福建东南沿海50m以下的地貌面与断裂活动性

THE GEOMORPHIC SURFACES BELOW 50 METRES IN FUJIAN SOUTHEASTERN COASTAL REGION AND THE FAULT ACTIVITY

通过对福建东南沿海海拔50m以下几个地貌面的时代确定,研究了长乐-诏安NE向断裂带和与之相交切的NW向断裂带第四纪以来的活动性。结果表明:区内50m以下几个地貌面分为侵蚀-剥蚀阶地和堆积阶地,属晚更新世以来几个时期所形成;断裂在切割某个地貌面时,其地貌面的形成年代可确定为该断裂的活动年代;长乐-诏安NE向断裂带中的平潭青峰-东山澳角断裂的有些地段为晚更新世晚期(Q3p)活动断裂,垂直滑动速率为1.1～2.2mm/a;长乐-东山前梧断裂主要活动时代在中更新世(Q2p);九龙江下游NW向断裂带中的江东桥(北溪)-海沧断裂,其NW段江东桥(北溪)断裂为早第四纪(Q1p-2)断裂,SE段海沧-钱屿断裂为晚更新世(Qp3)活动断裂。

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 ） × 10^4a BP for T1 terrace at about the early stage of the Holocene Epoch; （ 1.8 ~ 1 ） ×10^4a BP for T2 terrace in the late stage of the late Pleistocene and（4 ~ 1.8） × 10^4a 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 To , 13 - 17m for T1, 20m for T2 and 40m for T3. And their forming ages are in the late stage of the Holocene for To ; 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 To, 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 To, 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 To, （ 1 ~ 0.5 ） × 10^4a BP in the early stage of the Holocene for T1 ,（1.8 - 1） × 10^4a BP in the late stage of the late Pleistocene for T2 and（ 3.5 ~ 1.8） × 10^4a 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 ） × 10^4a BP, and in some individual areas, it is more than 4 × 10^4a 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 ac- tive 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（Q3p） 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（Qp^2）. 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（Qp^1-2）. And the southeastern segment, which is called the Haicang-Qianyu Fault, is a late Pleistocene （ Qp^3 ） active fault.