显微分析与宏观构造的对应-薄片原位独居石LASS和石榴石微钻取样精细构造年代学研究

The interrelationship between microstructure analysis and regional deformation and metamorphism is complex. Foliation inflection/intersection axes (FIA) preserved within porphyroblasts combination monazite U-Pb in situ dating technique, have revealed much more extensive histories of deformation and metamorphism than previously recognized in the study of orogenesis. Monazite U- Pb dating plays an important role in isotopic geochronology study. The interpretation of the age for monazites are not easy because the identification of the genesis are complex. This project mainly focus on the study of multi-stage growth garnet porphyroblasts collected from schist of Fenzishan group, Jiaobei Massif. Through field investigation, petrography study, macroscopic deformation and microstructure analysis, determine the FIA. Collect the U-Pb age and REE /Sm-Nd data from monazite simultaneously using LASS, based on the microscopic structure analysis. With the comparison of garnet Lu-Hf and Sm-Nd data acquire based on micro-drilling sampling technology and combine with the P-T calculation result, to interpret the relationship between monazite and garnet growth. Investigate the interrelationship between the multi-stage garnet porphyroblasts growth and regional deformation and metamorphism, based on the microscopic structure analysis and regional tectonic analysis data. Trying to provide accurate geochronology constrain for metamorphism and deformation, and improve the understanding of orogenesis.

显微构造与区域变质变形对应关系的判定是构造研究的难点。面理弯切轴结合独居石U-Pb原位定年，可将变斑晶成分环带记录的变质作用与包裹物迹线记录的变形有机联系，为造山过程研究提供了新思路。但独居石与寄主斑晶共生关系的复杂性，制约了独居石年龄数据的应用。本研究尝试以胶北地块粉子山群云母片岩典型多期生长石榴石变斑晶为研究对象，在野外构造解析和室内岩相学研究基础上，测定面理弯切轴，确定各期变质变形序列。在此基础上，运用LASS技术在薄片上原位获取多世代石榴石斑晶内不同构造部位独居石U-Pb年龄和REE、Sm-Nd同位素数据，通过与微钻取样技术采集的多世代石榴石斑晶不同构造变形期次样品的Lu-Hf和Sm-Nd定年数据的对比，综合温压计算结果，查明独居石与寄主斑晶的共生关系；结合区域构造分析数据，厘清石榴石斑晶多期生长与区域多期变形之间的对应关系，为变质变形提供精确年代学约束，提高对造山演化的全面认识。

本项目以胶东地区粉子山群云母片岩以及喜马拉雅造山带典型多期生长石榴子石变斑晶为研究对象，选择有代表性的地质剖面和关键样品，在详细野外观测和室内岩相学研究基础上，综合运用面理弯切轴测量方法、THERMOCALC视剖面温压计算方法以及CL、EBSD、电子探针微区成分分析、LASS原位分析、基于微钻取样的精确定年等分析测试手段。分析独居石物源、成因及与寄主斑晶的共生关系，查明多期生长独居石年龄数据与多世代石榴子石记录的变质作用与构造变质之间的对应关系。通过独居石和石榴子石精细构造年代学与区域构造解析数据的对比，探讨石榴子石变斑晶多期生长与区域多期变形之间的对应关系，将显微构造分析与区域变质变形有机统一。主要取得如下成果：.1）基于野外地质填图，通过构造几何关系和显微构造分析，厘定粉子山群三期构造变形；.2）石英EBSD组构分析与石榴子石斑晶记录的两期变斑晶包裹物迹线（核部S1和边部S2）结果一致；.3）锆石、独居石和金红石U-Pb年代学研究表明，胶北地块荆山群和粉子山群既经历了古元古代变质作用事件又在后期经历了三叠纪变质变形作用的改造；.4）金红石中Zr温度计为折返阶段提供温度条件限定（ca. 658~680℃）；.5）岩相学和相平衡模拟表明，胶北地块粉子山群石榴云母片岩经历了近等温升压的过程。其峰期的温压条件为~560℃和8kbar；.6) 多种同位素测年法有效示踪了苏鲁造山带俯冲-折返过程，认为俯冲阶段（240-220 Ma）和折返阶段（219-206Ma）的持续时间分别约为20 Ma和15 Ma，俯冲和折返的速率近一致，均为6-7 km/Ma。..上述创新性成果将显微构造与区域变质变形有机联系，对变质变形提供精确年代学约束，为造山过程研究提供了新思路。