大陆板内构造变形及其动力学机制

典型大陆板内变形发生在克拉通化的大陆岩石圈内部,距离同变形期活动板块构造边界数百至2000km以上。收缩变形主要表现为区域尺度的盆地构造反转、结晶基底与上覆盖层共同卷入变形的厚皮式逆冲构造,具有变形局部化特征。因为流变学分层特征不同,大陆板内变形可以发生在中上部地壳、整个地壳乃至岩石圈尺度上,表现为不同波长的地壳或岩石圈尺度纵弯弯曲。大陆岩石圈板块内部物质组成与结构的不均一性、流体活动、热作用、克拉通内盆地巨厚沉积产生的覆盖效应、地壳加厚等导致的岩石圈强度的局部降低等,是导致大陆板内变形以及应变局部化的原因。构造活化是大陆板内变形的重要方式。板块俯冲或碰撞远程效应被认为是大陆板内变形的主导动力学模型,但是放射性元素积累导致的岩石圈强度热弱化,或大陆冰川消退触发板内应力状态变化等导致大陆板内变形的动力学模型也应该引起关注。     

岩石圈HPE热弱化与陆内构造变形

大陆内部变形在很大程度受制于大陆岩石圈流变侧向不均一性,而温度(地热梯度)是影响地壳和地幔岩石流变性质的主导因素。由热引起的地壳/地幔岩石材料的热弱化是弱化的主要途径,为陆内变形准备了物质条件。在构造外力(板块相关的或非相关的)的作用下,这些受到热弱化的岩石材料极易发生变形,导致岩石圈内部的造山带和变形带的形成。文章试图在广泛的国内外文献搜集和综合分析基础上,介绍由生热元素(heat producing elements)聚集产生的地壳/地幔(岩石)热弱化以及随后地幔下降流构造力作用造成的大陆内部应变局部化和陆内构造变形。这些地幔下降流是由大陆岩石圈地幔重力(瑞利 泰勒型)不稳定性发育引起的。     

超高压变质岩的塑性流变学

岩石流变作用是大陆造山作用的基本特征,超高压岩石的形成和折返过程也是大陆深俯冲带内物质的复杂流变过程。要深入理解大陆造山带的造山作用和大陆壳岩石的深俯冲和折返动力学过程,必须对大陆地壳及地幔岩石的流变学进行深入研究。岩石圈流变学的主要研究内容主要包括流变学分层性、变形分解和应变局部化及大陆壳岩石部分熔融作用的流变学效应等。应用岩石圈流变学的基本原理和方法,分析了大别-苏鲁超高压变质带中超高压变质岩的塑性流变特点,探讨了超高压变质岩形成和折返过程的塑性流变学。     

大陆下地壳麻粒岩的流变学研究进展

大险下地壳麻粒岩的流变学研究可以解释地壳变形、壳幔物质交换以及岩石圈深部动力学过程等科学问题.前人通过研究各矿物的显微构造变形特征与变形机制,运用广义混合流变律探讨多矿物复合岩石的流变性质,结合水与流体对岩石变形强度的弱化作用,阐明在大陆下地壳变形环境下复矿麻粒岩的塑性变形和韧性流变性质.目前人们致力于对天然变形岩石和...     

深成构造作用及大陆壳流变学研究

大陆地壳结构具不均一性，由此表现出分层性。深成构造作用是应变局部化的过程，表现为韧性剪切变形作用。地壳中近水平或网络状反射体韧性剪切带的产生，为深成构造作用的结果。地壳结构的特点和深成构造作用都与大陆岩石圈流变性有密切的关系。另外，熔融作用对深成构造作用及岩石流变性也有重要的影响。     

石英C轴组构指示北大别造山后伸展期中-下地壳流变形式

造山带中-下地壳韧性流变形式反映深部岩石圈构造活动形式,是造山带深部岩石圈运动学及动力学研究的重要内容。前人对板块俯冲阶段造山带中-下地壳流动开展了较为深入的研究,但对造山后伸展期中-下地壳流变形式及其深部动力学认识不足。本次工作对北大别造山后伸展期中-下地壳岩石开展了详尽的构造观察和石英C轴组构分析,研究造山后伸展期中-下地壳流变形式。本次研究表明,中-下地壳流变带内岩石变形从边界区域的简单剪切变形为主导逐渐转变为在核部区域以纯剪切变形为主。流变带内部岩石变形特征表明北大别中-下地壳流变带的流变形式是介于活动边界条件下的透入性剪切流动和固定边界条件下韧性垮塌流动的过渡形式。这一流变形式可能是深俯冲太平洋板块的绕屈回撤和加厚造山带地壳活化韧性垮塌叠加的结果。     

变形岩石的显微构造与岩石圈流变学

岩石圈的流变学分析和岩石构造、显微构造证据揭示出大陆岩石圈具有显著的横向和纵向上的异向性，并具有明显的非板块表现。全面开展不同温度和压力条件下变形岩石的构造与显微构造分析，正确认识岩石圈不同层次上岩石的流变学规律、流动机理及其制约因素等，将成为后板块构造研究与新的岩石圈演化理论建立的基础和主要动力。岩石流动的宏观-微观尺度问题(岩石圈结构与流变性、边界弱化效应和岩石流变学与显微构造响应等)、岩石流动的时间问题(不同时间尺度岩石的流动性、实验室模拟与天然岩石流动的协调性、浅层岩石流动变形的有效定年等)、岩石流动的制约因素(内在的成分与结构、外在的物理与化学环境)将成为岩石圈流动与岩石变形显微构造研究的重要方面。现代化实验室建设和最新实验技术、手段的利用将成为解决上述科学问题的必要条件。     

变形岩石的显微构造与岩石圈流变学

岩石圈的流变学分析和岩石构造、显微构造证据揭示出大陆岩石圈具有显著的横向和纵向上的异向性,并具有明显的非板块表现.全面开展不同温度和压力条件下变形岩石的构造与显微构造分析,正确认识岩石圈不同层次上岩石的流变学规律、流动机理及其制约因素等,将成为后板块构造研究与新的岩石圈演化理论建立的基础和主要动力.岩石流动的宏观-微观尺度问题(岩石圈结构与流变性、边界弱化效应和岩石流变学与显微构造响应等)、岩石流动的时间问题(不同时间尺度岩石的流动性、实验室模拟与天然岩石流动的协调性、浅层岩石流动变形的有效定年等)、岩石流动的制约因素(内在的成分与结构、外在的物理与化学环境)将成为岩石圈流动与岩石变形显微构造研究的重要方面.现代化实验室建设和最新实验技术、手段的利用将成为解决上述科学问题的必要条件.     

中国大陆岩石圈壳幔韧性剪切带系统

众多地震测深剖面的地质构造解析显示,大陆岩石圈存在既有显著差异又有密切联系的两套断裂系统,即以地壳表层脆性剪切带为主的浅层断裂系统和以切割莫霍界面的壳幔韧性剪切带为主的深部断裂系统。根据地震测深速度结构特征,结合深部构造岩石地球化学的综合研究,将切割莫霍界面或壳幔过渡带的壳幔韧性剪切带划分为三类(俯冲带、缝合带和剪切带)五型(大陆岩石圈边缘海沟俯冲带、大陆岩石圈碰撞缝合带、挤压型壳幔韧性剪切带、伸展型壳幔韧性剪切带和走滑型壳幔韧性剪切带)。建立起中国大陆岩石圈构造变形由地壳表层向深部扩展以及由壳幔过渡带向地壳中上部扩展的岩石圈双向扩展模式。壳幔韧性剪切带既是无机成因天然气等深部流体的通道,又是地震活动区的发震构造之一,因此研究大陆岩石圈壳幔韧性剪切带具有重要学术价值和实际意义。     

大别—苏鲁区UHP变质岩构造学及流变学演化

在大别—苏鲁区的30个关键位置,对UHP/HP变质岩进行详细构造解析、大比例尺(1∶10000)制图并在区域尺度上进行观察和对比,以便揭示它们的构造几何学、变形条件和流变学演化。初步的研究结果指出,广泛出露的UHP/HP榴辉岩相岩石形成一个巨大的UHP/HP变质带,提供了一个观察中朝与扬子克拉通之间三叠纪大陆深俯冲-碰撞带过程的窗口。观察的显微构造及组构指出,UHP/HP变质带内岩石变形机制,无论是在榴辉岩相阶段还是在榴辉岩相后阶段,都是以塑性流变为主,其力学行为和组构特征都受组成矿物的强度、强度差等流变学特征,以及变形物理环境如压力、温度、应变速率、差异应力和流体含量等的制约。在俯冲/碰撞带内的变形分解作用于岩石圈不同层次及不同的构造阶段都曾发生,而且,在不同尺度上,应变局部化形成具高应变的剪切带网络,且一般显示典型的布丁-基质或碎斑-基质构造及流变学型式。根据构造、岩石、变质作用及地质年代学资料,借助于岩石圈流变学基本原理,提出一个大别—苏鲁区UHP/HP变质岩石流变学演化的工作模式,它涉及早期扬子与中朝克拉通间三叠纪(~250~230Ma)大陆深俯冲/碰撞、UHP/HP变质岩形成,相继深埋岩石的多期折返。特别强调UHP/HP岩石向地壳表层的折返,主要是构造过程,地面侵蚀作用是次要的。     

Strain localization as a key to reconciling experimentally derived flow-law data with dynamic models of continental collision

Published strength profiles predict strength discontinuities within and/or at the base of continental crust during compression. We use finite element models to investigate the effect of strength discontinuities on continental collision dynamics. The style of deformation in model crust during continued subduction of underlying mantle lithosphere is controlled by: (1) experimental flow-law data; (2) the crustal geotherm; (3) strain localization by erosion; (4) strain-softening and other localization effects. In the absence of erosion and other factors causing strain localization, numerical models with typical geothermal gradients and frictional/ductile rheologies predict diffuse crustal deformation with whole-scale detachment of crust from mantle lithosphere. This prediction is at odds with earlier model studies that only considered frictional crustal rheologies and showed asymmetric, focused crustal deformation. Without localization, model deformation is not consistent with that observed in small collisional orogens such as the Swiss Alps. This suggests that strain localization by a combination of erosion and rheological effects such as strain softening must play a major role in focusing deformation, and that strength profiles derived under constant strain rates and uniform material properties cannot be used to infer crustal strength during collision dynamics.     

Rheological stratification of the Indian continental lithosphere: Role of diffusion creep

Dynamic recrystallization and reduction in grain-size at large strains, e.g. in shear zones, leads to rheological weakening of the lithosphere and facilitates intense ductile deformation. In the present work, we include this effect into the rheological models of the Indian continental lithosphere to analyse its role in modifying the rheological structure and strength of the Indian lithosphere. The results computed by using quartz and felspar rheologies for the upper and lower crust, respectively, and grain-size dependent olivine rheology for the upper mantle, indicate an increase in the ductility of the mantle lithosphere.     

岩石扩散蠕变及其地质意义

总结了近十年来岩石扩散蠕变显微构造鉴别特征，研究方法的最新进展，矿物颗粒大小和流体（包括熔体和水）等是影响扩散蠕变的重要因素。扩散蠕变与位错蠕变和超塑性变形有密切关系，它的研究对大陆裂谷化过程，大陆碰撞带中岩石圈地幔强度弱化，中下地壳韧性剪切应变局限化以及与相变有关的矿物粒度细小化作用的分布有重要应用意义。     

Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

Emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures, conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones. Much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock-mechanics-based yield criteria for the inelastic deformations at the top and base. At mid-plate depths, stresses are likely to be supported elastically because bending strains and elastic stresses are low. The collisional tectonic regime, however, is far more complex because very large permanent strains are sustained at mid-plate depths and this requires us to include the broad transition between brittle and ductile flow. Moreover, important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid-plate depths.Two specific contributions of laboratory rock rheology research are considered in this paper. First, the high-temperature steady-state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks. Rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere. The thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm T_c above which (at geologic strain rates) the high-temperature ductile strength falls below some arbitrary strength isobar (e.g., 100 MPa). For olivine T_c is about 700°–800°C but for other crustal silicates, T_c may be as low as 400°–600°C, suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the Moho, as suggested by a number of workers on independent grounds. Put another way, the Moho is a rheological discontinuity. A second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere.     

中国大陆岩石圈等效粘滞系数的计算和讨论

大陆岩石圈的流变结构对岩石圈动力学过程有很大的影响,因此对岩石圈等效粘度的估计是大陆动力学研究中基础和重要的问题。文中对利用实验室流变实验结果估算岩石圈流变结构的计算方法中包含的多种不确定性进行了讨论,包括岩性、温度、应变速率、实验室速率数据外推到地质构造运动速率等因素对等效粘滞系数估算的影响,并以温度和应变速率的新研究成果为基础,对中国大陆地壳和上地幔等效粘滞系数做出了估计。中国中地壳等效粘滞系数一般在1021~1024Pa.s,下地壳等效粘滞系数在1021~1022Pa.s,其中青藏高原下地壳等效粘滞系数较低,约为1019~1020Pa.s;与前人研究认为青藏高原存在柔性下地壳流动的结论吻合。