A Mössbauer Spectroscopic Study of the Cooling History of Hypersthenes from Selected Members of the Taupo Pumice Formation, New Zealand

J. H. Johnston and K. E. Knedler
Chemistry Department, Victoria University of Wellington, Private Bag, Wellington, New Zealand

Summary: 57Fe Mössbauer spectroscopy has been used to determine the Mg2+-Fe2+ distribution between the two crystallographically inequivalent cation sites in hypersthenes from a stratigraphic tephra sequence of the Taupo Pumice formation, North Island, New Zealand. From these distributions and X-ray fluorescence analytical data, cooling histories were constructed using previously determined Mg2+-Fe2+ equilibrium isotherms for orthopyroxenes. The results showed that this cooling history geothermometer could be used to enable airfall and airflow tephra to be distinguished. In addition, they showed that the cooling rate of the above deposits correlated better with the deposit thickness, than with the distance of the deposit from the source.

Mineralogical Magazine; June 1979 v. 43; no. 326; p. 279-285; DOI: 10.1180/minmag.1979.043.326.10
© 1979, The Mineralogical Society
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