Hello,
Stretching lineations parallel to fold axes (I guess that in your
case are simultaneous) indicate orientation of (finite) stretching,
but not necessarily tectonic transport direction, which is associated
to non-coaxiality.
Stretching lineations parallel to tectonic transport occur under
simple or sub-simple shear regimes but if you consider deformation
under general non-coaxial flow with the non-coaxial component of
deformation at high angle to maximum stretching you may find what you
see in the field: asymmetric folds with the stretching parallel to
the axes. This are the b-lineations of Sanders and are very common in
the inner parts of ancient orogenic belts.
Cheers,
Sergio
>"S. Mitra" wrote:
>
> > On Tue, 7 Nov 2000, Wojciech Czaplinski wrote:
> >
> > > Hello,
> > > Before I say farewell and unsubscribe from this group, there is one
> > > question I want to ask:
> > > It is commonly believed, that stretching lineation in the shear zones
> > > marks the direction of tectonic transport. So why the hell is it usually
> > > parallel to the folds' axes? Seems in contrary to me...
> >
> > hello,
> > well this ia a thing which is related to subsequent stages of shearing
> > when the cylindrical folds with fold axes perpendicular to the transport
> > direction gets dragged down forming seath folds, with a hair pin bend
> > developed on the fold axis. this might seemingly look as if the fold axes
> > were parallel to the stretching lineation
>
>Well, I've never seen any of those cylindrical folds from the _early_
>stages of shearing... Besides, the folds with axes parallel to the
>lineation are mostly consistently asymmetric...
>
>greetings - Wojtek
________________________
Sergio Llana-Funez
Geologisches Institut
Dept. Erdwissenschaften
NO H 36
Sonneggstrasse 5
ETH Zentrum
CH-8092 Zürich
SWITZERLAND
Tel: 41 1 632 6129
Fax: 41 1 632 1030
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