K-Ar Ages of Cenozoic Volcanic Rocks from Gongjue Basin in Eastern Tibet
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摘要: 通过新生代高钾钙碱性中、酸性火山岩的年代学研究来了解青藏高原的隆升特征, 首次报道了藏东贡觉盆地新生代7个火山岩样品的K-Ar定年结果.全岩和黑云母的表面年龄均在40.8~46.2 Ma间(平均值为44.2 Ma).样品中放射成因Ar与K构成了一条相关性良好的、几乎通过原点的线性等时线, 表明它们有相同的成因和相近的形成时代, 而且样品中可能既无过剩Ar, 也无放射成因Ar的丢失, 代表着真实的成岩年龄(始新世中期).火山活动发生在印度-欧亚板块碰撞(50 Ma左右)后形成的构造环境中, 受陆内水平剪切-走滑断裂带控制.结合前人对藏东地区岩浆活动的年代学研究成果, 表明青藏高原东缘新生代岩浆活动具多期性.这种多期性可能反映着青藏高原阶段性隆升的壳-幔相互作用.Abstract: Based on the isotopic chronologic results of Cenozoic volcanic rocks from Gongjue basin in eastern Tibet, the uplifting of the Tibetan plateau was studied. The K-Ar diluted ages of seven volcanic rocks from the Gongjue basin in eastern Tibet are firstly reported. Apparent ages of the whole rock and their biotite are 40.8 to 46.2 Ma with an average of 44.2 Ma. Radiogenic Ar and K of the samples compose an isochron line with high correlation coefficient, which almost passes through the origin. The result indicates that there is neither residual Ar nor loss of radiogenic Ar in these samples. Therefore, they give the eruption ages of the volcanic rocks (i.e. middle Eocene). The volcanic activities in the studied region occurred in the post-collision tectonic setting of Indian-Eurasia plate collision (about 50 Ma) and were controlled by intra-continental horizontal shear faults. Evidences including the published data show that the Cenozoic volcanic activities in eastern Tibet vary greatly. The variety can be considered as the product of the crust-mantle interaction due to the multi-stage uplift in the (Tibetan) plateau.
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Key words:
- K-Ar dating /
- volcanic rock /
- Cenozoic /
- Gongjue basin /
- eastern Tibet
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图 1 青藏高原东缘古近纪盆地和新生代岩浆岩分布简图
据周江羽等(2003)和拉多幅地质图修改和简化, 图中同位素年龄值据相同文献
Fig. 1. Sketch map illustrating the distribution of Paleogene basins and Cenozoic magmatism in eastern Tibet
表 1 贡觉盆地新生代火山岩的K-Ar同位素年龄
Table 1. K-Ar isotopic age dating of Cenozoic volcanic rocks from Gongjue basin
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