Abstract
Cryptoperthitic alkali feldspars in the Cerro Colorado monzonites from the Atacama Desert, northern Chile, exhibit bluish iridescence. Three types of cryptoperthites are developed over a grain; fine and coarse cryptoperthites of Or-Ab-An ternary compositions around Or60-65Ab35-30An5, and Or-rich, An-poor cryptoperthite around Or70Ab26An4. The former ternary compositions point to crystallization at approximately 900°C. Hydrothermally turbid patch microperthites are not developed in the alkali feldspar, whereas turbid Or-rich veins with micropores display limited replacement of the cryptoperthites along the lamellae. The Or-rich veins are much richer in water than the cryptoperthitic regions. Blue cathodoluminescence of variable tint is observed over individual grains, except in the Or-rich veins. The Cerro Colorado alkali feldspars record an incipient state of alkali feldspars, which predates the low-temperature formation of patch microperthite in subsolvus granites. These feldspars are the first natural alkali feldspars with K-feldspathization without microperthite formation.
Original language | English |
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Pages (from-to) | 355-374 |
Number of pages | 20 |
Journal | European Journal of Mineralogy |
Volume | 28 |
Issue number | 2 |
DOIs | |
Publication status | Published - 2016 |
Keywords
- An-poor domain
- Cation-exchange
- Cryptoperthite
- Iridescent alkali feldspar
- Microcrack
- Micropore
- Monzonite
- Or-rich vein
- Replacement
ASJC Scopus subject areas
- Geochemistry and Petrology