Ikaite pseudomorphs in Neoproterozoic Dalradian slates record Earth’s coldest metamorphism
Calcite pseudomorphs have replaced euhedral ikaite (CaCO3.6H2O)porphyroblasts in Dalradian calcareous slates and metadolostones of western Scotland, with a volume decrease of at least 47%. Porphyroblast-fabric relationships indicate that the initial growth of ikaite post-dates a penetrative tectoni...
| Published in: | Journal of the Geological Society |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Geological Society of London
2015
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| Subjects: | |
| Online Access: | http://eprints.gla.ac.uk/104777/ http://eprints.gla.ac.uk/104777/1/104777.pdf |
| Summary: | Calcite pseudomorphs have replaced euhedral ikaite (CaCO3.6H2O)porphyroblasts in Dalradian calcareous slates and metadolostones of western Scotland, with a volume decrease of at least 47%. Porphyroblast-fabric relationships indicate that the initial growth of ikaite post-dates a penetrative tectonic fabric developed during upright folding. This is the first reported occurrence of metamorphic ikaite porphyroblasts and points towards growth within the slates during an ultra-low temperature metamorphism with an exceptionally low geothermal gradient. This event is associated with the penetration of long-lived and extreme permafrost deep into sub aerially exposed bedrock during Neoproterozoic glaciation. The presence of the well preserved pseudomorphs within the Easdale slates of the Argyll group implies that a Neoproterozoic orogenic unconformity exists above the stratigraphic position of theserocks. |
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