期刊
CHEMICAL GEOLOGY
卷 560, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.chemgeo.2020.119998
关键词
40Ar/39Ar geochronology; 40Ar/39Ar step-heating technique; Acid treatment; Alteration; Clay minerals; Atmospheric argon
资金
- University of Queensland Argon Laboratory (UQ-AGES)
- Research Training Program of the University of Queensland
- Australian Research Council
- construction of the Ar Laboratory at the University of Queensland
The presence of secondary phases in volcanic rocks and intrusive units may pose challenges for high resolution 40Ar/39Ar geochronology. Acid treatment is used to remove alteration products, but it has minimal impact on the accuracy of age determinations. Effective separation of atmospheric and radiogenic gases can successfully mitigate deleterious effects associated with alteration phases.
The presence of secondary phases (carbonates, zeolites, clay minerals, etc.) in volcanic rocks and subabyssal intrusive units (sills and dykes) often pose obstacles for high resolution 40Ar/39Ar geochronology as these phases may promote loss of radiogenic argon, production of interfering isotopes, or trapping of excessive atmospheric argon contents. Acid treatment is used to remove alteration products before sample irradiation and analysis. In an effort to assess and quantify the effects of alteration and the removal of alteration products by acid treatment on the accuracy and precision of 40Ar/39Ar analysis, three basalt samples from the Parana large igneous province previously dated in triplicate without acid treatment were dated again without and with acid treatment. Despite the presence of 14-28% clay minerals in the samples, which results in up to 67% atmospheric component in the total amount of 40Ar extracted from untreated grains, the presence of alteration phases and their removal by acid treatment have no significant role on the accuracy of 40Ar/39Ar step-heating ages. The only quantifiable effect is an similar to 0.1% increase in age precision for the acid-treated aliquots. The results reveal that effective separation of atmospheric and radiogenic gases in properly designed and sufficiently detailed step-heating experiments successfully obviates deleterious effects associated with some types of alteration phases, and it suffices to produce high-resolution ages. Therefore, acid treatment is a desirable but not essential step in high-resolution 40Ar/39Ar geochronology. Characterizing alteration phases, however, is an essential step as some secondary products (e.g., sericite, albite), if present, will not be leached during acid treatment and will significantly affect the accuracy of geochronological results either with or without acid treatment.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据