怒江河砂岩屑磷灰石裂变径迹结果与流域地貌演化

Detrital apatite fission track analysis and geomorphologic evolution of the Nujiang River area

河流搬运沉积的河砂作为流域内地质体的平均产物，可以有效地揭示整个流域内区域性的地质体热史演化。对同一河流进行分段采样能够揭示更为详实的热史演化差异。本文对滇西境内怒江上游至下游采集了7个河砂样品进行磷灰石裂变径迹定年，主要年龄峰值依次为：12．2Ma和12．8Ma，7．7Ma，5．3Ma、4．4Ma和4．9Ma，7．3Ma；总体上呈现出上游老、中游年轻、下游老的年龄格局。怒江中游河段相对年轻的流域热史经历说明中游河段较其他区域经受了构造地貌的快速演化。由于这一位置对应三江并流，而且气候作用与现代西南季风的水汽通道吻合，降雨量与上、下游流域截然不同。可以推断，气候因素导致了其快而新的构造地貌演化，促成代表年轻冷却历史信息的地质体被迅速剥露造就了怒江河道不同位置流域热史演化的差异。测得的7个样品所有年龄峰值可分为5个区段：5．3～4．4Ma、7．7～7．3Ma、12．8—10．7Ma、26．8～22．2．3Ma、48．7～30．1Ma，基本反映了流域范围新生代以来主要的热史演化阶段。此外，怒江不同河段河砂样品的分段性特征，证实河砂岩屑磷灰石裂变径迹分析方法在解释流域区域热史演化方面具有独特的优点。

River sand as an averaged product of catchment can reflect the regional thermal histories of the entire river basin. Sampling in different segments of one river is able to obtain more accurate information of the thermal history evolutions. Seven detrital sand samples were collected from different locations of the Nujiang River in western Yunnan to attempt to reveal the thermal history of the entire river basin through the apatite fission track（AFT）method. The samples show the main age peaks of 12.2 Ma, 12.8 Ma, 7.7 Ma, 5.3 Ma, 4.4 Ma, 4.9 Ma, 7.3 Ma respectively, presenting an interesting and extremely special pattern of ＇old on the sides and young in the center＇. The younger results in the center means the middle segment of Nujiang River got through relative quicker thermal histories. The youngest and special region lies in the three rivers parallel flowing area and water vapor channel of southwest monsoon, resulting in the significantly difference in precipitation patterns between the different segments. We therefore conclude that climate led to its rapid landscape evolution and then caused the youngest samples exposed in the middle segment of Nujiang River. All the AFT age peaks can be divided into five groups： 5.3 -4.4 Ma, 7.7 -7.3 Ma, 12.8 - 10.7 Ma, 26. 8 -22.2 Ma and 48.7 - 30. 1 Ma, documenting the main stages of Cenozoic thermal histories in Nujiang River Basin,western ~unnan. Furthermore, the prominent characters of the detrital river sand are identified, as an indication of segmentation to get more accurate thermal information.