苏鲁榴辉岩在俯冲峰期-折返早期的递进塑性变形过程及对超高压变质岩石折返动力学的启示

Progressive plastic deformation of eclogites in CCSD-MH from Sulu terrane, eastern China.

榴辉岩的变形特征严重影响俯冲板片的流变学行为,而石榴石的变形机制又直接制约着榴辉岩的变形属性。本文在结合前人研究的基础上,通过对中国大陆科学钻探(CCSD)主孔榴辉岩中石榴子石的典型变形特征的详细对比和分析,进一步证明了榴辉岩在俯冲峰期条件下可以发生强烈的塑性变形。且俯冲峰期-折返早期经历了从以恢复作用主导的位错蠕变,到动态重结晶、扩散蠕变,再到静态重结晶和矿物生长的连续递进变形过程。其中,从动态重结晶到高温静态重结晶的转换,结合短时增温、局部熔融等证据,共同证明了在苏鲁超高压变质岩石折返过程中存在一个短暂的低应力"热"区间,在此前后,折返机制和驱动力发生了转变。

The rheology property of the subduction slab is strongly influenced by the eclogites deformation which is further restricted by the deformation mechanism of garnets. Abundant information of deformation was preserved in the eclogites (specially in garnets) from the Chinese Continental Scientific Drilling Project (CCSD) main borehole in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The present thesis investigates them in detail and draw a conclusion that garnets did deformed as plasticity at the peak metamorphic conditions. Furthermore, a progressive deformation path for eclogites has been reconstructed from the peak to the early exhumation stage in which 3 typical deformation mechanisms are recognized: 1) strongly plastic deformation by recovery-accommodated dislocation creep at the peak metamorphic conditions; 2) dynamic recrystallization characterized by porphyroclast with serrated boundary surrounding by a mosaic of polygonal fine-grains during coesite eclogite-face retrograde metamorphism at the initial exhumation stage, and the diffusion creep increasing with the decreasing of the grain size; 3) static recrystallization and growth characterized by homogenization of grain size and straightening of grain boundaries corresponding to quartz eclogite-face retrograde metamorphism in the early exhumation stage. Depend oil the transition from dynamic to high-temperature static recrystallization, combining with other evidences (e.g. a short-time temperature rising and partial melting), it is suggested that there is a short low-stress and high-temperature phase between the first-stage fast exhumation driven by buoyancy and the second-stage slow uplift driven by compress ion-shear-stress induced probably by the synchronous TanLu strike-slip fault.