Single-shot laser ablation split stream (SS-LASS) petrochronology deciphers multiple, short-duration metamorphic events

Abstract

Single-shot laser ablation split stream (SS-LASS) petrochronology offers spatial resolution of <1μm per (surface) analysis. This enables the technique to interrogate metamorphic zircon overgrowths that are very thin, or that preserve a composite age structure. To demonstrate the advantages of SS-LASS, the technique was applied to metamorphic zircon overgrowths in five rocks from the Cordillera de la Costa, Venezuela. In these rocks, SS-LASS was able to decipher discrete, short-duration (<106yr) zircon growth events at c. 33.0, c. 28.3, c. 23.0 and c. 18.2Ma. Comparison with existing geo-/thermochronology suggests that the SS-LASS dates represent (hydro)thermal events that mark distinct episodes of tectonism affecting the northern margin of South America.With an external error of 5% incorporated into isotope ratios (as required to achieve satisfactory analytical precision), SS-LASS dates for reference materials were accurate to within 1.5% of published values. The SS-LASS technique is thus, in favorable cases, capable of providing <106yr resolution for Cenozoic rocks. Methods in ‘geospeedometry’—which employ forward models to reproduce observed diffusion length scales—have obtained anomalously short time scales of 104–106yr for metamorphism. The high spatial and temporal resolution of SS-LASS offers tremendous promise for investigating the veracity of these claims.