Lead isotope composition in volcanic rocks of Japan

摘要: Abstract Three series of volcanic rocks (pigeonitic, hypersthenic, and alkali rocks) are investigated as to their isotopic compositions lead. Each falls close a characteristic line with negative trend in the 206 Pb/ 207 Pb vs. 208 diagram. As fractional crystallization does not cause changes composition lead, this can be interpreted indicating difference original sources these three series. Meanwhile, within same suggests that magmatic differentation did always proceed under closed condition respect lead addition more or less enriched recent radiogenic took place. On other hand, it is shown increase content accompanied very commonly by abundance ratio Pb. This seems suggest exogenous (probably crustal) place during passage magma surface even believed free from contamination regarding major chemical components. According interpretation terms both zone melting systematic variation crust mantle, depth source inferred order olivine basalt > high-alumina (?) tholeiite. The experimental method (Masuda, 1962) employed study consists separation heating carbon, purification electrodeposition, preparation tetramethyl followed mass spectrometry.