关键词: 地貌面, 断裂活动性, 福建东南沿海

Abstract: In this paper,the fault tectonic activity of Fujian southeastern coastal region since the Quaternary is analyzed by studying the formation and development of several geomorphic surfaces below 50m.The results show:(1)the geomorphic surfaces below 50m in southeastern coastal region of Fujian can be classified into erosion-abrasion terrace and accumulational terrace.The former(mostly,red soil platforms)can be divided into 3stages:the elevations above sea level are 10～15m for T₁,20～25m for T₂ and 40～50m for T₃,respectively.Their forming ages are:(1～0.5)×10⁴a BP for T₁terrace at about the early stage of the Holocene Epoch;(1.8～1)×10⁴a BP for T₂ terrace in the late stage of the late Pleistocene and(4～1.8)×10⁴a BP for T₃terrace in the middle or late stage of the late Pleistocene.The accumulational terrace includes river terrace and marine terrace.The elevations above sea level of river terraces along the lower reaches of Jinjiang and plain are:9～12m for T₀,13～17m for T₁,20m for T₂ and 40m for T₃.And their forming ages are in the late stage of the Holocene for T₀;the early stage of the Holocene for T₁,the late stage of the late Pleistocene for T₂ and the middle or late stage of the late Pleistocene for T₃.The elevation levels of river terraces along the lower reaches of Jiulongjiang and plain are:12.5m for T₀,18m for T₁ and 29m for T₂.Their forming ages are the same as those of the lower reaches of Jinjiang.The elevations of marine terraces along the coast are:3～5m for T₀,10m for T₁,15～25m for T₂ and 30～50m for T₃;and their forming ages are:5000a BP in the late stage of the Holocene for T₀,(1～0.5)×10⁴a BP in the early stage of the Holocene for T₁,(1.8～1)×10⁴a BP in the late stage of the late Pleistocene for T₂ and(3.5～1.8)×10⁴a BP in the middle or late stage of the late Pleistocene for T₃,respectively.The terraces are composed of "old red sand",their stages can not be divided easily.The elevation level is 10～50m,the forming age is in the middle or late stage of the late Pleistocene,at about(3.5～1)×10⁴a BP,and in some individual areas,it is more than 4×10⁴a BP.(2)When a fault dissects a certain geomorphic surface,the forming age of this geomorphic surface can be assigned to be the active age of the fault.(3)In some areas,the geomorphic surfaces forming in the same age distributed along the NE-trending and the NW-trending faults show a differential elevation.It indicates that the two sets of faults are active in the late Pleistocene.The Pingtanqingfeng-Dongshan'aojiao Fault in the Changle-Zhaoan NE-trending fault zone is a late stage of the late Pleistocene(Q_p³)active fault.Its vertical slip rate is 1.1～2.2mm/a.The major active age of Changle-Dongshanqianwu Fault is in the middle Pleistocene(Q_p²).The northwestern segment of Jiangdongqiao(the north brook)-Haicang Fault,which is in the NW-trending fault zone along the lower reaches of Jiulongjiang,can be categorized as an early Quaternary fault(Q_p^1-2).And the southeastern segment,which is called the Haicang-Qianyu Fault,is a late Pleistocene(Q_p³)active fault.

Key words: Geomorphic surface, fault activity, Fujian southeastern coastal region