Oxygen isotope evidence for two-stage water-rock interactions of the Nianzishan A-type granite in NE China |
| |
Authors: | Chunsheng Wei Yongfei Zheng Zifu Zhao J. W. Valley |
| |
Affiliation: | WEI Chunsheng, ZHENG Yongfei, ZHAO Zifu & J. W. Valley 1. Laboratory for Chemical Geodynamics, University of Science and Technology of China, Hefei 230026, China; 2. Department of Geology and Geophysics, University of Wisconsin, Madison, WI53706, USA |
| |
Abstract: | 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 meteoric-hydro thermal alteration in the second stage. It is inferred that the 18O-depleted A-type granitic magma was derived from partial melting of subducted lower oceanic crust which was isotopically exchanged with seawater at high temperatures. In the process of granite emplacement into the upper crust, meteoric-hydrothermal circulation was triggered to overprint crystallizing granite under subsolidus conditions. |
| |
Keywords: | A-type granite water-rock interaction zircon oxygen isotopes geochemical recycling. |
本文献已被 SpringerLink 等数据库收录! |
| 点击此处可从《科学通报(英文版)》浏览原始摘要信息 |
|
点击此处可从《科学通报(英文版)》下载全文 |
|