准噶尔盆地乌夏前陆冲断带构造活动-沉积响应

Sedimentary Response to Permian Structural Movements in Wuxia Foreland Thrust Belt of Junggar Basin

通过研究乌夏前陆冲断带二叠系构造层序特征、沉积相特征、断裂特征及最具断裂构造活动指向性的扇体发育特征,认为二叠纪构造演化受海西运动晚期的影响经历了强烈俯冲碰撞造山期、弱冲断夹短暂伸展火山期和强烈冲断复活期三个阶段,并形成了众多走向不同却又彼此相互切割叠加的逆冲断裂,影响着地层的沉积与剥蚀,控制着断裂带和扇体的形成和演化。结果表明由早至晚扇体由山前向盆内呈前展式夹短暂退覆式叠置迁移特点,相应地,二叠纪以形成北东向和北东东向断裂为主,并从山前向盆地方向依次发育,其间夹杂短暂的后展式发育,构造活动强度逐渐由北西向南东方向迁移。因此,绝大多数同生断裂控制了扇体的沉积边界和分布,部分控制了其厚度和发育方向,扇体的迁移与控扇断裂的活动迁移具有很好的吻合性,断裂活动是控制乌夏地区沉积的主要因素。结果表明:二叠纪时期乌夏地区主要发育水下扇—扇三角洲—冲积扇—湖泊沉积体系,从下至上经历了饥饿深水阶段、复理石阶段和磨拉石阶段构造,其中扇体发育代表了最典型的沉积特征。

By analyzing Permian structural sequence, sedimentation and faults characteristics, the author thinks that Wuxia area was a peripheral foreland restricted by nappe in Permian, there mainly developed submarine fans, fan deltas, fluvial fans and lakes, from under to upside, experienced deep sea stage, flysch stage and molasse stage, among which fans acted as typical lithosomic bodies. At the same time, structural evolution experienced intense diving-collision orogenesis stage, weakly compress occlude instant extend stage and revived strong thrusted stage, generating many thrusting reverse faults to influence sedimentation and denudation and control formation and evolution of fault belt. It is showed that the Permian is characterized by a model of forward thrusting movement and gradual advance migration of fan bodies. That is to say, with the forward thrusting movement of synsedimentary faults controlling the fans from mountainous region to the edge of the Junggar basin, fan bodies distributed in all fault belts gradually developed and advanced from the edge to the center of the Junggar basin and the fan bodies became larger, showing an obvious sedimentary response of gradual advance migration. There is an excellent coupling between them, so faults activity can be looked upon as main factor in controlling sedimentation in Wuxia area.