Abstract Details
(2020) The Quest for Primary Magnetisation in Earth’s Oldest Materials
Harrison R, Taylor R, Tang F, Kuppili C, Ball M, Einsle J, Borlina C, Fu R, Weiss B, Rickard W, Saxey D & Reddy S
https://doi.org/10.46427/gold2020.962
06d: Room 2, Thursday 25th June 05:33 - 05:36
Richard Harrison
View all 2 abstracts at Goldschmidt2020
View abstracts at 8 conferences in series
Richard Taylor View all 3 abstracts at Goldschmidt2020
Fengzai Tang View abstracts at 2 conferences in series
Charan Kuppili
Matt Ball
Joshua F. Einsle View all 2 abstracts at Goldschmidt2020 View abstracts at 2 conferences in series
Caue Borlina View abstracts at 2 conferences in series
Roger Fu View abstracts at 2 conferences in series
Benjamin P. Weiss View all 3 abstracts at Goldschmidt2020 View abstracts at 3 conferences in series
William Rickard View abstracts at 2 conferences in series
David Saxey View abstracts at 2 conferences in series
Steven Reddy View all 2 abstracts at Goldschmidt2020 View abstracts at 9 conferences in series
Richard Taylor View all 3 abstracts at Goldschmidt2020
Fengzai Tang View abstracts at 2 conferences in series
Charan Kuppili
Matt Ball
Joshua F. Einsle View all 2 abstracts at Goldschmidt2020 View abstracts at 2 conferences in series
Caue Borlina View abstracts at 2 conferences in series
Roger Fu View abstracts at 2 conferences in series
Benjamin P. Weiss View all 3 abstracts at Goldschmidt2020 View abstracts at 3 conferences in series
William Rickard View abstracts at 2 conferences in series
David Saxey View abstracts at 2 conferences in series
Steven Reddy 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 Charles Magee on Monday 22nd June 12:13
Dear Dr Harrison, If the Hadean zircons have younger magnetite, then what is the oldest terrestrial primary magnetization?
Hi. Thanks for the question. The oldest published, unambiguous evidence is from 3.45 Ga (Tarduno, J. A., et al. 2010 Geodynamo, Solar Wind, and Magnetopause 3.4 to 3.45 Billion Years Ago. Science, 327(5970), 1238–1240. https://doi.org/10.1126/science.1183445). There is also new work by Claire Nichols from Greenland which suggests positive evidence for a field at 3.7 Ga (see presentation here https://goldschmidt.info/2020/abstracts/abstractView?id=2020003951#presentation). The zircon record could push this back even further, but we do have to work very hard indeed to convince ourselves that the signals are primary. Tarduno et al have just published new work arguing for primary signals. Check it out and see what you think! (Tarduno, J. A., Cottrell, R. D., Bono, R. K., Oda, H., Davis, W. J., Fayek, M., Erve, O. van ’t, Nimmo, F., Huang, W., Thern, E. R., Fearn, S., Mitra, G., Smirnov, A. V., & Blackman, E. G. (2020). Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo. Proceedings of the National Academy of Sciences, 201916553. https://doi.org/10.1073/pnas.1916553117)
Dear Dr Harrison, If the Hadean zircons have younger magnetite, then what is the oldest terrestrial primary magnetization?
Hi. Thanks for the question. The oldest published, unambiguous evidence is from 3.45 Ga (Tarduno, J. A., et al. 2010 Geodynamo, Solar Wind, and Magnetopause 3.4 to 3.45 Billion Years Ago. Science, 327(5970), 1238–1240. https://doi.org/10.1126/science.1183445). There is also new work by Claire Nichols from Greenland which suggests positive evidence for a field at 3.7 Ga (see presentation here https://goldschmidt.info/2020/abstracts/abstractView?id=2020003951#presentation). The zircon record could push this back even further, but we do have to work very hard indeed to convince ourselves that the signals are primary. Tarduno et al have just published new work arguing for primary signals. Check it out and see what you think! (Tarduno, J. A., Cottrell, R. D., Bono, R. K., Oda, H., Davis, W. J., Fayek, M., Erve, O. van ’t, Nimmo, F., Huang, W., Thern, E. R., Fearn, S., Mitra, G., Smirnov, A. V., & Blackman, E. G. (2020). Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo. Proceedings of the National Academy of Sciences, 201916553. https://doi.org/10.1073/pnas.1916553117)
Submitted by C. Ashley Norris on Thursday 25th June 01:22
I appreciate completely that this is highly technical, fiddly, painstaking work, but at the same time the final sample size of 2 is still rather small. How motivated are you to adjust your classification process to select for more samples? Or alternatively, if the classification is essential then open up the initial pool to hopefully find more viable samples?
Great question! Yes, I agree totally that the next stage in this work is to scale up the process and develop ways in which many many more crystals could be analysed. The biggest step in rejecting zircons in this study was to throw away all those younger than 3.5 Ga, simply because the focus was on the super old ones. However, there were thousands of younger crystals that could contain useful information if we can properly classify them and date the magnetisation! The scanning SQUID microscope has the potential to measure 100s of single crystals at once, which would enable 1000s of samples to be measured relatively easily (Caue who did the measurements may disagree with this statement...). Classification becomes key - the more we can learn about the different classes of zircon behaviour using a combination of SEM/CL/QDM/STEM/APT, the more useful information we will be able to extract. This could revolutionise the way we approach paleomagnetism of the Archean, especially as we improve our ability to date the formation of secondary magnetite.
I appreciate completely that this is highly technical, fiddly, painstaking work, but at the same time the final sample size of 2 is still rather small. How motivated are you to adjust your classification process to select for more samples? Or alternatively, if the classification is essential then open up the initial pool to hopefully find more viable samples?
Great question! Yes, I agree totally that the next stage in this work is to scale up the process and develop ways in which many many more crystals could be analysed. The biggest step in rejecting zircons in this study was to throw away all those younger than 3.5 Ga, simply because the focus was on the super old ones. However, there were thousands of younger crystals that could contain useful information if we can properly classify them and date the magnetisation! The scanning SQUID microscope has the potential to measure 100s of single crystals at once, which would enable 1000s of samples to be measured relatively easily (Caue who did the measurements may disagree with this statement...). Classification becomes key - the more we can learn about the different classes of zircon behaviour using a combination of SEM/CL/QDM/STEM/APT, the more useful information we will be able to extract. This could revolutionise the way we approach paleomagnetism of the Archean, especially as we improve our ability to date the formation of secondary magnetite.
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