Friday, September 21, 2007

Structural geology and tectonics: the past, the future?

The newest newsletter from the GSA Structure/Tectonics division is out, and there's some interesting historical stuff in it. The current division chair, Bill Dunne, was working on revising the by-laws, and he discovered that the definition of the division needed revising. Eric Erslev, the incoming chair, is going to be leading a discussion at the division business meeting about what "structural geology and tectonics" means today. (Oct. 30, 5:30 pm. I'll be sitting in the back with my Advanced Structure students, ready for a conversation about what the discussion really meant.)

The original 1981 definition of the division is pretty intriguing (as Bill Dunne pointed out):

Of general interest are process-oriented research, mechanical interpretation, and field examples that are sufficiently well-documented so as to serve as models for the interpretation of other areas. Mountain-belt structure and tectonics would lie within this range of interest, but one would probably exclude geometrical and plate tectonics, a topic adequately covered at the AGU meetings. (emphasis mine)

Wow. In 1981, the new GSA structure/tectonics division considered plate tectonics to be a specialized concept, relegated to discussion at those crazy AGU meetings. And here I had thought that my high school earth science textbook was absurdly out-of-date, leaving out any significant discussion of plate tectonics in the early 80's.

And now, plate tectonics is so integrated in every aspect of geology that it is difficult to say what it should or shouldn't include. And that makes it hard to decide what to cover in an undergraduate tectonics class (such as I'm teaching this semester*). I just finished talking about various geophysical techniques that were important in developing plate tectonics (and which are still important in understanding tectonics). I'm going to spend most of the rest of the class talking about how various tectonic settings are recorded by different types of rocks, and about how continents behave (what do you do with rocks that don't behave like rigid plates, anyway?), and about studies of other planets that don't have plate tectonics, but do have mountains.

So I'm curious: what does "tectonics" mean to the geoblogosphere? (And is it arrogant for the structural geologists to claim it as theirs?)

* In case it's hard to keep track of what I'm teaching: currently I'm teaching Earth Systems Science, Geologic Methods, Plate Tectonics, and Advanced Structural Geology. And labs. If I'm missing from the geoblogosphere next week, it's because I'm grading too many exams.


Ron Schott said...

Just a quick, off-the-top-of-my-head definition would say that "tectonics" incorportates any regional or global studies that deal with plate interactions. I tend to have a fairly broad view of tectonics, and I definitely wouldn't cede it entirely to the structural geologists. I consider my Ph.D. research to have been very much a tectonics study; I was doing geochemistry, petrographic and isotope studies of conglomerate clasts (mostly igneous in origin) to interpret their provenance, which in turn had implications for the crustal evolution and displacement history of terranes mostly located in the California segment of the Cordillera. Despite the lack of classical structural studies in this thesis, I identify most strongly with tectonics as the overarching theme that tied my research together.

CJR said...

Surely this just relates to the fact that plate tectonics took a fair amount of time to become established over in the US? Hence lots of old structural geologists not wanting anything to do with what they considered to be a foolish fad...

I pretty much mentally label anything which studies deformation at more than the outcrop scale as tectonics. And continental tectonics - where rigid plates are non-existent or at least very small - is one of the more interesting bits.

Kim said...


I tend to have a fairly broad view of tectonics

Me too. I mean, it ties geology together, so nearly any subdiscipline within geology can be used in tectonic problems, and tectonics has some kind of relevance for most subdisciplines.

And I'm barely a structural geologist, if PhD research is what counts. I did metamorphic petrology and thermochronology, but I also looked at microstructures, and my first job was to teach structural geology... so I'm a structural geologist now, almost by default.

Chris - would you consider something like, say, John Suppe's work on fold-and-thrust belts to be tectonics rather than structural geology? I tend to put anything involving the "how" of rock deformation into structure, whether it's dealing with geometries or kinematics or mechanics. The "why" (and the "where," and the "when," at least on a large scale) I would tend to put into tectonics.