Richard,
you might be interested in the following paper where we discuss such gradients:
Oliver Schenk, Janos Urai, Wouter van der ZeeEvolution of Boudins under progressively decreasing pore pressure - a case study of pegmatites enclosed in marble deforming at high grade metamorphic conditions, Naxos, Greece. American Journal of Science, 307,1009-1033 (2007)
you can download a reprint from
http://www.ged.rwth-aachen.de/files/publications/publication_600.pdf
kind regards,
Janos
Prof. Dr. Janos L. Urai
Structural Geology, Tectonics and Geomechanics
RWTH Aachen University, Lochnerstrasse 4-20
D-52056 Aachen, Germany
T: +49 241 809 5723 M: +49 151 140 42552
e-mail: [log in to unmask]
www.ged.rwth-aachen.de
On 13 Mar 2012, at 02:27, Richard Styron wrote:
Assembled tectonicists,
In a field area of mine in SW Tibet, I have structural and thermochronological evidence for an increase in extension (heave) of a normal fault from ~2-3 km to ~15-18 km over an along-strike distance of about 15 km; this accompanies a change from high- to low-angle normal faulting and core-complex-like features (e.g., a well-developed normal-sense mylonitic shear zone). There is no obvious sign of transfer of extension to other structures; at this latitude, the fault seems to be the only game in town (other faults do play a role at greater distances though). The fault itself is >50 km along strike, but the zone of highest extension and low-angle normal faulting is restricted to near the middle of the fault. I have had trouble finding analogs in the literature for this magnitude of increase in extension over such a short distance. Does anybody know of other systems like this?
I am also interested in what this might mean for crustal rheology. The upper plate shows little sign of deformation, although within 10 km of the fault, the hanging wall is covered in a thick pile of moraine and alluvium. But that magnitude of extensional gradient over that distance intuitively suggests to me that the elastic thickness of the crust is very thin, and probably rather weak. The hanging wall might be deforming via distributed shear some how. There is a bit of literature on this (e.g., Ebinger et al., 1999, Phil. Trans. Royal Soc. London) but I am not finding a whole lot. Are there any key studies or insights out there that I might borrow?
thanks,
Richard Styron
University of Kansas
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