Intergrowth of andesine and labradorite in marbles of the Central Alps
Abstract
Crystallographic intergrowth of An 34 andesine and An 66 labradorite which can be seen with a petrographic microscope in sections cut perpendicular to [001] has been observed in amphibolite facies calcsilicate rocks of the Central Alps. The texture indicates that both plagioclases grew simultaneously in equilibrium, andesine mainly nucleating on faces (1¯10), (110), (100) and (130) of labradorite. The chemical composition measured on the U-stage and confirmed by microprobe establishes the endmembers of the andesine-labradorite miscibility gap. As shown by X-ray and electron diffraction both endmembers have the same intermediate plagioclase structure with periodic antiphase boundaries parallel to 10¯3 and spaced 25 30 Å which is characteristic of the structure observed in andesine from igneous rocks. Two different types of domains have been observed; one is in contrast with e-reflections and the other with strong a-reflections.
- Publication:
-
Contributions to Mineralogy and Petrology
- Pub Date:
- December 1975
- DOI:
- 10.1007/BF00382446
- Bibcode:
- 1975CoMP...53..311W