关键词: 古大湖, 侵蚀基准面, 夷平面, 准平原化, 青藏高原

Abstract:

The Tibetan Plateau isostatically uplifted after contractional shortening and crustal thickening in Paleogene and is dominated by strikeslip and extension in Late Cenozoic. Very vast lakes formed in Early Miocene and Late Pleistocene in central Tibetan Plateau respectively, and large paleolakes formed in Pliocene and Early Pleistocene alternatively in northern and eastern Tibetan Plateau. Level of vast lakes had been base surface for incision in Early Miocene from (~24.1±0.6)Ma to (~14.5±05)Ma, and lakes and top lacustrine deposits of Wudaoliang Group became base surface for erosion and peneplanation since Late Miocene, which formed planation surface or peneplain of the Tibetan Plateau. Upstream incision of rivers led to westward motion of boundary between internally and externally drained regions and disappearance of paleo-lakes in Quaternary, and Quaternary incision of external rivers gradually formed present topography characterized by deep valleys, high mountains and remained peneplain in eastern Tibetan Plateau.

Key words:  vast paleo-lake, base surface for incision, planation surface, peneplanation, the Tibetan Plateau