The sillimanite zones of the Huntly-Portsoy area in the north-east Dalradian, Scotland

Abstract

SummaryThe distribution of andalusite, kyanite and sillimanite in an important part of the NE Dalradian is mapped. Sillimanite represents a late episode overprinted on the regional Andalusite and Kyanite Zones. The spatial distribution of sillimanite confirms that the heat source for the sillimanite-grade metamorphism in this area was the Newer (or Younger) Basic magma. The sillimanitic aureole of the Newer Basic intrusives is divisible into a Sillimanite Zone and a higher-grade Sillimanite—potash feldspar Zone. Relict andalusite is common in the Sillimanite Zone. Coarse muscovite replacing other minerals is primary in both zones, and should not be confused with late retrograde effects. Electron-probe analytical data on the Sillimanite–potash feldspar zone paragenesis of muscovite are presented. In this, its type area, the so-called ‘Boyne Line’ does not exist; the concept of such a tectonic dislocation arose through misinterpretation of the metamorphic effects.