Geochronology of shear zones: Use with caution

ORIOLO, SEBASTIÁN; FOSSEN, HAAKON; OYHANTCABAL, PEDRO; SIEGESMUND, SIEGFRIED; WEMMER, KLAUS; SCHULZ, BERNHARD

Congreso; XV Congreso Geológico Chileno; 2018

Assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere. The interpretation of thermochronological data from shear zones is, however, not straightforward. In the first place, closure temperatures (Dodson, 1973) depend on a number of factors, such as grain size, cooling rate and mineral composition, among others. Recalculations of closure temperature for muscovite considering parameters presented by Harrison et al. (2009) reveal, for instance, differences of ca. 40 °C for grain sizes of 500 and 100 μm. Likewise, variations of ca. 60 °C are obtained for cooling rates of 1 and 100 °C/my. Major differences are also observed when considering mineral compositions, as shown by Xannite for biotite and phlogopite (Grove and Harrison, 1996). In this case, closure temperature differences of >100 °C are obtained.