苏北地区前陆变形特征与形成机制

Characteristics and Formation Mechanism of the Foreland Deformation in the Subei Region

郯庐断裂带以东、苏鲁造山带南部的苏北地区,由于苏北盆地的大面积覆盖使得长期以来对该区前陆变形构造特征与形成机制了解不够。苏北盆地的大量勘探资料分析及其南侧海相盖层露头的系统观察表明,苏北地区海相盖层在中三叠世末印支期普遍遭受前陆变形而成为前陆褶断带,盖层与基底之间出现了区域性滑脱面。该前陆变形区自西北向东南可划分为根带、中带与锋带。海相盖层内逆冲断层与褶皱的走向自西向东呈现为由北北东向转变为北东东向的弧形变化,显示了郯庐断裂带左行平移牵引的影响。各类构造特征与海相盖层剥蚀程度表明,苏北地区前陆变形随着接近苏鲁造山带和郯庐断裂带而增强,远离则减弱。苏北地区前陆变形构造特征及变化规律,指示其变形动力来自北部苏鲁造山带的碰撞造山,前陆变形发生在造山带陆壳深俯冲阶段。前陆变形构造走向上的弧形变化及强度的向西增强是郯庐断裂带在前陆变形阶段左行平移的影响结果,并非后期平移改造所致,进而支持该断裂带在造山期发生了强烈的左行平移的认识。

Owing to large-scale cover by the Subei Basin, features and formation mechanism of foreland structures in the Subei region, south of the Sulu Orogen, and east of the Tan-Lu Fault Zone remain unclear. Analyses of many exploration data for the Subei Basin and field survey of the marine cover exposures suggest that the marine cover in the Subei region experienced foreland deformation during the Indosinian period at the end of Middle Triassic, and regional detachment occurring between the cover and basement in the foreland fold and thrust belt were observed. The foreland deformation region can be divided into root belt, middle belt, and front belt from NW to SE. Strikes of thrusts and folds in the marine cover show an arc-like change from NNE to ENE from west to east, showing dragging influence of the sinistral faulting along the Tan-Lu Fault Zone. Structural features and denudation degree of the marine cover imply that the foreland deformation in the Subei region increase toward the Sulu Orogen and Tan-Lu Fault Zone. Characteristics and changes of the foreland structures demonstrate that the foreland deformation resulted from collision of the Sulu Orogen which is synchronous with continental deep subduction in the orogen. The arc-like change of the structural strikes and westward increase of the deformation intensity are caused by the sinistral faulting along the Tan-Lu Fault Zone during the foreland deformation rather than later faulting. The foreland deformation features support the view that the Tan-Lu Fault zone experienced large-scale sinistral faulting during the orogenic period.