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The Skaergaard trough layering: sedimentation in a convecting magma chamber

The upper parts of the floor cumulates of the Skaergaard Intrusion, East Greenland, contain abundant features known as troughs. The troughs are gently plunging synformal structures comprising stacks of crescentic modally graded layers with a sharply defined mafic base that grades upward into plagioc...

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Autores principales: Vukmanovic, Z., Holness, M. B., Monks, K., Andersen, J. C. Ø.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Springer Berlin Heidelberg 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6560677/
https://www.ncbi.nlm.nih.gov/pubmed/31258174
http://dx.doi.org/10.1007/s00410-018-1466-1
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author Vukmanovic, Z.
Holness, M. B.
Monks, K.
Andersen, J. C. Ø.
author_facet Vukmanovic, Z.
Holness, M. B.
Monks, K.
Andersen, J. C. Ø.
author_sort Vukmanovic, Z.
collection PubMed
description The upper parts of the floor cumulates of the Skaergaard Intrusion, East Greenland, contain abundant features known as troughs. The troughs are gently plunging synformal structures comprising stacks of crescentic modally graded layers with a sharply defined mafic base that grades upward into plagioclase-rich material. The origin of the troughs and layering is contentious, attributed variously to deposition of mineral grains by magmatic currents descending from the nearby walls, or to in situ development by localised recrystallisation during gravitationally-driven compaction. They are characterised by outcrop-scale features such as mineral lineations parallel to the trough axis, evidence of erosion and layer truncation associated with migration of the trough axis, and disruption of layering by syn-magmatic slumping. A detailed microstructural study of the modal trough layers, using electron backscatter diffraction together with geochemical mapping, demonstrates that these rocks do not record evidence for deformation by either dislocation creep or dissolution–reprecipitation. Instead, the troughs are characterised by the alignment of euhedral plagioclase crystals with unmodified primary igneous compositional zoning. We argue that the lineations and foliations are, therefore, a consequence of grain alignment during magmatic flow. Post-accumulation amplification of the modal layering occurred as a result of differential migration of an unmixed immiscible interstitial liquid, with upwards migration of the Si-rich conjugate into the plagioclase-rich upper part of the layers, whereas the Fe-rich immiscible conjugate remained in the mafic base. Both field and microstructure evidence support the origin of the troughs as the sites of repeated deposition from crystal-rich currents descending from the nearby chamber walls. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00410-018-1466-1) contains supplementary material, which is available to authorized users.
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spelling pubmed-65606772019-06-26 The Skaergaard trough layering: sedimentation in a convecting magma chamber Vukmanovic, Z. Holness, M. B. Monks, K. Andersen, J. C. Ø. Contrib Mineral Petrol Original Paper The upper parts of the floor cumulates of the Skaergaard Intrusion, East Greenland, contain abundant features known as troughs. The troughs are gently plunging synformal structures comprising stacks of crescentic modally graded layers with a sharply defined mafic base that grades upward into plagioclase-rich material. The origin of the troughs and layering is contentious, attributed variously to deposition of mineral grains by magmatic currents descending from the nearby walls, or to in situ development by localised recrystallisation during gravitationally-driven compaction. They are characterised by outcrop-scale features such as mineral lineations parallel to the trough axis, evidence of erosion and layer truncation associated with migration of the trough axis, and disruption of layering by syn-magmatic slumping. A detailed microstructural study of the modal trough layers, using electron backscatter diffraction together with geochemical mapping, demonstrates that these rocks do not record evidence for deformation by either dislocation creep or dissolution–reprecipitation. Instead, the troughs are characterised by the alignment of euhedral plagioclase crystals with unmodified primary igneous compositional zoning. We argue that the lineations and foliations are, therefore, a consequence of grain alignment during magmatic flow. Post-accumulation amplification of the modal layering occurred as a result of differential migration of an unmixed immiscible interstitial liquid, with upwards migration of the Si-rich conjugate into the plagioclase-rich upper part of the layers, whereas the Fe-rich immiscible conjugate remained in the mafic base. Both field and microstructure evidence support the origin of the troughs as the sites of repeated deposition from crystal-rich currents descending from the nearby chamber walls. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s00410-018-1466-1) contains supplementary material, which is available to authorized users. Springer Berlin Heidelberg 2018-04-25 2018 /pmc/articles/PMC6560677/ /pubmed/31258174 http://dx.doi.org/10.1007/s00410-018-1466-1 Text en © The Author(s) 2018 Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
spellingShingle Original Paper
Vukmanovic, Z.
Holness, M. B.
Monks, K.
Andersen, J. C. Ø.
The Skaergaard trough layering: sedimentation in a convecting magma chamber
title The Skaergaard trough layering: sedimentation in a convecting magma chamber
title_full The Skaergaard trough layering: sedimentation in a convecting magma chamber
title_fullStr The Skaergaard trough layering: sedimentation in a convecting magma chamber
title_full_unstemmed The Skaergaard trough layering: sedimentation in a convecting magma chamber
title_short The Skaergaard trough layering: sedimentation in a convecting magma chamber
title_sort skaergaard trough layering: sedimentation in a convecting magma chamber
topic Original Paper
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6560677/
https://www.ncbi.nlm.nih.gov/pubmed/31258174
http://dx.doi.org/10.1007/s00410-018-1466-1
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