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

- SS-LASS capable of dating zircon rims < 1 μm (or rims with composite age structure) to within 106 yr, for Cenozoic rocks
- High spatial and temporal resolution of SS-LASS offers great promise for study of short-duration metamorphic phenomena.
- SS-LASS able to decipher four zircon growth events at 33.0, 28.3, 23.0 and 18.2 Ma in the Cordillera de la Costa, Venezuela
- (Hydro)thermal activity at 33.0, 28.3, 23.0 and 18.2 Ma mark episodes of tectonism affecting South American plate margin

Single-shot laser ablation split stream (SS-LASS) petrochronology offers spatial resolution of < 1 μm 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 (< 106 yr) zircon growth events at c. 33.0, c. 28.3, c. 23.0 and c. 18.2 Ma. 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 < 106 yr resolution for Cenozoic rocks. Methods in 'geospeedometry'-which employ forward models to reproduce observed diffusion length scales-have obtained anomalously short time scales of 104-106 yr for metamorphism. The high spatial and temporal resolution of SS-LASS offers tremendous promise for investigating the veracity of these claims.