西非裂谷系Grein坳陷构造几何学与运动学特征

doi:10.19657/j.geoscience.1000-8527.2022.085

摘要/Abstract

摘要：

西非裂谷系由一系列中—新生代裂谷盆地组成,Grein坳陷位于西非裂谷系北部,对其开展构造特征及形成演化过程研究对认识西非裂谷系形成演化具有重要意义。本文基于最新二维地震数据,对Grein坳陷开展构造几何学特征解析,在此基础上运用构造平衡恢复方法进行了构造运动学恢复,结合区域大地构造背景,对Grein坳陷的成因机制进行探讨。研究结果表明:(1)Grein坳陷整体呈缓坡断阶型半地堑结构,具有明显的“东断西超”特征。坳陷南北差异较大,北部呈断阶形态,南部为凹陷形态;(2)Grein坳陷白垩纪—第四纪构造演化包括两期裂谷作用,可划分为5个阶段,即早白垩世断陷沉积期(Ⅰ),晚白垩世稳定沉积期(Ⅱ),白垩纪末构造反转期(III),古近纪断陷沉积期(IV)和新近纪—第四纪稳定沉积期(V);(3)Grein坳陷白垩纪末构造反转期主要受非洲—阿拉伯板块与欧亚板块碰撞影响,板块碰撞使非洲板块内部发生了两次强烈构造事件,分别为晚白垩世圣通期(Santonian)和马斯特里赫特期(Maastrichtian),其中马斯特里赫特期(Maastrichtian)构造活动在Grein坳陷内部表现明显,该时期坳陷发生构造反转,西北部被抬升,使得上白垩统地层发生剥蚀。

关键词: Grein坳陷, 构造几何学, 运动学, 构造反转, 西非裂谷系

Abstract:

The West African rift system is made up of a series of Mesozoic-Cenozoic rift basins, and the Grein depression is located at the northern end of the system. Elucidating the structural geometry and kinematic characteristics of the depression is of great significance in understanding the evolution of the West African rift system.Based on the latest seismic data and the fine-scale interpretation of regional seismic profiles,the structural geometry and kinematic processes are revealed in the Grein depression. We also discussed the dynamic mechanism in combination with regional background analysis. The conclusions are as follows: (1)The Grein depression is a half-garden with gentle slope, which is characterized with fault in the east and over lapping in the west. There are fault terraces in the north and subsidence in the south;(2)The Cretaceous-Quaternary regional tectonic evolution includes two rifting phases, which can be divided into 5 stages from the Early Cretaceous,i.e.Early Cretaceous rifting(I), Late Cretaceous depression(II), End Cretaceous structural inversion(III), Paleogene rifting(IV) and Neogene and Quaternary depression(V); (3)In the Santonian (Late Cretaceous), the African-Arabian and Eurasian plates began to converge, which resulted in the Santonian and Maastrichtian intensive tectonic events in the African plate. The Maastrichtian tectonic event was clear in the Grein depression. During this period, the depression underwent tectonic inversion and the northwestern side was uplifted, resulting in the denudation of the Upper Cretaceous strata.

Key words: grein depression, structural geometry, kinematics, structural inversion, west African Rift system

中图分类号:

P542

庞思晨, 李传新, 毛凤军, 王涛, 袁圣强, 何松高, 师晨一. 西非裂谷系Grein坳陷构造几何学与运动学特征[J]. 现代地质, 2023, 37(02): 328-339.

PANG Sichen, LI Chuanxin, MAO Fengjun, WANG Tao, YUAN Shengqiang, HE Songgao, SHI Chenyi. Structural Geometric and Kinematic Characteristics of Grein Depression in the West African Rift System[J]. Geoscience, 2023, 37(02): 328-339.

图/表 11

图1 Grein坳陷区域位置(a)、地质简图(b)及东尼日尔盆地综合地层柱状图(c)[3,15]

Fig.1 Regional location (a) and geological map of Grein depression (b), and stratigraphic column of the eastern Niger Basin (c) [3,15]

图2 Grein 坳陷南部A-A'地震剖面及解释

Fig.2 Seismic profile and interpretation of A-A' in the southern Grein depression

图3 Grein 坳陷中部B-B'地震剖面及解释

Fig.3 Seismic profile and interpretation of B-B' in the central Grein depression

图4 Grein 坳陷北部C-C'地震剖面及解释

Fig.4 Seismic profile and interpretation of C-C' in the northern Grein depression

图5 Grein 坳陷D-D'地震剖面及解释

Fig.5 North-south seismic profile and interpretation of D-D' in the Grein depression

图6 下白垩统(a)及古近系Sokor1组(b)现今顶面构造图

Fig.6 Current top structural maps of Lower Cretaceous (a) and Paleogene Sokor 1 Formation (b)

表1 Grein坳陷主断裂关键要素统计结果

Table 1 Statistics of the key elements of Fault 1 and Fault 2 in the Grein depression

断裂		地层	A-A'剖面断裂			B-B'剖面断裂			C-C'剖面断裂
断裂		地层	上盘厚度 (m)	下盘厚度 (m)	断距 (m)	上盘厚度 (m)	下盘厚度 (m)	断距 (m)	上盘厚度 (m)	下盘厚度 (m)	断距 (m)
F₁	上白垩统		3450.98	缺失	缺失	3548.39	2838.71	425.81	1747.47	缺失	缺失
F₂	上白垩统		784.31	1705.88	缺失	1780.65	1354.84	缺失	缺失	缺失	缺失
F₁	下白垩统		2196.08	缺失	缺失	2374.19	2412.90	748.39	1676.77	缺失	缺失
F₂	下白垩统		1745.10	549.02	1705.88	1832.26	1535.48	309.68	缺失	缺失	缺失

图7 Grein坳陷主断层F1、F2断裂三维形态模式

Fig.7 3D models of Fault 1 and Fault 2 in the Grein depression

图8 Grein坳陷A-A'地震剖面F1、F2断裂与地层接触关系(具体位置见图2) (a)F2断裂原图;(b)晚期断裂原图;(c)F1断裂原图;(d)F2断裂解释图;(e)晚期断裂解释图;(f)F1断裂解释图

Fig.8 Contact relationship between Fault 1, Fault 2 and strata of seismic profile A-A'

图9 Grein坳陷C-C'、D-D'地震剖面Sokor组与Ma dama组接触关系(具体位置见图4、图5) (g)C-C'剖面上超现象原图;(h)C-C'剖面上超解释图;(i)D-D'剖面上超现象原图;(j)D-D'剖面上超解释图

Fig. 9 Contact relationship between the Sokor Formation and Madama Formation in seismic profilesC-C' and D-D'

图10 Grein坳陷南部A-A'剖面与北部C-C'剖面演化模式

Fig.10 Tectonic evolution models of seismic profile A-A' and C-C'

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