Geochronology of appinitic and related granitic magmatism in the W Highlands of Scotland: constraints on the timing of transcurrent fault movement

Abstract

The timing of appinitic and related granitic magmatism throughout the W Highlands of Scotland has been investigated using U-Pb geochronological techniques. An appinite from the Garabal Hill/Glen Fyne complex is dated at 429 ±2 Ma (zircon) and 422 ±3 Ma (titanite); appinites from Arrochar and Rubha Mór give titanite ages of 426 ± 3 Ma and 427 ± 3 Ma respectively. The Strontian granodiorite is 425 ±3 Ma (zircon) and 423 ±3 Ma (titanite), and a pyroxene-mica diorite from Rat again gives an age of 425 ± 3 Ma. The data show the value of using titanite to date basic rocks which may lack zircon, and of using inheritance-free phases in rocks which contain mostly inherited zircon. The narrow range of ages for this magmatism reported here contrasts with a broad smear of previously published ages, and indicates that the middle Silurian was a major period of transcurrent fault movement throughout the W Highlands. Voluminous magmatism of this age is also found in Newfoundland, highlighting the importance of this event in the wider context of the Caledonide orogen.