M6, a monazite reference material for fission-track thermochronology

Abstract

The newly established monazite fission track (MFT), with its ultra-low closure temperature (25-45 ℃), offers a power tool for investigating the latest stage of rock exhumation and the geomorphic evolution of the uppermost crust. However, the absence of a well-characterized reference material has hindered the standardization and inter-laboratory reproducibility of MFT dating. Here, we evaluated the suitability of M6 monazite, a gem-quality megacryst from Espírito Santo, southeast Brazil, as a reference material for MFT dating. Independent age determination conducted by three laboratories, using different microscopes and analytical procedures, yield reproducible results within analytical uncertainty. Using an initial track length of 10.6 ± 0.19 μm, we obtain a central age of 3.90 ± 0.07 Ma (1 SE; MSWD =1.6). Furthermore, M6 also exhibits highly uniform uranium content and remarkably consistent cerium content (22.9 ± 0.4 wt.%) makes it an excellent internal reference for U-Th concentration analysis via LA-ICPMS. The M6 reference material thus holds significant potential for advancing MFT annealing kinetics studies and for developing integrated U-Pb, FT, (U-Th)/He and trace element multi-dating through simultaneous LA-ICP-MS analysis.