Crystallization sequence and tectonic significance of andalusite, kyanite, and sillimanite 'triple point' localities, including a new locality: Lesjaverk, Norway.

Abstract

Rocks containing three Al 2 SiO 5 polymorphs (andalusite, kyanite, sillimanite) are uncommon; only ten localities have previously been reported. By determining the crystallization sequence of the polymorphs, tectonic/metamorphic histories can be unlocked. Two crystallization sequences have been proposed: (1) kyanite -> sillimanite -> andalusite (Idaho, New Mexico, Spain, Italy), and (2) andalusite -> kyanite -> sillimanite (Colombia, Turkey, Iran, Russia, South Korea, and Japan). The newest locality is Lesjaverk, Norway. Sequence (1) suggests continental collision whereas Sequence (2) suggests contact metamorphism. Using petrographic analyses of deformation and accessory minerals, microprobe analyses of rutile grains, temperature calculations using Zr-in- rutile thermometry, and evaluation of element substitution, crystallization sequence, temperatures, and elemental trends will be determined.