Physics
Scientific paper
Aug 1973
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1973gecoa..37.1823s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 37, Issue 8, pp.1823-1849
Physics
7
Scientific paper
The isotopic composition of lead from galenas and feldspars of granitic rocks covering a time span of 3600 m.y. is reviewed. Hew data are combined with data from the literature, all ratios being normalized to a fixed value for the isotopic composition of lead in an inter-laboratory reference sample. Comparison of feldspar and galena results show that the isotopic composition of initial lead in granitic rocks may be identical to, or more radiogenic than, that in coeval stratiform (or `single stage') ore deposits. The isotopic evolution of terrestrial lead over the past 3600 m.y. deduced from the stratiform ore data does not fit the closed system source. The data are best fitted to evolution models in which the value of (U 238 /Pb 204 normalized to the present day) in the source has increased either over approximately the past 3.6 billion years or since the time of formation of the Earth. A limited number of high precision data for strontium likewise indicate open system isotopic evolution. In this system the Rb/Sr ratio appears to have decreased as a function of time. Physical models that explain the data are presented. Either mantle differentiation or crustal contamination processes could account for the change in in the source for the lead. The strontium data and some detailed studies of the isotopic composition of lead in oceanic volcanic rocks support mantle differentiation rather than crustal contamination. The exact nature of the mantle differentiation process cannot be specified, although empirical data favoring the existence of such a process are given. The best estimate of the age of the Earth, calculated with the data from 2750 and 3290 m.y.-old lead ores, is 4660 m.y.
Krishna Sinha A.
Tilton George R.
No associations
LandOfFree
Isotopic evolution of common lead does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Isotopic evolution of common lead, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Isotopic evolution of common lead will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1221688