Stages of Cenozoic Tectonic Movement in Hexi Corridor, Gansu Province
- TAN Lihua,YANG Jingchun,DUAN Fengjun
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Hexi corridor, located on the northern margin of the Qinghai-Xizang plateau, is one of the most typical regions of compressional tectonic basins in northwest China. Accompanying the uplift of the Qinghai-Xizang plateau since the late Paleogene, the four basins of the corridor began subsiding and accepting deposits. Since then, at least seven tectonic movement stages can be identified. According to the results of absolute dating(includes ESR, TL and IRSL dates) and relative dating(includes rock-weathering rinds and palaeomagnetic stratigraphy) of Cenozoic strata and landforms, the seven movements occurred at about 37.7, 30.3-29.5, 24.5-22.2, 4.66, 2.47-2.23, 1.95-1.48 and 0.80Ma-present, each of them represented by uncomformity and deformation of strata, active folding and faulting, and geomorphic evolution. The first tectonic movement stage took place at the beginning of Oligocene after a long period of erosion and denudation since the late Cretaceous. The forth stage, characterized by the preliminary accumulation of gloomy conglomerate (Yumen formation), is the turning point of Cenozoic tectonic movement as the intensity of tectonic activity became obviously stronger. It is in the latest stage that the main part of modern landform evolved. Some important morphologic units, including piedmont platform, transverse uplifts and northern mountains, generated or strongly deformed and uplifted in the stage. On the other hand, less deform tracks can be found in strata. Further divisions are made in order to avoid that the interval time between two neighbouring movements became shorter and shorter as time passed because latelyformed records preserved better. For example, mainly according to the luminescence ages of river terraces, at least five tectonic substages can be identified during the latest stage. They tarted at about 800, 350, 250, 150 and 40ka respectively. Furthermore, in the tectonic substage started from 150ka, four tectonic events, which took place at 145, 110, 90 and 70ka respectively, can be identified, and in the last substage, three tectonic events(40, 30 and 10ka) can be identified.