Dear Carl,
Thank you for the references. In general I am seeing that in the
Himalayan Granites (both paleozoic and proterozoic but not the
tertiary leucogranites) strike of both mesoscopic and magnetic
foliation are similar (mostly), but the dip is much steeper in case of
magnetic foliation. I think it is because of tertiary collissional
tectonics. But as per your suggestion I would look into the mineralogy
in detail now. Things may not be as straight forward as I thought. I
believe analysis of composite fabric in these granitoids will throw
more light in the tectonic evolution of the whole orogeny. Till now
there is very few work on the field and magnetic fabric of these
granites. I would like to discuss this problem in detail once I
finalise my data set. That'll be higly beneficial for me.
Best Regards
koushik
On Mon, Apr 6, 2009 at 3:04 PM, Carl Stevenson <[log in to unmask]> wrote:
> To follow Seth Kruckenburg's suggestion, if you can do thermomag, the original reference (as far as I know) is:
>
> Orlicky, O., 1990, Detection of Magnetic Carriers in Rocks - Results of Susceptibility Changes in Powdered Rock Samples Induced by Temperature: Physics of the Earth and Planetary Interiors, v. 63, p. 66-70.
>
> Related is:
>
> Trindade, R. I. F., T. M. M. Nguema, and J. L. Bouchez, 2001, Thermally enhanced mimetic fabric of magnetite in a biotite granite: Geophysical Research Letters, v. 28, p. 2687-2690.
>
> And then in relation to the above we did some heating and high field experiments - we didn't get inverse AMS:
>
> Stevenson, C. T. E., W. H. Owens, and D. H. W. Hutton, 2007, Flow lobes in granite: the determination of magma flow direction in the Trawenagh Bay Granite, N. W. Ireland, using anisotropy of magnetic susceptibility: Geological Society of America Bulletin, v 119, p. 1368-1386.
>
> Cheers
> Carl
>
>
> -----Original Message-----
> From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of koushik sen
> Sent: 06 April 2009 05:04
> To: [log in to unmask]
> Subject: Re: on composite fabric in granitoids
>
> Thank you everyone. the suggestions and references will be of great
> help. I dont have MFK here but will definitely do thermal demag to
> have a idea about the magnetominerology. SEM of biotite (for
> inclusions) may also be a good idea. Thank you again.
>
> Best Regards
> Koushik
>
> On Mon, Apr 6, 2009 at 4:35 AM, Seth Kruckenberg <[log in to unmask]> wrote:
>> As suggested by C. Stevenson, the combination of thermomagnetic analyses +
>> hysteresis properties should give you a good indication if you have multiple
>> magnetic phases (e.g. biotite + magnetite subfabrics) contributing to your
>> AMS (e.g. biotite + magnetite subfabrics). You may want to consider, if you
>> haven't already, looking at representative thin sections of your samples for
>> the presence of inclusions in the mafic silicates or for the presence of
>> sulfides that could complicate the interpretation further. If your samples
>> are dominantly paramagnetic, inclusion of magnetite within biotite can
>> actually yield a net inverse AMS as discussed by Borradaile and Werner.
>>
>> Borradaile, G. J. and T. Werner (1994). "Magnetic anisotropy of some
>> phyllosilicates."
>> Tectonophysics 235: 223-248.
>>
>> Cheers and best of luck! Seth
>>
>> /*--------
>> Seth C Kruckenberg --> [log in to unmask]
>> Structure, Tectonics, & Metamorphic Petrology Research Group,
>> Department of Geology & Geophysics,
>> 108 Pillsbury Hall, University of Minnesota, 310 Pillsbury Dr SE,
>> Minneapolis, MN, 55455
>> http://www.umn.edu/~kruc0030
>> ---------*/
>>
>>
>>
>>
>>
>> On Apr 5, 2009, at 7:46 AM, koushik sen wrote:
>>
>>> Can anyone provide me some references regarding development of
>>> composite fabric in granitic rocks i.e. where the mesoscopic
>>> fabric(magmatic/gneissosity) and magnetic fabric (AMS) fabric are
>>> discordant? I am presently working on some Proterozoic and Paleozoic
>>> granitoids of Himalaya and there is discrepancy in their field and AMS
>>> fabric. This must have been caused by the Tertiary orogeny. Can anyone
>>> provide information about similar work from other parts of the world?
>>>
>>> Best Regards
>>> Koushik
>>>
>>> --
>>> Dr. Koushik Sen
>>> Scientist 'B'
>>> Wadia Institute of Himalayan Geology
>>> Dehra Dun- 248001
>>> India
>>
>
>
>
> --
> Dr. Koushik Sen
> Scientist 'B'
> Wadia Institute of Himalayan Geology
> Dehra Dun- 248001
> India
>
--
Dr. Koushik Sen
Scientist 'B'
Wadia Institute of Himalayan Geology
Dehra Dun- 248001
India
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