西南天山榴辉岩的显微构造及其变形机制探讨

岩石、矿物的显微构造是岩石变形、变质等各种地质作用最直观的记录。新疆西南天山高压变质带中榴辉岩的显微构造研究,对认识其在地壳深俯冲过程中的岩石、矿物变形机制有十分重要的意义。西南天山榴辉岩的显微构造研究发现:绿辉石的动态重结晶亚晶粒化和颗粒边界迁移、云母的扭折和波状消光、方解石的机械双晶等显微变形现象,表明动态恢复作用、位错滑移和位错攀移为主的晶质塑性变形机制是榴辉岩的主要变形机制;石榴子石呈无变形刚性特征,具有变斑晶包迹结构,说明固态物质扩散迁移是榴辉岩的另一个重要变形机制;石榴子石多具有良好的晶型,说明石榴子石是在静变质状态下稳态生长而成,这与大别—苏鲁高压—超高压变质带有明显区别。因此,笔者认为位错蠕变、动态重结晶主导的晶质塑性变形和固态物质扩散迁移组合的显微构造变形现象,是西南天山高压—超高压变质榴辉岩的显微构造组合特征。这样的组合特征可能代表了洋壳深俯冲经历高压—超高压变质作用榴辉岩变形机制。     

新太古代大洋岩石圈地幔的显微变形探讨——以遵化蛇绿混杂岩带为例

遵化新太古代蛇绿混杂岩中的地幔岩显微构造以粗粒镶嵌构造为主,矿物颗粒多以弧形边界紧密镶嵌,部分岩石出现粒间熔体.橄榄石出现残斑构造、动态重结晶和拉长变形,铬铁矿出现典型的高温拉分构造,表现出活跃的动态恢复、粒间滑移和扩散蠕变,显示出大洋上地幔高温条件下塑性流变的特征,是大洋板块侧向扩张的深部表现.遵化蛇绿岩的地幔岩除了具有强烈的构造变形之外,部分豆荚状铬铁矿保留有豆状、豆壳状等岩浆结构和构造,并且有未变形的纯橄岩和辉石岩侵入,说明位于一个岩浆较强烈活动的位置.高温塑性侧向剪切变形和强烈的岩浆活动表明遵化蛇绿岩形成于快速扩张的洋脊,类似阿曼蛇绿岩.遵化蛇绿岩的围岩出现石英条带、核幔构造、动态重结晶和云母鱼等显微构造变形,对应着蛇绿岩侵位到陆壳之后,从中部地壳向上地壳抬升的构造运动过程.     

彭灌断裂带的构造特征

讨论了彭灌断裂带的宏观及微观变形特征。宏观构造、显微构造特征反映出该断裂带为一条脆性逆冲推覆断裂，其变形机制主要为碎裂作用。断层主要产于中生代地层之中，并有叠置的推覆岩片夹于其中，主要活动时期是在喜马拉雅期。     

吉林西林河地区糜棱岩显微构造及其地质意义研究

介绍了吉林西林河地区糜棱岩的显微构造特征 ,指出韧性变形是该区太古宙断裂变形的主导变形机制 ,同时阐述了在该区研究糜棱岩显微构造的重要意义     

显微组构分析在判别压性、压扭性断裂上与宏观鉴定的一致性

本文就福建永安二迭系石英砂岩中三条较典型的压性、压扭性断层中的定向标本进行显微构造 研究和岩组分析，对室内外观测数据进行权衡和对比，探索天然变形岩石组构的宏、微观变化规律． 结论是： １． 宏、微观构造岩的特征一致； ２．从三条断层带中的水平切片所测得的石英变形页理极点图相类似，都具较完善的斜方对 称，变形页理极点最密区的钝角平分线方向都为主压应力（σ１）的方向； ３．三条断层带中的不同方向的切片中。石英光轴岩组图也都呈近斜方对称，且其点极密的位 置即为σ１的位置； ４．从上述两种岩组图求得的σ１位置基本一致，以此求得的断层滑动线的产状与宏观所测的数 据的平均误差只有４°． 以上表明，显微构造研究和显微分析在鉴定断裂的力学性质上是行之有效的手段．     

江油至北川一带石炭系灰岩构造变形分析

笔者对江油、北川一带地区出露的石炭系中下统所谓瘤状灰岩进行了构造成因与变形机理分析,并通过对岩石中变形体所进行的有限应变测量及显微构造分析,阐述了该区域内的构造变形特征,初步确定了这类位于特殊部位上的构造岩的变形机制,同时为进行龙门山断褶带的构造特征研究。提供了部分资料和依据。     

甘肃白银厂劈理构造的特征研究

白银厂是一个经历了多期变形的地区,各种小型构造现象非常丰富。对在石英角斑岩系中相当发育的S_1劈理的宏观特征和显微构造的分析研究表明,在不同岩性和构造变形强度不同的岩石中,劈理的形态和发育程度呈现出有规律地变化。而且劈理的性质很复杂,任何一个简单的机制都不可能解释所有观察到的显微构造特征。因此,对这些特征的解释导致提出了一个定向成核择优生长和压溶作用的联合作用的成因模式。     

舜耕山断层的显微构造特征及其意义

舜耕山断层是低温快速变形的产物,它经历了两期或两期以上的构造作用。它是简单剪切作用下的浅层次的脆性变形,局部为微弱的韧性变形。其形成时的差异应力约为89MPa。通过对舜耕山断层构造岩的显微构造和超显微构造特征、组构分析的研究,和对舜耕山断层形成时的变形条件的论述,从而为阐述淮南煤田南缘逆冲推覆构造的形成机制提供了依据。     

琼东南盆地崖城区微观构造变形特征及油气地质意义

在琼东南盆地中深层地层中,圈闭边界形成、储层流体空间分布、岩石强度变化等要素,不仅与沉积单元、岩石组分相关,还与微观构造变形有一定的关系。通过岩心和镜下观测对琼东南盆地崖城区微观构造的发育特征进行研究,分析岩石组分与微观构造类型之间的关系,探讨不同类型微观构造变形的形成机制,并通过孔隙度、渗透率测试定量评价微观构造的发育对研究区储层物性的改造作用。研究表明：研究区发育微裂缝、碎裂带、微观涂抹带和硅酸盐混合变形带4种微观构造类型;变形带内黏土矿物含量是发育微观变形类型的主要控制因素,黏土矿物体积分数小于20%时主要发育碎裂带,黏土矿物体积分数大于50%时主要发育微观涂抹带,黏土矿物体积分数介于20%～50%之间时主要发育硅酸盐混合变形带;微观构造的发育对研究区储层物性具有一定的影响,其中微裂缝的发育能够有效提高原岩孔隙度和渗透率,而微观变形带的发育对储层物性的改造作用较为有限。     

广西大福楼锡多金属矿床铅同位素地球化学

为了探讨广西南丹大厂矿田大福楼锡多金属矿床的成矿物质来源及其源区特征,对矿石的铅同位素组成特征及其成矿构造环境进行分析与研究.研究结果表明:大福楼锡矿w(206pb)/w(204pb)=17.478～18.431,均值为17.991,极差为0.953;w(207 pb)/w(204pb)=15.440～15.717,均值为15.582,极差为0.277;w(20spb)/w(204pb)=37.556～38.839,均值为38.233,极差为1.283;φ介于0.592～0.638之间,μ为9.26～9.69,w(Th)/w(U)=3.74～3.97.根据Zartman构造模式图,大福楼锡矿床金属硫化物铅同位素数据聚为2个区域,即上地幔与造山带以及造山带与上地壳演化线之间,表明矿石铅既有地幔来源也包含上地壳成分或来自于上地壳,矿床的矿石铅并非全部由花岗岩浆所提供.另外,根据Doe铅同位素构造环境判别图,铅同位素投影点具有集中分布的特点,主要分布于造山带与下地壳演化线之间,即造山带演化线的上方,再次证实上地壳也为成矿提供了部分铅源,即上地壳也是成矿物质的来源之一.大福楼锡多金属矿床成矿作用与造山构造事件有关,矿床主要形成于造山带构造环境中.     

Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet

How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The upper crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the upper crust of southern Tibet and the underthrusting Indian crust. Such coupling is inconsistent with the presence of active 'channel flow' beneath southern Tibet, and suggests that the Indian crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet.     

Coexisting brittle-ductile fracturing mechanisms in fault zones of the upper crust level

Microstructural and sub-microstructural studies are conducted on calcite marble taken from the Autseib fault zone, Damara region, Namibia, SW Africa. The characteristic microstructural styles of rocks deformed in the upper crust are analyzed, including mainly the two microstructural contrasts in the tectonites: (i) coarse grains (centimeter scale) in primary rocks and in deformed clasts and extremely fine grains (micron scale) in the matrix; and (ii) macroscopic cataclastic (brittle) and microscopic mylonitic (ductile) textures. The coexistence of the macroscopic brittle and microscopic ductile textures is better explained by deformation through a comprehensive association of intragranular twinning and kinking, intraand intergranular ductile fracturing, and pressure solution along grain boundaries. Ductile fracturing, i.e. fracturing triggered and accommodated by twinning and fluid-enhanced dislocation creep and dynamic recrystallization, is among the most important mechanisms of rock deformation in the shallow crust, while grain size reduction and dynamic recrystallization are primarily nucleated and distributed due to the incoherencies along some boundaries, e.g. kink band boundaries, fractures and grain boundaries in the deformed grains.     

Destruction geodynamics of the North China craton and its Paleoproterozoic plate tectonics

Much attention has been paid in the last two decades to the physical and chemical processes as well as temporal-spatial variations of the lithospheric mantle beneath the North China Craton. In order to provide insights into the geodynamics of this variation, it is necessary to thoroughly study the state and structure of the lithospheric crust and mantle of the North China Craton and its adjacent regions as an integrated unit. Based on the velocity structure of the crust and upper mantle constrained from seismological studies, this paper presents various available geophysical results regarding the lithosphere thickness, the nature of crust-mantle boundary, the upper mantle structure and deformation characteristics as well as their tectonic features and evolution systematics. Combined with the obtained data from petrology and geochemistry, a mantle flow model is proposed for the tectonic evolution of the North China Craton during the Mesozoic-Cenozoic. We suggest that subduction of the Pacific plate made the mantle underneath the eastern Asian continent unstable and able to flow faster. Such a regional mantle flow system would cause an elevation of melt/fluid content in the upper mantle of the North China Craton and the lithospheric softening, which, subsequently resulted in destruction of the North China Craton in different ways of delamination and thermal erosion in Yanshan, Taihang Mountains and the Tan-Lu Fault zone. Multiple lines of evidence recorded in the crust of the North China Craton, such as the amalgamation of the Archean eastern and western blocks, the subduction of Paleo-oceanic crust and Paleo-continental residue, indicate that the Earth in the Paleoproterozoic had already evolved into the plate tectonic system similar to the present plate tectonics.     

Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge

The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is consistent either with pollution from recycled, ancient altered oceanic crust and sediments, or with ancient continental crust or lithosphere. The radiogenic isotopic signature may therefore be the result of contamination of the upper mantle by plumes containing recycled altered ancient oceanic crust and sediments, detachment and dispersal of continental material into the shallow mantle during rifting and breakup of Gondwana, or contamination of the upper mantle by ancient subduction processes. The identification of a process operating on a scale large enough to affect major portions of the Indian mid-ocean ridge basalt source region has been a long-standing problem. Here we present hafnium and lead isotope data from across the Indian-Pacific mantle boundary at the Australian-Antarctic discordance region of the Southeast Indian Ridge, which demonstrate that the Pacific and Indian upper mantle basalt source domains were each affected by different mechanisms. We infer that the Indian upper-mantle isotope signature in this region is affected mainly by lower continental crust entrained during Gondwana rifting, whereas the isotope signature of the Pacific upper mantle is influenced predominantly by ocean floor subduction-related processes.     

Continuing Colorado plateau uplift by delamination-style convective lithospheric downwelling

The Colorado plateau is a large, tectonically intact, physiographic province in the southwestern North American Cordillera that stands at ～1,800-2,000?m elevation and has long been thought to be in isostatic equilibrium. The origin of these high elevations is unclear because unlike the surrounding provinces, which have undergone significant Cretaceous-Palaeogene compressional deformation followed by Neogene extensional deformation, the Colorado plateau is largely internally undeformed. Here we combine new seismic tomography and receiver function images to resolve a vertical high-seismic-velocity anomaly beneath the west-central plateau that extends more than 200?km in depth. The upper surface of this anomaly is seismically defined by a dipping interface extending from the lower crust to depths of 70-90?km. The base of the continental crust above the anomaly has a similar shape, with an elevated Moho. We interpret these seismic structures as a continuing regional, delamination-style foundering of lower crust and continental lithosphere. This implies that Pliocene (2.6-5.3?Myr ago) uplift of the plateau and the magmatism on its margins are intimately tied to continuing deep lithospheric processes. Petrologic and geochemical observations indicate that late Cretaceous-Palaeogene (～90-40?Myr ago) low-angle subduction hydrated and probably weakened much of the Proterozoic tectospheric mantle beneath the Colorado plateau. We suggest that mid-Cenozoic (～35-25?Myr ago) to Recent magmatic infiltration subsequently imparted negative compositional buoyancy to the base and sides of the Colorado plateau upper mantle, triggering downwelling. The patterns of magmatic activity suggest that previous such events have progressively removed the Colorado plateau lithosphere inward from its margins, and have driven uplift. Using Grand Canyon incision rates and Pliocene basaltic volcanism patterns, we suggest that this particular event has been active over the past ～6?Myr.     

Deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains

Fine structures of the crust and upper mantle of the basin-and-range juncture on the northwestern margin of the Qinghai-Tibetan Plateau are first delineated by the deep seismic reflection profile across the juncture zone between the Tarim Basin and the West Kunlun Mountains. Evidence is found for the northward subduction of the northwest marginal lithosphere of the Qinghai-Tibetan Plateau and its collision with Tarim lithosphere beneath the West Kunlun Mountains. The lithosphere image of the face-to-face subduction and collision determines the coupling relationship between the Tarim Basin and the West Kunlun Mountains at the lithosphere scale and reflects the process of continent-continent collision.     

Deformation in the Three Gorges Reservoir after the first impoundment determined by GPS measurements

Currently,theongoingThreeGorgesProject(TGP)isthebiggesthydraulicprojectintheworld andtheThreeGorgesdamwillbeoneofthehighest dams.Standing185mhigh,itwillbeholding3.92×1010m3ofwaterwhencompletedin2009.Howev er,previousresearchesandhistoricalrecordshave shownthatsuchahugecontentofwatermighttrig germinorandmediateearthquakes[1—4],becausea decreaseoffrictiononanactivefaultduetoporepres surediffusenessandenhancedwaterpermeationcould causefaultintermittentunlockingtoreleaseseismic energy[4,5—8]…     

Genesis of continental seismogenic zone and a new fault zone model

Experiments were conducted repeatedly on Mannari granite under different temperature and confining pressure conditions. Systematic micro- and submicro-structural and mechanical analyses of granite samples deformed under 1.5 GPa (confining pressure), at 25℃—650℃temperatures and at 2× 10^-6 s^-1 strain rate show the brittle-ductile deformation microstructures and microstructural associations similar to those observed in naturally deformed crustal rocks and minerals. Brittle fracturing and crystalline plasticity co-exist and react with each other in the brittle-ductile transition domain of the continental lithosphere. The interaction between the different mechanisms in the transitional domain results in the variation of anomalous strength values, which may best explain the genesis of the continental seismogenic zone. A new fault zone model is proposed on the basis of detailed micromechanical and microstructural analyses.     

大陆下地壳和岩石圈地幔中的水:基于捕虏体的红外光谱分析

根据对华北克拉通汉诺坝和女山两个捕虏体产地的麻粒岩和橄榄岩的FTIR实验测定,分析讨论了大陆深部岩石圈内水含量和分布上的一些显著特点.结果表明,大陆下地壳和岩石圈内矿物的水含量无论在横向还是垂向分布上都是明显不均一的,造成这些不均一性的机制可能复杂多样.     

论海沟—岛弧—弧后盆地复合体系的形成机制

海沟一岛孤一弧后盆地复合体系的成因与软流圈及岩石圈的流变性有关,以前者为主,并遵循流体运动的最小阻力原理。俯冲有两种类型:一是大洋岩石圈向大陆岩石圈的俯冲,二是大洋岩石圈之间的俯冲。弧后扩张及岛弧升高在时间上的滞后现象,也可以用此原理来说明。