珠江口盆地番禺4洼古近系文昌组构造变形特征及成因机制

Characteristics and Formation Mechanism of Structural Deformation in the Paleogene Wenchang Formation in the Panyu 4 Sag,Pearl River Estuary Basin

珠江口盆地番禺4洼古近系文昌组构造变形强烈。基于三维地震资料精细解释与编图,对该区主控断裂活动性、沉积中心迁移特征及洼陷结构进行分析,认为番禺4洼古近系文一段沉积期发生了重要的构造事件:文一段沉积之前,受NW—SE向伸展作用,近NE向断裂强烈活动,沉积中心近NE向展布,北部次洼具有"东西双断"的特征,中部变换带和南部次洼具有"东断西超"的特征;文一段沉积期,EW向断裂强烈活动,多个沉积中心发育,西南斜坡带具有"北断南超"的特征,同时北部次洼、中部变换带和南部次洼依次遭受由强变弱的剥蚀作用。构造变形特征的差异表明,文一段沉积时期是区域应力场方向由NW—SE向近SN向发生顺时针转变的过渡时期。进一步研究表明:太平洋板块及印度板块相对于欧亚板块的汇聚运动使得区域应力场方向发生转变是控制该区构造变形的主因。这一应力体制转变所引起的构造变形不仅发生在番禺4洼,而且在中国东部新生代盆地中广泛存在。

Tectonic deformation of the Paleogene Wenchang Formation in the Panyu 4 sag of Pearl River Estuary Basin is intense. According to seismic interpretation,fault activity,migration characteristics of the sedimentation center and depression structural analysis,this study concluded that there was a major tectonic movement in the first stage of the Wenchang Formation. Before that,due to the NW-SE stretching,the intense NE-trending faulting may have led to the NE-trending distribution of sedimentation centers. The northern sub-region has the bipolar（ E and W） faulted characteristics. The central and southern sub-regions are featured by faulting in the east and structural overlapping in the west. In the first stage of the Wenchang Formation（ during which EWtrending faulting was intense） a EW-trending and a NE-trending sedimentation center were formed. The southwestern slope is featured by faulting in the north and structural overlapping in the south. In the northern sub-region,denudation of the central and southern sub-regions was likely changed from strong to weak. Difference in tectonic deformation indicated that the first stage of the Wenchang Formation was the transition period from NWto NW-trending extension. Furthermore,the stress regime of the tectonic transform surface was the result of theconvergence between the Pacific,India and Eurasian plates. This tectonic phenomenon can be found not only in the Panyu 4 sag,but also in other Cenozoic basins of east China.