The oxygen isotope ratios of whole-rock, common rock-forming minerals and zircon from Mesozoic A-type granitic pluton at Nianzishan in northeastern China were analyzed by the conventional BrF5 method and the laser-pro...The oxygen isotope ratios of whole-rock, common rock-forming minerals and zircon from Mesozoic A-type granitic pluton at Nianzishan in northeastern China were analyzed by the conventional BrF5 method and the laser-probe technique, respectively. Both whole-rock and rock-forming minerals show large δ18O variations up to 5.5‰ with significant oxygen isotope disequilibrium between zircon and the other minerals, whereas the δ18O values of zircon are tightly clustered between 3.12‰ and 4.19‰ and thus lower than the normal-mantle δ18O values. These results indicate that the Nianzishan A-type granite experienced two-stage water-rock interactions subsequentially. The remarkably low zircon δ18O values are genetically due to sea-water exchange with granite protolith in the first stage, and the oxygen isotope disequilibrium fractionations between zircon and rock-forming minerals are caused by mete-oric-hydrothermal alteration in the second stage. It is inferred that the 18O-depleted A-type granitic magma展开更多
基金This workwas supported by the Chinese Academy of Sciences (Grant No. KZCX2-107)the National Natural Science Foundation of China (Grant No. 49603043) and the University of Science and Technology of China (Grant No. KB0724).
文摘The oxygen isotope ratios of whole-rock, common rock-forming minerals and zircon from Mesozoic A-type granitic pluton at Nianzishan in northeastern China were analyzed by the conventional BrF5 method and the laser-probe technique, respectively. Both whole-rock and rock-forming minerals show large δ18O variations up to 5.5‰ with significant oxygen isotope disequilibrium between zircon and the other minerals, whereas the δ18O values of zircon are tightly clustered between 3.12‰ and 4.19‰ and thus lower than the normal-mantle δ18O values. These results indicate that the Nianzishan A-type granite experienced two-stage water-rock interactions subsequentially. The remarkably low zircon δ18O values are genetically due to sea-water exchange with granite protolith in the first stage, and the oxygen isotope disequilibrium fractionations between zircon and rock-forming minerals are caused by mete-oric-hydrothermal alteration in the second stage. It is inferred that the 18O-depleted A-type granitic magma
