Sunday, 19 September 2010

word of the day

While reading a journal article* today I encountered a word I’d not noticed before: Aulacogen. The first mention in the article was "Continental extension that fails to lead to ocean opening and subsequently undergoes compression can occur at failed arms of ocean basins (aulacogens) and at intracontinental settings isolated from plate margins".

A quick check shows that there are 220 articles in scopus with that term used. (For comparison—“continental extension” yields 4,780 articles in scopus.) This is a somewhat specialized term, so I don’t feel bad that I missed noticing it (if, indeed, it has even been mentioned in the articles and textbooks I’ve read hitherto). Thus far my research has focused on the results of compression, be it deformation or metamorphism, rather than extension, so there would be no reason for me to think about what happens when extension starts and then stops before an ocean basin forms.

*Cawood, P. A., Kröner, A., Collins, W. J., Kusky, T. M., Mooney, W. D. and Windley, B. F. (2009). Accretionary orogens through Earth history. Geological Society Special Publication: 1-36.


Lockwood said...

I hadn't thought to do a web search, but this was a term that I had wondered if it was considered obsolete. I encountered it in historical geology (3rd class of our first year sequence) with respect to the Mississippi Valley Rift, and I recalled it as a failed rift, rather than focused on subsequent compression. I only encountered it a few more times in my class work, and only in passing.

Another such word is "obduction," which was used to denote accretion of ophiolitic terranes. My understanding is that these are currently believed to be the result of back-arc spreading almost exclusively, not accretion per se.

Silver Fox said...

Thanks for bringing up this word. I've heard it several times with regard to the geology of the west, and had thought it had something to do with "allochthon." Now I know better.

"Obduction" is used quite a bit in Nevada, often in reference to emplacement of the Roberts Mountains allochthon and later Golconda allocthon, both of which generally place deep ocean cherts and siliclastics over carbonates. For example, see this 2006 paper, which relates back-arc spreading to nearly coeval accretion.

Maybe the definition of the latter word has broadened?