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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