鹤庆-再源断裂带中段晚更新世以来的走滑活动

Strike-slip Activities since the Late Pleistocene at the Middle Segment of the Heqing-Eryuan Fault Zone, Northwest Yunnan

鹤庆–洱源断裂带是滇西北活动断裂系的重要组成部分,对其性质、特征和活动历史的研究可为区域地震活动评价和震害防御提供依据,也可为青藏高原东南缘构造变形特征、历史和方式提供基础数据。通过对鹤庆–洱源断裂带中段基岩山区的室内外调查和研究,结合光释光和14C定年,初步查明该段断裂具有复杂的空间展布格局,由多条左旋走滑性质的分支断裂构成,它们共同吸收了断裂带在鹤庆盆地南端与洱源盆地北端之间的走滑分量;运动性质以左旋走滑为主,局部地段兼具正断或逆冲性质;剖面地层断错和覆盖关系表明该段断裂在晚更新世活动强烈,现有证据表明最新活动时代约为距今2万年。结合区域构造环境,作者认为鹤庆–洱源断裂带中段晚更新世以来的活动是对青藏高原强烈隆升的响应,其左旋走滑符合滇中次级块体顺时针转动模型,是块体旋转在角端的局部应变响应。

The Heqing-Eryuan fault zone is an important part of the active fault system in the Northwest Yunnan. The study of the nature, characteristics and active history of this fault can provide not only the basic information for seismic safety and engineering evaluation, but also important information for understanding of the characteristics, history and patterns of the structural deformation of the southeastern margin of the Tibetan Plateau. Based on geological investigation in the middle segment（bedrock mountain area） of the Heqing-Eryuan fault zone and combined OSL and 14 C dating, we preliminary suggest that the middle segment of the Heqing-Eryuan fault zone consists of several branches of sinistral strike-slip fault which collectively accommodate the pull-apart distance during basin formation at the end of the faults. This fault segment exhibits mainly sinistral strike-slip properties, and locally displays normal or reverse fault features. The geological evidence and dating results indicate that the activities of this fault segment were intensive in the Late Pleistocene and the latest activity age was later than 20, 000 a B.P.. Combined with regional tectonic settings, we suggest that the activities of the Heqing-Eryuan fault since the Late Pleistocene were the responses to the strong uplift of the Tibetan Plateau, whereas the sinistral strike-slip was resulted from the clockwise rotation of the Central Yunnan sub-block in response to the deformation at the corner of the block.