Diagrams of Th vs U in zircon for all Skaergaard samples, granophyres, sills, and related rocks. The dashed lines in panels a–j represent constant values of Th/U. The average 2σ uncertainty in Th and U analyses is smaller than the analytical symbols. (a) Upper Border Series LZa’ (SK08-190), LZb’ (SK08-124), and LZc’ (SK08-128). (b) UBS MZ’ (SK08-137), UZa’ (SK08-158), UZb’ (SK08-154), and UZc’ (SK08-27, SEB87-212B). (c) Layered Series LZa (458245, SEB87-227A) and LZc (SEB87-231B). (d) Marginal Border Series LZc^* (SEB87–248). (e) Sandwich Horizon from Kilen (SK08-110, SK08–104). (f) Sandwich Horizon from Basistoppen (SK11–56). (g) Related rocks: Precambrian gneiss (SK11-131) and contaminated sample of LZa^* (SEB87-242, PPL). (h) Sydtoppen sill (SK08-35) and Tinden sill (SK11–190). (i) Granophyres in UZc (SEB87-215, 458649) and UZc’ (SK08-99). (j) Granophyre in UZa (SEB87–211).