Pyroxene separation by HF leaching and its impact on helium surface-exposure dating

作者：Bromley Gordon R M^*; Winckler Gisela; Schaefer Joerg M; Kaplan Michael R; Licht Kathy J; Hall Brenda L

来源：Quaternary Geochronology, 2014, 23: 1-8.

DOI：10.1016/j.quageo.2014.04.003

• Pyroxene
• Cosmogenic helium
• Surface-exposure dating
• Acid leaching

Cosmogenic He-3 surface-exposure dating has become an important tool in earth surface sciences. Pyroxene, together with olivine, is the principal mineral phase for this technique, making He-3 particularly appropriate for volcanic lithologies. However, two important factors that affect the viability of the method are the extensive, thus expensive, preparation procedure and the often under-constrained purity of pyroxene separates. Here, we present an approach to preparing pyroxenes for He-3 dating, adapted from the quartz-separation method for Be-10 and Al-26 analyses, which utilises hydrofluoric-acid leaching to improve pyroxene purity and streamline the pyroxene separation procedure. In addition to producing abundant sample in relatively little time, the results of two experiments demonstrate that acid leaching (i) yields samples of higher purity than conventional methods, reflected in slightly elevated He-3 concentrations, and (ii) reduces He-4 concentrations, in turn elevating the He-3/He-4 ratio. This new protocol for preparing pyroxenes thus has the potential to increase the precision and accuracy of cosmogenic He-3 surface-exposure dating.

• 出版日期2014-10