拉萨地块西部亚热区则弄群火山岩锆石U-Pb年龄及其地质意义
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摘要
以拉萨地块西部亚热区出露的则弄群英安岩及流纹岩为研究对象,采用LA-ICP-MS法对样品进行了锆石U-Pb测年。结果表明,则弄群中英安岩年龄(51.3±0.4 Ma)与流纹岩年龄(50.1±0.3 Ma)均明显晚于已发表的则弄群火山岩年龄(108.6~131 Ma),而与林子宗群火山岩年龄(30.43~69.97 Ma)相符。据此,该地区原来认为的则弄群火山地层应该要重新厘定为林子宗群,结合前人的研究成果,表明整个拉萨地块西部地区分布的则弄群火山岩地层的时代归属需要重新考虑。
The evolution of Neo-Tethys and associated magmatism during Mesozoic-Cenozoic is a topic of much debate in geoscience. This research of Neo-Tethys and its evolution is of great significance to the structure evolution of southern margin of the Lhasa block. With the dacite and rhyolite of the Zenong Group exposed in Yare area as the study object,in a detailed field investigation and the basis of previous research,and the method of LA-ICP-MS,the author got the zircon dating of the volcanic rocks. The result is that the ages of the zircon from the dacite( 51. 3 ± 0. 4 Ma) and the rhyolite( 50. 1 ± 0. 3 Ma) gathered in the stratum of Zenong all younger than the accepted ages( 108. 6-131 Ma) but consistent with the ages of the volcanic rocks of the Linzizong Group( 30. 43-69. 97 Ma). So,the author found the formation in this area which was once thought as"Zenong Group"may be the Linzizong Group. Combined with previous research,it indicates that the chronostratigraphy of Zenong volcanic rock formation distributing in the whole west of Lhasa block should be redefined.
The evolution of Neo-Tethys and associated magmatism during Mesozoic-Cenozoic is a topic of much debate in geoscience. This research of Neo-Tethys and its evolution is of great significance to the structure evolution of southern margin of the Lhasa block. With the dacite and rhyolite of the Zenong Group exposed in Yare area as the study object,in a detailed field investigation and the basis of previous research,and the method of LA-ICP-MS,the author got the zircon dating of the volcanic rocks. The result is that the ages of the zircon from the dacite( 51. 3 ± 0. 4 Ma) and the rhyolite( 50. 1 ± 0. 3 Ma) gathered in the stratum of Zenong all younger than the accepted ages( 108. 6-131 Ma) but consistent with the ages of the volcanic rocks of the Linzizong Group( 30. 43-69. 97 Ma). So,the author found the formation in this area which was once thought as"Zenong Group"may be the Linzizong Group. Combined with previous research,it indicates that the chronostratigraphy of Zenong volcanic rock formation distributing in the whole west of Lhasa block should be redefined.
引文
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