40 Ar / 39 Ar and K---Ar dating of altered glassy volcanic rocks: the Dabi Volcanics, P.N.G.

Details 40 Ar / 39 Ar and K---Ar dating of altered glassy volcanic rocks: the Dabi Volcanics, P.N.G. 40 Ar / 39 Ar and K---Ar dating of altered glassy volcanic rocks: the Dabi Volcanics, P.N.G.

Nov 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982gecoa..46.2181w&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 46, Issue 11, pp.2181-2190

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Scientific paper

K---Ar and 40 Ar / 39 Ar ages have been determined for altered submarine tholeiitic and boninite (high-Mg andesite) lavas from the Dabi Volcanics, Cape Vogel Peninsula, Papua New Guinea. 40 Ar / 39 Ar whole rock total fusion and plateau ages identify a Late Paleocene age for the tholeiitic lavas (58.9 ± 1.1 Ma) and also for the boninitic lavas (58.8 ± 0.8 Ma). Apparent K---Ar ages for the same samples range from 27.2 ± 0.7 to 63.9 ± 4.5 Ma, and young K---Ar ages for glassy boninites are probably due to variable radiogenic 40 Ar ( 40 Ar * ) loss. These new ages effectively reconcile previously ambiguous age data for the Dabi Volcanics and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast PNG during the Late Paleocene. Smectites, developed as alteration products after glass in oceanic lavas commonly do not retain 39 Ar during or subsequent to irradiation, but in some cases may contain 40 Ar*. In the absence of other factors modifying K and Ar contents, samples which have not lost 40 Ar * from smectite and suffer 39 Ar loss only, are interpreted to have been altered immediately subsequent to the crystallization of the lava; whereas samples which have lost 40 Ar * as well as 39 Ar may be the result of either recent alteration, or of continuous 40 Ar * loss since the time of crystallization.

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