Supplementing Nigel's citations, quoting from:
"J. L. Rosenfeld and G. P. Eaton, 1958, Trip A: Stratigraphy, Structure, and the Metamorphism in the Middle Haddam Quadrangle and Vicinity, 50th Annual Meeting of the New England Intercollegiate Geological Conference, Wesleyan University, Middletown, Connecticut." [photocopy on request]
we said:
"In many cases, fine grained clots of sillimanite show by their approximately-equivalent size and shape that they are pseudomorphs after the kyanite porphyroblasts with which they coexist." In the guidebook we also described the field stop and discussed at length the P-T path indicated in relation to the P-T boundary between the two minerals then recently determined by S. P. Clark and others (1957).
Also in:
"H. G. Adams, L. H. Cohen and J. L. Rosenfeld, 1975,
Solid Inclusion Piezothermometry II: Geometric Basis, Calibration for the Association Quartz-Garnet, and Application to Some Pelitic Schists,
V. 60, pp. 584-598."
on p. 596-597 we show a photomicrograph of a selvage of bent sillimanite needles on a bent kyanite porphyroblast near Bronich in the Lukmanier Pass region, Switzerland, far north of the mapped sillimanite isograd. The sillimanite needles show less bending than the kyanite porphyroblast and are therefore later. We considered the occurrence as evidence of a P-T path from the kyanite field of stability into the sillimanite field of stability as a result of unloading that took place late in the Alpine orogeny, possibly facilitated by the strain energy of bending. The description is related to the work on solid inclusion piezothermometry (a.k.a. "thermobarometry").
John
Hi all,
If the discussion is widening, kyanite pseudomorphing andalusite is reported in:
Ahmed-Said and Tanner, P-T conditions during emplacement, and D2 regional metamorphism, of the Ben Vuirich Granite, Perthshire, Scotland. Mineralogical Magazine, 2000; v. 64, p. 737-753.
and back in 1968 Graham Chinner (Min Mag 36, 1052-1068) recorded (for the first time ?) sillimanite replacing kyanite in the Limpopo belt.
?
Nigel Harris
On Thursday30 Jul 2009, at 16:35, [log in to unmask] wrote:
Hi all,
we studied a similar occurrence in:
Cesare B., Gomez-Pugnaire M.T., Sanchez-Navas A. & Grobety B. (2002)
Andalusite - sillimanite replacement (Mazarrón - SE Spain):
microstructural and TEM study.American Mineralogist, 87. 433-444.
Another partial pseudomorph of Sil on And, with the involvement of
staurolite inclusions, is in:
Cesare B. (1994) Hercynite as the product of staurolite decomposition in
the contact aureole of Vedrette di Ries, eastern Alps, Italy.
Contributions to Mineralogy and Petrology, 116, 239-246
For more on epitaxy among Al2SiO5 polymorphs see also:
Cesare B. and Grobety B. (1995) Epitaxial replacement of kyanite by
staurolite: a TEM study of the microstructures. American Mineralogist.,
95, 78-86
Regards,
Bernardo
--
Bernardo Cesare
Dipartimento di Geoscienze
Via Giotto, 1, I-35137 PADOVA ITALY
Tel: ++39-049-8272019 Fax: ++39-049-8272010
email: [log in to unmask]
web site: http://www.dmp.unipd.it/bernardo/bernardo.html
Hi,
Following on Bob Tracy's comment, I attach two images of sillimanite after
andalusite from the LPHT metamorphic rocks of the Peninsular Ranges
batholith, Baja California, Mexico. As a side note, Ron Vernon was
actually
in the field with me the year (1997 or 1998?) that I collected this
sample.
We could actually see the large chiastolitic grain shapes in the samples,
so
assumed that it was andalusite. We also noted some blue coloration and I
was
excited about the possibility of finding kyanite. Turns out it is all
sillimanite - barely a trace of remnant andalusite in the samples
collected.
The EBSD data show that sillimanite with three different c-axis
orientations
replaced the chiastolite grains. Note that the sillimanite crosses grew
between the chiastolitic sector zone boundaries. Note also that the
sillimanite replacing the main body of the andalusite has recrystallized.
I would be interested to know if anyone has seen this type of
microstructure
before. We are considering possibly working this up for a short
publication.
Cheers - Scott
*************************************************************************
Scott E. Johnson
Department of Earth Sciences
5790 Bryand Global Sciences Center
University of Maine
Orono, ME 04469-5790
USA
email: [log in to unmask]
phone: (207) 581-2142
Fax: (207) 581 2202
<blocked::http://www.geology.um.maine.edu/user/scott_johnson/HM.html>
http://www.geology.um.maine.edu/user/scott_johnson/HM.html
<blocked::http://www.geology.um.maine.edu/geodynamics/>
http://www.geology.um.maine.edu/geodynamics/
*************************************************************************
From: Metamorphic Studies Group [mailto:[log in to unmask]]
On
Behalf Of Robert Tracy
Sent: Sunday, July 26, 2009 7:29 AM
To: [log in to unmask]
Subject: Re: oriented sillimanite after ?andalusite
Hanan Kisch's comments are very interesting. When I first saw the
photomicrographs, I immediately thought of sillimanite replacements of
andalusite (sometimes quite large original andalusite crystals up to cm in
scale) that occurs in rocks of southern New Hampshire and central
Massachusetts USA. In many cases the replacement (a pseudomorphing of a
kind) is complete, but the single large original chiastolite grain shapes
(commonly even with carbonaceous crosses) are perfectly preserved by finer
grained aggregates of sillimanites in multiple orientations, but all
apparently sharing a common c-axis orientation. In thin sections cut
across
the foliation and lineation of the rock, the classic diamond shapes of the
individual sillimanite grains can be seen in the replacements. John
Rosenfeld wrote an admirable description of this phenomenon in a paper in
American Journal of Science in 1969 (the Al-silicate issue), and several
papers or field guides by Peter Robinson and his students in the late
1970s
and early 1980s also describe these composite replacement textures.
The replacement occurs at sillimanite + K-feldspar grade and commonly with
migmatization, probably at T of ca. 750C at roughly 0.6 GPa. Our
interpretation was of an early low-P contact metamorphic phase related to
magmatism in a Taconic back-arc setting, succeeded by an increase in P as
well as T in a more regional event , although still dominated by magmatic
heating (so-called "anti-clockwise P-T trajectory" similar to that
described
in the New England terrane of Australia by Ron Vernon and Bill Collins).
My
impression is that whereas Hanan's case from Norway represents two
distinct
events separated in time, the New England USA occurrence is more likely a
continuum that starts in the ca, 440-445 Ma time frame with contact
metamorphism and the regional phase is likely at 430-435. Looking back
again
at his message, however, there is a striking similarity of timing and
overall character (not uncommon for Caledonian phenomena in Norway,
northern
UK and in the northern Appalachians).
Bob Tracy
Hanan Kisch wrote:
Dear Dr Homam,
A belated comment.
Coarse sillimanite porphyroblasts (Kisch 1962, Plate VII, fig. 2 and Plate
VII, fig. 1) along the western contact of the Fongen-Hyllingen gabbro
complex in the Tydal area, central Caledonides of the eastern Trondheim
region, contain sillimanite in two orientations (ibid., Plate VII, fig.
2).
This silimanite was probably formed as replacement of andalusite, which
occurs further south in the contact aureole of the southern termination of
the gabbro (Vogt 1941; Birkeland & Nilsen 1972). The gabbro was dated as
late Silurian; together with its contact aureole, it was overprinted by
late-Caledonian staurolite-kyanite grade regional metamorphism.
References :
Kisch, H.J. (1962) Petrographical and geological investigations in the
southwestern Tydal region, Sör-Tröndelag, Norway. Acad. Proefschr., Univ.
of Amsterdam, 136 pp.
Vogt, Th. (1941). Geological notes on the Dictyonema locality and the
upper
Gauldal district in the Trondheim area. Norsk Geol. Tidsskr. 20, 171-192.
Birkeland, T. & Nilsen, O. (1972) Contact metamorphism associated with
gabbros in the Trondheim region. Norges Geol. Unders. 273, 13-22.
I hope that this is some help.
Regards,
Hanan Kisch
Dear All
As Freshte (Ranjbar) supervisor I would like to express my honest
acknowledgement for your valuable comments regarding andalusite query.
What
we have in region seems to be a very complex metamorphic case but most
probably a contact metamorphism followed by a regional deformation.
Andaluasit as medium to large fully oriented grain, garnet, fibrolite and
cordierite (?) can be seen in thin sections. No staurolite has been found.
Using different direction sectioning from the sample helped us to find
what
was the mineral. As a matter of fact it was noting but an oriented growth
of
sillimanite in andalusite, very similar with that reported by Prof. Vernon
(1987) from Juan Tabo area, USA.
Best Regards
Dr. S. M. Homam
_____
_____
Share your memories online with anyone you want. Learn more.
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Prof. Hanan J. Kisch
Department of Geological and Environmental Sciences
Ben-Gurion University of the Negev
P.O.B. 653, Beer-Sheva 84105, Israel
Tel.: +972 8 646 1290
Fax (Dept office): +972 8 647 2997 and +972 8 647 7655
E-mail: [log in to unmask]
--
Dr. Robert J. Tracy
Department of Geosciences
5064 Derring Hall
Virginia Tech
Blacksburg VA 24061-0420
Office Phone: 540-231-5980
Fax: 540-231-3386
e-mail: [log in to unmask]
--
This message has been scanned for viruses and
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believed to be clean.
Hi all,
If the discussion is widening, kyanite pseudomorphing andalusite is reported in:
Ahmed-Said and Tanner, P-T conditions during emplacement, and D2 regional metamorphism, of the Ben Vuirich Granite, Perthshire, Scotland. Mineralogical Magazine, 2000; v. 64, p. 737-753.
and back in 1968 Graham Chinner (Min Mag 36, 1052-1068) recorded (for the first time ?) sillimanite replacing kyanite in the Limpopo belt.
<p06210201c697da2a1d1c>
Nigel Harris
On Thursday30 Jul 2009, at 16:35, [log in to unmask] wrote:
Hi all,
we studied a similar occurrence in:
Cesare B., Gomez-Pugnaire M.T., Sanchez-Navas A. & Grobety B. (2002)
Andalusite - sillimanite replacement (Mazarrón - SE Spain):
microstructural and TEM study.American Mineralogist, 87. 433-444.
Another partial pseudomorph of Sil on And, with the involvement of
staurolite inclusions, is in:
Cesare B. (1994) Hercynite as the product of staurolite decomposition in
the contact aureole of Vedrette di Ries, eastern Alps, Italy.
Contributions to Mineralogy and Petrology, 116, 239-246
For more on epitaxy among Al2SiO5 polymorphs see also:
Cesare B. and Grobety B. (1995) Epitaxial replacement of kyanite by
staurolite: a TEM study of the microstructures. American Mineralogist.,
95, 78-86
Regards,
Bernardo
--
Bernardo Cesare
Dipartimento di Geoscienze
Via Giotto, 1, I-35137 PADOVA ITALY
Tel: ++39-049-8272019 Fax: ++39-049-8272010
email: [log in to unmask]
web site: http://www.dmp.unipd.it/bernardo/bernardo.html
Hi,
Following on Bob Tracy's comment, I attach two images of sillimanite after
andalusite from the LPHT metamorphic rocks of the Peninsular Ranges
batholith, Baja California, Mexico. As a side note, Ron Vernon was
actually
in the field with me the year (1997 or 1998?) that I collected this
sample.
We could actually see the large chiastolitic grain shapes in the samples,
so
assumed that it was andalusite. We also noted some blue coloration and I
was
excited about the possibility of finding kyanite. Turns out it is all
sillimanite - barely a trace of remnant andalusite in the samples
collected.
The EBSD data show that sillimanite with three different c-axis
orientations
replaced the chiastolite grains. Note that the sillimanite crosses grew
between the chiastolitic sector zone boundaries. Note also that the
sillimanite replacing the main body of the andalusite has recrystallized.
I would be interested to know if anyone has seen this type of
microstructure
before. We are considering possibly working this up for a short
publication.
Cheers - Scott
*************************************************************************
Scott E. Johnson
Department of Earth Sciences
5790 Bryand Global Sciences Center
University of Maine
Orono, ME 04469-5790
USA
email: [log in to unmask]
phone: (207) 581-2142
Fax: (207) 581 2202
<blocked::http://www.geology.um.maine.edu/user/scott_johnson/HM.html>
http://www.geology.um.maine.edu/user/scott_johnson/HM.html
<blocked::http://www.geology.um.maine.edu/geodynamics/>
http://www.geology.um.maine.edu/geodynamics/
*************************************************************************
From: Metamorphic Studies Group [mailto:[log in to unmask]]
On
Behalf Of Robert Tracy
Sent: Sunday, July 26, 2009 7:29 AM
To: [log in to unmask]
Subject: Re: oriented sillimanite after ?andalusite
Hanan Kisch's comments are very interesting. When I first saw the
photomicrographs, I immediately thought of sillimanite replacements of
andalusite (sometimes quite large original andalusite crystals up to cm in
scale) that occurs in rocks of southern New Hampshire and central
Massachusetts USA. In many cases the replacement (a pseudomorphing of a
kind) is complete, but the single large original chiastolite grain shapes
(commonly even with carbonaceous crosses) are perfectly preserved by finer
grained aggregates of sillimanites in multiple orientations, but all
apparently sharing a common c-axis orientation. In thin sections cut
across
the foliation and lineation of the rock, the classic diamond shapes of the
individual sillimanite grains can be seen in the replacements. John
Rosenfeld wrote an admirable description of this phenomenon in a paper in
American Journal of Science in 1969 (the Al-silicate issue), and several
papers or field guides by Peter Robinson and his students in the late
1970s
and early 1980s also describe these composite replacement textures.
The replacement occurs at sillimanite + K-feldspar grade and commonly with
migmatization, probably at T of ca. 750C at roughly 0.6 GPa. Our
interpretation was of an early low-P contact metamorphic phase related to
magmatism in a Taconic back-arc setting, succeeded by an increase in P as
well as T in a more regional event , although still dominated by magmatic
heating (so-called "anti-clockwise P-T trajectory" similar to that
described
in the New England terrane of Australia by Ron Vernon and Bill Collins).
My
impression is that whereas Hanan's case from Norway represents two
distinct
events separated in time, the New England USA occurrence is more likely a
continuum that starts in the ca, 440-445 Ma time frame with contact
metamorphism and the regional phase is likely at 430-435. Looking back
again
at his message, however, there is a striking similarity of timing and
overall character (not uncommon for Caledonian phenomena in Norway,
northern
UK and in the northern Appalachians).
Bob Tracy
Hanan Kisch wrote:
Dear Dr Homam,
A belated comment.
Coarse sillimanite porphyroblasts (Kisch 1962, Plate VII, fig. 2 and Plate
VII, fig. 1) along the western contact of the Fongen-Hyllingen gabbro
complex in the Tydal area, central Caledonides of the eastern Trondheim
region, contain sillimanite in two orientations (ibid., Plate VII, fig.
2).
This silimanite was probably formed as replacement of andalusite, which
occurs further south in the contact aureole of the southern termination of
the gabbro (Vogt 1941; Birkeland & Nilsen 1972). The gabbro was dated as
late Silurian; together with its contact aureole, it was overprinted by
late-Caledonian staurolite-kyanite grade regional metamorphism.
References :
Kisch, H.J. (1962) Petrographical and geological investigations in the
southwestern Tydal region, Sör-Tröndelag, Norway. Acad. Proefschr., Univ.
of Amsterdam, 136 pp.
Vogt, Th. (1941). Geological notes on the Dictyonema locality and the
upper
Gauldal district in the Trondheim area. Norsk Geol. Tidsskr. 20, 171-192.
Birkeland, T. & Nilsen, O. (1972) Contact metamorphism associated with
gabbros in the Trondheim region. Norges Geol. Unders. 273, 13-22.
I hope that this is some help.
Regards,
Hanan Kisch
Dear All
As Freshte (Ranjbar) supervisor I would like to express my honest
acknowledgement for your valuable comments regarding andalusite query.
What
we have in region seems to be a very complex metamorphic case but most
probably a contact metamorphism followed by a regional deformation.
Andaluasit as medium to large fully oriented grain, garnet, fibrolite and
cordierite (?) can be seen in thin sections. No staurolite has been found.
Using different direction sectioning from the sample helped us to find
what
was the mineral. As a matter of fact it was noting but an oriented growth
of
sillimanite in andalusite, very similar with that reported by Prof. Vernon
(1987) from Juan Tabo area, USA.
Best Regards
Dr. S. M. Homam
_____
_____
Share your memories online with anyone you want. Learn more.
<http://clk.atdmt.com/UKM/go/134665338/direct/01/>
<http://clk.atdmt.com/UKM/go/134665338/direct/01/>
Prof. Hanan J. Kisch
Department of Geological and Environmental Sciences
Ben-Gurion University of the Negev
P.O.B. 653, Beer-Sheva 84105, Israel
Tel.: +972 8 646 1290
Fax (Dept office): +972 8 647 2997 and +972 8 647 7655
E-mail: [log in to unmask]
--
Dr. Robert J. Tracy
Department of Geosciences
5064 Derring Hall
Virginia Tech
Blacksburg VA 24061-0420
Office Phone: 540-231-5980
Fax: 540-231-3386
e-mail: [log in to unmask]
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.