Ultramicrostructures Of The Ultrahigh-Pressure Metamorphic Rocks From Dabie-Sulu Terrane

Research of ultrahigh-pressure (UHP) metamorphic belt was significant for improve comprehension of plate boundary subduction process, crust-mantle interaction and orogenic belt dynamic course, continent and global dynamics course. An important Problem was how continent crust subduct and exhumate. To answer the problem needed integrated research of metamorphic petrology, geochemistry, isotope chronology, structural geology and so on. Research of deformational mechanism and deformational history correlate microstructural characteristics of UHP metamorphic rock and research of subduction depth information correlate special exsolution structure could provided important evidence for tectonic model of continent crust subduction and exhumation. Used transmission electron microscopy (TEM) and electron probe microanalysis (EMPA), we particular researched ultramicrostructural characteristics of main minerals of eclogite, garnet-peridotite and Jadeite-quartzite in Dabie-Sulu UHP metamorphic belt and discussed its geological significance. Conclusions as follows:1, According to the deformational degree, UHP eclogites in continental collision orogens can be divided into foliated eclogites and massive eclogites. The deformation characteristics of garnets in both types of eclogites, sampled from the borehole of the Chinese Continental Scientific Drilling (CCSD), have been studied by TEM. The following results have been obtained: (1) Dislocation density of garnet in foliated eclogites is about 1.2×l0¹⁰/cm², three order of magnitudes higher than that of massive eclogite. Clusters of water molecules coexisting with dense dislocations indicate that the dominant deformation mechanism of the elongated garnet in foliated eclogite is hydrolysis weakening dislocation glide. (2) In the massive eclogites, the garnets with low dislocation density and with no visible clusters of water molecules are mainly rigid although a few dislocation nets have been observed. (3) In both types of eclogite the dominant slip system of garnet is 1/2<111>{110}, and the minor is <100>{010}.Three possible forms of water in elongated garnets are discussed in this paper. The first form is polarization water molecules, which is absorbed in dislocation tubes. The second form is interstitial water molecules diffusing into crystal lattice through surface and dislocation tubes. The third form is 4OH^- water molecules replacing SiO₄^4-. In addition, possible hydrolysis weakening mechanisms of garnets in foliated eclogites have been discussed: the major mechanism is water induced dislocation glide meanwhile water induced diffusion and grain boundary glide play a minor role. Moreover, the problem of shape preferred orientation (SPO) of deformed garnets not corresponding with lattice preferred orientation (LPO) is also discussed. Elongated garnets with weak LPO have been determined by the characteristic of their crystal structure. Therefore, the possibility that dislocation creep is the dominant deformation mechanism of garnets can not be excluded.2, Research of omphacite from eclogite at shuanghe in Dabie mountains by TEM indicated...