Monazite U-Pb and trace-element data were gathered using LASS (laser-ablation split-stream ICP-MS) from the Western Gneiss Region, Norway, to investigate the petrologic significance of monazite trace-element compositions and to better understand the timing of (ultra)high-pressure (UHP) metamorphism during the Caledonian Orogeny.

Monazite from six samples contains up to 3 % common Pb, resulting in discordant U-Pb analyses. These high-common-Pb monazites are characterized by high Sr, weak Eu anomalies, and low Y+HREE. This composition is consistent with (ultra)high-pressure metamorphism during which feldspar (the largest reservoir for Eu and Sr) was absent, and the modal abundance of garnet (the largest reservoir of Y and HREE) was highest.

Sr and common Pb in monazite provide a tool for constraining the timing and duration of high-pressure processes within Earth's crust. More generally, Sr in monazite is a potential indicator of feldspar instability and may be applicable in other geologic settings, such as igneous systems in which the abundance of feldspar changes due to melting and crystallization. Sr measurements can be incorporated into geochronology workflows using the Sr concentrations calculated for monazite reference materials 44069 and Bananeira.