%0 Journal Article
%T Multiple monazite growth in the  reskutan migmatite: evidence for a polymetamorphic Late Ordovician to Late Silurian evolution in the Seve Nappe Complex of west-central J mtland, Sweden
%A Majka J
%A Be¡¯eri-Shlevin Y
%A Gee D G
%A Ladenberger A
%J Journal of Geosciences
%D 2012
%I 
%R 10.3190/jgeosci.112
%X Monazite from granulite-facies rocks of the  reskutan Nappe in the Scandinavian Caledonides (Seve Nappe Complex, Sweden) was dated using in-situ U-Th-total Pb chemical geochronology (CHIME). Multi-spot analyses of a non-sheared migmatite neosome yielded an age of 439 ¡À 3 Ma, whereas a sheared migmatite gave 433 ¡À 3 Ma (2¦Ò). Although the obtained dates are rather similar, a continuous array of single dates from c. 400 Ma to c. 500 Ma suggests possibly a more complex monazite age pattern in the studied rocks. The grouping and recalculation of the obtained results in respect to Y-Th-U systematics and microtextural context allowed distinguishing several different populations of monazite grains/growth zones. In the migmatite neosome, low-Th and low-Y domains dated at 455 ¡À 11 Ma are considered to have grown under high-grade sub-solidus conditions, most likely during a progressive burial metamorphic event. The monazites with higher Th and lower Y yielded an age of 439 ¡À 4 Ma marking the subsequent partial melting event caused by decompression. The youngest (423 ¡À 13 Ma) Y-enriched monazite reveals features of fluid-assisted growth and is interpreted to date the emplacement of the  reskutan onto the Lower Seve Nappe. In the sheared migmatite, the high-Th and low-U (high Th/U) monazite with variable Y contents yielded an age of 438 ¡À 4 Ma, which is interpreted to date the partial melting event. Relatively U-rich rims on some of the monazite grains again reveal features of fluid-assisted growth, and thus their age of 424 ¡À 6 Ma is interpreted as timing the nappes emplacement. These results call, however, for further more precise, isotopic (preferably ion microprobe) dating of monazite in the studied rocks.
%K Scandinavian Caledonides
%K geochronology
%K monazite
%K partial melting
%K metamorphism
%U http://www.jgeosci.org/content/jgeosci.112_majka.pdf