Rapid, paced metamorphism of blueschists (Syros, Greece) from laser-based zoned Lu-Hf garnet chronology and LA-ICPMS trace element mapping

Unravelling the timing and rate of subduction-zone metamorphism H2O release requires linking time to compositional changes petrogenetic indicator minerals in blueschists eclogites. Garnet is a key mineral this regard, as it forms by, records, H2O-releasing reactions that can be linked pressure temperature conditions. These placed using chronology. Bulk-or multi-grain ages are norm garnet While these provide important precise constraints on across both facies, duration, rates style growth—crucial parameters petrological geochemical evolution subducting oceanic crust—remain unconstrained. Domain dating, i.e., dating individual growth zones, necessary investigate aspects, but generally impeded “common”-sized grains due sample size requirements. To overcome limitations, we use low-loss micro-sampling by laser cutting combined with Lu-Hf We used approach precisely date multiple zones 1-cm grain from glaucophane-bearing micaceous schist Cycladic Blueschist Unit (CBU), Syros Island, Greece. The analysis was major- trace-element mapping (EPMA, LA-ICPMS) petrogenesis. core mantle chemically comparable identical age within 0.1 Myr precision (2σ), indicating an initial pulse at 51.8 ± Ma (MSWD = 1.13). two rim which distinct, were resolvably younger 51.3 0.2 0.67). Integrated data, time-resolved record extremely fast, pulsed fluid-release reactions, such chloritoid breakdown. considered near-instantaneous subduction scales, re-equilibration far outpaces analysed associated upper-subunit CBU affinities, does not share last part prograde history rest CBU, margin sub-unit. interpret our sliver became attached base ophiolitic sub-unit thrusted onto lower unit high-pressure. Beyond providing insights into processes, new protocol for zoned geochronology “common-sized” opens possibilities constraining causes pace tectonic processes general.