Rapid high-resolution U-Pb LA-Q-ICPMS age mapping of zircon

Zircon commonly exhibits textural evidence for distinct growth events (e.g. polyphase core-rim structures) and evidence for Pb mobility not linked to discrete crystallization episodes (Pb loss, incorporation of common Pb, high-temperature Pb mobilization). Interpreting complex U-Pb zircon age data therefore requires imaging of zircon crystals and texturally-controlled sampling to constrain the fine-scale processes affecting the U-Pb zircon systematics. High-resolution U-Pb laser-ablation quadrupole inductively coupled plasma mass spectrometry (LA-Q-ICPMS) zircon age maps were undertaken on zircon sampled from syn-tectonic granitoid suites from the Peruvian Eastern Cordillera that exhibit textural evidence for clearly-defined cores and rims. The images were acquired by rastering a 7 mu m spot with a 3.5 J cm(-2) fluence, with scan speeds of 3 mu m s(-1) and a 10 Hz repetition rate (ThermoScientific iCAP-Qc setup) and scan speeds of 20 mu m s(-1) and a 45 Hz repetition rate (Agilent 7900 system). The mapping-experiment duration for individual zircons was as fast as 10 minutes (Agilent 7900 setup). 91500 zircon was employed as the primary reference material, and secondary-standard data (Temora, Plesovice, WRS-1348, FC-1, Fish Canyon, Tardree) typically reproduce within 1% of their published crystallization ages. Zircon rim concordia ages derived from the U-Pb age maps are consistent with independent secondary ion mass spectrometry (SIMS) and thermal ionisation mass spectrometry (TIMS) constraints. Two-dimensional kernel density estimation of the combined U-Pb data from each map define clear discordia mixing lines between the rim- and core-age components, and also show Pb loss and common Pb vectors. Potential applications of the technique include the characterisation of complex polyphase zircons and characterising the U-Pb systematics of key samples for time-intensive U-Pb TIMS dating.