Cryptoperthitic and replacive intergrowths with iridescence in monzonitic rocks from Cerro Colorado, northern Chile

Satoshi Nakano, Shoji Kojima, Kuniaki Makino, Masahiro Kayama, Hirotsugu Nishido, Junji Akai

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

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 languageEnglish
Pages (from-to)355-374
Number of pages20
JournalEuropean Journal of Mineralogy
Volume28
Issue number2
DOIs
Publication statusPublished - 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

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