Uranium, thorium, potassium and argon in marine phillipsites

Details Uranium, thorium, potassium and argon in marine phillipsites Uranium, thorium, potassium and argon in marine phillipsites

Oct 1970

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1970gecoa..34.1053b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 34, Issue 10, pp.1053-1066

Computer Science

4

Scientific paper

Analyses of elements at trace levels in phillipsites from Pacific Ocean deposits indicate the mineral continues to grow within the sedimentary column.The thorium and uranium concentrations decrease while the mineral concentrations increase with depth in the deposit. This observation can be explained by a continuous growth of the phillipsite within the deposits. The varying concentrations of uranium and thorium in phillipsite, fish teeth and clay minerals from given levels of the core indicate a competition by such substances for the dissolved phases of these elements. Phillipsites from the surface layers (upper 20 cm) of widely separated deposits have "apparent K-Ar ages" > 10 6 yr. Systematic variations in this ratio occur with depth. At three levels a differentiation of the Ar -40/ K -40 ratio with respect to size is observed, the larger crystals having smaller ratios and vice versa. Treatment of three samples with HCl, presumably removing about 40 per cent of the outer layers of the crystals, increased the concentration of radiogenic argon by almost a factor of two. Heating experiments indicate that loss of argon by diffusion is of minor importance. Idealized models of continuous spherical growth of the mineral over long time intervals, and assuming dr / dt = constant , indicate the time dependence of the Ar -40/ K -40 ratios for a growing crystal. Most of the results can be explained by modified versions of such models. Without additional knowledge about the many parameters involved in marine phillipsite formation, however, these minerals are not suitable for dating by the K-Ar method.

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