北京怀柔崎峰茶-琉璃庙地区岩石磁组构特征及其构造意义

磁组构是指磁化率的各向异性。北京崎峰茶－琉璃庙地区岩石磁组构造特征是磁各向异性度Ｐ值、磁椭球扁率Ｅ＞０为主、磁面理发育而磁线理很差。本区构造变形强烈，以压扁变形为主，Ｓ－Ｎ向构造带是东盘上升、西盘下降，Ｅ－Ｗ向构造带是上盘由南向北逆冲。     

鲁西地区韧性剪切带岩石磁组构分析及其构造意义

岩石磁组构分析可用来研究岩石的组构特征及构造变形。鲁西地区韧性剪切带岩石磁组构具有磁各异性度Ｐ和磁百分率各向异性值Ｈ高、磁化率量值椭球呈压扁状、磁面理发育而磁线理不发育的特点。区内韧性剪切带变形强烈,以压扁作用为主,最大主压应力方向近ＮＥ和Ｓ－Ｎ向,以右旋运动为主。韧性剪切带形成以后,区内主要经历了热蚀变和脆性变形,韧性变形很弱     

鲁西地区韧性剪切带岩磁组构分析及其构造意义

岩石磁组构分析了可用来研究岩石的组构特征及构造变形。鲁西地区韧性剪切带岩石磁组构具有磁各异性度Ｐ和磁百分率各向异性值Ｈ高、磁化率量值椭球呈压扁状、磁面理发育而磁线理不发育的特点。区内韧性剪切带变形强烈,以压扁作用为主,最大主压应力方向近ＮＥ和Ｓ－Ｎ向,以右旋运动为主。韧性剪切带形成以后,区内主要经历了热蚀变和脆性变形,韧性变形很弱。     

柴达木盆地西部新生界磁组构特征及其构造意义

柴达木盆地西部狮子沟一带新生代沉积岩磁组构分析结果显示, 岩石磁组构具有磁面理发育、磁线理不发育、磁化率量值椭球呈压扁状的特点; 磁化率各向异性度P值不大, 反映总体构造变形相对较弱。岩石磁组构反映的应力状态总体为以NE向挤压为主, 与轴向NW的背斜构造发育相一致。该区岩石磁组构大多具有原始沉积磁组构特征, 磁面理产状大体上反映沉积岩层的层理, 同时也记录了受NE向挤压作用的痕迹。根据岩石磁组构与地层层理之间的关系分析, 柴西地区两翼不对称的狮子沟背斜具有断展褶皱性质, 其形成与下部的花土沟逆冲断层向南西方向的仰冲有关。      

阿尔泰南缘东段变形岩石磁组构分析

磁组构是指岩石磁化率的各向异性,磁组构方法已经被广泛应用于构造变形分析。阿尔泰南缘东段地区岩石磁组构特征是磁各向异性度P值大,反映本区总体韧性剪切变形强烈。萨尔布拉克—科克萨依脆性劈理化带和玛因鄂博韧性剪压构造带的E>0占优势,磁面理发育,部分样品磁线理发育,反映变形以压扁变形为主,主压应力方向为NE(NEE)向,伴随弱的左行剪切;达拉维孜—阿热勒托别韧性流变构造带和锡泊渡—富蕴深层次变晶糜棱岩带E>0和E<0均存在,磁面理和磁线理均发育,反映以剪切变形为主;其中达拉维孜—阿热勒托别构造带主压应力方向为NE(NEE)向,为左行剪切,而锡泊渡—富蕴构造带主压应力方向为SN向,为右行剪切。在达拉维孜—阿热勒托别构造带中的哈腊苏铜矿和卡拉先格尔—老山口一带一些叠加蚀变矿化的强变形岩石的P值明显减小,说明在韧性变形之后发生过矿化热液作用导致磁化率各向异性发生了均一化。结合区域构造分析,可以认为萨尔布拉克—科克萨依构造带、达拉维孜—阿热勒托别构造带和玛因鄂博构造带构成一个完整的板块碰撞聚合带,而锡泊渡—富蕴构造带可能为在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(或断片)。     

胶东大磨曲家金矿床岩石磁组构、构造变形与金矿化

在胶东地区招远-平度断裂带上的大磨曲家金矿区选取了典型的构造区域进行岩石磁组构研究。沿着断裂带在不同构造部位的36个采样点钻取了112个定向岩心样品,所有样品均沿勘探线布置。磁组构研究显示,研究区以弱磁性岩石为主,总体上,胶东群变质岩的磁化率值较高,而玲珑黑云母花岗岩的磁化率值较低,尤以碎裂程度高的强蚀变岩的磁化率值最低;磁化率各向异性方位主要为NE向挤压,磁组构所指示的构造应力场与大磨曲家矿区的区域挤压应力方向是相同的;对具不同程度矿化的81线的Au含量与80线磁组构各向异性度(P值)进行对比研究发现,P值与金品位呈负相关关系;弱矿化糜棱岩中的金矿化在磁面理发育的岩石中较为发育,成矿晚期,Au元素含量随着岩石磁性的减弱而增加,特别是在强应变后弛豫阶段矿液充填于相对张性的石英脉中Au含量最高。     

喀喇昆仑断裂带磁组构特征及其构造意义

本文讨论了喀喇昆仑断裂带的磁组组构特征。磁化率几何平均值随岩石所含矿物不同而有很大改变,校正磁各向异性度ＰＪ在变形强弱不同的岩石中有较大区别。大多数磁化率椭球体有良好的磁面理和最短轴方位,表现出强烈的压扁型应变型式;最短轴方位被视为最大主应力方向,在工作区呈ＮＥ－Ｓ工有低至中等大小的倾角,由于喀喇昆仑断裂走向ＮＮＷ＝ＳＳＥ,表明其走滑运动为右旋,在不同地区断裂两盘则有不同的垂向差异运动。同位素测年     

广东河台金矿围岩磁组构特征、年代学及与金矿化关系

河台金矿田是目前粤西、桂东南已发现最大的金矿田,大部分矿体产出在剪切带糜棱岩中,是典型的与剪切带有关的金矿床。在构造研究上,前人只注重糜棱岩的构造分析工作,而忽视了同样作为矿体围岩的混合花岗岩和片岩的研究。目前为止,矿体围岩的形成时代、变质变形特征以及与成矿之间的关系尚不清楚。我们在野外观测、显微构造分析的基础上,对河台金矿的混合花岗岩和片岩展开了磁组构分析工作。岩石磁组构分析结果显示:样品的平均磁化率Κm值总体较小,顺磁性矿物主导了样品的磁组构;磁化率各向异性度P值均1.04,范围在1.044～1.648之间;磁化率椭球体形状参数T总体0;扁率E值多1,或接近于1;在弗林图解中,数据主要集中在压扁区,少部分有剪切特征;混合花岗岩最小磁化率轴的方位表明岩石受到的主压应力呈NNW-SSE或近S-N向;片岩的磁面理呈NE向,磁线理呈NW或NNW向近水平,反映岩石受到左行走滑导致的挤压或者韧性拉长变形的特征。磁组构特征总体反映出河台地区的岩石磁化率椭球体以压扁型为主,磁面理较磁线理发育,经历了较强烈的近SN向弥散性的挤压作用和局部韧性剪切变形。此外,河台金矿的混合花岗岩LA-ICP-MS锆石U-Pb年龄为251.7±1.7 Ma。在成矿过程中,岩石校正后的磁各向异性度Pj值与金属元素Au、Cu含量呈弱的负相关关系,说明岩石矿化蚀变作用晚于构造变形作用。结合各岩石的宏观片理、显微构造和前人的年代学工作,推测河台地区地质事件的早晚顺序依次是混合岩化→剪切变形→金矿形成。     

黄河源地区磁组构特征及其地质意义

黄河源区位于青藏高原东北部,区内主要为三叠系沉积地层,发育一系列由北向南的推覆构造带,间有早期近直立的韧性剪切带。笔者对黄河源地区巴颜喀拉山群沉积岩进行了磁组构分析,结果显示岩石磁化率各向异性度P值和磁化率百分率各向异性度H值均不大,反映该地区总体韧性变形较弱,较强韧性变形仅发育于局部地段;岩石磁组构具有磁面理发育、磁线理不发育、磁化率椭球呈压扁形椭球体的特点,反映在挤压应力作用下,岩石发生了压扁变形,主应力方位主要为NNE-SSW(近SN)向,其次为NE-SW向。根据岩石磁组构分析认为黄河源地区存在两条韧性剪切带,韧性剪切带与现今湖泊水体的展布有一定的耦合关系;北部韧性剪切带沿现今黄河河谷分布,控制着扎陵湖、鄂陵湖和玛多"四姐妹湖"的展布;南部韧性剪切带沿岗纳格玛错—野牛沟一线展布,控制着岗纳格玛错和尕拉拉错等残余湖泊的分布。     

吕梁—晋北地区晚前寒武纪镁铁质岩墙群侵位方式的磁组构证据

华北克拉通区内的吕梁－晋北地区广泛发育晚前寒武纪镁铁质岩墙群，该地区近ＥＷ向和ＮＷ－ＮＮＷ向岩墙的磁组构测量结果表明，岩墙群磁各向异性与岩墙侵位的关系密切，磁化率的长轴能指示其岩浆侵位的流向，该区的岩墙群的岩浆源位于东侧的燕辽拗拉槽处，岩浆沿岩墙走向以一定爷角由ＥＳＥ朝ＮＷ－ＮＮＷ向流动，具板内裂谷模式。     

Anisotropy of magnetic susceptibility as an indicator for palaeocurrent analysis in folded turbidites (Outer Western Carpathians,Poland)

The anisotropy of magnetic susceptibility is a well-known geological proxy in revealing the directional tectonic and sedimentological features of rocks, although it can be ambiguous in situations where these two factors co-occur. This paper demonstrates the usefulness of the anisotropy of magnetic susceptibility in determining palaeotransport directions in turbiditic rocks that underwent subsequent thrusting and folding. This study demonstrates that the magnetic lineation is largely unsuitable as a palaeocurrent direction proxy, and suggests that the imbrication of magnetic foliation is better in such cases. Moreover, the anisotropy of magnetic susceptibility results were analyzed in reference to a joint and fold study within the framework of the regional structural geology. Magnetic fabric investigations were conducted in the eastern part of the Outer Western Carpathians (south-east Poland). During the study, a total of 191 oriented palaeomagnetic samples were collected from three outcrops (Nasiczne, Dwernik and Hoczew) in the Krosno Beds, Silesian Unit. For the purpose of sedimentological analysis, 121 m of turbidite successions were documented and 126 directional sedimentary structures were measured. The magnetic anisotropy of sandstones revealed typical sedimentary fabrics, often overprinted by variably intense tectonic deformation. Oblate susceptibility ellipsoids from Nasiczne showed tilt coherent with the palaeoflow direction, whereas the rocks from Dwernik and Hoczew contained triaxial magnetic fabric developed during compressional palaeostress. This paper suggests that medium-grained and coarse-grained sandstones, preferably with high mica content, are the most suitable for palaeotransport reconstructions among the studied lithologies.     

Magnetic fabrics in garnet peridotites–pyroxenites and host felsic granulites in the South Bohemian Granulites (Czech Republic): Implications for distinguishing between primary and metamorphism induced fabrics

In the high-grade Moldanubian Zone of the European Variscides, numerous bodies of ultramafic rocks occur embedded in granulite. The anisotropy of magnetic susceptibility and its low-field variation as well as the anisotropy of magnetic remanence were used to investigate magnetic fabrics of some ultramafic bodies and host granulite. In granulite, the magnetic foliation is roughly parallel to the metamorphic foliation and the magnetic lineation is near the mineral alignment lineation. In ultramafite, the magnetic foliation is relatively scattered spatially, but mostly oriented in a different way than that in granulite. The magnetic lineation is also scattered, but still relatively well defined spatially. Again, its orientation is mostly different than that of granulite. The magnetic fabric in ultramafic rocks is therefore different from that in the host granulite even though both rock types underwent at least partially common structural history. The componental movements forming the granulite fabric, mostly during amphibolite facies retrograde metamorphism, were evidently not intensive enough to strongly overprint the magnetic fabric of ultramafite. The ultramafite is therefore strong enough to maintain its pre-metamorphism fabric even at such high temperatures and pressures that are characteristic of high amphibolite facies retrograde metamorphism.     

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     

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

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.     

岩石磁组构在断裂变形性状与期次研究中的应用——以广西博白-合浦断裂为例

岩石磁化率椭球体的三个轴与应变椭球体的三个轴方向相平行,并具有一定的共构关系.变形岩石的磁组构参数P、T、F、L以及磁化率椭球体主张量方向等可以用来定量地表征岩石变形的性状及期次.本文通过实测和计算27个样品的磁组构参数,研究了博白-合浦断裂带的变形性状与期次,结果表明:博白-合浦断裂带大致经历了三期构造变形作用,不同时期具不同性质的构造变形.变形性状分别表现为韧性、韧-脆性及脆性变形,应变行为分别表现为平面、非平面和线性应变.     

藏东昌都地区侏罗纪岩石磁组构研究及其构造意义

本文对藏东昌都地区侏罗纪汪布组、东大桥组和小索卡组红层共71个采点开展了磁组构(AMS)研究。磁组构测试结果表明,早侏罗世汪布组岩石磁线理较磁面理发育,磁化率各向异性度较高,磁化率椭球最小轴K3散布于层面缩短方向,代表了与构造成因相关的磁组构;中侏罗世东大桥组和晚侏罗世小索卡组岩石则磁面理较磁线理发育,磁化率各向异性度较低,磁化率椭球最小轴K3与层面近垂直,指示了原生沉积磁组构。早侏罗世汪布组地层的磁组构揭示了其构造应力场方向为NE-SW向。中侏罗世东大桥组的磁组构指示了其沉积时的古水流方向为SE向(138.3°),而晚侏罗世小索卡组磁组构指示了其沉积时的古水流方向为NNW向(328.3°)。古水流方向的明显变化揭示了昌都地区从中侏罗世到晚侏罗世沉积物物源发生了相应的转变,表明昌都地区南早北晚的隆升过程。     

长江中游堤防溃口沉积物的磁组构特征

通过对 1998年 8月 1日湖北 竹牌 洲湾溃口沉积物的系统采样和磁组构测量与计算 ,发现溃口沉积物的磁组构特征为 :由溃口扇的扇顶→扇缘 ,磁组构参数各向异性度 P、磁面理度 F、磁线理度 L、水流速度函数因子 Fs的统计平均值均具有由大逐渐变小的特点 ;在溃口扇的不同部位磁化率量值椭球的主轴平均方向具有不同的特点 ,其规律是 :在扇顶或扇缘处平均方向变化较大 ,尤其在扇缘处 ,最大磁化率主轴方向比较随机 ,没有明显的主方向 ,而在扇中磁化率量值椭球的主轴平均方向比较稳定 ,最大主轴的优选方向比较明显。初步探讨和建立了长江中游现代溃堤溃口沉积物的磁组构特征识别标志