【作者】 刘贵；

【导师】 周永胜；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2013， 博士

【摘要】 华北克拉通减薄是近年来地学界的热点问题，拆离断层形成与地壳伸展减薄是华北克拉通岩石圈减薄的浅部响应，而拆离断层内岩石的流动及变形机制直接受控于岩石流变学状态。对于华北克拉通地壳流变研究，流变实验和天然样品流变分析多数集中在下地壳，对于与拆离断层对应的中上地壳流变实验研究比较少。目前为止，有关于地壳伸展和拆离断层形成相关的岩石流变实验处于空白状态。中地壳岩石经历了变质变形作用，发育有强烈的变形组构。为了研究先存组构对中地壳长英质岩石流变的影响，本论文选择华北克拉通北部辽东拆离断层中具有变形组构的花岗片麻岩和糜棱岩为实验样品，开展了两组样品在实验压缩方向分别平行和垂直面理组构的高温高压流变实验（共4组）。实验条件为温度600-890℃，围压800-1200MPa，应变速率1×10^-4/s×10^-5/s为主，少量10^-6/s。实验数据经过了轴压摩擦力扣除和因样品变形产生面积变化的校正等处理，获得了校正后的力学数据，并求取了流变参数。利用偏光显微镜，扫描电镜对实验样品进行微观结构与变形机制的研究；通过透射电镜能谱与电子探针，分析了熔体的分布和成分特征；采用电子背散射（EBSD）分析获取了岩石中石英C轴组构变化的极图。探讨不同组构方向岩石的力学参数和微观特征以及实验变形对原有组构的构造置换作用。另外为了对比组构的影响，还分析了在温度650℃-1000℃，压力1050-1100MPa条件下均匀样品石英闪长岩高温高压流变后样品的微观结构和熔体特征。为研究地壳拆离断层带形成与演化规律，完善拆离断层带形成演化和地壳伸展减薄模型提供必要的实验室数据。论文获得的主要进展如下：（1）先存组构对花岗质岩石的脆塑性转化机制没有影响。糜棱岩和花岗片麻岩样品在600-800℃的低温阶段处于半脆性变形域；800-890℃的高温时转变为塑性变形。在半脆性变形域，2组糜棱岩和花岗片麻岩样品中，长石以脆性破裂为主，石英碎裂和动态重结晶作用共存。在塑性变形域，长石含有晶内微破裂，但在部分长石边缘出现动态重结晶形成的亚颗粒；石英表现出以亚颗粒化为主的塑性变形特征，而且随着温度升高，石英亚颗粒化程度增强，石英原有细颗粒条带逐渐被新形成的亚颗粒条带所替代；黑云母、角闪石、绿泥石集合体拉长形成条带，在高温下（800℃以上）黑云母和角闪石出现脱水熔融，熔体边缘发现有淬火形成微晶角闪石和黑云母雏晶。而均匀样品石英闪长岩在低温条件下（650℃）处于脆塑性转化域，长石以脆性变形为主，而石英和黑云母以位错滑移为主。在850℃条件下，长石含有晶内微破裂，发育机械双晶，石英亚颗粒化，角闪石出现脱水熔融。在900-1000℃条件下，长石机械双晶，石英亚颗粒化，大部分角闪石和黑云母出现不同程度的脱水熔融。显然，含先存组构的花岗片麻岩、糜棱岩与均匀样品石英闪长岩的脆塑性转化、塑性变形温度条件，以及主要矿物的变形机制基本相同。（2）样品强度和流变参数表明，组构对岩石半脆性—塑性变形的力学强度和激活能有显著影响，但对应力指数影响不大，即组构只影响岩石变形的难易程度，不影响岩石的变形机制和应变方式。在塑性变形阶段，两组糜棱岩给出的应力指数平均都为3左右，两组花岗片麻岩的应力指数平均都在2左右。但糜棱岩在垂直面理组构（PER）和平行面理组构（PAR）的激活能分别为Q=438kJ/mol和Q=193kJ/mol，花岗片麻岩在垂直面理方向（PER）和平行面理方向（PAR）的激活能分别为Q=380.0kJ/mol和Q=246.4kJ/mol。显然，在垂直面理组构的岩石的激活能要大一些。在相同的应变速率和温度条件下，糜棱岩和花岗片麻岩样品在压缩方向垂直面理时的强度都比平行面理时的强度要高。（3）实验变形组构置换了样品中原有组构。糜棱岩和花岗片麻岩实验变形形成的石英和黑云母、角闪石、绿泥石条带改造了样品原有面理组构，其中，垂直面理组构的样品中新形成的变形组构通过构造置换作用，把原有组构彻底改造；平行面理组构的样品，主体继承了原有组构，这导致垂直面理组构的样品强度高于平行面理组构的样品。表明平行面理组构的岩石更易于变形。在石英闪长岩高温变形实验中，部分样品内含有定向分布的大颗粒斜长石，斜长石长轴方向与最大主应力方向（σ1）大角度相交（接近90°），大颗粒斜长石发生机械双晶和弯曲。样品的这种结构与糜棱岩和花岗片麻岩中的垂直面理组构相类似。显然，组构对岩石强度具有显著的控制作用。这意味着岩石组构与最大主应力方向大角度相交或呈垂直方向时，不利于岩石变形和拆离断层的形成，反之均匀岩石或岩石组构与最大主应力方向小角度相交，有利于岩石变形，容易发育拆离断层。（4）实验变形形成的新的石英c轴定向，彻底改造了原有石英c轴组构。EBSD分析表明，实验初始样品中，糜棱岩和花岗片麻岩石英的c轴极密区均位于Z轴附近，底面<a>滑移，为低温底面滑移形成的组构。糜棱岩高温实验变形后新形成的细粒石英组构发生了明显变化，其中，垂直面理组构样品在800℃-840℃-850℃的组构分别为底面<a>—柱面<a>—柱面<c>；平行面理组构样品在840℃-850℃-890℃的组构分别为柱面<a>（菱面<a>）—柱面<c>—柱面<c>，基本符合中温条件下的滑移系规律。花岗片麻岩垂直面理组构样品的石英组构<c>轴极密区位于X轴附近，为柱面<c>滑移；平行面理组构样品的石英组构<c>轴极密区位于Z轴附近，伴有少量的X轴极密，底面<a>滑移和柱面<c>滑移。表明垂直面理组构的样品石英变形改造比平行面理组构的样品更彻底。（5）角闪石、黑云母脱水熔融对样品强度有微弱的影响，熔体成分显示脱水熔融为局部非均匀非平衡的部分熔融。花岗片麻岩在840℃时和糜棱岩在840-850℃时的应力-应变曲线中出现应变软化行为，即随着实验应变增大，熔体含量增加，熔体对样品变形有弱化的趋势。角闪石脱水形成的熔体以团块状分布于角闪石矿物边缘，黑云母脱水形成的熔体以星点状或树枝状分布于黑云母与长石和石英颗粒边缘，显示出熔体的空间分布非均匀。熔体中主要氧化物含量表明熔体成分受参与熔融的矿物成分控制，其中，黑云母周围的熔体主要来源于黑云母本身，但角闪石边缘的熔体除了来自角闪石外，部分石英、钾长石及钛铁矿等参与了熔融，显示出非平衡部分熔融特征。更多还原

【Abstract】 The thinning of the lithosphere of North China craton is a focused research topicin recent years. The detachment fault and crustal extension are thought to be theresponse of shallow crust to this process. In the detachment fault, the viscous flow anddeformation mechanism of rocks are controlled by rheology of the middle to lowercrust, where the rocks usually have strongly deformed fabric due to metamorphismand deformation. However, rheological experiments in the literatures have beenperformed using isotropic samples, and experimental data on effects of fabric onrheology of anistropic rocks are still scarce.In order to investigate the effect of preexisting fabric on the rheology of felsicrocks in the middle to lower crust, deformation experiments were performed underhigh temperature and high pressure conditions using strongly foliated, fine-grainedgranitic gneiss and mylonite samples collected from the a detachment fault of easternLiaodong in the North China craton. The samples were drilled from natural graniticgneiss and mylonite with the cylinder axis parallel to the foliation and perpendicularto the foliation. The rheological experiments of the two kinds of rocks were carriedout with the compression direction parallel to the foliation and perpendicular to thefoliation at temperatures of600-890℃, confining pressure of800MPa-1200MPa andstrain rate range of1×10^-4/s-2.5×10^-6/s. The mechanical data were corrected toeliminate axial dynamic friction, as well as stress difference for changing in thecross-sectional area by assuming a constant volume of the sample. Based on thecorrection, stress-strain data were obtained and the flow law parameters werecalculated. The microstructures and deformation mechanisms were studied underoptical microscope and scanning electron microscopy （SEM）; melt compositionsproduced by dehydration melting of hornblende and biotite were analyzed with thescanning electron microscopy and Energy-dispersive X-ray spectroscopy （EDAX）microanalyses; and the trends of quartz c-axis orientation of starting samples andexperimental deformed samples were measured using electron backscattereddiffraction （EBSD）. To understand the effect of the fabric to rheology of rocks,microstructures and melt characteristics of experimentally deformed quartz dioritesamples with homogeneous texture were also analyzed in this study. The major newresults are obtained as follows:（1） Pre-existing fabric has no effect on the deformation mechanism of the graniticrocks. At temperature from600to800℃，the deformation mechanism of myloniteand granitic gneiss samples is in the semi-brittle deformation regime; at temperaturefrom800to890℃, the deformation mechanism of samples is transformed into plastic deformation.In the semi-brittle deformation regime, the deformation of feldspar grains isaccommodated by brittle fractures, and the quartz grains were deformed by cataclasisand dynamic recrystallization. In the plastic deformation regime, intracrystallinemicro-fractures formed in feldspar grains, and sub-grains formed by dynamicrecrystallization were also found on the grain edge of some feldspar crystals.However, grains of quartz are dominated by sub-grain rotation. With increasingtemperature, more subgrains of quartz appeared, and new quartz subgrain bandsformed in deformed samples, which replaced the original fine-grained quartz bandscompletely. Aggregates of biotite, hornblende and chlorite were elongated and formednew bands. At the high temperature（800℃）, dehydration melting appeared in grainboundaries of biotite and hornblende, and some new micro-crystalline hornblendegrains were found in some localities of the melt. Similar to that, the experimentallydeformed samples of quartz diorite with homogeneous texture underwentbrittle-plastic transition at lower temperature（650℃）, with feldspar dominated bybrittle fracture, and quartz and biotite dominated by dislocation glide. At850℃,intra-granular micro-fractures and mechanical twins were found in feldspar grains,and subgrains were found in quartz. Dehydration melting was seen in grain rims ofhornblende. At900℃-1000℃, the mechanical twins were the major features forfeldspar and subgrains commonly developed in quartz, and most of hornblende andbiotite grains were dehydrated to different extents. Obviously, it was shown thatcharacteristics of the brittle-plastic transition, temperature condition for plasticdeformation and deformation mechanism of the major minerals in foliated graniticgneiss and mylonite are basically similar to that of the uniform samples of quartzdiorite.（2） The strength of samples and flow law parameters indicate that pre-existingfabric of samples has a significant effect on the strength of samples and activationenergy, but it has a negligible effect on the stress exponent. That means pre-existingfabric only controls the degree of difficulty for rock deformation, but probably has noapparent effect on macroscopic deformation modes and deformation mechanisms ofrocks.In the plastic deformation regime, averaged stress exponent is3for both of thetwo groups of mylonite, and it is2for two groups of granitic gneiss. However, theactivation energies of mylonite samples with compression direction perpendicular（PER） to the foliation and parallel to the foliation （PAR） are438kJ/mol and193kJ/mol, respectively. The activation energy values of granitic gneiss samples withPER and PAR to the foliation are respectively380.0kJ/mol and246.4kJ/mol. Evidently the activation energy of experimentally deformed samples with PER isapparently higher than that of samples with PAR. So the flow strength of myloniteand granitic gneiss samples with PER is stronger than that with PAR under identicalstrain rate and temperature conditions.（3） The new fabric bands developed in the deformation process replaced theoriginal foliation of samples. The quartz bands and aggregates of biotite, hornblendeand chlorite bands which formed during experimental deformation transformed theoriginal foliation of samples. In the deformation process, the original foliation of themylonite and granitic gneiss samples with PER were totally destroyed and replaced bythe new foliation. The deformed zone of the samples with PAR followed the originalfoliation and the shear deformation enhanced the deformation bands which led to thelower flow strength of samples with PAR compared to that of PER samples. In otherwords, the samples with PAR are easier to deform. In the deformation experiments onquartz diorite, some samples contain large feldspar grains of preferred orientation.The orientation of long axis in coarse feldspar grains is nearly perpendicular tomaximum principal stress. Mechanical twinning and bending were found in the largefeldspar grains. It suggests that this kind of structure is similar to mylonite andgranitic gneiss samples with PER. Obviously, the fabric pattern has a significanteffect on the strength of rock. This means that when the foliation of rock isperpendicular to the orientation of maximum principal stress, the deformation of rockand detachment fault development are not favored, while in homogeneous rock or inrocks of foliation with a small angle to the orientation of maximum principalstress, the deformation of rock and detachment fault develop easily.（4） C-axis of the new quartz grains formed in the deformation experiment has newlattice preferred orientation, which transformed the original c-axis fabric of preferredorientation in quartz. EBSD measurements showed that the C-axis of quartz instarting mylonite and granitic gneiss samples are localized within Z-max domain forbasal <a> slip, suggesting the basal slip in low temperature deformation. Theexperimental deformed samples of mylonite show apparent change in quartz fabric.The quartz fabrics in samples with PER are basal<a> slip, prism<c> slip and prism<a> slip respectively at the temperatures of800℃,840℃and850℃. The quartzfabrics in samples with PAR are prism<a> slip（rhomb<a> slip）, prism<c> slip andprism<c> slip for temperatures of840℃,850℃and890℃separately. Theresults are consistent with the well-known dominant slip systems under moderatetemperature. The C-axis of quartz in experimental deformed granitic gneiss sampleswith PER localized near the X-axis, indicating prism<c> slip. In the samples withPAR, the C-axis of quartz is localized near Z-axis, accompanied by small amount of C-axis localized near X-axis, indicating basal <a>slip and prism<c> slip. These factsshow the quartz fabric in experimentally deformed PER samples experienced morecomplete structural replecement than that of PAR samples.（5） The dehydration melting of hornblende and biotite have a weak influence onthe strength of samples. The composition of melt shows that dehydration melting islocalized, heterogeneous and non-equilibrium partial melting. The stress-strain curveof the granitic gneiss sample shows strain-softening at840℃. Similar softeningoccurred in mylonite samples in the temperature from840℃to850℃. Thesephenomena indicate that with the increase of strain and accumulation of melt content,the dehydration melting has the effect of work softening during deformation ofsamples under high temperature. The melt dehydrated from hornblende is localized inthe grain rims of hornblende, while the melt dehydrated from biotite is localized aspoint-like and thin films at the grain boundaries between biotite, feldspar and quartz.The distribution of partial melt of hornblende and biotite shows strong heterogeneity.The contents of main oxides in the melt show that the composition of melt iscontrolled by the minerals which participated in the partial melting, showingcharacteristics of non-equilibrium partial melting. The compostion of melt near biotiteis exactly similar to that of biotite, showing melt mainly came from grains of biotite.However, the composition of melt in the grain margin of hornblende is different fromthat of hornblende, and it seems that melt came not only from the grains ofhornblende, quartz, feldspar, but also from ilmenite.更多还原