碎屑鋯石同位素示蹤研究(I)：以孟加拉盆地為例

The interactions between tectonic uplift, river erosion and alluvial deposition are fundamental
processes that have continued to shape the Earth’s landscape we see today. Understanding of the
relations or causal links among these processes, which are on-going and particularly active in
mountainous regions such as the Himalayas, has attracted wide interests involving not only
geomorphology, sedimentology and structural geology, but also hydrology, river engineering and
mitigation of natural hazards. In this project, we propose to explore the relations between active
tectonics and alluvial deposition records around the eastern Himalayan syntaxis, by performing
in-situ U-Pb dating and Hf isotope analyses of detrital zircons from the late Tertiary-Quaternary
sedimentary formations from the Bengal Basin. The aims of this study include: (1) to test the
famous “tectonic aneurysm” model for the formation of the Namche Barwa syntaxis, within which
the Tsangpo River cuts a cross-strike gorge through the eastern Himalayas and heads south to the
Brahmaputra River in the foreland; (2) to test the popular hypothesis of river piracy linked with the
Namche Barwa tectonics such that the Tsangpo River was the upper reach of the Irrawaddy River
and it got captured by the Brahmaputra River only recently, say, within 4-5 million years from
now; and (3) to better understand the Indian monsoon’s evolution in the late Cenozoic and causal links between active tectonics and climate in this region based on the above two tests and
evaluations of relevant geologic information. This project that involves investigations from high
mountains (the roof of the Earth and sediment’s major source provenance) to foreland basin (part
of the largest sedimentary sink in the world) would depend essentially upon our work in
southeastern Tibet done in the past 2-3 years to constrain the source components and a field
excursion to Bangladesh and NE India to be collaborated with local geologists for collecting
samples. The proposed in-situ zircon U-Pb experiments will be performed at the SHRIMP-II lab in
the Chinese Academy of Geological Sciences, Beijing, while the Hf isotope measurements using
LA-MC-ICPMS still have to reply heavily upon a continued collaboration with the GEMOC
center, Macquarie University, Australia, before the newly purchased state-of-the-art machine of
ours is fully set up in this department.