阿尔泰富蕴-青河一带东段变形岩石X光组构分析

通过对新疆阿尔泰南缘东段地区主要构造带变形岩石的X光岩组分析,认为该区岩石变形比较强烈,石英变形机制以中低温底面型或近底面型滑移为主,部分为中高温柱面Ⅰ型滑移系。属于中浅—中等层次(10～15km,T=300～450℃,p=0.25～0.40GPa)的韧脆性—韧性变形。达拉维孜-阿热勒托别剪切流变构造带和库尔提-玛因鄂博韧性剪压变形带变形的物理化学条件相似,结合区域地质分析,这2个带与萨尔布拉克-科克萨依脆性挤压劈理化带一起可能组成一个完整的板块(微陆块)聚合变形带。而锡泊渡(635水库)-富蕴变晶糜棱岩带岩石变形的条件明显不同,温度压力偏高,说明其具有不同的演化历史,可能为古生代期间被强烈改造的具有前震旦纪结晶基底的微大陆的残留。     

电子背散射衍射(EBSD)技术在地壳构造变形研究中的应用

电子背散射衍射(EBSD)技术是岩组学研究的一项革命性新技术。该技术可以对传统的岩石薄片进行分析,实用性高,观测精度达到亚微米级别。配合扫描电子显微镜、阴极发光、波谱、能谱分析设备,EBSD技术可以对透明和非透明的任何对称性晶体进行取向测量,快速获取晶体显微结构、微区成分与晶体学参数,可以对晶体开展形貌观察、晶体优选方向(CPO)、取向差分析、物相鉴定、应变测量、晶界分析、变形机制、位错滑移系、晶内变形、温压条件研究。结合聚焦离子束(FIB)技术,可以获取矿物的三维结构图像。对地壳的主要矿物进行组构分析,结合野外矿物变形特征与试验岩石学研究成果,可以开展地壳构造运动学、动力学的研究。本文介绍岩组学的研究历史,以及EBSD技术在地壳常见矿物石英、钾长石、斜长石、角闪石以及假熔岩构造变形研究中的最新进展与典型实例,并对EBSD研究结果中一些潜在的不确定性因素进行了讨论。     

Anisotropy of magnetic susceptibility of eclogites: mineralogical origin and correlation with the tectonic fabric (Cabo Ortegal,Spain)

Abstract

The fabric and the anisotropy of magnetic susceptibility of the Cabo Ortegal eclogite (NW Spain) are studied. These mafic rocks were metamorphosed and deformed under high pressures and temperatures between 390 and 370 Ma in a subduction/collision tectonic setting. Massive eclogite slices and deformed eclogite in shear zones have bulk magnetic susceptibilities of 31 to 82·10^?5 S.I. and 28 to 75·10^?5 S.I., respectively. The paramagnetic mineral fraction is the principal magnetic susceptibility carrier. This fraction includes notably garnet and clinopyroxene as matrix minerals, and ilmenite and rutile as accessory constituents. Though magnetic anisotropy degree varies between 3.1 % and 6.6 %, variations of this parameter in each rock type are marked. In the deformed eclogite, magnetic lineation (K_max) and the pole to the magnetic foliation (K_min) are coaxial and coincident with macroscopic petrofabric elements (foliation and lineation). In the massive eclogite, the magnetic fabric is dispersed along the principal structural planes and inversions are associated with samples with small degrees of anisotropy. The anisotropy of magnetic susceptibility is interpreted as being due to the crystallographic preferred orientation and spatial organisation of the polymineralic aggregate. Relating the evolution of the symmetry of magnetic fabric to the symmetry of petrofabric or deformation is rather precluded since susceptibility has multiple origins and bulk magnetic fabric is due to minerals of different symmetry. © Elsevier, Paris     

Scales of deformation partitioning during exhumation in a continental subduction channel: A petrofabric study of eclogites and gneisses from NW Spain (Malpica‐Tui Allochthonous Complex)

Deformation partitioning is identified as the fingerprint of late Palaeozoic continental subduction that affected various lithologies whose field relationship, thermobarometric and petrofabric features are closely related. Different modes of deformation partitioning can be identified within medium temperature, high‐P eclogite lenses, between them and the host gneisses, and within the latter. Development of foliations and lineations with a coherent attitude in all these rocks and their related structural petrology demonstrate that eclogite enclosures and their country rocks underwent a common, pervasive deformational event. The published P–T stability fields of the eclogite phases that define the microscopic fabric are used to define the metamorphic conditions prevailing during the deformation event and relate it to the subduction process. The mineral equilibria of the gneisses (ortho‐ and paragneisses) fail to record the full range of those P–T conditions, but the field relationships show that eclogites were originally basic dykes emplaced in acid igneous rocks and demonstrate that the eclogites and gneisses shared a common tectonometamorphic evolution. Deformation partitioning within the latter occurred at variable scales and involved (1) meso macroscale preservation of virtually undeformed metagranite bodies, surrounded by (2) pervasively foliated and lineated gneisses, and (3) the simultaneous microscale operation in the latter of ductile and brittle–ductile mechanisms at conditions above 500°C and below 1.5 GPa. A subduction channel tectonic setting is proposed to explain the subduction of upper to mid‐crustal igneous rocks and exhumation subsequent to high‐P metamorphism. Its currently accessible dimensions, and its organization into several lithotectonic units mapped as nappes support tectonic amalgamation of units several km³ in volume. Maximum burial in the subduction channel likely reached depths shallower than the lithostatic pressure implied by geobarometric calculations, possibly conditioned by a sudden pressure drop during the initial retrogression stages accompanying exhumation.     

鲁西地区韧性剪切带显微构造研究及岩组分析

通过对鲁西地区韧性剪切带显微构造及岩组特征等的研究,认为该区韧性剪切带具有多期次、多方向、多性质的变形特点,韧性变形主体具有右行剪切性质,最大主压应力方位为ＮＥＮＥＥ。从岩组分析结果可知,区内岩石韧性变形较强,并且复杂,变形以压剪性变形为主,石英变形机制主要为柱在滑移,韧性变形时温度较高。石英自由位位错密度法应力估算结果说明,区内最大差应力为７５．４ＭＰａ,平均值６８．４５ＭＰａ,金矿体的赋存与构     

利用岩矿记忆信息恢复基岩潜山裂缝储层形成的机制

基岩储层具有当今油气储层研究的两大难题,即特殊且致密的基质岩性和储集空间。变质岩作为基岩岩性之一,其储集空间－裂缝的形成与动力作用密切相关。构造动力是致密基岩产生裂缝的主要因素,岩石矿物将记忆其在地质历史过程中所经历的动力特征。在准确采取定向岩心的基础上,利用声发射技术（ＡＥ）和岩组学方法可以恢复基岩储层在地质历史过程中所受应力期次和应力方向,从而了解储层的动力机制。应用上述原理恢复辽河大民屯凹陷     

河北省衡水地区第四纪中—晚期标准地层剖面的建立及其地质含义

依据河北省衡水市西北郊区纪家庄、赵家屯井孔岩心,采用岩性描述、岩相划分、地层测年、古气候孢粉样品分析及钻孔间地层对比等方法,结合前人的研究成果,获取如下认识:(1)纪家庄井孔(ZK1)、赵家屯井孔(ZK2)岩心揭示出衡水地区全新统厚度为8~9 m,上更新统厚度为31~36 m,中更新统厚度为72~75 m;(2)依据各井孔及岩心所揭示的同一岩组底界海拔高程,推测研究区位于向东方向缓倾的古斜坡带上;(3)以岩石地层学、年代地层学为主导,结合以气候地层(孢粉地层)、宏观特征为主并与微观标志相结合的综合划分原则,多井孔岩心揭示出研究区同一地质年代岩组厚度相当,且中更新世以来处于较为稳定的整体沉降环境中,不存在明显的差异升降运动。     

Deformation, high-pressure metamorphism and exhumation of ultramafic rocks in a deep subduction/collision setting (Cabo Ortegal, NW Spain)

New petrological and microstructural data from various metaperidotite 'boudins' within large ductile shear zones in the Cabo Ortegal allochthonous complex in NW Spain have important implications for the tectonic models of the area. The peridotites (mylonitic garnet harzburgite, Ti-clinohumite and magnesite–olivine orthopyroxenite) contain mineral assemblages that equilibrated at high- to ultra-high-pressure metamorphic conditions as well as microstructures of tectonic origin formed at temperatures well above 800  °C. Olivine and orthopyroxene fabrics resulted from flow at high temperature (>1000  °C) and solid-state non-coaxial plastic flow at intermediate temperature (800–900  °C). Flow caused dynamic recrystallization and formation of moderate to strong lattice preferred orientations under low to moderate differential stresses and strain rates characteristic of upper mantle and deep crustal deformation. The microstructures and textural relationships suggest that the mylonitic garnet harzburgite represents mantle fragments with lithospheric and asthenospheric imprints, whereas the olivine orthopyroxenite resulted from serpentinite burial to depths where it acquired a characteristic high/ultra-high-pressure metamorphic signature. Both types of ultramafites converged to a common site in a subduction zone that was later incorporated during continental collision to the NW Iberian Massif as exotic, allochthonous complexes that record structural and metamorphic evidence of the earliest phases of the Hercynian orogeny.