高级变质地体中多期变质事件的甄别:以东南极埃默里地区为例

Deciphering multiple metamorphic events in high-grade metamorphic terranes: A case from the Amery area of East Antarctica

在多期高级变质地体中确定每期变质事件的性质、时代和P-T轨迹是一项非常困难的研究工作,也是变质地质学研究领域的前沿课题。将精细的地质年代学研究与详细的构造解析和岩石学观察相结合,这是建立同位素年龄与变质事件之间有机联系的最好方法。使用这种方法来甄别东南极埃默里地区格林维尔期和泛非期高级变质事件获得了初步的成功,基本上查明了两期变质事件的影响范围、变质时代和P-T演化,但也存在许多尚未解决的科学问题。一般而言,在同一变质地体中发育两期/多期具有不同构造指向的挤压-伸展变形、保存不同类型(如顺时针和逆时针)或者不连续的P-T演化轨迹以及含有两组/多组变质年龄等可视为存在多期变质事件的标志。当前对多期高级变质作用叠加的研究中还存在两个不清楚的岩石学问题,其一是早期变质作用对晚期变质重结晶施加了什么样的影响?其二是晚期变质作用如何叠加在早期变质矿物组合之上?所以,探索多期高级变质事件的叠加机理、变质行为及控制因素仍是未来岩石学家的艰巨任务。

It is very difficult to determine the nature,timing and P-T path of each metamorphic event in multiple high-grade metamorphic terranes. This is also a frontier issue in the field of metamorphic geology. Careful geochronology coupled with detailed structural analysis and petrographical observations remains the best way to correlate ages to metamorphic events. Using this method,researchers have successfully deciphered the Grenvillian and Pan-African high-grade metamorphic events in the Amery area of East Antarctica. The affecting ranges,ages and P-T evolutions of two metamorphic events are roughly revealed,but many scientific problems have been not solved yet. In general,the development of two-or multi-phase compressional-extensional deformation cycles with different structural orientations,the preservation of different（ clockwise or anticlockwise） or discontinuous P-T paths,and the existence of two-or multigroups of metamorphic ages can be taken as indicators of multiple metamorphism occurring in a metamorphic terrane. There are two unsolved petrological problems on studies of multiple high-grade metamorphic overprinting. The first is what early metamorphism control on late metamorphic recrystallization. The second is how late metamorphism overprint on early metamorphic assemblages. It is obvious that searching the overprinting mechanism,metamorphic behavior and controlling factor of multiple highgrade metamorphic events is a tough task in future for petrologists.