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Dear Richard, We have recently been looking at displacement gradients and differential exhumation on a set of normal faults in the Gulf of California rift. Maximum finite displacement was not as high as in your case, but we did see increases in fault displacement from <1-2km to ~7-9km over an along-strike distance of about 10-15km, and this too is accompanied by a change from high- to low-angle normal faulting (although there are no mylonites exposed). In our case, the faults are highly curviplanar and exhibit a series of antiformal/synformal megamullions with different "fold" limbs showing different fault kinematics. We attributed both the megamullions and the changes in fault kinematics to the constrictional strain regime of the PA-NA plate boundary. Have a look at the following papers (sorry for the shameless advertising) for additional details on the structural and thermochronological evolution (and stay tuned for a paper on the stratigraphic evolution of the supra-detachment basin currently in review): Seiler, C., Fletcher, J.M., Quigley, M.C., Gleadow, A.J.W., and Kohn, B.P., 2010, Neogene structural evolution of the Sierra San Felipe, Baja California: Evidence for proto-gulf transtension in the Gulf Extensional Province? Tectonophysics, v. 488, p. 87-109. Seiler, C., Fletcher, J.M., Kohn, B.P., Gleadow, A.J.W., and Raza, A., 2011, Low-temperature thermochronology of northern Baja California, Mexico: Decoupled slip-exhumation gradients and delayed onset of oblique rifting across the Gulf of California. Tectonics, v. 30, p. TC3004. King regards, Christian On 13/03/2012 12:27 PM, 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 -- Dr Christian Seiler School of Earth Sciences University of Melbourne Victoria 3010, Australia Email: [log in to unmask] Phone: +61 (0)3 8344 6910 Fax: +61 (0)3 8344 7761