Reappraisal of the applicability of MK-1 apatite as a reference standard for (U[sbnd]Th)/He geochronology

Abstract

The (UTh)/He dating technique is widely used in studying the shallow-crustal geological processes including exhumation of orogenic belts, surface weathering, fault motion, topographic evolution. A reference material with homogeneous composition and highly reproducible (UTh)/He dates is crucial to get accurate and precise date results for the unknown samples. As the most commonly used reference material, the Durango apatite has its limitations such as heterogeneous distribution of parent isotopes and large date dispersion for different fragments. In order to overcome the shortcomings of Durango apatite and meet the increasing demand for reference material, we developed a new reference material, MK-1 apatite, which was collected from the Mogok metamorphic belt (MMB) of Myanmar, for the (UTh)/He community. In this study, we presented dating results of 191 apatite fragments in six different laboratories, which showed highly reproducible dates and Th/U ratios, with an average date of 18.01 ± 0.37 Ma (sd.) and Th/U ratio of 0.72 ± 0.06 (sd.) respectively. Combined with textural and compositional results in the previous study (Wu et al., 2019), we concluded that he MK-1 apatite could serve as a good new reference material for (UTh)/He geochronology. We use the weighted mean dates of 17.99 ± 0.02 Ma that obtained from six different laboratories as the intercalibrated dates for the new reference material.