Abstract Details
(2020) Cooling Rates in High Pressure Granulite from Southern Brasília Orogen (SE-Brazil)
Fumes RA, Luvizotto GL, Valeriano CDM & Moraes R
https://doi.org/10.46427/gold2020.770
04h: Room 1, Friday 26th June 22:27 - 22:30
Regiane Andrade Fumes
George Luiz Luvizotto View abstracts at 6 conferences in series
Claudio De Morisson Valeriano
Renato Moraes View abstracts at 9 conferences in series
George Luiz Luvizotto View abstracts at 6 conferences in series
Claudio De Morisson Valeriano
Renato Moraes View abstracts at 9 conferences in series
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Submitted by Shah Wali Faryad on Tuesday 23rd June 16:26
Cooling Rates in High Pressure Granulite from Southern Brasília Orogen (SE-Brazil) Fumes RA, Luvizotto GL, Valeriano CDM & Moraes R It is a little bit strange for me that plagioclase is stable across the whole selected pressure range. I wonder if this not a problem of solution model used. What are the evidence that rutile forms during retrograde stage? I would expect its replacement or overgrown by ilmenite-titanite at such conditions. From the grossular map it seems that garnet still preserves prograde zoning. Is it possible to preserve such zoning at such high temperature and duration time of 55 Ma from peak temperature of 850 oC to 600 oC, where diffusion in garnet is effective?
Thank you very much for your good questions. We have used the White et al. (2014) activity-composition models and the plagioclase melts at high pressure and temperature (in the peak assemblage), this feature is in agreement with what we observed in our samples. Rutile forms in several parts of the P-T-t path, probably in the peak and also during the retrograde path; the Zr in rutile temperatures presents a large spread (the higher values shows us the HP granulite conditions in agreement with the pseudosection), some rutile crystals presents ilmenite lamella, lower Zr content and zircon inclusions, that indicates to be formed in the retrograde path. The rutile is also observed in all textures (included in garnet, kyanite, in the leucosome and in the matrix). Despite the rutile crystalized in the peak and in the retrograde, the closure temperature of Pb in rutile is ca. 600 ?C considering the size of our rutile according to Cheniak, 2000, so we used the rutile age to constrain the age of this part of the retrograde path. We observed a clearly grossular zoning in some garnet porphyroblasts, unfortunately we don’t have a model of diffusion for our sample and we only have what the maps show, so we can’t go further yet with this discussions. This is a really interesting feature that we need to study further. The decrease of the temperature should also decrease the diffusion in the garnet, but we don’t know exactly how much time the samples stay in the high temperature conditions, we only know the time to the peak to 600 ?C. Thank you again.
Cooling Rates in High Pressure Granulite from Southern Brasília Orogen (SE-Brazil) Fumes RA, Luvizotto GL, Valeriano CDM & Moraes R It is a little bit strange for me that plagioclase is stable across the whole selected pressure range. I wonder if this not a problem of solution model used. What are the evidence that rutile forms during retrograde stage? I would expect its replacement or overgrown by ilmenite-titanite at such conditions. From the grossular map it seems that garnet still preserves prograde zoning. Is it possible to preserve such zoning at such high temperature and duration time of 55 Ma from peak temperature of 850 oC to 600 oC, where diffusion in garnet is effective?
Thank you very much for your good questions. We have used the White et al. (2014) activity-composition models and the plagioclase melts at high pressure and temperature (in the peak assemblage), this feature is in agreement with what we observed in our samples. Rutile forms in several parts of the P-T-t path, probably in the peak and also during the retrograde path; the Zr in rutile temperatures presents a large spread (the higher values shows us the HP granulite conditions in agreement with the pseudosection), some rutile crystals presents ilmenite lamella, lower Zr content and zircon inclusions, that indicates to be formed in the retrograde path. The rutile is also observed in all textures (included in garnet, kyanite, in the leucosome and in the matrix). Despite the rutile crystalized in the peak and in the retrograde, the closure temperature of Pb in rutile is ca. 600 ?C considering the size of our rutile according to Cheniak, 2000, so we used the rutile age to constrain the age of this part of the retrograde path. We observed a clearly grossular zoning in some garnet porphyroblasts, unfortunately we don’t have a model of diffusion for our sample and we only have what the maps show, so we can’t go further yet with this discussions. This is a really interesting feature that we need to study further. The decrease of the temperature should also decrease the diffusion in the garnet, but we don’t know exactly how much time the samples stay in the high temperature conditions, we only know the time to the peak to 600 ?C. Thank you again.
Submitted by Bianca Németh on Friday 26th June 18:41
Hi Regiane, nice work, congrats! My question is that if you have multiple generations of minerals, did you observe any differences/connection in the P-T-t data between the different generations? Do you know how much fast could be the uplifting/unroofing of the granulite terrain? I asked this because you were talking about retrograde path, and since the garnets do not seem to be symplectitic. (In the Pannonian Basin, the formation of symplectites is associated with the formation of a lithosphere (extension), during which the pressure drop related to the thinning of the crust, that caused the formation of kelifitic edges of garnets at depths of about 15 and 30 km and 850-1050 ° C in the lower crust.)
Hi Regiane, nice work, congrats! My question is that if you have multiple generations of minerals, did you observe any differences/connection in the P-T-t data between the different generations? Do you know how much fast could be the uplifting/unroofing of the granulite terrain? I asked this because you were talking about retrograde path, and since the garnets do not seem to be symplectitic. (In the Pannonian Basin, the formation of symplectites is associated with the formation of a lithosphere (extension), during which the pressure drop related to the thinning of the crust, that caused the formation of kelifitic edges of garnets at depths of about 15 and 30 km and 850-1050 ° C in the lower crust.)
Submitted by Bianca Németh on Friday 26th June 18:50
Hi Regiane, nice work, congrats! My question is that if you have multiple generations of minerals, did you observe any differences/connection in the P-T-t data between the different generations? Do you know how much fast could be the uplifting/unroofing of the granulite terrain? I asked this because you were talking about retrograde path, and since the garnets do not seem to be symplectitic. (In the Pannonian Basin, the formation of symplectites is associated with the formation of a lithosphere (extension), during which the pressure drop related to the thinning of the crust, that caused the formation of kelifitic edges of garnets at depths of about 15 and 30 km and 850-1050 ° C in the lower crust. But those are xenoliths.)
Hi Regiane, nice work, congrats! My question is that if you have multiple generations of minerals, did you observe any differences/connection in the P-T-t data between the different generations? Do you know how much fast could be the uplifting/unroofing of the granulite terrain? I asked this because you were talking about retrograde path, and since the garnets do not seem to be symplectitic. (In the Pannonian Basin, the formation of symplectites is associated with the formation of a lithosphere (extension), during which the pressure drop related to the thinning of the crust, that caused the formation of kelifitic edges of garnets at depths of about 15 and 30 km and 850-1050 ° C in the lower crust. But those are xenoliths.)
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