Fluid inclusion 40Ar/39Ar geochronology of andalusite from syn-tectonic quartz veins: New perspectives on dating deformation and metamorphism in low-pressure metamorphic belts

Syn-tectonic quartz veins are widely present in low- to medium-grade metapelitic belts, however, dating these is challenging due the lack of suitable target minerals for most geochronological methods. Andalusite a common K-poor aluminosilicate mineral veins. In this study, we demonstrate feasibility fluid inclusions andalusite using 40Ar/39Ar gentle stepwise crushing technique. Three samples syn-tectonic from Chinese Altai, Central Asia yielded similar gas release patterns. The first steps generated significant excess 40Ar which likely originated secondary inclusions. These gave anomalously old and quickly declining apparent ages. following less concordant well-defined Early Permian ages 282–277 Ma. were dominated by degassing intra-crystal liquid-rich inclusion planes. Two crushed powder experiments selected additional heating furnace much younger age 216 Laser muscovite flakes two investigated one chloridized biotite sample different andalusite-bearing vein 243–241 Ma 214 Ma, respectively. Compared with gases released experiments, extracted showed distinct Cl–K–Ca compositional characteristics near atmospheric initial 40Ar/36Ar value. observations suggest that 1) contrary wisdom, nesosilicates preferably preserved rather than lattices, 2) K (Ar) contamination K-bearing solid phases negligible during crushing. As such, could be considered as timing growth record more recent cooling events. youngest reflect sericitization chloritization samples, evidenced petrologic x-ray mapping results. Furthermore, agree monazite/zircon U–Pb (280–273 Ma) leucogranite pegmatite dykes metamorphic (299–262 low-pressure rocks region. results geochronology can used constrain deformation associated metamorphism terranes, also provide complete pictures tectono-thermal evolution combination traditional geochronology.