Also in this hot summer, someone standing close of their office desk and
open their eyes and brains when some interesting discussions has begun in
tectonic mailing data-base.
In fact, I think that discussion between simple shear against pure shear
is not only interesting for the didactical student stimulation....
Moreover, it can appoint some keys to understand why we found differences
between the deformation style in the lower crust (where usually we found
more evidences of pure shear against simple shear), and the upper crust
(where volume change is easier that in lower crust and consequently the
wide the shear bands are bigger).
On the other hand, kinematics criteria and its implications also must be
analysing careful.
First, because it need a 3D stress field analyse as appoint the last
Passchier work's and many field evidences that everybody has found in lower
crust outcrops (x, y and z components of stress tensor must be define in
order to know exactly how we must be interpret the developed fabric), and
second, if we trait to define the stress principal components from the
deformed state be must know exactly the kind of strain mechanism operative
in these rock, because s1 is containing in the stretching plane, if we have
simple shear, but the stretching plane include stretching lineation, which
is non always parallel to s1 and the intersection grain shape lineation,
which define the true s1 position).
Any way, really I think both extremes mechanisms coeval in almost cases.
This considerations open other discussion windows, like Newtonian
mechanical against the theory of potential, etc..., Thereby it happen
still enjoying this hot summer
Hasta la vista babes.
Francisco J. Fernández
Dpto de Geología
Área de Geodinámica
Universidad de Oviedo
C/Arias de Velasco SN
33005 Oviedo. Spain
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if God does not throw dice in physics, why would we settle for just pure
shear
in geoscience?
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http://www.geol.uniovi.es/Users/FJFdez.html
phone: 34-985103150
FAX 34-985103103
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