大陆裂谷中断层的演化：北贝加尔盆地西南端构造地貌证据

EVOLUTION OF FAULTS IN A CONTINENTAL RIFT: MORPHOTECTONIC EVIDENCE FROM THE SOUTHWESTERN TERMINATION OF THE NORTH BAIKAL BASIN

北贝加尔盆地西南端位于贝加尔盆地中部,包括Olkhon岛及其邻区,文中研究了这个区域的构造地貌格架。北贝加尔盆地西南端的构造地貌类型是由走滑构造末端的一系列雁列构造、裂谷断层及次级断层的末端复合构造控制。朝着海的方向Olkhon地区次级断层包括4个连续的末端复合构造Primorsky断层带,Buguldeika-Chernorud地堑—MaloyeMore裂谷盆地—Ushkaniy断层带,Tazheran高原—Olkhon岛鞍部和淹没的Akademichesky山脊,Olkhon断层带。这个末端构造被横向断层切为几段,其活动时间在南西最年轻,向北东逐渐加大,同时断层垂直断距从数十米增至2000余米,且断层带变得更为宽阔,也更为复杂。Pri-morsky断层带向北东从西南端简单的线性断层崖,变为断层围限的断块系统,再变为上升和沉降(盆地)块体系统,并最终汇入一个盆地之中;沿着这个方向裂谷边界断层则突然地复合于盆地构造中。这种构造地貌类型记录了断层演化的时间和空间关系,即从属于递进的沉降和加宽直至最终发育为盆地。因此其趋势是发育完好的湖盆、陆地构造直至被水淹没。陆地构造淹没趋势及没有断层围限块体的盆内构造组合可能是与犁式断层旋转相关的陆内裂谷的共同特点,并具一般裂谷的打开机制。

We studied the morphotectonic framework of the southwestern termination of the North Baikal Basin including the Olkhon Island and its surroundings located in the central part of the Baikal Basin. The morphotectonic pattern of the region is produced by a distal series of en-echelon structures positioned en-echelon along their strike and of lateral series of rift faults consisting of several parallel distal series of structures. The lateral series of faults in the Olkhon Region includes four successive distal series of structures arranged in the seaward direction as.. Primorsky fault zone, Buguldeika-Chernorud graben-Maloye More rift basin-Ushkaniy fault zone, Tazheran Plateau--saddles of Olkhon Island and submerged Akademichesky ridge, Olkhon fault zone. The distal series are cut by transverse faults into a sequences of separate segments with their age increasing progressively northeastward with the youngest ones at the southwestern end. The vertical offset of the faults in the segments increases in the same direction from tens of meters to over 2 000 m, and the fault zones become broader and acquire a more complex structure. The Primorsky fault zone changes northeastward from a simple linear fault scarp on at its southwestern end to a system of fault-hounded blocks, then to a system of uplifted and subsided blocks （basins）, and finally gradesing into a basin; the rift border faults are changed suddenly into within-basin structures in the same direction. This pattern of morphotectonic structures records the space and time evolution of faults, which are subject to progressive subsidence and broadening to finally develop into basins. Following this tendency, in the conditions of a lake basin, land structures eventually become submerged marine ones. The tendency of submergence of land structures and formation of within-basin structures out of tilted fault-hounded blocks may be a common feature of continental rifting associated with rotational listric faulting and controlled by general rift opening.