High Precision Zircon Sims Zr Isotope Analysis

Zirconium isotope is a very promising tracer to investigate geological processes such as magmatic crystallization and differentiation, and to tackle the secular evolution of the continental crust. With zircon being its major hosting mineral, developing analytical technique with high accuracy, high precision and high efficiency is critical to facilitate its geological applications. This study presents an analytical method to measure zircon Zr isotope compositions by secondary ion mass spectrometry (SIMS). With careful sample preparation to limit the topography effect and instrumental tuning for maintaining its stability, we demonstrate that large geometry SIMS can provide zircon Zr isotope measurements with high accuracy, high precision and high efficiency. Based on extensive testing on our CAMECA IMS 1280HR, the recommended instrumental tuning parameters are: a primary beam intensity of similar to 30 nA, a beam diameter of similar to 20 x 15 mu m(2), a mass resolution power of 2400 and a raster size of 15 x 15 mu m(2), with Zr-94 and Zr-90 being collected by static Faraday cups via a signal accumulation time of 20 cycles x 4 s. By analyzing zircon reference materials commonly used for U-Pb and O analysis (i.e., 91500, Penglai, Plesovice, and Mudtank), we have achieved a delta Zr-94 repeatability of 0.04-0.07 parts per thousand (2SD, n = 33-75), and the Zr isotope compositions of zircon reference materials measured by SIMS agree remarkably well with those defined by double-spike solution methods. Our method consumes similar to 1.2 ng materials in a single spot analysis (similar to 0.9 mu m pit depth), together with its high spatial resolution (similar to 13 x 14 x 0.3 mu m(3) for data collection) and high efficiency (similar to 4 minutes per analysis), it is expected that our SIMS Zr isotope analytical method will be very useful for studying precious materials (e.g., zircon in lunar soil) and to facilitate big data research (e.g., detrital zircon study).