Dear Santanu,
We have recently published a paper about the behavior of monazite in
the Svecofennian diatexites from Sweden. It might help you a bit.
Please, have a look on this:
Högdahl K., Majka J., Sjöstrom H., Persson Nilsson K., Cleasson S.,
Konečny P. 2012. Reactive monazite and robust zircon growth in
diatexites and leucogranites from a hot, slowly cooling orogen:
implications for the Palaeoproterozoic tectonic evolution of the
central Fennoscandian Shield, Sweden. Contributions to Mineralogy and
Petrology, vol. 163, 167-188, doi: 10.1007/s00410-011-0664-x.
Best,
Jarek
Cytowanie Santanu Kumar Bhowmik <[log in to unmask]>:
> Dear Matt, Mike and Nigel,
>
> Many thanks for giving me fruitful suggestions on the issue, and
> Matt for a very detailed analysis on the various possibilities that
> exist in interpreting monazite growth in high-grade rocks. I am
> aware of the majority of the mentioned references and also the
> interpretations. But the issue that I was looking at is whether
> monazite can grow during prograde granulite facies metamorphism e.g.
> in the T range of 700-800 oC as the muscovite dehydration melting
> and the first biotite melting reactions are crossed in the pelites
> with heating! Matt rightly inferred this.
>
> My query stemmed from the observations in monazites from the c.1.6
> Ga granulites of the CITZ. Some of these monazites preserve a
> pre-melting core of Paleoproterozoic age. These are ovoid to
> ellipsoidal in shape with high Y (Y2O3=1.5-2 wt%) and low Th
> (ThO2=1.5-3 wt%) contents. These cores are variously altered, but
> maintaining their original shapes. At least two alteration zones,
> radial from the surviving core are recognisable: (a) the innermost
> one (zone 1 for example, is still high in Y (as in the core) but
> with significant enrichment in Th (ThO2=6-7 wt%). Commensurate with
> textural observation, relatively high HREE of zone1 is similar to
> that of the unaltered core, implying that zone1 is genetically
> linked to the Paleoproterozoic core. (b) the outermost alteration
> zone (zone 2)in contrast shows progressive depletion in Y (Y2O3→
> 0)but with high Th content as in zone 1. The unaltered and altered
> cores are variously resorbed and overgrown by a new monazite which
> has an euhedral crystal shape. This variety of overgrowth monazite
> is compositionally distinct by being enriched in Th (ThO2=8-10 wt%)
> but depleted in Y (Y2O3=0). Despite error in monazite chemical ages,
> mean monazite ages of the alteration zone and overgrowth monazites
> show younging fron zone 1 (1614 Ma) through zone 2 (1602 Ma) to
> overgrowth (1595 Ma), consistent with textural predictions.
>
> While the overgrowth monazite can be correlated with crystallisation
> from partial melt at TMax condition or immediately following TMax
> along the retrograde path (as Mike has suggested), to me the
> interpretations for alteration zone monazites 1 and 2 in terms of
> simple cooling from TMax (or involving a number of punctuated melt
> crystallisation stages) may not be that straight forward.
>
> My interpretation for alteration zones 1 and 2 are: (a) zone 1
> monazite equilibrated with melt generated by muscovite dehydration
> melting (high Y, no Grt stable); (b)zone 2 monazite equilibrated
> with the first appearance of peritectic Grt, marking initiation of
> biotite melting. It is in this text, I am thinking whether
> alteration zones 1 and 2 monazites which are the products of
> dissolution-reppt of Paleoproterozoic monazite (which I think is of
> detrital origin) can be equated with prograde monazite growth!
>
> I am aware of the limitation of the interpretation. There are
> textural and compositional supports that old monazites are
> dissolving in melt, but equally monazite is also growing in
> equilibrium with melt as Harlov's recent experimental work on
> dissolution-reppt of monazite (Harlov et al., 2011, CMP) predicts.
> The question is can we consider these alteration zone monazites to
> have grown along the heating path? I am aware of a few publications
> which predicted this for zircon (Vavra et al., 1999; Williams, 2001;
> Rubatto et al., 2001; Hermann and Rubatto, 2003).
>
> Sorry for this rather longish mail and for your patience.
>
> With best wishes,
>
> Santanu
>
> ----- Original Message -----
> From: "Michael Brown" <[log in to unmask]>
> To: [log in to unmask]
> Sent: Saturday, March 10, 2012 6:45:42 AM
> Subject: Re: [geo-metamorphism] Monazite growth in anatectic melt
>
> Hi Santanu
>
> I agree with Matt Kohn that a lot of the complexity relates to
> crystallization along the high-T retrograde path down to the elevated
> solidus for residual rocks. One point we made in the following paper, is
> that ages vary because the final solidus T varies according to how
> residual the rock is i.e. how much melt it lost on the prograde path. So
> with slow cooling at 1C/Ma, a 10-20C difference in solidus equals a 20
> Ma difference in age.
>
> See: Reno, B.L., Piccoli, P.M., Brown, M. and Trouw, R., 2012. In situ
> chemical dating of monazite from the Southern Brazília Belt, Brazil.
> Journal of Metamorphic Geology, 30, 81-112 (Article first published
> online: 20 SEP 2011 | DOI: 10.1111/j.1525-1314.2011.00957.x).
>
> Regards,
> Mike
>
>
> On 3/9/12 7:51 AM, Santanu Kumar Bhowmik wrote:
>> Dear friends,
>>
>> Apology for multiple posting. I am looking for reference on
>> monazite dissolution and reprecipitation at the onset of partial
>> melting in metapelites. I am particularly interested in studies
>> which documented new growth of monazite, coinciding with muscovite
>> dehydration melting. Are there specific compositional attributes in
>> monazite and associated minerals which are suggested to constrain
>> the mentioned melting process? Is it possible to relate an
>> increased cheralite content in the newly produced monazite with the
>> participation of plagioclase in the muscovite melting reaction,
>>
>> muscovite + plagioclase + quartz →K-feldsparss + aluminosilicate + melt?
>>
>> With best wishes,
>>
>> Santanu
>>
>> ----------------------
>> Dr. Santanu Kumar Bhowmik
>> Professor
>> Department of Geology& Geophysics
>> Indian Institute of Technology
>> Kharagpur-721 302
>> India
>> Ph: 91-3222-283390(O), 283391(R), 279766(R)
>> Mobile:91-9434041791
>>
>
> --
> __________________________________________________________
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> Michael Brown, Professor of Geology
>
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