几内亚福雷卡里亚YML铁矿区构造变形特征及控矿规律研究

Yemsaliya(简称YML)铁矿区位于几内亚福雷卡里亚省东南部,Rokelide造山带北部,其太古宙地体中赋存有丰富的条带状铁矿(BIF).研究区内岩矿层由一系列复式褶皱构成,北西走向,主体是复式向斜形态;区内发育三种面理,分别为早期的褶皱层理S0、后生面理S1和后期的褶劈理S2.根据数据分析,结合构造变形特征、岩性特征、构造规模及发育程度可将区内的褶皱构造变形和面理置换过程划分为前期和后期.从前期到后期,褶皱构造样式从明显的紧闭复合同斜型向开阔的复合型过渡,岩石也从塑性向脆性过渡.区内发生的面理置换类型为,前期S1置换S0;后期S2置换S1和S0,前期的置换作用最强.在深入剖析YML铁矿区构造变形特征的基础上,总结出一套褶皱构造变形和面理置换对铁矿床的控制规律,对同类型矿床的找矿工作具有借鉴意义.     

汶川─理县志留系茂县群无根钩状褶皱构造初步解析

钩状褶皱又称无根钩状褶皱，是区域变质岩中广泛发育的特有构造形态之一，与面状构造置换密切相关。对它的研究，有助于恢复大型褶皱形态和变质岩原岩产状。本文初步探讨了四川汶川─理县志留系茂县群中广泛发育的无根钩状褶皱的形态、产状、成因和与大型褶皱构造的关系。     

云南墨江金矿含镍金绿色蚀变岩的构造地球化学特征及时空演化

采用构造变形筛分、同位素地球化学定年约束和构造蚀变岩的常量 微量元素地球化学研究等方法,对墨江镍金矿床中含金镍绿色蚀变带进行详细研究,探讨其形成和时 空演化规律,以及与金、镍成矿关系,提出本区含镍金绿色蚀变带形成与演化可分为三个期次:早期含镍金绿色蚀变带形成于(251 9±4 32)Ma,产于韧性剪切带中,形成含铬绢云母 绢云母(S2)组成的切层剪切面理;中期含镍金绿色蚀变岩形成于燕山早期(169 37～180 6Ma),产于高角度脆韧性剪切带中,形成铬绢云母 含铬绢云母组成的透入性剪切面理换(S3)和绿泥石拉伸线理;晚期含金绿色蚀变糜棱岩形成于燕山晚期(71 14～149 98Ma),产于左旋走滑脆韧性剪切带中,发育铬伊利石(S4)和铬绿泥石(S4)组成透入性剪切变形面理置换,与脆韧性剪切带的主体产状一致,韧性剪切构造带内发育,走滑构造带中十分发育,形成褶皱变形带(倾竖褶皱、鞘褶皱)及含金蚀变岩。     

圆锥状褶皱的几何分析

长期以来,地质学家习惯于把不同类型和不同成因的褶皱的基本形态当作圆柱状几何性状处理,建立了褶曲构造的基本几何要素,并且以此作为划分构造均匀区段的几何准则。从最近十余年来关于区域变质造山带的大量观测研究证明,还有另一种褶皱,即圆锥状褶皱,广泛发育于褶皱复杂的变质岩系之中,在不同尺度上显示其控制作用和对区域构造格架的影响。     

湘东北煤田滑脱构造及其区域地质背景

湘东北煤田构造复杂,主要表现为褶皱和断裂,尤以逆冲推覆和滑覆构造较为发育,多期次的构造叠加、切割及剥蚀,呈现构造窗和飞来峰,使含煤岩系在平面上零星分布。探讨本区滑脱构造发育的区域地质背景,运用推覆构造理论深入分析了引起逆冲推覆构造和滑覆构造的形成机制,对掌握煤炭资源分布规律、评价湖南煤炭资源潜力有一定的指导意义。     

根据煤质特征探讨滕南煤田断层形成的时代

滕南煤田为全隐蔽式煤田,位于山东西南部。含煤地层为石炭二叠系。煤田基盘为中奥陶统马家沟组,上覆地层为上侏罗统和第四系。区域构造发育史与华北其它地区相似,燕山运动形成本区构造格局。煤田内褶皱平缓,以断裂发育为特征,并有浅成岩体侵入。本区构造格局如图1。     

陕西省勉县七里沟地区多金属成矿地质条件及找矿前景分析

勉县七里沟地区位于汉江大断裂与略褒大断裂交汇部位的勉略阳三角区内,各种褶皱与次级断裂构造发育,侵入岩及各种脉岩分布广泛,并产出有小型铅锌重晶石矿及铜金矿点.通过对区内地层、构造、岩浆活动、变质作用、矿化特征的综合分析,结合R型聚类分析结果、构造地球化学特征及区内断裂构造控矿特点,划分出南部七里沟-艾叶口多金属成矿区和北西部张家坪-黑沟铜金成矿区两个有望找矿区段,初步认为本区具有寻找大型有色金属矿的基本条件.     

太行山中北段褶皱构造序列

太行山中北段中－深变质岩区的褶皱构造变形复杂，不同期次间叠加改造强烈，构造置换作用明显，作者采用变质岩区构造解析方法，在观察，测量，分析了大量构造面，线组构的基础上，划分出５期褶皱构造，建立了本区的构造变形序列，并认为构造变形经历了从强塑性变表到韧脆性变形的演化过程，反映出地壳从纵向增厚作用转变为变质核杂岩隆升的演化过程。     

藏北羌塘中部晚古生代增生杂岩的发现及其地质意义

西藏中部羌塘变质岩带发育复理石碎屑建造和片理化玄武岩建造,都经历了强烈的构造置换作用;还发育早—晚古生代大理岩岩片、无根勾状褶皱和大理岩与蓝片岩组成的同斜褶皱,不同时代的榴辉岩呈岩块出露。这些地质体呈岩片产出,经历了多期构造叠加和置换,原岩总体为碎屑岩、泥质岩、硅质岩、碳酸盐岩及枕状玄武岩、辉长岩建造。宏观上发育明显的区域性置换面理,为典型的造山带增生杂岩。     

藏北羌塘中部晚古生代增生杂岩的发现及其地质意义

西藏中部羌塘变质岩带发育复理石碎屑建造和片理化玄武岩建造,都经历了强烈的构造置换作用;还发育早—晚古生代大理岩岩片、无根勾状褶皱和大理岩与蓝片岩组成的同斜褶皱,不同时代的榴辉岩呈岩块出露。这些地质体呈岩片产出,经历了多期构造叠加和置换,原岩总体为碎屑岩、泥质岩、硅质岩、碳酸盐岩及枕状玄武岩、辉长岩建造。宏观上发育明显的区域性置换面理,为典型的造山带增生杂岩。     

辽宁省本溪北台铁矿的构造控制规律——运用构造解析解决找矿问题的一个实例

本溪北台铁矿为产于太古宙鞍山群中的BIF.矿体形态、产状均甚复杂.构造解析表明,这种复杂性是由于经受了至少三期构造变形所引起的.本文在详细剖析各期构造变形及其对铁矿体的控制规律的基础上,提出了深部找矿方向,已得到实践验证,经济效果显著.     

构造置换及其控矿规律——以吉林板石沟铁矿为例

 强烈的塑性变形使华北地台东北部太古宙鞍山群中的吉林板石沟铁矿发生强烈的构造置换;造成原始仅有二三层的铁矿褶皱重复,在X(包络线)、Y(枢纽线)方向均被拉断,形成透镜状的复式褶皱勾状体。现有的19个矿组均为这种复式褶皱的转折端,并多呈"Z"型不对称形式。根据以上控矿规律本文提出两个找矿方向,一是包络线方向,另一是枢纽线方向,对1、3矿组具体地做了勘探设计。目前本文的勘探设计已得到勘探验证,新增铁矿储量数千万吨。     

鞍山附近“樱桃园组”的构造样式及其时代讨论

本文区分了“樱桃园组”岩石在元古主构造旋回的三幕变形,详细描述了各幕SFL组合和按区段进行了投影。主变形幕D₁的构造最发育,F₁控制着本区的岩性分布。构造序列及样式变化显示由高塑性向脆性的变形格式。本组与下伏的太古鞍山群变粒岩在构造序列、样式和变质相上都有显著差异,过去许多地质学家把二者混划为一个单位,统名“鞍山群”,属太古宙。但本组与上覆的辽河群(上元古)的构造样式和变质相却相似,故其时代相当于早元古Ferrian期。     

构造置换及其控矿规律——以吉林板石沟铁矿为例

强烈的塑性变形使华北地台东北部太古宙鞍山群中的吉林板石沟铁矿发生强烈的构造置换;造成原始仅有二三层的铁矿褶皱重复,在X(包络线)、Y(枢纽线)方向均被拉断,形成透镜状的复式褶皱勾状体。现有的19个矿组均为这种复式褶皱的转折端,并多呈"Z"型不对称形式。根据以上控矿规律本文提出两个找矿方向,一是包络线方向,另一是枢纽线方向,对1、3矿组具体地做了勘探设计。目前本文的勘探设计已得到勘探验证,新增铁矿储量数千万吨。     

The Horto-Baratinha itabirite-hosted iron ore: A basal fragment of the Espinhaço basin in the eastern São Francisco Craton

The Horto-Baratinha (HBD) iron ore deposit is located at the eastern border of São Francisco Craton, comprising BIF-hosted high-grade bodies (>60 wt.% Fe) associated with polydeformed quartz-mica-schists, amphibole-schist of Statherian maximum deposition age, enclosed by Statherian granitoids of the Borrachudos Suite and Neoarchean gneiss. All the sequence is crosscut by undeformed dikes and sills of pegmatitic bodies probably formed during Late Ediacaran-Cambrian. The metasedimentary sequence is stratigraphically correlatable with the Orosirian-Statherian Serra da Serpentina and Serra de São José Groups that comprise the basal units of the Espinhaço Supergroup and was intensively segmented into distinct tectonic blocks. The sedimentary/diagenetic bedding of the metamorphosed BIF (itabirite) is generally transposed by an axial planar schistosity. The lamellar hematite from itabirite is the oldest iron oxide generation, which was formed during the syn-deformational stage, parallel-oriented to the rock foliation. The (keno)magnetite grains from itabirite, iron ore and pegmatite bodies developed as idioblasts that grew over the foliation formed during late and post-deformational stages. Magnetite oxidizes subsequently to martite and granular hematite. Coarse lamellar hematite crystals randomly oriented in the border of the pegmatitic bodies also formed during the post-deformational stage due to hydrothermal reaction with itabirite. The country rocks have undergone at least three stages of deformation developed during the syn-collisional and late-collisional (Ediacaran to early-Cambrian) phases of the Brasiliano Orogeny: stage 1 with the development of a pervasive foliation (S₁), parallel to axial plane to tight folds and transposition of all sedimentary structures; stage 2 with folding of S₁; stage 3 with refolding of S₁. Both fold systems interfere with each other making up a dome and basin refolding shape. During the late-collisional (Ediacaran to early-Cambrian) and post-collisional/gravitational collapse (Cambrian) the sequence was intruded by anatectic pegmatitic bodies, which are part of the Eastern Brazilian Pegmatite Province, one of the most significant pegmatitic regions worldwide. The fluid related with these intrusions could be related with the Si leaching, crystallization of magnetite and granular hematite, and consequent formation of high-grade iron bodies.     

山西太古代——中生代构造应力场

本文采用历史分析与力学分析相结合的原则,研究山西太古代至中生代五次主要构造运动的形变特征、主应力方向及分布规律。中太古代晚期（阜平运动）以SSW向挤压为主;晚太古代末期（五台运动）、早元古代末期（吕粱运动）和侏罗纪（燕山运动）受SE—SEE向挤压;白垩纪（四川运动）以SSW向挤压为特征。五次构造运动的最大主压应力均呈近水平方向。     

Tectonic Imprints of the Hazara Kashmir Syntaxis on the Mesozoic Rocks Exposed in Munda,Mohmand Agency,Northwest Pakistan

Two well-developed mesoscopic folds, D_2 and D_3, which postdate the middle amphibolite metamorphism, were recognized in the western hinterland zone of Pakistan. NW–SE trending D_2 folds developed during NE–SW horizontal bulk shortening followed by NE–SW trending D_3 folds, which developed during SE–NW shortening. Micro- to mesoscopically the NW–SE trending S2 crenulation cleavage, boudins and mineral stretching lineations are overprinted by D_3. The newly established NW–SE trending micro- to mesoscopic structures in Munda termed D_2, which postdated F_1/F_2, is synchronously developed with F3 structures in the western hinterland zone of Pakistan. We interpret that D_2 and D_3 folds are counterclockwise rotated in the tectonic event that has evolved the Hazara Kashmir Syntaxis after the main phase Indian plate and Kohistan Island Arc collision. Chlorite replacement by biotite in the main matrix crenulation cleavages indicates prograde metamorphism related with D_2. The inclusion of muscovite and biotite in garnet porphyroblasts and the presence of staurolite in these rocks indicate that the Barrovian metamorphic conditions predate D_2 and D_3. We interpret that garnet, staurolite and calcite porphyroblasts grew before D_2 because the well developed S2 crenulation cleavage wraps around these porphyroblasts.     

Structural evolution of Mesozoic complexes in Western Chukotka

Detailed structural investigations were carried out in the Pevek area in order to verify the tectonic evolution of the Mesozoic thrust and fold belt in Chukotka. South-vergent F₁ folds in Triassic rocks were proved to be the earliest structures formed during the first deformation stage DI. These structures were deformed by north-vergent folds F₂ that were formed during the second deformation stage DII. North-vergent folds are the main structures of the Jurassic–Lower Cretaceous complex. The fold structures of the first two stages are deformed by shear folds F₃ finishing the stage DII. All these structures are deformed by submeridionally trending normal faults referred to the deformation stage DIII.     

Structure of the Nagavali Shear Zone,Eastern Ghats Mobile Belt,India: Correlation in the East Gondwana Reconstruction

Interpretation of satellite data in combination with regional field traverses, delineating the major structural features such as the Nagavali and Vamsadhara Shear Zones and associated fold patterns, provides a synoptic picture of the regional tectonic framework of the central part of the Eastern Ghats Mobile Belt. The complex geology of the study area can broadly be grouped into three distinct deformational events. D₁ fabrics represented by near flat-lying gneissic foliations, paralleling the lithological banding are best preserved in low strain domains and are related to Middle to late Archaean thrusting (3000-2600 Ma). The second deformational event D₂ is characterized by the development of shear zones and associated mylonitic fabrics and magmatism probably during 1450-850 Ma. The Pan-African thermal (500-550 Ma) overprint is restricted to shear zones in the form of reworking. Regionally, the central part of the Eastern Ghats Mobile Belt can be divided into five distinct structural domains based on structural geometry of folds, foliations and lineations. A three-dimensional block diagram of the Nagavali and Vamsadhara Shear Zones involving fold-thrust tectonics associated with westward thrusting is presented here. A correlation of Pan-African Shear Zones in adjacent continents wrapping around the Archaean Dharwar Craton in the reconstruction of Rodinia and East Gondwana supercontinent suggests an east-west convergence.     

Archaean tectonics in the Agnew supracrustal belt,Western Australia

The Agnew supracrustal belt consists of a greenstone sequence (interlayered metabasalt, differentiated gabbroic sills, ultramafic bodies, and black volcanogenic sediment) unconformably overlain by granitoid-clast conglomerate and meta-arkose. The base of the preserved sequence is intruded by grey tonalite with a crudely concordant upper contact, and by small discordant bodies of leucogranite.An early deformation (D1) produced isoclinal folds and a regional penetrative foliation. These structures were probably gently dipping when formed. D2 produced large-scale NNW-trending upright folds, a regional foliation, and a vertical N-trending ductile fault on the west side of the belt. D2 structures indicate a combination of ENE-WSW shortening, and right-lateral shear along the ductile fault. Both D1 and D2 were accompanied by metamorphism under upper greenschist to lower amphibolite facies conditions.The interpreted sequence of tectonic events is (1) deposition of the greenstone sequence on an unknown basement; (2) intrusion of large volumes of tonalite, separating the supracrustal rocks from their basement; (3) erosion of mafic rocks and tonalite to produce the clastic sedimentary sequence; (4) the first deformation; (5) intrusion of small volumes of leucogranite; (6) the second deformation.The bulk of the granitoid rocks were emplaced before the first recognisable deformation. Thus the granitoid magma cannot have been produced by partial melting of previously downbuckled ‘greenstone belt’ rocks, nor can the large-scale upright folds (D2) be a result of forceful emplacement of the magma — two common postulates for Archaean terrains. The D2 folds are closely related to the ductile fault bounding the zone: these structures, which give the present N-trending tectonic belt its form, are the youngest features in the terrain.