (but certainly not exclusively) used these days to describe structures in the Alps, whereas "thrust sheet" is the term mainly used to describe structures in the Rockies, Scottish Highlands and elsewhere. However, nothing is ever simple when it comes to terminology - you can still find reference to the "Moine Nappe", although "Moine Thrust Sheet" is much more common. I have one source that says that a thrust sheet becomes a nappe if the displacement is greater than 10 km (page 521). Robert Hatcher refers to type F thrust sheets, that involve folding and completely plastic behaviour, which would generally be referred to as "nappes". I'll keep on looking to see if some degree of clarity appears. Mikenorton (talk) 12:46, 28 April 2013 (UTC)[reply]

Thanks to both of you for your prompt attention to this issue. SBaker43 (talk) 17:24, 1 May 2013 (UTC)[reply]

Typically low angle thrust faults

If they are "thrust over another rock mass typically at a low angle," when are they thrust over at a high angle? Please add this information if you want to qualify that it is only "typically" low angle. Thanks. -68.107.137.178 (talk) 17:31, 28 April 2013 (UTC)[reply]

Seems the nappes or thrust sheets as used in the literature involve low angle to near horizontal movement over relatively long distances. Do you know of high angle nappes? The diagram in the article illustrates the concept. Vsmith (talk) 18:09, 28 April 2013 (UTC)[reply]

This is not "typically" at a low angle, it is at a low angle. You are the one who reinserted the qualifier, so that they sentence now means, "usually," or "most often," although it can also means characteristically, it is not being used to characterize thrust faults and does not enhance the meaning of the sentence. If low angle does not need to be qualified, then just leave it at low angle. The qualifier simply adds a level of variance where it does not exist. Since you now challenge me to add "high angle" thrust faults, why are you qualifying nappes to be only "typically" low angle? -68.107.137.178 (talk) 18:20, 28 April 2013 (UTC)[reply]

I've had a go at rewording it some, though I sense that the whole thing probably needs redoing. Mikenorton (talk) 20:21, 28 April 2013 (UTC)[reply]

Yes, but it is a bit better. Thanks. -68.107.137.178 (talk) 20:41, 28 April 2013 (UTC)[reply]

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Who first described nappes (thrust sheets)?

The current text suggests, with little in the way of supporting sources, that Bertrand was the first to propose large scale thrust movement and that "Several years later, nappe structure was investigated in northwestern Scotland by Charles Lapworth." This doesn't really seem to fit with the timeline that I can find. His work on the Glarus, with his reinterpretation of Heim's double-fold as a surface of displacement was published in 1884,[1] the same year that Peach and Horne and Geikie published the former's interpretation of the Eriboll area and in which the term "thrust-plane" first appeared, quoting Geikie "The distance to which this horizontal displacement has reached is almost incredible. In Durness, for example, the overlying schists have certainly been thrust westwards across all the other rocks for at least ten miles." Through Lapworth's contact with Heim, and Peach and Horne's contact with Lapworth and Callaway (amongst others and all before 1884), this was simply one of those ideas whose time had come and the best that can be said is that the thrust/nappe hypothesis was arrived at by multiple groups working in different countries at almost the same time - the same can be said for Törnebohm in Sweden and McConnell in Canada. Major advances are rarely the result of an individual working alone. I'm going to try to reword this in an attempt to do justice to everyone involved - this was not a race - there's no gold medal. Mikenorton (talk) 19:46, 23 July 2018 (UTC)[reply]