【作者】 梁凤华；

【导师】 许志琴；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2009， 博士

【摘要】 中国大陆科学钻探工程(CCSD)主孔0～800m岩性段的榴辉岩和石榴橄榄岩中保存有丰富的变质与变形信息。本论文通过对其中各种变形现象的详细分析,证实了榴辉岩和石榴橄榄岩在俯冲峰期的条件下可以发生并确实发生了强烈的塑性变形,橄榄岩与榴辉岩的构造混合产状就是在此过程中由于流变强度的差异性形成的。建立了俯冲峰期-折返早期的塑性递进变形过程和机制转换:恢复作用与位错蠕变——动态重结晶与扩散蠕变——静态重结晶与生长作用是连续递进的过程。并结合变质特征,划分了榴辉岩/石榴橄榄岩在俯冲-折返过程中变质变形演化的六个阶段:俯冲过程中的变质构造分异、俯冲峰期阶段的塑性流变、折返初期的动态重结晶过程、短时增温低应力阶段、折返中期的缓慢挤出过程、后期伸展与韧-脆性转换,进而建立了P-T-t-D演化轨迹。俯冲-折返的整个过程中,都伴随着变质与变形的相互促进:进变质过程中,由原岩成分的不均一、强烈的剪切应力及自由流体参与下的组分迁移等共同作用的变质构造分异过程形成了榴辉岩中典型的条带状构造;榴辉岩与石榴石橄榄岩接触边界金云母方辉反应带的形成和颗粒增粗现象是剪切作用、变形机制转换、变质反应和流体作用不断交叉进行,互相促进的结果;另外,折返早期透入性微型剪切带、强烈的动态重结晶和扩散蠕变、有流体参与的榴辉岩和橄榄岩交换反应等为橄榄岩与其他岩石的物质交换提供了有利条件,并使Si不饱和的橄榄岩中形成了锆石。通过应变计算和组构测试,推测苏鲁超高压榴辉岩和石榴橄榄岩在俯冲峰期左右处于以简单剪切为主,兼具收缩的应变场中,收缩机制可能来源于高密度板片前端的向下拉伸。根据榴辉岩/石榴橄榄岩中发现的从动态重结晶到静态重结晶的转换、矿物由高密度位错到大部分区域位错消失的变化、流体作用下的矿物迅速生长加粗、出溶体精细静态共生结构的形成以及局部熔融条带和包裹体等现象,结合前人对俯冲板块折返机制的研究,提出在以浮力为驱动的第一阶段快速折返和以挤压剪应力驱动的第二阶段缓慢抬升之间存在一个以低应力和增温为特征的短时区间,为大陆地壳俯冲折返的机制和动力学提供了变质变形方面的新证据。更多还原

【Abstract】 Abundant information of deformation and metamorphism are preserved in the eclogites and peridotites from the 0～800m-deep main borehole of the Chinese Continental Scientific Drilling Project (CCSD) in the Sulu ultrahigh-pressure (UHP) metamorphic terrane, eastern China. The present thesis investigates them individually in detail and then focus on the interaction between them. Combining field, optical, TEM observations, EBSD measurements for texture and microstructure with investigations metamorphism characteristics of eclogites and peridotites, the P-T-t-D path has been reconstructed which includes 6 stages of deformation and metamorphic process: 1) metamorphic-tectonic differentiation during subduction corresponding to prograde metamorphism, 2) strongly plastic rheologic deformation by recovery-accommodated dislocation creep at the peak metamorphic conditions, 3) dynamic recrystallization characterized by porphyroclast with serrated boundary surrounding by a mosaic of polygonal fine-grains active during coesite eclogite-face retrograde metamorphism at the initial exhumation stage, 4) static recrystallization and growth facilitated from a short low-stress and high-temperature interval corresponding to quartz eclogite-face retrograde metamorphism in the early exhumation stage, 5) slow extrusion along the penetrative shear zones at the main exhumation stage with amphibolite and epidote amphibolite-face retrograde metamorphism and 6) transition from ductile to brittle deformation at the post-exhumation extension stage with green schist-face retrograde metamorphism.The interaction between deformation and metamorphism ran through the whole process from subduction to exhumation. In addition to the band structure benefited from the metamorphic-tectonic differentiation, there are other two typical examples else, i.e. the distribution of phlogopite and enstatite and their coarser-grain features at the touch boundary between eclogites and peridotites, and the occurrence of zircons in peridotites which is characterized by Si dissaturation. All of those phenomena are facilitated from the interaction among different deformation mechanisms, metamorphic reactions and fluid actions. Specially depend on those relationship, it is concluded 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 compression-shear-stress induced probably by the synchronous TanLu strike-slip fault.更多还原