Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions
We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of mo...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Springer Berlin Heidelberg
2021
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| Online Access: | https://hdl.handle.net/1721.1/132770 |
| _version_ | 1811081286947700736 |
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| author | Monteiro, Aristle Duraiswami, Raymond A. Mittal, Tushar Pujari, Shrishail Low, Upananda Absar, Ahsan |
| 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 Monteiro, Aristle Duraiswami, Raymond A. Mittal, Tushar Pujari, Shrishail Low, Upananda Absar, Ahsan |
| author_sort | Monteiro, Aristle |
| collection | MIT |
| description | We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of most samples from F5 (especially those from within the core) are not linear but instead show kinks. These kinks are attributed to a rise in plagioclase nucleation due to degassing following the brecciation of the crust. Since it is difficult to constrain cooling time for ancient lava flows, we used the products of nucleation rates (Jt, 1.64 × 10–8 to 1.45 × 10–5 μm−3) and growth rates (Gt, 2.1 to 156 μm) with time. When compared with natural analogues as well as experimental results for basalt crystallisation, these values suggest a much faster lava cooling rate (~ 1 to 7℃/hr) than a conductive cooling model (≤ 0.1 ℃/hr). The CSDs for F3 fan with depth suggesting that the lava flow might represent local accumulation (ponding?) in a transitional lava flow field. CSDs for F5 show little variation with depth, with the exception of kinks for samples from the lower crust and core. The relatively higher number density of plagioclase microcrysts in our rubbly pāhoehoe (F5) and their CSD patterns are similar to those measured for transitional lavas from Hawaii. The vesicle data and CSDs indicate that brittle deformation was the primary mode of transition within these lavas. Identifying occurrence of thick ponded lavas within vertical stacks of rubbly pāhoehoe flows in the upper stratigraphic levels of the Deccan Traps are critically important as they demonstrate complex cooling styles, crystallisation histories, and emplacement dynamics. Transitional lavas such as rubbly pāhoehoe are important components of large CFB provinces such as the Deccan Traps and constitute nearly 46 to 85% of all lava types. Modelling of continental flood basalt provinces should therefore account for these diversities within lavas, and any oversimplified version using end-member morphotypes is unrealistic and untenable. |
| first_indexed | 2024-09-23T11:44:21Z |
| format | Article |
| id | mit-1721.1/132770 |
| institution | Massachusetts Institute of Technology |
| language | English |
| last_indexed | 2024-09-23T11:44:21Z |
| publishDate | 2021 |
| publisher | Springer Berlin Heidelberg |
| record_format | dspace |
| spelling | mit-1721.1/1327702024-06-03T17:18:22Z Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions Monteiro, Aristle Duraiswami, Raymond A. Mittal, Tushar Pujari, Shrishail Low, Upananda Absar, Ahsan Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of most samples from F5 (especially those from within the core) are not linear but instead show kinks. These kinks are attributed to a rise in plagioclase nucleation due to degassing following the brecciation of the crust. Since it is difficult to constrain cooling time for ancient lava flows, we used the products of nucleation rates (Jt, 1.64 × 10–8 to 1.45 × 10–5 μm−3) and growth rates (Gt, 2.1 to 156 μm) with time. When compared with natural analogues as well as experimental results for basalt crystallisation, these values suggest a much faster lava cooling rate (~ 1 to 7℃/hr) than a conductive cooling model (≤ 0.1 ℃/hr). The CSDs for F3 fan with depth suggesting that the lava flow might represent local accumulation (ponding?) in a transitional lava flow field. CSDs for F5 show little variation with depth, with the exception of kinks for samples from the lower crust and core. The relatively higher number density of plagioclase microcrysts in our rubbly pāhoehoe (F5) and their CSD patterns are similar to those measured for transitional lavas from Hawaii. The vesicle data and CSDs indicate that brittle deformation was the primary mode of transition within these lavas. Identifying occurrence of thick ponded lavas within vertical stacks of rubbly pāhoehoe flows in the upper stratigraphic levels of the Deccan Traps are critically important as they demonstrate complex cooling styles, crystallisation histories, and emplacement dynamics. Transitional lavas such as rubbly pāhoehoe are important components of large CFB provinces such as the Deccan Traps and constitute nearly 46 to 85% of all lava types. Modelling of continental flood basalt provinces should therefore account for these diversities within lavas, and any oversimplified version using end-member morphotypes is unrealistic and untenable. 2021-10-07T14:33:57Z 2021-10-07T14:33:57Z 2021-10 2021-05 2021-10-07T03:33:29Z Article http://purl.org/eprint/type/JournalArticle 1432-0819 https://hdl.handle.net/1721.1/132770 Monteiro, A., Duraiswami, R.A., Mittal, T. et al. Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions. Bull Volcanol 83, 67 (2021) en https://doi.org/10.1007/s00445-021-01485-w Bulletin of Volcanology Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. International Association of Volcanology & Chemistry of the Earth's Interior application/pdf Springer Berlin Heidelberg Springer Berlin Heidelberg |
| spellingShingle | Monteiro, Aristle Duraiswami, Raymond A. Mittal, Tushar Pujari, Shrishail Low, Upananda Absar, Ahsan Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title | Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title_full | Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title_fullStr | Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title_full_unstemmed | Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title_short | Cooling history and emplacement dynamics within rubbly lava flows, southern Deccan Traps: insights from textural variations and crystal size distributions |
| title_sort | cooling history and emplacement dynamics within rubbly lava flows southern deccan traps insights from textural variations and crystal size distributions |
| url | https://hdl.handle.net/1721.1/132770 |
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