Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
Ditto Ruben. Graham On Wed, Mar 19, 2014 at 4:10 AM, Ruben Garcia rubengarcia85...@gmail.com wrote: After being on Facebook for a week I gotta say LIKE to Karen's post. On Tue, Mar 18, 2014 at 8:08 PM, Karen Ziegler kzieg...@unm.edu wrote: Hi Mendy and list, Here is my input on the oxygen isotopes: Oxygen isotopes in unequilibrated samples will show a large range of values, because they do retain their initial oxygen isotope values of their individual components. Magmatic crystallization temperatures, for example, will give different minerals-pairs certain fractionations (that are dependent on the crystallization temperature) (e.g. Friedman O'Neil, 1977). So, there is a certain expected range of oxygen isotope compositions in bulk samples, depending on how much of each mineral is in your bulk sample. Once metamorphism sets in, this inter-mineral fractionation decreases more and more - as temperature goes up. So, you'd expect the range of oxygen isotope values to shrink/collapse in their range as metamorphism increases. The same way you would expect the chemical characteristics, e.g., Fe-content, to become more homogeneous, to have a smaller range, with increasing degree of metamorphism. O-isotope values per se will not tell you the metamorphic grade, but the range of individual analyses of a given sample will be an indicator of the degree of metamorphism. The oxygen isotope values of UOCs depends on how you have selected you sample. As Jeff said, oxygen heterogeneity in these objects bulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. The proportion of chondrule to coarse to fine matrix is important Š.. The best way to approach this is to do a detailed component/mineral-separation of the UOCs, analyze the chondrules vs. the matrix, analyze the olivines and the pyroxenes, etc. Comparing olivine O-isotopes, e.g., is much more useful that comparing bulk O-isotope values. Karen On 3/16/14 6:39 PM, Jeff Grossman jngross...@gmail.com wrote: Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
I haven’t had much time to post lately, but am really appreciating these informative discussions. Thanks! Doug Ross d...@dougross.net On Mar 18, 2014, at 8:08 PM, Karen Ziegler kzieg...@unm.edu wrote: Hi Mendy and list, Here is my input on the oxygen isotopes: Oxygen isotopes in unequilibrated samples will show a large range of values, because they do retain their initial oxygen isotope values of their individual components. Magmatic crystallization temperatures, for example, will give different minerals-pairs certain fractionations (that are dependent on the crystallization temperature) (e.g. Friedman O'Neil, 1977). So, there is a certain expected range of oxygen isotope compositions in bulk samples, depending on how much of each mineral is in your bulk sample. Once metamorphism sets in, this inter-mineral fractionation decreases more and more - as temperature goes up. So, you'd expect the range of oxygen isotope values to shrink/collapse in their range as metamorphism increases. The same way you would expect the chemical characteristics, e.g., Fe-content, to become more homogeneous, to have a smaller range, with increasing degree of metamorphism. O-isotope values per se will not tell you the metamorphic grade, but the range of individual analyses of a given sample will be an indicator of the degree of metamorphism. The oxygen isotope values of UOCs depends on how you have selected you sample. As Jeff said, oxygen heterogeneity in these objects bulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. The proportion of chondrule to coarse to fine matrix is important ?.. The best way to approach this is to do a detailed component/mineral-separation of the UOCs, analyze the chondrules vs. the matrix, analyze the olivines and the pyroxenes, etc. Comparing olivine O-isotopes, e.g., is much more useful that comparing bulk O-isotope values. Karen __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
Hi Mendy and list, Here is my input on the oxygen isotopes: Oxygen isotopes in unequilibrated samples will show a large range of values, because they do retain their initial oxygen isotope values of their individual components. Magmatic crystallization temperatures, for example, will give different minerals-pairs certain fractionations (that are dependent on the crystallization temperature) (e.g. Friedman O'Neil, 1977). So, there is a certain expected range of oxygen isotope compositions in bulk samples, depending on how much of each mineral is in your bulk sample. Once metamorphism sets in, this inter-mineral fractionation decreases more and more - as temperature goes up. So, you'd expect the range of oxygen isotope values to shrink/collapse in their range as metamorphism increases. The same way you would expect the chemical characteristics, e.g., Fe-content, to become more homogeneous, to have a smaller range, with increasing degree of metamorphism. O-isotope values per se will not tell you the metamorphic grade, but the range of individual analyses of a given sample will be an indicator of the degree of metamorphism. The oxygen isotope values of UOCs depends on how you have selected you sample. As Jeff said, oxygen heterogeneity in these objects bulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. The proportion of chondrule to coarse to fine matrix is important Š.. The best way to approach this is to do a detailed component/mineral-separation of the UOCs, analyze the chondrules vs. the matrix, analyze the olivines and the pyroxenes, etc. Comparing olivine O-isotopes, e.g., is much more useful that comparing bulk O-isotope values. Karen On 3/16/14 6:39 PM, Jeff Grossman jngross...@gmail.com wrote: Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary and carbonaceous chondrites by Grossman and Brearley 2005, I realized that a key tool used in the analysis of NWA 7731 and NWA 8276 was not present in the literature. So, I'll start with this first part of questions: In my discussions with Dr. Agee, he mentioned that the
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
Thank you so much Karen. Mendy Ouzillou On Mar 18, 2014, at 8:08 PM, Karen Ziegler kzieg...@unm.edu wrote: Hi Mendy and list, Here is my input on the oxygen isotopes: Oxygen isotopes in unequilibrated samples will show a large range of values, because they do retain their initial oxygen isotope values of their individual components. Magmatic crystallization temperatures, for example, will give different minerals-pairs certain fractionations (that are dependent on the crystallization temperature) (e.g. Friedman O'Neil, 1977). So, there is a certain expected range of oxygen isotope compositions in bulk samples, depending on how much of each mineral is in your bulk sample. Once metamorphism sets in, this inter-mineral fractionation decreases more and more - as temperature goes up. So, you'd expect the range of oxygen isotope values to shrink/collapse in their range as metamorphism increases. The same way you would expect the chemical characteristics, e.g., Fe-content, to become more homogeneous, to have a smaller range, with increasing degree of metamorphism. O-isotope values per se will not tell you the metamorphic grade, but the range of individual analyses of a given sample will be an indicator of the degree of metamorphism. The oxygen isotope values of UOCs depends on how you have selected you sample. As Jeff said, oxygen heterogeneity in these objects bulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. The proportion of chondrule to coarse to fine matrix is important Š.. The best way to approach this is to do a detailed component/mineral-separation of the UOCs, analyze the chondrules vs. the matrix, analyze the olivines and the pyroxenes, etc. Comparing olivine O-isotopes, e.g., is much more useful that comparing bulk O-isotope values. Karen On 3/16/14 6:39 PM, Jeff Grossman jngross...@gmail.com wrote: Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary and carbonaceous chondrites by Grossman and Brearley 2005, I realized that a key tool used in the analysis of
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
After being on Facebook for a week I gotta say LIKE to Karen's post. On Tue, Mar 18, 2014 at 8:08 PM, Karen Ziegler kzieg...@unm.edu wrote: Hi Mendy and list, Here is my input on the oxygen isotopes: Oxygen isotopes in unequilibrated samples will show a large range of values, because they do retain their initial oxygen isotope values of their individual components. Magmatic crystallization temperatures, for example, will give different minerals-pairs certain fractionations (that are dependent on the crystallization temperature) (e.g. Friedman O'Neil, 1977). So, there is a certain expected range of oxygen isotope compositions in bulk samples, depending on how much of each mineral is in your bulk sample. Once metamorphism sets in, this inter-mineral fractionation decreases more and more - as temperature goes up. So, you'd expect the range of oxygen isotope values to shrink/collapse in their range as metamorphism increases. The same way you would expect the chemical characteristics, e.g., Fe-content, to become more homogeneous, to have a smaller range, with increasing degree of metamorphism. O-isotope values per se will not tell you the metamorphic grade, but the range of individual analyses of a given sample will be an indicator of the degree of metamorphism. The oxygen isotope values of UOCs depends on how you have selected you sample. As Jeff said, oxygen heterogeneity in these objects bulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. The proportion of chondrule to coarse to fine matrix is important Š.. The best way to approach this is to do a detailed component/mineral-separation of the UOCs, analyze the chondrules vs. the matrix, analyze the olivines and the pyroxenes, etc. Comparing olivine O-isotopes, e.g., is much more useful that comparing bulk O-isotope values. Karen On 3/16/14 6:39 PM, Jeff Grossman jngross...@gmail.com wrote: Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary and carbonaceous chondrites by Grossman and Brearley 2005, I realized that a key tool used in the
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary and carbonaceous chondrites by Grossman and Brearley 2005, I realized that a key tool used in the analysis of NWA 7731 and NWA 8276 was not present in the literature. So, I'll start with this first part of questions: In my discussions with Dr. Agee, he mentioned that the heterogeneity of the oxygen isotope results is important because it indicates that the material has not been metamorphosed by heat or shock. Any heating would have caused the oxygen to begin to equilibriate. So, is the oxygen isotope analysis something that should be added to the list of factors used in evaluating low sub-types? Or is it a proxy for more complex tests? I am hoping that Karen Ziegler can also add some insights. The second set of questions is perhaps more complex. What is the scientific importance of the 3.00 subtype? I can get this one kicked off, but would appreciate a more nuanced answer than what I can provide. The subtype 3.00 represents the earliest glimpse of the properties of proto- planetary material in our solar system. A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. An implication of the unequilibrated nature of this material is that the parent body had to be quite small for it not to differentiate in any way. Though both scientifically important, what different types of insights do we gain from CAIs versus subtype 3.00 material? The answer is I am sure that they complement each other, but in what way. Which is oldest? The rarity of this type of material cannot be underestimated since between the only 3 known (Semarkona, NWA 7731 and NWA 8276), there is only 1,561g available for research and/or collectors. Of that total weight, Semarkona's 691g is almost unattainable. So, once again NWA delivers the goods! Regards, Mendy Ouzillou __ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list
Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis
Thanks Jeff! Yes, I do hope that we see more responses. Mendy Ouzillou - Original Message - From: Jeff Grossman jngross...@gmail.com To: 'Met-List' meteorite-list@meteoritecentral.com Cc: Sent: Sunday, March 16, 2014 4:39 PM Subject: Re: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Mendy and list, My comments: Oxygen: I would say that O isotope heterogeneity as described here is not a good measure of metamorphism. Oxygen heterogeneity in these objecbulk samplests will be a function of sample size, as fine matrix grains equilibrate much more quickly than coarse ones. If you analyze small aliquants of sample, most UOCs will be heterogeneous. If, on the other hand, we were talking about the O isotope heterogeneity of individual olivine grains, akin to how we measure FeO in olivine, you might be able to devise a metamorphic parameter. But so far, I'm not aware of anybody devising a way to use O isotopes to measure metamorphic grade. The meaning of type 3.00: you said, A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. This is incorrect. It means the material is unaffected by thermal metamorphism. Semarkona is shock stage S2, so it has been seen elevated pressures due to impacts on the parent body. It also shows abundant evidence for light aqueous alteration. You can think of all these things as independent processes. Semarkona saw little heat, but got a little shocked and a little bit wet. Many CM chondrites saw little heat, but a lot of water. I would call these CMs type 3.00 as well, but traditional usage has coined another term for really wet chondrites, namely type 2. Oh well. Metamorphically, they are type 3.00. Some chondrites saw little shock and a lot of thermal metamorphism. Anyway, all type 3.00 means is that the object saw little prolonged secondary heating. The parent body may have been too small to differentiate, or it may have formed too late to take advantage of heat sources like Al-26 (and there may be other possibilities). We are always looking for material that escaped processing on asteroids to learn about the origin of the solar system. Type 3.00 chondrites are good for doing such studies. CAIs are also important for early solar system studies, and we're fortunate that the meteorites richest in CAIs tend to be low petrologic types that escaped heating on asteroids as well; many carbonaceous chondrites are like this. I hope this is a start at answering your questions. Jeff -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list- boun...@meteoritecentral.com] On Behalf Of Mendy Ouzillou Sent: Sunday, March 16, 2014 12:46 PM To: Met-List Subject: [meteorite-list] The scientific importance of subtype 3.00 meteorites and oxygen isotope analysis Well, with the LPSC going on starting this week, I sure hope we get some participation from our scientific contributors to these questions. Someone asked me to explain the scientific importance of meteoritic material with a 3.00 subtype. Reading through The onset of metamorphism in ordinary and carbonaceous chondrites by Grossman and Brearley 2005, I realized that a key tool used in the analysis of NWA 7731 and NWA 8276 was not present in the literature. So, I'll start with this first part of questions: In my discussions with Dr. Agee, he mentioned that the heterogeneity of the oxygen isotope results is important because it indicates that the material has not been metamorphosed by heat or shock. Any heating would have caused the oxygen to begin to equilibriate. So, is the oxygen isotope analysis something that should be added to the list of factors used in evaluating low sub-types? Or is it a proxy for more complex tests? I am hoping that Karen Ziegler can also add some insights. The second set of questions is perhaps more complex. What is the scientific importance of the 3.00 subtype? I can get this one kicked off, but would appreciate a more nuanced answer than what I can provide. The subtype 3.00 represents the earliest glimpse of the properties of proto- planetary material in our solar system. A subtype of 3.00 means that the material has survived unchanged by heat (radioactive decay, pressure, impact/shock, etc.) or aqueous alteration since its formation. An implication of the unequilibrated nature of this material is that the parent body had to be quite small for it not to differentiate in any way. Though both scientifically important, what different types of insights do we gain from CAIs versus subtype 3.00 material? The answer is I am sure that they complement each other, but in what way. Which is oldest? The rarity of this type of material
