A POINT-COLLISION MECHANICAL MODEL AND TECTONIC PRESSURE FORMING IN DABIE OROGENIC BELT
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摘要: 依据大别造山带的地质特征及古地磁证据, 提出大陆动力学非规则边界陆-陆点碰撞模型, 采用数值模拟方法, 分析点碰撞所引起的构造应力集中及其影响因素, 探讨构造压力在大别山超高压变质岩形成过程中所起的作用, 推测可能形成的深度范围.研究表明: 在本文的模拟条件下, (1) 大陆碰撞初期产生的构造应力场中的平均压力在碰撞点附近增大了约5~9倍.在边界力为100 MPa的情况下, 构造压力在超高压中所占的比例约为20 %~35 %; (2) 由于有构造压力的作用和影响, 超高压变质岩的形成深度有可能被提升20~35 km; (3) 仅考虑碰撞方式, 不计岩石物性差异和其他因素的影响, 构造应力的影响有限, 静岩压力在超高压变质岩形成过程中仍占据主导地位.Abstract: Based on the geological feature and the paleomagnetic evidence of the collision of the North and South China Blocks, a point-collision model for the collision of A-A type is given to study phenomenon of stress concentration in Dabie orogenic belt. By using finite element method, we discuss the effect of tectonic pressure on forming UHP metamorphic rocks and its possible forming depth. The results show that: On the condition of this paper, (1) The initial collision between two continents would cause the tectonic average stress near the collisional point to increase by 5-9 times as compared with regional stress field. Under the 100 MPa boundary force, the proportion of tectonic pressure in UHP is about 20%-35%. (2) For the reason of having action of tectonic pressure, UHP rocks likely form in the depth of 65-80 km. (3) If we solely consider the collision way but not the differences of rock mechanical property and other factors, the influence of tectonic stress is limited and lithostatic pressure will still play a main role in forming UHP metamorphic rocks.
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图 1 大别造山带陆-陆点碰撞有限元计算模型
Fig. 1. Model of point-collision between two continents in Dabie orogenic belt for calculation using finite element method
图 3 大陆点碰撞引起构造应力集中
接触面积A4/A1=4时: a.构造应力σ3/σb等值线; b.沿剖面AA′的构造应力; σ3.最大主压应力, σeqv.等效应力, σm.平均应力, S3.最大主偏应力(下同)
Fig. 3. Tectonic stress concentration due to point-collision of blocks (in case of A4/A1=4)
图 4 点碰撞引起的构造应力σ3随接触面积变化
Fig. 4. Tectonic stress σ3 varying with contact area
a.A=1;b. A=3;c.A=5;d.A=7
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