Talk:Brittle–ductile transition zone

Wiki Education Foundation-supported course assignment
This article was the subject of a Wiki Education Foundation-supported course assignment, between 14 January 2021 and 5 May 2021. Further details are available on the course page. Student editor(s): Dadams305. Peer reviewers: Shelby Crisp.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 16:17, 16 January 2022 (UTC)

Untitled
Although it is correct that the increase in pressure with depth is an important part of defining the brittle-ductile transition zone by increasing the resistance to brittle fracture, it is equally important to consider the reduction in ductile strength with increasing depth and higher temperature. —Preceding unsigned comment added by Mikenorton (talk • contribs) 18:57, 10 October 2006


 * How would increased depth/pressure reduce the ductile strength? -- Petri Krohn 17:27, 11 October 2006 (UTC)

The ductile strength of minerals is decreased by increasing the temperature for a constant strain-rate. There is generally also a pressure dependence but the effect of temperature dominates. Mikenorton 21:57, 11 October 2006 (UTC)

Petri, to elaborate, the temperature dependence of strength is shown by experimentally derived ductile flow laws of the form

$$\dot{\epsilon}=A \sigma^n exp(-\frac{Q}{RT})$$

where $$\dot{\epsilon}$$ is the strain rate, $$\sigma$$ is the strength, n an exponent that varies from one (a Newtonian flow) upwards, A is a constant dependent on the material, Q the activation enthalpy for the process and T the absolute temperature

This is known as power-law flow and is generally thought to be a good representation of the ductile deformation of the lower parts of the crust and lithosphere e.g. http://www.geology.ucdavis.edu/~gel219/F05_billen/lecture3.pdf or http://www.uwgb.edu/dutchs/structge/strsparm.htm see also Creep (deformation)

It is therefore not correct to say that "deep rock does not become soft", it does but this is only half of the story because the brittle strength increase with depth as the increased confining pressure prevents fracture-related dilatancy, it is the combination of the two effects that is important. The link that you provided only tells half the story and so does the extra text you put in, best to leave it all out I think. Mikenorton 20:35, 16 November 2006 (UTC)

Evaluation of Article Content
Everything contained within the article is relevant to the topic in significant enough ways that they should be included. The cited information may be out of date as the newest source referenced in the article is from 2006, with the other two sources being from 2004 and 1990. Overall, the page is relatively short and could be expanded upon by more clearly explaining the idea that brittle-ductile transition zones do not occur at uniform depth and instead rely on a number of factors including material type and temperature. While the jargon is not flagrant, there are plenty of words which could be switched out to make their meanings more clear in context. The page does link to two other Wikipedia pages which are related, however, one of these two pages is not properly mentioned in the page itself and is only linked at the bottom.

Dadams305 (talk) 03:25, 2 March 2021 (UTC)