青藏高原北部第四纪早期断裂活动的 新生性变化初步研究*

关于第四纪早期构造事件的年代学研究取得了大量数据,但对构造事件的表现形式缺乏认识。文章通过对海原断裂带内拉分盆地演化趋势及年代学研究,认为海原断裂带内的最新拉分盆地形成于1.6MaB.P.之后,代表一次新断裂的形成时期,且新断裂走向与先存断裂有一定的逆时针夹角。通过对青藏高原中部可可西里-东昆仑断裂带构造地貌的遥感解译和强震破裂调查,认为可可西里-东昆仑断裂带是一条具有新生性的强震构造带,新断裂形成时期为1.10~0.65MaB.P.之间,其构造带内的新生性断裂走向与先存断裂亦有一定的逆时针方向夹角。两条断裂带具有一致的演化趋势,说明在早更新世中后期存在区域性的构造事件,该事件表现为一系列新生性断裂的产生。

PRELIMINARY ANALYSIS ON AN EARLY QUATERNARY NEW FAULT TRACE IN NORTH OF TIBETAN PLATEAU

Haiyuan Fault Zone and(Kekexili-East) Kunlun Fault Zone are main regional strike slip fault zones in Northern Tibetan Plateau.There is a series of pull-apart basins developed in different periods in the Haiyuan Fault Zone.The Laolongwan Basin developed in Neocene is the largest one.At northeast of the Laolongwan Basin,a series of smaller pull-apart basins are existing.By analyzing the strata and morphostructures at edges of these latest pull-apart basins,we believe that the latest pull-apart basins in the Haiyuan Fault Zone were generated later than 1.6MaB.P.,indicating a new tectonic period when a new fault was generated.The direction of the newly generated fault had a counterclockwise angle with the original fault.A series of strong earthquakes occurred along the(Kekexili-East) Kunlun Fault Zone in Central Tibetan Plateau.Surface rupture of earthquakes indicated a new fault in that zone.Through the study of the new fault trace and morphostructures by earthquake surface rupture investigation and satellite image interpretation,we suggest that the Kekexili-East Kunlun Fault Zone is a zone with many new generated faults,which were generated between 1.1MaB.P.and 0.65MaB.P.,and also have counterclockwise angles with the original faults. Beside the Haiyuan Fault Zone and the Kekexili-East Kunlun Fault Zone,many other fault zones in Northeastern Tibet Plateau can be found to have new fault traces.Most of these new fault traces have counterclockwise angle with the original faults.This is consistent with the clockwise rotation of the Tibetan Block.We thus presume that a tectonic event might occur at middle to late Early Pleistocene in Northeast of Tibetan Plateau.In this paper we have attempted to discover the fault activities in order to reveal the characteristics of the regional tectonic event along with the uplifting of the Tibetan Plateau in Early Quaternary,and to accumulate data for study style and distribution of each tectonic event.