Discussion on ‘The structural interpretation of domainal trace lineation: an example from the Mona Complex, Anglesey’

Abstract

In a recent short note, Lisle (2013) uses an example from the New Harbour Group of Anglesey, UK, to illustrate a type of structural lineation he terms ‘domainal trace lineation’. This is a form of intersection lineation manifested in fine banding, considered to be the intersection of one domainal foliation (e.g. crenulation cleavage) on another domainal foliation. If Lisle’s interpretation is correct, it implies that the New Harbour Group has at least four phases of deformation, compared with the two that are recognized in the underlying South Stack Group at Rhoscolyn (e.g. Shackleton 1969; Treagus et al . 2003). Furthermore, if the pervasive lineation in the New Harbour Group is considered to be an intersection lineation, this has significant consequences for the regional tectonics. As noted by Lisle, the much-described lineation in the New Harbour Group has been described as a ‘stretching lineation’ by Shackleton (1969), Powell (1979) and Roper (1992), and a ‘quartz stretching lineation’ by Phillips (1991). In a paper overlapping Lisle’s, we describe it as a ‘quartz elongation lineation’ (L1) that is folded with the S1 foliation (Treagus et al . 2013). Lisle notes that only Hudson & Stowell (1997) considered the prominent lineation in the New Harbour Group to be an ‘intersection lineation’. Nevertheless, on the basis of one locality, …