Hello Manuel, Dani, Giorgio, John and others,
I agree that the orientation of porphyroclasts cannot be easily used to
calculate the vorticity number of the matrix due to particle
stabillization. Giorgio emphasized the role of slip / decoupling
between matrix and particle as a factor that stabillizes particles. An
alternative mechanism is of course the partitioning of vorticity around
rigid particles in anastomosing shear bands or cleavage septae. The
rotation of rigid particles in viscous fluids as a function of particle
shape, particle viscoisty, variable flow parameters, interaction
between adjacent particles, matrix-particle decoupling etc. has been
extensively studied in experiment, but very few articles have tested
the models against quantitative orientation data from natural
porphyroclasts or porphyroblasts. Giorgi's work is a notable exception
in this respect, but more work is needed. Some other papers I know of
include:
Hayward, N., 1992. Microstructural analysis of the classical spiral
garnet porphyroblasts of south-east Vermont: evidence for non-rotation.
Journal of Metamorphic Geology 10, 567-587.
Visser, P. Mancktelow, N.S., 1993. The rotation of garnet
porphyroblasts around a single fold, Lukmanier Pass, Central Alps.
Journal of Structural Geology 14, 1193-1202
Forde, A. & Bell, T.H., 1993. The rotation of garnet porphyroblasts
around a single fold in the Lukmanier Pass, Central Alps: Discussion.
Journal of Structural Geology 15, 1365-1368.
Hickey, K.A.and Bell, T.H. , 1999. Behaviour of rigid objects during
deformation and metamorphism: a test using schists from the Bolton
syncline, Connecticut, USA. Journal of Metamorphic Geology, 17,
211-228.
P.M. Evins, 2005. A 3D study of aligned porphyroblast inclusion trails
across shear zones and folds. Journal of Structural Geology
27,1300–1314
These studies make it clear that direct application of straight-forward
fluid dynamics is not possible.
Regards,
Domingo
On 7 Oct 2005, at 17:20, Giorgio Pennacchioni wrote:
> Hello Manuel,
> I agree with Dani's opinion. In most natural mylonites, the reason
> for porphyroclasts stabilization is not the presence of a component
> of pure shear in the flow. Therefore, the orientation of
> porphyroclasts cannot be easily used to calculate the vorticity
> number.
> There is an extensive recent bibliography about the topic.
> The following papers of mine (as well the Dani's papers) can be
> useful to illustrate what I mean:
> • Pennacchioni, G., Di Toro, G. and Mancktelow, N.S., 2001.
> Strain-insensitive shape preferred orientation of porphyroclasts in
> Mont Mary mylonites. Journal of Structural Geology 23/8, 1281-1298.
> • Mancktelow, N.S., Arbaret, L. and Pennacchioni, G., 2002.
> Experimental observations on the effect of interface slip on rotation
> and stabilization of rigid particles in simple shear and a comparison
> with natural mylonites. Journal of Structural Geology 24/3, 567-585
> • Ceriani, S., Mancktelow, N.S., and Pennacchioni, G., 2003.
> Analogue modelling of the influence of shape and particle/matrix
> interface lubrication on the rotational behaviour of rigid particles
> in simple shear. Journal of Structural Geology 25, 2005-2021.
> See also
>
> • ten Grotenhuis, S.M., Passchier, C.W., Bons, P.D., 2002a. The
> influence of strain localization on the rotation behaviour of rigid
> objects in experimental shear zones. Journal of Structural Geology 24,
> 485–499.
> Marques and co-workers also published numerous papers about numerical
> and analogue experiments on porphyroclast behaviour with in a viscous
> matrix . You can see their last work, which contain a comprehensive
> list of references, between the in-press paper on JSG. I also suggest
> reading:
> • Mandal N, Samanta SK, Bhattacharyya G, et al.Rotation behaviour of
> rigid inclusions in multiple association: insights from experimental
> and theoretical models .JOURNAL OF STRUCTURAL GEOLOGY 27 (4): 679-692
> 2005
> • Mandal N, Bhattacharyya G, Chakraborty C.Extensional detachment at
> the inclusion-matrix interface in a multiple inclusion system JOURNAL
> OF STRUCTURAL GEOLOGY 26 (10): 1773-1781 2004
>
> regards
> Giorgio
>
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>> From: Dani Schmid <[log in to unmask]>
>> Subject: particles
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>>
>> Hi Manuel,
>>
>> you can find some publications on my website that may be relevant:
>>
>> http://folk.uio.no/schmid/publications.html
>>
>> As you will see I don't believe that there are many cases where
>> particle
>> stabilization is due to combinations of pure and simple shear.
>>
>> regards,
>>
>> Dani
>>
>> --------------------------------------------
>> Dani Schmid
>> Physics of Geological Processes
>> University of Oslo
>> Pb 1048 Blindern
>> 0316 Oslo
>> Norway
>>
>> fon: +47 22 85 64 84
>> mob: +47 98 00 01 20
>> fax: +47 22 85 51 01
>> skype: dw_schmid
>> http://folk.uio.no/schmid
>> =======================================================
>
> Prof. Giorgio Pennacchioni
>
> Dipartimento di Geologia, Paleontologia e Geofisica
> Università di Padova
> Via Giotto 1 - 35137 Padova
> Italy
>
> Phone: +39-049-8273938
> mobile: 333 9158584
> fax: +39-049-8272070
> e-mail: [log in to unmask]
>
> ========================================================
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