A Morarian age for the ‘younger Moines’ of central and western Scotland
MUCH of our recent knowledge of the Moine metasediments1,2, which extend from the Moine Thrust across the Great Glen Fault to the boundary of the Dalradian Supergroup3,4 (Fig. 1), stems from the western Moine region. Here, late-Precambrian, Morarian ages (740–780 Myr) have been established from pegmatites in the Morar Division5, and a Grenvillian age (1,030 ±50 Myr) from the Granitic Gneiss of Ardgour in the Glenfinnan Division6. The ‘Central Highland Granulites’, generally regarded as ‘younger Moine’2,6, are little known geologically. Here we briefly outline the results of field (by M.A.J.P.) and radiometric investigations (by O.v.B.) in the Central Highland Granulites and the western Moines, which have fundamental implications for the evolution of these extensive metamorphic rocks, and for the nature of the Grenvillian–Caledonian interval in this sector of the North Atlantic Crust.
Grenville age for rocks in the Moine of north-western Scotland
THERE is considerable debate concerning both the age of sedimentation of the Moine Series and its tectonometa-morphic history. Though several workers have argued for the presence of Precambrian metamorphic and tectonic features within the Moine (see, for example, ref. 1), others have considered these features to be essentially of Caledonian age (see ref. 2). In consequence, syntheses of the evolution of north-western Scotland during Proterozoic and early Phanerozoic time include the Moine either as an older part of the Dalradian sedimentary prism which became involved in both early and late Caledonian orogenic activity3, or as a pre-Dalradian sediment wedge affected by pre-Dalradian (Morarian) subduction4.
Time and Heritage
As a historian studying what can be considered a form of intellectual history, I have slowly come to adopt Michel de Certeau’s observation made at the end of the 1980s that ‘objectifying the past, for the last three centuries, has undoubtedly left unconsidered time within a discipline that has continued to use it as a taxonomic instrument’. To a certain degree, time has become commonplace for the historian who has preserved or instrumentalized it. It is not considered because it is inconceivable, but because we do not think of it or, more simply, we do not think about it. As a historian attempting to pay attention to the time I’m living in, I have thus, like many others, noticed the swift development of the category of the present until it has become obvious that the present is omnipresent. This is what I refer to here as ‘presentism’.