Geochronological investigation of the Ingdal Granite Gneiss and discordant pegmatites from the Western Gneiss Region, Norway

A seven-point (three zircon and four titanite) U-Pb discordia-line from the Ingdal granite gneiss defines
upper- and lower-intercept ages of 1653 ± 2 Ma and 396 ± 5 Ma interpreted as the time of Ingdal granite
emplacement, and the time of gneiss formation and partial Pb-loss from zircon and titanite during a
regional metamorphic event, respectively. These isotopic data suggest that this part of the Western
Gneiss Region was heated and cooled very quickly at both the upper,- and lower-intercept ages, and that
it did not experience significant Sveconorwegian (ca. 1250-900 Ma) or Finnmarkian (ca. 530--480 Ma)
isotopic disturbance. A six-point Rb-Sr whole-rock errorchron (MSWD = 11) from the same body of
the Ingdal granite gneiss defines a date of 1665 ± 49 Ma interpreted as a less precise age of granite
emplacement. Rb-Sr mineral dates from three strongly discordant, non-foliated granite pegmatites fall
in the age range of 415-379 Ma. A Rb-Sr biotite date of 372 ±4 Ma from the Ingdal granite gneiss
establishes a minimum age of isotopic disturbance in the region.