The source of Dalradian detritus in the Buchan Block, NE Scotland: application of new tools to detrital datasets

摘要

Detrital zircons from four samples of upper Dalradian metasedimentary rocks from the Buchan Block in the NE Grampian Highlands of Scotland were analysed by laser ablation inductively coupled plasma mass spectrometry to establish their U-Pb age and trace element composition. The analysed grains (magmatic cores) mainly yield concordant ages ranging from Neoproterozoic to Eoarchaean. Kernel density plots of the data show pronounced peaks in the late Mesoproterozoic, Palaeoproterozoic and Neoarchaean eras. The data are indistinguishable from detrital zircon age spectra from Dalradian rocks elsewhere, an interpretation supported by application of a non-parametric multidimensional scaling algorithm, and are consistent with a Laurentian source. Similar to existing studies from other Dalradian rocks, the age spectra from the Buchan Block reveal an increase in the relative proportion of older detritus with time, suggesting derivation from late Mesoproterozoic (Grenville) then Palaeoproterozoic orogens before widespread exposure and denudation of their Archaean basement rocks. Application of a novel approach to estimate the most likely time of radiogenic-Pb loss indicates that some detrital zircon grains were affected by element mobility around 470-450 Ma as a result of Grampian orogenesis.