【作者】 陈晓锋；

【导师】 刘正宏； 徐仲元；

【作者基本信息】 吉林大学 ， 构造地质学， 2007， 硕士

【摘要】 一直以来,对于韧性变形带的研究主要集中在地壳中浅层次上,而且常常以糜棱岩作为韧性变形带的典型构造岩,对于下地壳变形带研究则较少。大青山高级变质杂岩区以发育各种片麻岩、变质深成岩等高级变质岩为特征,经历了多期次变形变质作用,构造样式非常复杂,东西向深层次韧性变形带正是在这样的背景上产生的。本文通过野外踏勘,剖面观测与记录确定韧性变形带是应变分解的产物,具有典型的线性强应变带与透镜状弱应变域的分布特征;通过对变形带中的变形变质矿物组合、流体包体以及石榴石-黑云母温压计的分析,确定变形温压环境为高角闪岩-麻粒岩相;通过构造形迹特征及产状的分析,可推测变形带是在南北块体斜向水平会聚碰撞形成的;在镜下,通过对该变形带中构造片麻岩与典型糜棱岩显微组构的对比研究,从而推测在富长英质的下地壳,岩石变形机制主要是扩散蠕变及熔体强化的颗粒流动,影响深层次变形机制的主要因素为温度、熔体以及差应力。更多还原

【Abstract】 Ductile deformation zones(DDZ) , also called high stain zones, exist extensively in the earth from supra-crust to lower crust. They sometimes have two common characters, one is they look like straight lines ; another is they have tectonites with high strain .More and more studies on DDZ indicate that we may resolve some puzzles related to structure and movement of crust lithosphere if we understand the relationship between the characters of ductile deformation zones and the deformation process, metamorphism, magmatic activity. A majority of DDZ reported distribute in supra-middle crust all the time, while few DDZ reported distributing in lower crust are recoginized, and people always consider mylonite as the representative of tectonite of DDZ. There are all kinds of high grade metamorphites ,including gneisses, metamorphic intrusive rock and so on , exposing in Daqingshan high grade metamorphic complexes area. This area have been deformed and metamorphosed for many times in Precambrian, so the structure style of the area is rather complicated, and the DDZ of lower crust strikingW-E formed during these stages. On the base of many researchers’work , Daqingshan DDZ would be studied in this thesis in term of three aspects which are the dimensional characters of DDZ, the structure traces of DDZ, and the microstructure characters and deformation mechanism of tectonites sampled from the DDZ, to open out how the DDZ formed and what is the deformation mechanism of rock in lower crust.1 . The dimensional characters of DDZ and theirs explanation of deformation partitioning The Daqingshan DDZ strike W-E, look like straight lines, and parallel with each other. As intense strain zones of foliation zones striking W-E and dipping S-N steeply, these zones charactered by developing dipping steeply dense straight gneissosity or bandings structure and S-C structure in cross-profile ; while those zones deforming gently laying between them charactered by developing upright folds dipping mildly. The dimensional characters of DDZ and the structure trace characters of high strain zones and low strain zones both accord with the theory of deformation partitioning put forward by T.H. Bell for the first time, and only this theory could explain reasonablely the geometry distributing characters of linear high stain zones and lentoid low stain zones.2.The temperature , pressure and chronology analysis of DDZDaqingshan DDZ formed at high amphibolite-granulite facies conditions which could be proved by deformaed and metamorphosed mineral aggregates, liquid inclusions in polycrystalline quartz banding and so on. The temperature is about 710℃and the pressure is about 0.6GPa, which are acquired by computing garnet- biotite geothermobaromete, quantitatively expaining the deformation conditions of DDZ. The chron of DDZ is between 1900-2200Ma through isotope analysis of single zircon grain selected from intrusives forming the same time as the DDZ.3.The movement mode of DDZThe structure traces of DDZ show that they are produced by the combination of pure and simple shear. The foliations and bandings striking W-E and dipping S-N steeply of the DDZ indicate that they were effected by horizontal S-N pure shear ,while W-E striking sinistral movemet indicates they are effected by W-E simple shear at the same time. The combination effect of pure and simple shear indicate the DDZ is a production of deformation partitioning which is resulted in oblique horizontal colliding between Yin Shan land mass and E Er Duo Si land mass.4.The microcosmic deformation mechanism of DDZ in lower crustWe could understand the microcosmic deformation mechanism of DDZ in lower crust through analyzing the microstructure characters of tectonites in DDZ. Microstructure study show the characters of tectonic gneiss of DDZ in lower crust are different from that of in supra-middle crust. Mylonite have smaller grain , made of porphyroclasts and groundmass, single grain is stretched to a banding; and most grains always exhibit intense intracrystalline deformation characters, for example, undulated extinction, deformed ripples, subgrain and so on . Compared with mylonite, the grain size of tectonic gneiss is near uniform; neither porphyroclasts nor groundmass exsit in tectonic gneiss; most grains touch each other with three-joint point configuration. Tectonic gneiss always develop banding foliation which may result in effect of rock partly molten , but have few intracrystalline deformation characters. These microstructure differences between mylonite and tectonic gneiss indicate that the microcosmic deformation mechanism of mylonite is different from that of tectonic gneiss. Mylonite laying in supra-middle crust may be controlled by dislocation creep during deformation while tectonic gneiss laying in lower crust may be controlled by diffusion creep and granula flow strengthened by melt, which indicate rock deformation mechanism in lower crust riched in quartzofeldspathic may be effected mainly by temperature, melt or liquid ,and differential stress.更多还原