Abstract Details
(2020) How Well do We Know Reaction Pathways in Metamorphic Rocks?
Konrad-Schmolke M
https://doi.org/10.46427/gold2020.1353
The author has not provided any additional details.
04h: Room 5, Thursday 25th June 22:00 - 22:03
Matthias Konrad-Schmolke
View all 2 abstracts at Goldschmidt2020
View abstracts at 9 conferences in series
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
Submitted by Renee Tamblyn on Monday 22nd June 03:56
That was excellent, thank you Matthias.
Thank you for the compliment :-)
That was excellent, thank you Matthias.
Thank you for the compliment :-)
Submitted by Simon Cuthbert on Tuesday 23rd June 11:34
Thanks for a fascinating talk! The formation of amorphous silicate "films" or pockets at reacting grain boundaries seems to be superficially similar to melting reactions. Are there actually similarities here and can we learn more about solid-solid reactions from our understanding of melting processes?
Hi Simon, the question of how the amorphous material behaves is, to my opinion, one of the crucial aspects. Is it always precipitating in the very near vicinity or is it mobile and able to transport elements over distances larger than a few microns? Under which physico-chemical conditions is it mobile? I think there are some interesting practical applications, such as in CO2 sequestration, where we could use the high reactivity of such a phase to precipitate carbonates in pyroxenites or amphiboles, as pyroxenes and amphiboles seem to be highly reactive during this mechanism. I think it might also be the other way round, we learn something about melts from such nano-scale observations: nano-aggregates as precursors for crystal nuclei have been observed in melt experiments (Helmy et al., 2013, NComm). So, at least parts of the reaction mechanism are observed at high temperatures.
Thanks for a fascinating talk! The formation of amorphous silicate "films" or pockets at reacting grain boundaries seems to be superficially similar to melting reactions. Are there actually similarities here and can we learn more about solid-solid reactions from our understanding of melting processes?
Hi Simon, the question of how the amorphous material behaves is, to my opinion, one of the crucial aspects. Is it always precipitating in the very near vicinity or is it mobile and able to transport elements over distances larger than a few microns? Under which physico-chemical conditions is it mobile? I think there are some interesting practical applications, such as in CO2 sequestration, where we could use the high reactivity of such a phase to precipitate carbonates in pyroxenites or amphiboles, as pyroxenes and amphiboles seem to be highly reactive during this mechanism. I think it might also be the other way round, we learn something about melts from such nano-scale observations: nano-aggregates as precursors for crystal nuclei have been observed in melt experiments (Helmy et al., 2013, NComm). So, at least parts of the reaction mechanism are observed at high temperatures.
Submitted by Shah Wali Faryad on Tuesday 23rd June 14:38
Thank you for nicely documented reaction progress, from dissolution of minerals, through fluid-mediated transport, element exchange to formation of the product phase, the process which we mostly observe during retrogression or exhumation of high-pressure rock. What do you think about prograde reactions during pressure and temperature increase? Here the new phase in equilibrium and fluid phase is removed.
Dear Wali, thanks for the interesting question. At least parts of the reaction mechanism have been observed in prograde, dehydrating rocks. Sarah Incel and co-workers (Incel et al., 2017, EPSL) have observed similar reaction textures with an amorphous phase between gln and cpx. In their experiments gln is dehydrating and cpx is precipitating. So, I think that the reaction mechanism is not restricted to re-hydration and retrograde reactions - but there is much more to discover at the nano-scale!
Thank you for nicely documented reaction progress, from dissolution of minerals, through fluid-mediated transport, element exchange to formation of the product phase, the process which we mostly observe during retrogression or exhumation of high-pressure rock. What do you think about prograde reactions during pressure and temperature increase? Here the new phase in equilibrium and fluid phase is removed.
Dear Wali, thanks for the interesting question. At least parts of the reaction mechanism have been observed in prograde, dehydrating rocks. Sarah Incel and co-workers (Incel et al., 2017, EPSL) have observed similar reaction textures with an amorphous phase between gln and cpx. In their experiments gln is dehydrating and cpx is precipitating. So, I think that the reaction mechanism is not restricted to re-hydration and retrograde reactions - but there is much more to discover at the nano-scale!
Submitted by Donald Hickmott on Thursday 25th June 15:43
Very nice talk! How widespread are such amorphous grain boundary features in lower-crustal rocks? Are they more than just a 'curiosity'? You might consider using neutron pair distribution function analysis to investigate.
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic. Hide
Very nice talk! How widespread are such amorphous grain boundary features in lower-crustal rocks? Are they more than just a 'curiosity'? You might consider using neutron pair distribution function analysis to investigate.
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic. Hide
Submitted by Matthias Konrad-Schmolke on Thursday 25th June 16:59
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic.
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic.
Submitted by Joshua David Vaughan-Hammon on Thursday 25th June 19:19
Hello Matthias. Thank you for the illuminating talk. I just have a question regarding the formation of porosity via localised channels as modelled by Connolly and Podladchikov. Do you think this process is still viable at such small scales? From what I know, these porosity channels are in part dependent on density differences (within the Darcy flux). Thanks, Joshua.
Dear Joshua, that is a very good question. I was generally wondering about the fluid migration mechanism in these samples. We have quantified the porosity and its interconnectivity, but with such small pores and a corresponding high resolution of the X-ray tomography the sample size is limited to a few millimetres. However, the porosity in the pyroxenes is largely interconnected at least in the mm-range. In neighbouring glaucophanites, that are the products of the hydration, the (fewer) pores are largely isolated. So, the larger scale fluid flux mechanism is unclear. Regarding your question, I would not claim that I have an answer, but I am sure Jamie is willing to expand on this topic. Nevertheless, I think that these samples contain some important information about the fluid pathway creation. Apart from the formation of the nano-porosity they show signs of partly healed micro fractures, such as described in Jamtveit et al 2009 as well as pores formed during the crystallisation of one of the pyroxene generation that are used as primary fluid pathways. And I guess that these features can be seen in many HP/LT rocks (see also Plümper et al., 2016, NGeo). Matthias
Hello Matthias. Thank you for the illuminating talk. I just have a question regarding the formation of porosity via localised channels as modelled by Connolly and Podladchikov. Do you think this process is still viable at such small scales? From what I know, these porosity channels are in part dependent on density differences (within the Darcy flux). Thanks, Joshua.
Dear Joshua, that is a very good question. I was generally wondering about the fluid migration mechanism in these samples. We have quantified the porosity and its interconnectivity, but with such small pores and a corresponding high resolution of the X-ray tomography the sample size is limited to a few millimetres. However, the porosity in the pyroxenes is largely interconnected at least in the mm-range. In neighbouring glaucophanites, that are the products of the hydration, the (fewer) pores are largely isolated. So, the larger scale fluid flux mechanism is unclear. Regarding your question, I would not claim that I have an answer, but I am sure Jamie is willing to expand on this topic. Nevertheless, I think that these samples contain some important information about the fluid pathway creation. Apart from the formation of the nano-porosity they show signs of partly healed micro fractures, such as described in Jamtveit et al 2009 as well as pores formed during the crystallisation of one of the pyroxene generation that are used as primary fluid pathways. And I guess that these features can be seen in many HP/LT rocks (see also Plümper et al., 2016, NGeo). Matthias
Submitted by Matthias Konrad-Schmolke on Thursday 25th June 19:47
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic.
Dear Donald, that is a very good question. I applied for grant money to do experiments in the range between 90 and 400°C because there is no data or samples available in this temperature range. But so far it is still to be explored how widespread this reaction mechanism is. My guess is that it might occur frequently, but is only preserved if the rocks are "quenched" as the amorphous phase will certainly recrystallise quickly above 300-400°C. The enhanced transport capacity of such amorphous media might explain why we observe high mobility of otherwise refractory elements, such as the 4+. I also wonder whether highly poikiloblastic minerals, such as the"fishnet" garnets that practically precipitate along grain boundaries are crystallising from an amorphous transport medium. Thanks a lot for the idea with the PDF. We have a brand new neutron source here in southern Sweden (Lund) and I guess they might be interested in this topic.
Submitted by Chloe Bonamici on Thursday 25th June 21:06
Such a useful summary! Do you think that the properties of a mobile amorphous phase is more fluid-like or more solid-like? Does the amorphous phase fall along the continuum of highly polymerized supercritical fluids that Manning and collaborators have described? Can the amorphous phase could move along grain boundaries as well as within nanopores?
Such a useful summary! Do you think that the properties of a mobile amorphous phase is more fluid-like or more solid-like? Does the amorphous phase fall along the continuum of highly polymerized supercritical fluids that Manning and collaborators have described? Can the amorphous phase could move along grain boundaries as well as within nanopores?
Submitted by LeeAnn Srogi on Thursday 25th June 21:51
Hello, Matthias - thank you for an excellent talk! Can you say more about what is meant by the "mobility" of the amorphous material? What is mobile and in what sense and scale? Thank you very much! LeeAnn
Hello, Matthias - thank you for an excellent talk! Can you say more about what is meant by the "mobility" of the amorphous material? What is mobile and in what sense and scale? Thank you very much! LeeAnn
Sign in to ask a question.