胶南晚中生代大珠花岗岩岩体的脆性变形机制

BRITTLE DEFORMATIONAL MECHANISMS OF LATE MESOZOIC DAZHUSHAN GRANITIC BODY(JIAONAN,SHANDONG)

在长期变化的构造应力作用下,胶南大珠山花岗岩岩体自早白垩世冷凝冷却以来发生强烈的脆性破裂变形,形成了多样的破裂类型如岩脉、节理和断层。在该岩体冷凝冷却早期侵入的细晶花岗岩脉和稍后形成的N-S向节理组反映出与同期区域构造应力场协调的N-S向挤压作用,而后伴随着揭顶剥蚀,出现了交替变化的构造应力场形成了岩体内主导的NW-NNW向和NE向节理组。整体上,恢复出的岩体内构造应力场发生顺时针方向旋转,最大水平挤压由早期的N-S向偏转为晚期的近E-W向。构造应力场的长期变化、平行节理作用和节理断层化作用造成了研究区复杂的破裂型式和破裂序列。

Since the cooling and consolidation in the end of early Cretaceous, the Dazhushan granitic body has been intensively fractured under the changing tectonic stress field, in the form of dyke sets, joint sets and faults of variable trend. The approximate parallelism in trend between the earliest joint set and the earlier dyke set indicates the in-situ N-S trending horizontal compression that produced them, in accordance with the contemporary regional tectonic stress field. Afterwards, the dominant joint sets, NW-NWW and NE trending, were generated under an alternately changing stress field that was probably attributed to up-roofing erosion. As a whole, the maximum horizontal compressional stress tended to rotate clockwise from N-S to E-W direction with time. The complexity of fracture pattern and of fracture sequence in the area were due to the long-term variability of the tectonic stress field, faulting along the existing joints, and parallel jointing.