Metasomatic origin of the Himalayan banded tourmaline leucogranite.
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| Title: | Metasomatic origin of the Himalayan banded tourmaline leucogranite. |
|---|---|
| Authors: | Dyck, Brendan1 (AUTHOR) brendan.dyck@ubc.ca, Larson, Kyle P.1 (AUTHOR) |
| Source: | Contributions to Mineralogy & Petrology. Jul2023, Vol. 178 Issue 7, p1-20. 20p. |
| Subjects: | Tourmaline, Muscovite, Melt crystallization, Metasomatism, Plagioclase |
| Geographic Terms: | Nepal, Himalaya Mountains |
| Abstract: | Leucogranite bodies are ubiquitous in the upper structural levels of the Himalayan metamorphic slab. Their formation has ramifications for myriad processes including the generation of crustal melts and orogenic heat budgets. One particularly enigmatic variety of the Himalayan leucogranites, abundant in the Langtang region of Nepal, are the banded tourmaline leucogranites; typified by centimetre-scale compositional banding between tourmaline-rich and quartzo-feldspathic domains. Here, we use in-situ Rb–Sr isotopic chemistry and microstructural analysis to show these banded tourmaline leucogranites do not represent a direct product of melt crystallization but instead were formed by metasomatism of psammitic country-rock. This metasomatism was likely driven by the release of boron-rich volatiles during the crystallization of neighboring muscovite–biotite leucogranite bodies. Rb–Sr isochrons based on biotite–plagioclase ± white mica and K-feldspar data define overlapping dates of ca. 17.5 Ma from both the banded tourmaline leucogranite and its paired muscovite–biotite leucogranite. The characteristic banding appearance of these rocks is a product of heteroepitaxial nucleation of tourmaline on biotite folia and the replacement of pre-existing biotite and plagioclase with tourmaline and K-feldspar. The heteroepitaxy relationship of tourmaline on biotite is characterized by the {10–10} face of tourmaline parallel to biotite (001), with the tourmaline c-axis parallel to either the biotite [110] or [010] direction. One of the broader implications of our findings is that field estimates based on the volume of coarse-grained leucocratic outcrop overestimates the amount of melt generated at the top of the Himalayan slab. [ABSTRACT FROM AUTHOR] |
| Copyright of Contributions to Mineralogy & Petrology is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
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| Header | DbId: egs DbLabel: Engineering Source An: 165112743 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Metasomatic origin of the Himalayan banded tourmaline leucogranite. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Dyck%2C+Brendan%22">Dyck, Brendan</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> brendan.dyck@ubc.ca</i><br /><searchLink fieldCode="AR" term="%22Larson%2C+Kyle+P%2E%22">Larson, Kyle P.</searchLink><relatesTo>1</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Contributions+to+Mineralogy+%26+Petrology%22">Contributions to Mineralogy & Petrology</searchLink>. Jul2023, Vol. 178 Issue 7, p1-20. 20p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Tourmaline%22">Tourmaline</searchLink><br /><searchLink fieldCode="DE" term="%22Muscovite%22">Muscovite</searchLink><br /><searchLink fieldCode="DE" term="%22Melt+crystallization%22">Melt crystallization</searchLink><br /><searchLink fieldCode="DE" term="%22Metasomatism%22">Metasomatism</searchLink><br /><searchLink fieldCode="DE" term="%22Plagioclase%22">Plagioclase</searchLink> – Name: SubjectGeographic Label: Geographic Terms Group: Su Data: <searchLink fieldCode="DE" term="%22Nepal%22">Nepal</searchLink><br /><searchLink fieldCode="DE" term="%22Himalaya+Mountains%22">Himalaya Mountains</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Leucogranite bodies are ubiquitous in the upper structural levels of the Himalayan metamorphic slab. Their formation has ramifications for myriad processes including the generation of crustal melts and orogenic heat budgets. One particularly enigmatic variety of the Himalayan leucogranites, abundant in the Langtang region of Nepal, are the banded tourmaline leucogranites; typified by centimetre-scale compositional banding between tourmaline-rich and quartzo-feldspathic domains. Here, we use in-situ Rb–Sr isotopic chemistry and microstructural analysis to show these banded tourmaline leucogranites do not represent a direct product of melt crystallization but instead were formed by metasomatism of psammitic country-rock. This metasomatism was likely driven by the release of boron-rich volatiles during the crystallization of neighboring muscovite–biotite leucogranite bodies. Rb–Sr isochrons based on biotite–plagioclase ± white mica and K-feldspar data define overlapping dates of ca. 17.5 Ma from both the banded tourmaline leucogranite and its paired muscovite–biotite leucogranite. The characteristic banding appearance of these rocks is a product of heteroepitaxial nucleation of tourmaline on biotite folia and the replacement of pre-existing biotite and plagioclase with tourmaline and K-feldspar. The heteroepitaxy relationship of tourmaline on biotite is characterized by the {10–10} face of tourmaline parallel to biotite (001), with the tourmaline c-axis parallel to either the biotite [110] or [010] direction. One of the broader implications of our findings is that field estimates based on the volume of coarse-grained leucocratic outcrop overestimates the amount of melt generated at the top of the Himalayan slab. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Contributions to Mineralogy & Petrology is the property of Springer Nature and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1007/s00410-023-02020-0 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 20 StartPage: 1 Subjects: – SubjectFull: Tourmaline Type: general – SubjectFull: Muscovite Type: general – SubjectFull: Melt crystallization Type: general – SubjectFull: Metasomatism Type: general – SubjectFull: Plagioclase Type: general – SubjectFull: Nepal Type: general – SubjectFull: Himalaya Mountains Type: general Titles: – TitleFull: Metasomatic origin of the Himalayan banded tourmaline leucogranite. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Dyck, Brendan – PersonEntity: Name: NameFull: Larson, Kyle P. IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 07 Text: Jul2023 Type: published Y: 2023 Identifiers: – Type: issn-print Value: 00107999 Numbering: – Type: volume Value: 178 – Type: issue Value: 7 Titles: – TitleFull: Contributions to Mineralogy & Petrology Type: main |
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