Hello Koushik,
This is rather broad question that may not have a
simple and short answer. The following is just a
list of suggestions and many competent colleagues
will certainly add to this.
REFERENCES
In granitic rocks, one of the minerals that is
best understood from a microstructural point of
view is quartz. In my experience it is also one
of the most sensitive mineral to successive
deformation events. The following references
might be of interest to your research:
*Gapais, D. and Barbarin, B., 1986. Quartz fabric
transition in a cooling syntectonic granite
(Hermitage Massif, France). Tectonophysics, 125:
357-370.
*Paterson, S.R., Vernon, R.H. and Tobish, O.T.,
1989. A review of criteria for the identification
of magmatic and tectonic foliations in
granitoids. Journal of Structural Geology, 11(3):
349-363.
*Bouchez, J.L., Delas, C., Gleizes, G., Nédélec,
A. and Cuney, M., 1992. Submagmatic
microfractures in granites. Geology, 20: 35-38
(although this concerns mainly feldspars)
*Kruhl, J.H., 1996. Prism- and basal-plane
parallel subgrain boundaries in quartz: a
microstructural geothermobarometer. Journal of
Metamorphic Geology, 14: 581-589.
*Okudaira, T., Takeshita, T. and Toriumi, M.,
1998. Prism- and basal-plane parallel subgrain
boundaries in quartz: a microstructural
geotherobarometer. Journal of Metamorphic
Geology, 16: 141-146.
*Trepmann, C.A. and Stöckhert, B., 2003. Quartz
microstructures developed during non-steady state
plastic flow at rapidly decaying stress and
strain rate. Journal of Structural Geology, 25:
2035-2051.
* Fitz Gerald, J.D. and Stünitz, H., 1993.
Deformation of granitoids at low metamorphic
grade. I: Reactions and grain size reduction.
Tectonophysics, 221: 269-297.
* Stünitz, H. and Fitz Gerald, J.D., 1993.
Deformation of granitoids at low metamorphic
grade. II: Granular flow in albite-rich
mylonites. Tectonophysics, 221: 299-324.
SEPARATING TWO THERMAL EVENTS
If I understand correctly, the problem that you
are trying to solve is to separate two
deformation events. If the two events have
occurred at significantly different temperatures,
quartz microstructures associated with each event
might be distinguishable. Cathodoluminescence
might prove to be a useful tool.
SEPARATING TWO STRUCTURAL EVENTS
If the two events occurred under relatively
similar conditions of temperature, your best shot
might be to check if in different spatial domains
one of the two events might be best preserved
than the other one. If the two events have
different principal strain direction, then
perhaps quartz C-axes fabrics might be the
solution.
HOPE FROM FLUID INCLUSION STUDIES
Finally, in the mining world, subtle differences
between successive deformation events can be
resolved by looking at the composition of fluid
inclusions in quartz as well as the systematic
orientation of fluid inclusion trails (as a
response to local stress).
I hope this helps and best of luck,
Sincerely,
Eric
>Hi,
>My query is in relation with the Pre-Himalayn
>granites [Proterozoic and Pan-African] of the
>Himalayas. Can anyone help me regarding how to
>infer the effect of Himalayan Orogeny in the
>microstructures of these granites and the
>associated mylonites? Since these Granites may
>have imprints of solid state deformation fabric
>on them due to Pre-Himalayan tectonics as well I
>find it challenging to work out the signature
>of Himalayan tectonics on them. I would like to
>know if there are any microstructural criteria
>to resolve solid state deformation fabrics
>related to emplacement and expansion of these
>bodies and that caused by a much younger
>tectonic event. This will be of immense help to
>use these granites as strain intensity gauges
>since they are widespread along almost all the
>major tectonic division of the Himalayas. I hope
>I have coneyed my problem properly. Will wait
>for suggestions.
>
>Best Regards
>Koushik
>
>--
>Dr. Koushik Sen
>Scientist 'B'
>Wadia Institute of Himalayan Geology
>Dehra Dun- 248001
>India
--
Dr Eric Ferre
Associate Professor
Department of Geology
Southern Illinois University
Mailcode 4324
Carbondale, IL 62901
USA
E-mail: [log in to unmask]
Phone: +1 (618) 453-7368
Fax: +1 (618) 453-7393
Office: Parkinson Hall, room 301B
http://www.geology.siu.edu/people/ferre/index.html
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