U–Pb age of titanite in the Mylonite Zone, southwestern Sweden

• DOI: 10.1080/11035899309454823
• Publication Date: 2010-01-07T17:46:35Z
• Authors: Leif Johansson; Åke Johansson
• Keywords: 01 natural sciences; 0105 earth and related environmental sciences

Abstract U–Pb dating of titanite from a mafic lens in the Mylonite Zone in southwestern Sweden yields an almost concordant age of c. 920 Ma. The titanite formed during retrogression of granulite-to amphibolite-facies rocks. Sources for Ti and Ca in titanite were Fe-Ti oxides and relatively grossular-rich garnets, respectively. Deformation is contemporaneous with or post-dates the growth of titanite, which took place at temperatures above c. 550AC. The obtained U–Pb age of titanite is close to the Sm-Nd isochron ages of garnet-bearing granulite-facies mineral assemblages in the Varberg area just south of the Mylonite Zone. Since the blocking temperature is higher for Nd diffusion in garnet than for the Pb diffusion in titanite it is suggested that the rocks of the Mylonite Zone were undergoing amphibolite-facies deformation, uplift and cooling while the granulites of the Varberg area were still at a considerably higher temperature.