First successful in-situ LA-ICPMS U–Pb dating of recrystallized, metamorphic sulfate constraints deformation phases on western Crete, Greece

Abstract

We report three U–Pb sulfate ages from the recently identified Intra-PQ Thrust within the Phyllite–Quartzite (PQ) Nappe of the Ionian high-pressure belt of the external Hellenides in the eastern Mediterranean. Crosscutting relations show that a distinct pressure-solution laminae/microlithon fabric is the oldest deformation structure. Two analyses of sulfate minerals that are part of this structure yielded indistinguishable dates, with a weighted average of 20.03 ± 5.96 Ma. The crosscutting fabric with alteration halos of the sulfate provided a date of 9.37 ± 4.64 Ma. The initial 207Pb/206Pb ratios are ~ 0.40 and thus distinctively lower than the terrestrial model lead isotope ratio of 0.84 for the calculated ages. This can only be explained if the dated sulfate precipitated from a fluid enriched in radiogenic 206Pb, probably sourced by the surrounding country rock through (partial) dissolution of older U-rich minerals. The dates of ~ 20 Ma agree with recently reported fault-gouge ages of 26–21 Ma from the Intra-PQ Thrust. The study demonstrates, for the first time, the possibility of dating sulfate minerals in metamorphosed rocks applying the U–Pb system. Graphical abstract