Formation and erosional decay of peneplains in the northern Gandise belt, Tibetan Plateau, revealed by low-temperature thermochronology and cosmogenic nuclides

大规模的半干旱平原是青藏高原最突出的地貌要素，但人们对其形成和随后的演化却知之甚少。通过应用低温热年代学、沉积物物源分析和宇宙成因核素，我们的目标是（1）确定西藏中南部的夷平面阶段，（2）重建造山后侵蚀和盆地形成的古地理和地质背景，（3）量化第四纪低起伏面的侵蚀速率和切割平原的河流的切割速率，（4）评价第四纪古平原是否长期被冰覆盖。我们的初步结果表明，不同的结构块体有不同的热历史。暴露在平原上的基底岩石冷却到磷灰石FT和He闭合温度以下（约100 ℃）。110和70 °C）之间的89和35 Ma。花岗岩基岩和砂砾样品中的10 Be浓度产生6-12 m Ma-1的局部侵蚀速率，而全流域的侵蚀速率仅略高（11-18 m Ma-1）。这表明该平原地区非常稳定，在过去的数百万年里几乎没有受到侵蚀的影响。

Large-scale peneplains constitute the most prominent geomorphic element of the Tibetan Plateau, but little is known about their formation and subsequent evolution. By applying lowtemperature thermochronology, sediment provenance analysis, and cosmogenic nuclides we aim to (1) date the planation phase in south-central Tibet, (2) reconstruct the paleogeography and geologic setting during post-orogenic erosion and basin formation, (3) quantify the Quaternary erosion rate of the low-relief surfaces and the incision rate of rivers dissecting the peneplains, and (4) evaluate whether the peneplains were covered by ice for extended periods in the Quaternary. Our preliminary results suggest that different structural blocks have variable thermal histories. Basement rocks exposed at the peneplains cooled below apatite FT and He closure temperatures (ca. 110 and 70 °C, respectively) between 89 and 35 Ma. 10Be concentrations in granitic bedrock and grus samples yield local erosion rates of 6-12 m Ma-1, whereas catchment-wide erosion rates are only slightly higher (11-18 m Ma-1). This demonstrates that the peneplain region is extremely stable and has barely been modified by erosion in the last millions of years.