MK‐1 Apatite: A New Potential Reference Material for (U‐Th)/He Dating

Abstract

The (U‐Th)/He dating technique has been widely used for several decades to constrain the timing of low temperature geological processes. Recent research has shown that the commonly used reference material (the Durango apatite) often yields dispersed fragment dates that are beyond analytical uncertainties. Here, we report a new apatite (U‐Th)/He dating reference material, MK‐1, which was collected from the Mogok metamorphic belt in Burma. Electron probe microanalysis and backscattered electron images of two randomly selected fragments indicate that this apatite is chemically and structurally homogeneous. We performed single‐grain (U‐Th)/He dating on thirty randomly selected fragments of this material. (U‐Th)/He dating results from multiple laboratories show that fragments of the MK‐1 apatite megacryst yielded reproducible results, with a mean date of 18.0 ± 0.2 Ma. The Th/U ratio of this apatite is homogeneous. Nine randomly selected fragments registered a narrow range of effective uranium (eU) mass fractions (326–354 μg g−1), with a mean value of 336.6 ± 10.3 μg g−1. Twenty‐four in situ (U‐Th)/He dates yielded a mean value of 18.0 ± 0.2 Ma (MSWD = 0.41), indistinguishable from the results obtained by the conventional method. All the results suggest that this apatite has the potential to become a new reference material for (U‐Th)/He geochronology.

Apatite U‐Pb Dating with Common Pb Correction Using LA‐ICP‐MS/MS

“…The 204 Pb-corrected weighted mean 206 Pb/ 238 U and Wetherill concordia ages are indistinguishable (20.8 AE 0.4/0.7 Ma and 20.8 AE 0.4/0.7 Ma respectively) with MSWD values of 0.48 and 0.27 (Figure 6n, o). These three ages are in good agreement within uncertainty with the U-Pb apatite age of 21.53 AE 0.11 Ma (Wu et al 2019).…”

“…The MK‐1 apatite yielded a U‐Pb age of 21.53 ± 0.11 Ma by LA‐ICP‐MS (unpublished data) and a (U‐Th)/He age of 18.0 ± 0.2 Ma, with a homogenous U content of ˜ 266.8 µg g ‐1 (Wu et al . 2019). The reappraised (U‐Th)/He date of MK‐1 apatite was 17.99 ± 0.02 Ma from six different laboratories (Wu et al .…”

“…These three ages are in good agreement within uncertainty with the U‐Pb apatite age of 21.53 ± 0.11 Ma (Wu et al . 2019).…”

“…-MK-1 apatite. MK-1 apatite was collected from the Mogok metamorphic belt (MMB), Myanmar, and is used as a new apatite (U-Th)/He dating reference material (Wu et al 2019). The MK-1 apatite is a centimetre-scale gemstone megacryst with a blue colour, which was hosted in ruby-bearing marble (M1, mainly ruby-titanitediopside marble and spinel-bearing marble) (Themelis 2008).…”

Age determination of oriented rutile inclusions in sapphire and of moonstone from the Mogok metamorphic belt, Myanmar

“…http://www.minsocam.org/ citrine), lapis-lazuli (lazurite), danburite, scheelite, titanite, topaz, tourmaline (rubellite, elbaite, schorl), hackmanite etc., as well as some rare sorts like painite, poudretteite, periclase, johachidolite, sodalite, taaffeite, ekanite, axinite, chondrodite, sinhalite, jeremejevite, kornerupine, etc. (e.g., Themelies 2008 and references therein; Harlow and Bender 2013;Guo et al 2016;Wu et al 2019). Gem mining in the MMB is thought to have started around 1044 AD (Themelies 2008).…”