下地壳韧性剪切带中糜棱面理褶皱变形机制与模拟（以辽宁台里为例）

One NE striking lower crustal granitic mylonite facies belt are exposed in the coastal areas of Taili Village, Liaoning province of Northeast China. The mylonitic foliations are folded in small scale. In the same narrow shear zone, the folding of foliations appears both brittle and ductile deformation characteristics, and a variety of final shapes. The existing model cannot interpret the deformation mechanism in this area perfectly. This projector will select this ductile shear zone as a typical example. Through field quantitative observation, fine deformation structure mapping and microstructure analysis, a system analysis about the geometry and kinematics of typical folding of the mylonitic foliations in this shear zone will be performed. A precise finite strain field, temperature and pressure conditions of deformation, the distribution and difference of the rheological properties of rock in space would be obtained. And on this basis, using physical and numerical modeling, the folding process of mylonitic foliations, stress and strain field will be simulated and compared. Based on the existing models, we hope to propose a new reasonable model thinking about shear rock anisotropy and rheological difference, to explain the deformation mechanism of mylonitic foliation folds in the ductile shear zone. The results would be important to understand the rheological behavior of rocks and the physical anisotropy properties in the local high strain zone of lower crustal of the North China Craton.

辽宁台里海滨地区出露NE向展布的下地壳花岗质糜棱岩带。糜棱面理发生小尺度褶皱变形。在狭窄的同一剪切带内，面理褶皱同时具有脆韧性变形特征，且形式多样。其变形机制难以用已有模型进行完全合理的解释。本课题以该地区剪切带为研究实例，通过野外定量观测、精细变形行迹填图和显微构造分析，对该糜棱岩带内的典型糜棱面理褶皱变形的几何学和运动学进行定量解析，获得该变形带内的精细有限应变场，以及变形温压条件和岩石流变学性质在空间上的分布规律和差异。采用物理模拟和数值模拟实验对糜棱面理的褶皱变形过程、应力和应变场特征进行模拟和对比。尝试提出一种更为合理的剪切带内糜棱面理褶皱变形机制模型。从糜棱面理褶皱变形机制的角度，研究下地壳同一构造层次剪切带内岩石结构、矿物成分、显微组构和微观裂隙对岩石力学各向异性和流变学差异的影响。对认识华北克拉通下地壳局部化高应变区的岩石流变学行为和物理各向异性具有重要意义。

辽宁台里地区出露NE向花岗质混合岩变形带,面理变形复杂、形式多样、非均一性强，与岩石成分和流变学性质密切相关。本课题：①对变形带内岩相分布和变形构造进行精细填图和运动学解析。认为主变形期发生于220Ma，先期花岗质片麻岩部分熔融和晚期花岗质岩浆底劈侵位引起强烈混合岩化作用和面理化变形。混合岩面理晚期叠加变形表现为伸展剪切条带、石香肠应变局部化和面理膝折条带3种类型，记录了从高温韧性变形到低温脆性变形过程。②伸展剪切条带以C`剪切条带和非对称剪切布丁为主要类型，为强烈压扁面理发育晚期受平行面理伸展作用形成。其类型与混合岩条带层厚密切相关：厚度<20mm，以C`剪切条带为主；厚度>20mm，以非对称剪切布丁为主。③建立岩性界面窗棱构造几何参数描述模型，依据观测数据，对其变形过程进行有限元数值模拟。获得几何参数与有效粘度比定量关系，估算二长花岗岩与粗粒花岗质片麻岩有效粘度比值为0.01~0.5。岩石流变学性质与石英和长石颗粒粒度密切相关，变形机制以高温扩散蠕变为主导。④建立面理香肠化构造几何特征参数描述模型，以此为构造流变计，建立混合岩成分、香肠化类型与岩石流变学性质三者之间的关系和演化谱系。部分熔融阶段，淡色体比暗色体能干性低，完全重结晶固态变形阶段，能干性倒转，淡色体具有更高能干性和有效粘度。随淡色体成分比例增加，岩石强度逐渐增高，力学性质由非均一性—非均一性——均一性演化。面理香肠化依次发育：暗色体面理布丁、对象布丁、单层布丁、多层、复合布丁、淡色体面理布丁。岩石能干性由高到低为：石英脉、粗粒伟晶岩脉、粗粒全熔混合岩、中粒淡色体、细粒暗色体。⑤对混合岩面理晚期膝折条带进行野外观测和物理模拟实验。结果表明：共轭膝折带的共轭角不随应变增加而改变，而膝折带宽度和发育数量随总体应变增加而增加，直到应变为10%时停止。研究结论对认识混合岩化过程中岩石流变学性质演化及华北克拉通中、下地壳应变局部化岩石流变学行为具有科学意义。