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A Potential (U‐Th)/He Zircon Reference Material from Penglai Zircon Megacrysts
Author(s) -
Li Youjuan,
Zheng Dewen,
Wu Ying,
Wang Ying,
He Huaiyu,
Pang Jianzhang,
Wang Yizhou,
Yu Jingxing
Publication year - 2017
Publication title -
geostandards and geoanalytical research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.037
H-Index - 73
eISSN - 1751-908X
pISSN - 1639-4488
DOI - 10.1111/ggr.12168
Subject(s) - zircon , geology , geochemistry , basalt , geochronology , closure temperature , magma , volcano , mineralogy
In this study (U‐Th)/He dating of the Penglai zircons, which occur as abundant megacrysts in Neogene alkaline basalts in northern Hainan Province, south‐eastern China, was undertaken. A weighted mean age of 4.06 ± 0.35 Ma (2 s ) with a mean square weighted deviation ( MSWD ) of 1.79 was obtained from eighteen fragments of four zircon megacrysts using single‐crystal laser fusion He determinations and the U‐Th isotope dilution ( ID ) method. The (U‐Th)/He ages are consistent, homogeneous and systematically slightly younger than the preferred 206 Pb/ 238 U age of 4.4 ± 0.1 Ma (95% confidence interval) determined by ID ‐ TIMS and subsequently published U‐Pb results. The U‐Pb isotopic system in zircon has a high closure temperature of ~ 900 °C, and the preferred U‐Pb age may record both the time since eruption and the zircon residence time in the magma chamber. In contrast, the closure temperature of the zircon (U‐Th)/He system is ~ 190 °C and the zircon megacrysts were brought quickly to the surface by the host basaltic magma. Thus, the (U‐Th)/He age represents the timing of the eruption. Based on the unlimited quantity, large grain size, mostly weak broad zoning, rapid cooling and homogenous (U‐Th)/He ages, we consider the Penglai zircons suitable for use as a reference material in (U‐Th)/He isotope geochronology.