【摘要】 应用高精度热电离质谱技术 ,测定了长白山天池锥体 11个火山岩样品的U ,Th同位素组成。结果发现 ,天池火山岩中铀不平衡同位素体系以2 38U放射性过剩为特征 (即2 30 Th/ 2 38U放射性比值小于 1) ,表明了岩浆过程中水的参与作用 ;而样品δ2 34U <10‰ ,说明浅部循环水不是造成上述2 38U过剩的原因。由此推断 ,含水组分在岩浆源区参与了部分熔融过程 ,这可能是太平洋俯冲板块脱水作用的结果。更多还原

【Abstract】 samples of lava and pumice from the cone of Changbaishan Tianchi Volcano, Jiling, China were measured for their uranium and thorium isotopic compositions by using the high precision U-series TIMS method. The results indicate that the U-series disequilirium system is characterized by excess of 238U (namely the radioactivity ratio of 230Th/ 238U less than 1), showing the fluids has worked in the magmatic reservoir. This may suggests that the fluids, which participated in the melting of the source rock, came from the dehydration of the subduced Pacific plate.更多还原