南迦巴瓦峰第四纪隆升期次划分的热年代学证据

喜马拉雅东构造结南迦巴瓦峰核心区附近一个高程剖面上的8个片麻岩样品裂变径迹中值年龄介于0.71~2.07 Ma之间,平均封闭径迹长度在14.51~15.87 μm之间,标准偏差都小于0.84 μm;其冷却年龄和径迹长度所作"香蕉图"显示出三期快速的抬升期,分别发生在距今0.71 Ma、1.23 Ma、2.05 Ma.结合已有磷灰石裂变径迹冷却年龄等值线图显示出南迦巴瓦峰核心区呈复式背斜状快速隆升,而外围拉萨地体和冈底斯构造单元隆升速率慢的空间分布特征等,分析认为这种差异隆升主要受构造作用主导,气候变化造成的均衡抬升起次要作用.

Thermochronological evidence for division of Quaternary uplifting stages of Mt. Namjagbarwa

The eastern Himalayan syntaxis is an important eastern end hinge of the Himalayan orogenic belt, where coupling effect of the tectonic uplifting and climatic is very dramatic. In the area, the Mt. Namjagbarwa is as high as 7782 m and the Yarlung Zangbo Great Canyon flows around this peak. This area has been the most concerned region for tectonic geology study at present. The objective of this research is to reveal Quaternary uplift and exhumation history and provide the evidence for uplifting periods of Mt. Namjagbarwa core area. In this work, we collected eight samples from a vertical profile near the Gega village, Mt. Namjagbarwa core region in the eastern Himalayan syntaxis, with elevations ranging from 3022 m to 4048 m. The samples are dated at the lab of Apatite to Zircon Inc Company with the LA-ICP-MS method. We obtain reliable AFT cooling central ages and track length data of the eight samples. Apatite fission track central ages of the eight gneiss samples are from 0.71 to 2.07 Ma, their mean confined track lengths are from 14.51 to 15.87 μm, and length standard deviations are less than 0.84 μm. The boomerang pattern constructed by AFT cooling ages and track lengths indicate that three times of uplifting events, which occurred at 0.71 Ma, 1.23 Ma, 2.05 Ma, respectively. The research shows that the Namjagbarwa core region experienced a fast uplift, while the peripheral Lhasa block uplifted slowly relative to the Namjagbarwa massif, representing the spatial distribution features. Then we infer that this kind of spatial differential uplifting pattern is dominated by tectonic events, and isostatic rebound uplifting only play a minor role.