哇洪山断裂带中段岩石磁组构特征及其地质意义

对哇洪山断裂带中段变形岩石磁组构分析表明,断裂带及其外围构造岩磁化率百分率各向异性H值(普遍>5%,断裂带>10%)较高,说明岩石经历了较强的韧性变形,岩石磁组构具有磁面理发育、磁线理不发育、磁化率量值椭球呈压扁状的特点.由构造岩磁化率最小轴推断的韧性变形期最大主压应力方位主要为近E-W向,由此推断该期断裂带的水平运动性质为左旋.沿断裂带走向构造岩磁组构参数有明显的变化,反映构造变形特征沿断裂带走向有一定差异,其中阿移项、哇沿河—巴硬格莉沟—加木恩韧性变形较强,而红柳沟—蒙高、老沿等地相对较弱.晚华力西期及其以后岩体(脉)H值不高,说明岩石无明显韧性变形,反映韧性变形早于此类岩体(脉)形成.

Characteristics of rock magnetic fabric in middle Wahongshan fault zone and its geological significance

The Wahongshan fault zone in Qinghai province is one of the most important faults in western China. Magnetic fabric of the tectonites and some plutons and veins along the middle segment of the fault are studied. The characteristics of the tectonites from the faults are: (1) the values of H , which symbolize the degree of the magnetic anisotropy, are high (>5% in general and >10% in fault zone); (2) the magnetic susceptibility ellipsoid is flattened; (3) the magnetic foliation is well developed ,but the magnetic lineation is poor developed. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly E-W,so the horizontal movement sense of the shear zones is sinistral.The variations of H,P,F,L,E values along the strike of the fault zones show that the deformation characteristics are different along the fault.The ductile deformations in Ayixiang and Wayanhe-Bayinggeligou-Jiamuen are stronger than the deformations in Hongliugou-Menggao and Laoyan. Because of the low H values of the plutons and veins formed in or after late Hercynian, these rocks have no significant ductile deformation, which indicates that the rocks formed after the formation of the Wahongshan ductile shear zone.