Physics
Scientific paper
Jan 1964
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1964gecoa..28....1p&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 28, Issue 1, pp.1-22
Physics
18
Scientific paper
On a continental scale, leads in K-feldspars from North America were found to deviate from closed system evolution such that there is an excess of Pb 206 and, in lesser extent, Pb 208 which increases as the age of the feldspar decreases. This effect can be shown to result from the transport of uranium and thorium, over long periods in the past, from the interior of the earth to an outer mantle layer which functioned as a source of segments of continental crust that were formed and isolated at different times and locations. The effect is decisive in defining, as a function of time, the rates of transport of uranium, thorium and lead from the inner mantle to the outer mantle : there was a sharp decrease in the rates of transport of these three elements during the first one hundred m.y. after the earth was formed; during the remaining aeons, lead transport became essentially zero while uranium and thorium transport remained appreciable. The effect also suggests that the bulk of the North American continent was formed during the interval 3500-2500 m.y. ago.
Patterson Claire
Tatsumoto Mitsonobu
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