青藏高原河流氧同位素区域变化特征与高度预测模型建立

REGIONAL VARIATION OF RIVER WATER OXYGEN ISOTOPE AND EMPIRICAL ELEVATION PREDICTION MODELS IN TIBETAN PLATEAU

利用氧同位素作为古高度计重建造山带的古高度是近年发展起来的应用比较广泛的方法。本文通过对青藏高原河水δ^18Ow（SMOW）的空间分布特征分析，表明高原南北δ^18Ow（SMOW）由于水汽来源和水汽循环方式不同存在显著差异。以中央分水岭山脉为界，南部6’的。（SMOW）平均值为-15．6‰左右，北部为-8．6‰左右；南部氧同位素值随高度的平均变化率为-0．24‰／100m，北部为-0．15‰／100m。分别建立了藏北地区和藏南地区河水氧同位素和高度的关系，同时应用可可西里及昆仑山口现代食草动物牙齿釉质、尼玛盆地现代土壤碳酸盐的氧同位素值对所建立的经验模型进行了检验，表明这两个模型分别应用于藏北和藏南地区古高度的恢复是可行的，为今后青藏高原古高度研究工作的开展提供了定量的计算方法。

Oxygen isotope is one of the widely applied methods in recently years to reconstruct paleoelevation of the world＇s major orogens. It has made a significant contribution to the uplifting history research of Himalayan and Gandese Mountains in South Tibet. The North Tibetan Plateau uplifting history,however,is poorly confined for the lack of quantitative relationship between local δ^18Ow values and elevations. In this paper we study the regional variations of the δ^18Ow values of river water from different vapor sources and recycling patterns,which show distinctive difference between the North and South Tibetan Plateau partitions by the Central Tibet Watershed Mountain Range. The average δ^18Ow value is - 15.6‰ and δ^18Ow -elevation gradient is -0.24%0/100m in the South Tibetan Plateau, whereas -8.6‰ and -0.15‰/100m, respectively in the North. The latitudinal gradient is 0. 9872 per degree from 28~N to 38~N and the longitudinal variations of the 6180 values keep stabilized at the same or close latitude zones, although they highly differentiate from each other between the North and the South. The relationships between δ^18Ow values and elevations can be expressed respectively as second order polynomial of the South （ 1 ） and the North （2） as follows ： δ^18Ow （SMOW） =5E-07H2-0.0052H-1.4432（Rz =0.871） （1） δ^18Ow （SMOW） = - 1E - 07 H2 - 0. 0023 H - 2. 8996 （ R2 = 0. 7026 ） （2） Considering complex influence factors to the oxygen isotopic values of river water,we assume the uncertainty of δ^18Ow as ＋- 1‰. Then the error formulas（3）AH =7.5 δ^18Ow（SMOW） ＋255 for the South and （4）zlH = -7.3 δ^18Ow （SMOW） ＋ 520 for the North could be used to evaluate the elevation uncertainties. We employed modern carbonate δ^18Ow values of herbivore enamels in Hoh Xil areas and Kunlun Mountain and soils in Nima Basin to verify the elevation prediction models. The results indicate that the elevation prediction models are feasible and strongly sensitive to elevation change,which offer a quantitative method for paleoelevation reconstruction of Tibetan Plateau, especially the North Tibetan Plateau.