A zircon LA-ICPMS reverse depth profiling analysis method and its geological application

Abstract

Zircon U–Pb dating by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) is a widely used analytical method in the field of geology. However, the U–Pb dating of zircons with complex interior structures has always been a challenge in laser in situ analysis. To address this issue, we introduce a novel method, termed reverse depth profiling, for LA-ICPMS U–Pb dating of such zircons. This method combines the traditional LA-ICPMS method with depth profiling, analyzing the over-polished zircon from core to rim. We applied this method to zircons from the Himalayan leucogranites in Dinggye and garnet-bearing granitic gneiss in Yadong. The method allows the successful dating of zircon rims as narrow as only 0.6 μm. Characterized by high sample analysis efficiency, superior vertical spatial resolution, and optimal data utilization, this method enhances the success rate of U–Pb dating of structurally complex zircons. Valid geochronological information on the inherited cores and magmatic/metamorphic rims of zircons can be obtained by this method, which has great potential for unraveling complex magmatic and metamorphic events in tectonically active regions in geological history.