Oxygen Isotopes of Whole-Rock and Zircon and Zircon U-Pb Ages of Meta-Rhyolite from the Luzhenguan Group and Associated Meta-Granite in the Northern Dabie Mountains
详细信息
- 责任者：Liu Jingbo (State Key Laboratory of Lithospheric Evolution ; Institute of Geology and Geophysics ; Chinese Academy of Sciences ; Beijing 100029 ; China) ; Zhang Lingmin
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(5)
- 关键词：变火山岩 ; metavolcanic rocks ; 铀—铅计时 ; U-Pb dating ; 大别山 ; Dabie Mountains
- 页码：p.1511-1524
- 图表：illus., 2 tables, 39 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The rhyolites of the Luzhenguan Group and associated granitoids in the northern Dabie Mountains formed in the Neoproterzoic Era. SIMS U-Pb analyses of zircons yield age of 757Ma from two rhyolitic samples,and ages of 757Ma to 770Ma from other three granitic samples,and these ages are interpreted as magmatic crystallization ages. The whole-rock oxygen isotopic compositions of the studied samples display low to negative δ18 O values,suggesting that the rhyolite of the Luzhenguan Group and associated granitoid suffered meteoric water-in hydrothermal alteration. SIMS oxygen isotopic analyses of zircons show that the rim parts of a few of zircon grains were reworked after magmatism,but the parts of oxygen isotopic changes have not been reset in their U-Pb system,thus the alteration cannot be dated through zircon U-Pb age but is only constrained to occur after 757Ma. Low δ18 O magmatic zircons with 2. 8‰ ～ 4. 0‰ δ18 O values are present in the sample studied,which directly crystallized from low δ18 O magmas. Low δ18 O magma was formed via the remelting of previous altered rocks,and in this sense,meteoric water-in hydrothermal alteration in rocks occurred before 770Ma. These time evidences suggest that the rhyolites of the Luzhenguan Group and associated granitoids record meteoric water-in hydrothermal alterations older than 770Ma and younger than 757Ma, which cannot be correlated with the Neoproterzoic glacial events in the Yangtze craton via time.
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