Mathematics – Logic
Scientific paper
Aug 1976
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976gecoa..40..905v&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 40, Issue 8, pp.905-914
Mathematics
Logic
27
Scientific paper
The Sr isotopic composition of `seawater', as measured on carbonate rocks, shows a composite pattern during geologic history. All known Archaean data are compatible with contemporaneous upper mantle 87 Sr/ 86 Sr values. This is followed by a strong increase in the radiogenic component during the 2.5-2.1 b.y. period, a less pronounced increase during the remaining portion of the Proterozoic and a decrease during the Phanerozoic. The trend closely resembles the K 2 O/Na 2 O secular variations in composition of igneous and sedimentary rocks ( et al, Bull. Geol. Soc. Amer . 85 , 843-858, 1974) and probably reflects the fractionation state of the contemporary crust. The data are compatible with recent suggestions of three major tectonic regimes during geologic history: greenstone belts during the Archaean, mobile belts during the Proterozoic and plate tectonics during the Phanerozoic. They also indicate that continental crust during the Archaean contributed only subordinate Sr into the meteoric cycle.
Compston William
Veizer Ján
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