贵德盆地黄河出现的古地磁年代及其意义

PALEOMAGNETIC CONSTRAINT ON APPEARANCE OF THE YELLOW RIVER IN THE GUIDE BASIN IN THE NE TIBETAN PLATEAU AND ITS GEOMORPHOLOGIC IMPLICATIONS

发源于青藏高原的黄河,其形成与青藏高原隆起有密切关系,因此,黄河上游的形成演化,对于研究青藏高原的隆升以及黄河水利的开发利用等均有重要的实际意义和科学价值。青藏高原东北部的贵德盆地发育巨厚的新生代地层,其最上部的一套湖相沉积代表了黄河出现之前的最后沉积。古地磁测年表明这套地层的结束时代约为1 8Ma,指示黄河在本区大约同时出现,是青藏运动C幕的产物,此后至今黄河已净下切了约940m,指示本区高原的快速隆起,不支持青藏高原在中新世达到最大高度然后垮塌的观点。

The Yellow River, originating from the northeastern Tibetan Plateau, was formed with the uplift of the Tibetan Plateau, so knowledge of the geomorphologic evolution of the river will provide important information for the evolution history of the Yellow River and the uplift process of the Tibetan Plateau. The Guide basin, one of the representative Cenozoic basins crossed by the Yellow River on the NE Tibetan Plateau, has thick Cenozoic strata deposited. The uppermost part of the strata is lacustrine siltstone and mudstone formed by the preYellow River drainage. The end of the lacustrine deposits was accompanied by the appearance of the Yellow River in the basin. Detailed paleomagnetism analysis of the lacustrine deposits shows that they were ended at about 18 Ma, indicating the approximate appearance age of the Yellow River in the basin was also 18 Ma. Since then, the great downcutting has continued to the present, giving rise to an incision of about 940 m from the basin surface to the present river level (the incision rate at 522 m/Ma). This indicates that the northeastern Tibet has experienced rapid and great uplift since the early Pleistocene, which does not support the viewpoint that the Tibetan Plateau attained its maximum height in the middle Miocene and collapsed since then.