Exhumation of the high-pressure Richarddalen Complex in NWSvalbard: Insights from 40Ar/39Argeochronology

40Ar/39Ar dating of white mica from foliated metamorphic rocks of the Caledonian orogen of NW Svalbard was performed using the single-grain fusion technique. Two samples, an augen orthogneiss and a mica schist, were collected from the high-pressure Richarddalen Complex. Three additional mica schist samples were collected from the tectonically underlying Montblanc Unit. 40Ar/39Ar analysis of white mica separates yielded weighted average 40Ar/39Ar dates of 446.1 +/- 1.1, 438.4 +/- 1.1, 439.4 +/- 1.2, 439.8 +/- 1.5 and 439.3 +/- 1.0 Ma, with the oldest date provided by the Richarddalen mica schist. The single-grain fusion 40Ar/39Ar dating was accompanied by geochemical mapping of white mica using a microprobe. We interpret the oldest date as the age of cooling after a Late Ordovician high-pressure event and the four younger dates to represent the timing of subsequent deformation associated with assembly of a Caledonian nappe stack.

Automated summary

This study used 40Ar/39Ar dating to determine the ages of white mica in the Caledonian orogen of NW Svalbard. The results reveal that the oldest age represents the cooling age, while the other ages indicate the timing of subsequent deformation associated with the Caledonian nappe stack.