Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis
The Gore Mountain Garnet Amphibolite (GMGA), part of the Mesoproterozoic Grenville Province in the Adirondack Highlands, NY, USA, is an iconic rock type known for hosting the world’s largest garnets (up to 1 m diameter). We present a new detailed petrographic study of these rocks. Field relations, w...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Oxford University Press (OUP)
2021
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| Online Access: | https://hdl.handle.net/1721.1/132666 |
| _version_ | 1811097597453008896 |
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| author | Shinevar, William J Jagoutz, Oliver VanTongeren, Jill A |
| 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 Shinevar, William J Jagoutz, Oliver VanTongeren, Jill A |
| author_sort | Shinevar, William J |
| collection | MIT |
| description | The Gore Mountain Garnet Amphibolite (GMGA), part of the Mesoproterozoic Grenville Province in the Adirondack Highlands, NY, USA, is an iconic rock type known for hosting the world’s largest garnets (up to 1 m diameter). We present a new detailed petrographic study of these rocks. Field relations, whole-rock, and mineral major and trace element chemistry suggest that these rocks formed via a prograde hydration reaction of a metagabbro during an increase in pressure and temperature. Laser ablation inductively coupled plasma mass spectrometry U–Pb geochronology applied to zircon interpreted to be metamorphic in origin dates this reaction to 1053·9 ± 5·4 Ma (2σ; MSWD = 0·94), during the Ottawan Orogeny (1090–1020 Ma). Our results on peak metamorphic P–T conditions based on thermobarometry, diffusion models, and thermodynamic modelling indicate that these rocks formed at ultrahigh-temperature (>900 °C) conditions (P = 9–10 kbar, T = 950 ± 40 °C), significantly hotter than previously estimated. Diffusion models pinned by nearby cooling ages require the GMGA to initially cool quickly (9·1 °C Ma–1), followed by slower cooling (2·6 °C Ma–1). The two-stage cooling history for the GMGA could reflect initial advection-dominated cooling followed by conduction-dominated cooling once flow ceases. Our results suggest that the region was hot enough to undergo topography-driven lower crustal flow similar to that hypothesized for modern Tibet for 20–0 Ma (25–0 Ma when the effects of melt are included). |
| first_indexed | 2024-09-23T17:02:09Z |
| format | Article |
| id | mit-1721.1/132666 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T17:02:09Z |
| publishDate | 2021 |
| publisher | Oxford University Press (OUP) |
| record_format | dspace |
| spelling | mit-1721.1/1326662022-09-29T23:12:37Z Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis Shinevar, William J Jagoutz, Oliver VanTongeren, Jill A Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Woods Hole Oceanographic Institution The Gore Mountain Garnet Amphibolite (GMGA), part of the Mesoproterozoic Grenville Province in the Adirondack Highlands, NY, USA, is an iconic rock type known for hosting the world’s largest garnets (up to 1 m diameter). We present a new detailed petrographic study of these rocks. Field relations, whole-rock, and mineral major and trace element chemistry suggest that these rocks formed via a prograde hydration reaction of a metagabbro during an increase in pressure and temperature. Laser ablation inductively coupled plasma mass spectrometry U–Pb geochronology applied to zircon interpreted to be metamorphic in origin dates this reaction to 1053·9 ± 5·4 Ma (2σ; MSWD = 0·94), during the Ottawan Orogeny (1090–1020 Ma). Our results on peak metamorphic P–T conditions based on thermobarometry, diffusion models, and thermodynamic modelling indicate that these rocks formed at ultrahigh-temperature (>900 °C) conditions (P = 9–10 kbar, T = 950 ± 40 °C), significantly hotter than previously estimated. Diffusion models pinned by nearby cooling ages require the GMGA to initially cool quickly (9·1 °C Ma–1), followed by slower cooling (2·6 °C Ma–1). The two-stage cooling history for the GMGA could reflect initial advection-dominated cooling followed by conduction-dominated cooling once flow ceases. Our results suggest that the region was hot enough to undergo topography-driven lower crustal flow similar to that hypothesized for modern Tibet for 20–0 Ma (25–0 Ma when the effects of melt are included). NSF (Grant EAR-1722935) 2021-09-30T15:16:13Z 2021-09-30T15:16:13Z 2021-01 2020-06 2021-09-29T16:38:10Z Article http://purl.org/eprint/type/JournalArticle 0022-3530 1460-2415 https://hdl.handle.net/1721.1/132666 Shinevar, William J. et al. "Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis." Journal of Petrology 62, 4 (January 2021): egab007. © 2021 Oxford University Press en http://dx.doi.org/10.1093/petrology/egab007 Journal of Petrology Creative Commons Attribution-Noncommercial-Share Alike http://creativecommons.org/licenses/by-nc-sa/4.0/ application/pdf Oxford University Press (OUP) Prof. Jagoutz |
| spellingShingle | Shinevar, William J Jagoutz, Oliver VanTongeren, Jill A Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title | Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title_full | Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title_fullStr | Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title_full_unstemmed | Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title_short | Gore Mountain Garnet Amphibolite Records UHT Conditions: Implications for the Rheology of the Lower Continental Crust during Orogenesis |
| title_sort | gore mountain garnet amphibolite records uht conditions implications for the rheology of the lower continental crust during orogenesis |
| url | https://hdl.handle.net/1721.1/132666 |
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