摘要:
长株潭地区第四纪断裂发育,但与其相关的研究工作非常薄弱.本文根据野外观测资料和第四纪沉积等厚图,结合前人已有资料,对长沙—湘潭一带第四纪断裂发育特征进行了归纳总结,初步厘定了第四纪断裂活动期次,探讨了断裂活动的时代和构造背景.区内第四纪规模断裂以NE 向为主,次为NNE 向和NW 向,个别EW 向~NW W 向;不同走向断裂均可为正断裂或逆断裂;部分断裂为晚更新世以来仍有活动的活动断裂.湘潭九华奔驰路开挖剖面上产状陡倾的小断裂发育,并可分为NW 向左行走滑断裂、NE 向右行走滑断裂、EW 向左行走滑断裂以及NNE 向正断裂等4组.根据奔驰路小断裂的活动期次,结合规模断裂的发育特征和区域构造背景,初步总结提出长沙—湘潭地区第四纪断裂活动可分为4期:第一期为NE 向、NNE 向、NW 向、EW 向的规模正断裂和小型正断裂,形成于早更新世—中更新世中期的区域伸展构造环境;第二期为NE 向~NNE 向规模逆断裂,形成于中更新世晚期区域NW 向挤压应力;第三期为奔驰路NW 向左行走滑与N E 向右行走滑小断裂,形成于中更新世末—晚更新世区域EW 向挤压应力;第四期为N W 向逆断裂及奔驰路EW 向左行走滑小断裂,形成于晚更新世—全新世区域NE 向挤压.上述第一期断裂可能与地幔上隆背景下深部物质迁出导致洞庭盆地及周缘产生伸展断陷有关;后3期断裂可能分别与菲律滨板块、青藏块体、印度—澳大利亚板块的挤压有关.本文研究反映出区域第四纪构造变形特征、构造体制及动力机制的复杂性.
Abstract:
There occurred a large number of Quaternary faults in Changsha-Xiangtan-Zhuzhou area. But the study of the faults is still weak.According to field investigation,contour line of Quaternary deposits thickness and former data, the authors summarized characteristics of Quaternary faults in Changsha-Xiangtan area, distin-guished stages of the faults initially,and probed into the ages and tectonic settings of the faults.The Quaternay large scale faults are mainly with NE-trending, second with NNE- or NW-trending and little with EW- to NWW-trending.The faults with different trends can be normal or reverse faults.Some are active fault that move since Late Pleistocene.There occurred Quaternary small steep faults at the artificial section in Benci Road, Ji-uhua,Xiangtan,which can be subdivided into four groups according to trends and nature such as NW-trending sinistral strike-slip faults, NE-trending dextral strike-slip faults, EW-trending sinistral strike-slip faults and NNE-trending normal faults.According to the stages of the small faults at Benci Road, and combined with the characteristics of large scale faults and regional tectonic settings,the authors put forward preliminary recognitions that the Quaternary faults in Changsha-Xiangtan area can be subdivided into four stages: the faults of the first stage are NE-, NNE-, NW- and EW-trending large scale and small normal faults, which were formed during Early Pleistocene-middle of Middle Pleistocene and in regional extensional tectonic setting;the faults of the sec-ond stage are NE-to NNE-trending thrust faults,which were formed in late of Middle Pleistocene and were con-trolled by NW-trending major pressure stress;the faults of the third stage are NW-trending sinistral strike-slip small faults and NE-trending dextral strike-slip small faults at Benci Road, which were formed during late of Middle Pleistocene-Late Pleistocene and were controlled by EW-trending major pressure stress;the faults of the fourth stage are NW-trending thrust faults and the small EW-trending sinistral strike-slip faults at Benci Road, which were formed during Late Pleistocene-Holocene and were controlled by NE-trending major pressure stress. Of the four stages faults,the first were probably related with the extension and subsidence of Dongting Basin and its adjacent areas,which can be caused by the movement of deep matter to outside under the upwelling of mantle;the faults of the later three stages can be related with the compressions of Philippine Sea plate, Qinghai-Tibet block and India-Australia plate,respectively.This study revealed the complexities of Quaternary regional tectonic deformations,tectonic regimes and dynamic mechanisms.