U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge
New U/Pb analyses of zircon and xenotime constrain the timing of magmatism, magmatic assimilation, and hydrothermal metamorphism during formation of the lower crust at the Mid-Atlantic Ridge. The studied sample is an altered gabbro from the Vema lithospheric section (11N). Primary gabbroic minerals...
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American Geophysical Union (AGU)
2018
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| Online Access: | http://hdl.handle.net/1721.1/118167 https://orcid.org/0000-0001-9722-469X |
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| author | Jöns, Niels Lissenberg, C. Johan Bach, Wolfgang Kylander-Clark, Andrew Hacker, Bradley Rioux, Matthew Bowring, Samuel A. Dudas, Francis O. |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Jöns, Niels Lissenberg, C. Johan Bach, Wolfgang Kylander-Clark, Andrew Hacker, Bradley Rioux, Matthew Bowring, Samuel A. Dudas, Francis O. |
| author_sort | Jöns, Niels |
| collection | MIT |
| description | New U/Pb analyses of zircon and xenotime constrain the timing of magmatism, magmatic assimilation, and hydrothermal metamorphism during formation of the lower crust at the Mid-Atlantic Ridge. The studied sample is an altered gabbro from the Vema lithospheric section (11N). Primary gabbroic minerals have been almost completely replaced by multiple hydrothermal overprints: cummingtonitic amphibole and albite formed during high-temperature hydration reactions and are overgrown first by kerolite and then prehnite and chlorite. In a previous study, clear inclusion-free zircons from the sample yielded Th-corrected ²⁰⁶Pb/²³⁸U dates of 13.528±0.101 to 13.353±0.057Ma. Ti concentrations, reported here, zoning patterns and calculated Th/U of the dated grains are consistent with these zircons having grown during igneous crystallization. To determine the timing of hydrothermal metamorphism, we dated a second population of zircons, with ubiquitous <1-20μm chlorite inclusions, and xenotimes that postdate formation of metamorphic albite. The textures and inclusions of the inclusion-rich zircons suggest that they formed by coupled dissolution-reprecipitation of metastable igneous zircon during or following hydrothermal metamorphism. Th-corrected ²⁰⁶Pb/²³⁸U dates for the inclusion-rich zircons range from 13.598±0.012 to 13.503±0.018Ma and predate crystallization of all but one of the inclusion-free zircons, suggesting that the inclusion-rich zircons were assimilated from older hydrothermally altered wall rocks. The xenotime dates are sensitive to the Th correction applied, but even using a maximum correction,206Pb/238U dates range from 13.341±0.162 to 12.993±0.055Ma and postdate crystallization of both the inclusion-rich zircons and inclusion-free igneous zircons, reflecting a second hydrothermal event. The data provide evidence for alternating magmatism and hydrothermal metamorphism at or near the ridge axis during accretion of the lower crust at a ridge-transform intersection and suggest that hydrothermally altered crust was assimilated into younger gabbroic magmas. The results of this study show that high-precision U-Pb dating is a powerful method for studying the timing of magmatic and hydrothermal processes at mid-ocean ridges. Key words: zircon; xenotime; hydrothermal; Mid-Atlantic Ridge; Vema; mid-ocean ridge |
| first_indexed | 2024-09-23T10:53:19Z |
| format | Article |
| id | mit-1721.1/118167 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T10:53:19Z |
| publishDate | 2018 |
| publisher | American Geophysical Union (AGU) |
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| spelling | mit-1721.1/1181672024-05-15T08:16:54Z U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge Jöns, Niels Lissenberg, C. Johan Bach, Wolfgang Kylander-Clark, Andrew Hacker, Bradley Rioux, Matthew Bowring, Samuel A. Dudas, Francis O. Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Rioux, Matthew Bowring, Samuel A Dudas, Francis O New U/Pb analyses of zircon and xenotime constrain the timing of magmatism, magmatic assimilation, and hydrothermal metamorphism during formation of the lower crust at the Mid-Atlantic Ridge. The studied sample is an altered gabbro from the Vema lithospheric section (11N). Primary gabbroic minerals have been almost completely replaced by multiple hydrothermal overprints: cummingtonitic amphibole and albite formed during high-temperature hydration reactions and are overgrown first by kerolite and then prehnite and chlorite. In a previous study, clear inclusion-free zircons from the sample yielded Th-corrected ²⁰⁶Pb/²³⁸U dates of 13.528±0.101 to 13.353±0.057Ma. Ti concentrations, reported here, zoning patterns and calculated Th/U of the dated grains are consistent with these zircons having grown during igneous crystallization. To determine the timing of hydrothermal metamorphism, we dated a second population of zircons, with ubiquitous <1-20μm chlorite inclusions, and xenotimes that postdate formation of metamorphic albite. The textures and inclusions of the inclusion-rich zircons suggest that they formed by coupled dissolution-reprecipitation of metastable igneous zircon during or following hydrothermal metamorphism. Th-corrected ²⁰⁶Pb/²³⁸U dates for the inclusion-rich zircons range from 13.598±0.012 to 13.503±0.018Ma and predate crystallization of all but one of the inclusion-free zircons, suggesting that the inclusion-rich zircons were assimilated from older hydrothermally altered wall rocks. The xenotime dates are sensitive to the Th correction applied, but even using a maximum correction,206Pb/238U dates range from 13.341±0.162 to 12.993±0.055Ma and postdate crystallization of both the inclusion-rich zircons and inclusion-free igneous zircons, reflecting a second hydrothermal event. The data provide evidence for alternating magmatism and hydrothermal metamorphism at or near the ridge axis during accretion of the lower crust at a ridge-transform intersection and suggest that hydrothermally altered crust was assimilated into younger gabbroic magmas. The results of this study show that high-precision U-Pb dating is a powerful method for studying the timing of magmatic and hydrothermal processes at mid-ocean ridges. Key words: zircon; xenotime; hydrothermal; Mid-Atlantic Ridge; Vema; mid-ocean ridge National Science Foundation (U.S.) (Grant OCE‐0727914) National Science Foundation (U.S.) (Grant OCE‐0960892) National Science Foundation (U.S.) (Grant EAR‐1250522) 2018-09-25T15:58:26Z 2018-09-25T15:58:26Z 2015-04 2014-10 2018-09-20T16:44:10Z Article http://purl.org/eprint/type/JournalArticle 2169-9356 2169-9313 http://hdl.handle.net/1721.1/118167 Rioux, Matthew et al. “U-Pb Dating of Interspersed Gabbroic Magmatism and Hydrothermal Metamorphism During Lower Crustal Accretion, Vema Lithospheric Section, Mid-Atlantic Ridge.” Journal of Geophysical Research: Solid Earth 120, 4 (April 2015): 2093–2118 © 2015 The Authors https://orcid.org/0000-0001-9722-469X http://dx.doi.org/10.1002/2014JB011668 Journal of Geophysical Research: Solid Earth Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/ application/pdf American Geophysical Union (AGU) Wiley |
| spellingShingle | Jöns, Niels Lissenberg, C. Johan Bach, Wolfgang Kylander-Clark, Andrew Hacker, Bradley Rioux, Matthew Bowring, Samuel A. Dudas, Francis O. U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title | U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title_full | U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title_fullStr | U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title_full_unstemmed | U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title_short | U-Pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion, Vema lithospheric section, Mid-Atlantic Ridge |
| title_sort | u pb dating of interspersed gabbroic magmatism and hydrothermal metamorphism during lower crustal accretion vema lithospheric section mid atlantic ridge |
| url | http://hdl.handle.net/1721.1/118167 https://orcid.org/0000-0001-9722-469X |
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