ESR dating of volcanic ash

Abstract

Radiation-induced centres of Al, Ti, Ge and E′ occurring in the natural quartz of various geological materials were discussed a decade ago by McMorris^1,2; but it is only recently that the peroxy centre for natural flint³, the E′ centre for quartz from a fault⁴ and the Ge centre for quartz from welded tuff⁵ have been used for electron spin resonance (ESR) dating. The ages of volcanic ash or lava have been obtained by thermoluraieescence (TL) dating using fine (2–11-µm) volcanic glass⁶ or plagioclase feldspar⁷ respectively. However, ESR dating of volcanic ash has proved extremely difficult because signal intensities of radiation-induced centres measured at room temperature are weak compared with the interfering signals from paramagnetic impurities such as Fe³⁺ and Mn²⁺. Here we have used a signal from a quartz aluminium centre, measured at 77 K, where it is several orders of magnitude greater than those of the E′ or Ge centres at room temperature. The aluminium-centre ESR signal can also be observed in plagioclase feldspar and volcanic glass, allowing the age of the volcanic debris to be determined using any of the three mineral compounds.