柴北缘锡铁山地区滩间山群构造变形分析

初步构造变形分析表明 ,柴北缘锡铁山地区的早古生代变质火山岩系 -滩间山群在加里东期碰撞造山过程中经历了两期构造变形 :第一期为垂直造山带的挤压缩短变形 ,形成一系列紧闭褶皱、区域片理和大型韧性剪切带 ;第二期为平行造山带的挤压缩短变形 ,形成区域透入性共轭破劈理或膝折带。这两期变形是柴北缘加里东期碰撞造山带的斜向碰撞造山过程中不同阶段变形特征的体现。这种构造型式可能对于认识斜向碰撞造山带的构造动力学的转换过程具有重要意义。     

京北琉璃庙地区变质杂岩变质变形特征

琉璃庙地区变质杂岩主要由变质上壳岩、变质深成侵入杂岩及其脉岩群组成.它们多数经韧性变形改造形成各种类型糜棱岩和构造片岩.研究表明,变质上壳岩原岩主要以钙碱性火山(熔)岩为主.本区变质杂岩经历了三期变质变形作用,即高角闪岩相区域变质作用形成大型复式同斜紧闭褶皱;绿帘角闪岩相动力变质作用及强烈的韧性变形,形成了以蓝闪石为特征的不同强度的糜棱岩带;绿片岩相动力变质作用和韧脆性变形作用.     

PETROLOGY AND AGE OF THE KINNAR KAILAS GRANITE:EVIDENCES FOR AN ORDOVICIAN POST-OROGENIC EXTENSION IN THE HIGHER HIMALAYAN CRYSTALLINE, SUTLEJ, INDIA.

PETROLOGY AND AGE OF THE KINNAR KAILAS GRANITE:EVIDENCES FOR AN ORDOVICIAN POST-OROGENIC EXTENSION IN THE HIGHER HIMALAYAN CRYSTALLINE, SUTLEJ, INDIA     

内蒙古中部中元古代韧性剪切变形及其形成的构造背景

内蒙古中部新太古界色尔腾山岩群、新太古代和古元古代片麻状英云闪长岩(基底岩系)与白云鄂博群长城系都拉哈拉组、尖山组和渣尔泰山群长城系书记沟组、增隆昌组(盖层)之间的韧性剪切变形特征相同。糜棱面理走向近东西,总体倾向北,倾角变化较大。不同区域的糜棱面理上发育程度不同的矿物拉伸线理,其指示的运动学方向为上盘岩系向北(北西或北东)的斜落。接触带基底岩系由糜棱片岩、糜棱岩等组成;接触带盖层下部岩系由糜棱岩化石英岩、糜棱岩化灰岩、板岩等组成,盖层上部岩系书记沟组、都拉哈拉组石英岩发育掩卧褶皱,尖山组、增隆昌组板岩和灰岩发育石香肠构造和褶叠层构造。变质相由基底岩系的低角闪岩相—高绿片岩相逐渐过渡为上覆盖层的低绿片岩相。沉积特征、变质变形特征、运动学特征等均显示白云鄂博群、渣尔泰山群长城系为同一被动陆缘沉积,韧性剪切变形是同一期构造作用的产物。形成机制为长城系相对于基底岩系的大规模向北(北西或北东)伸展拆离,形成于低温、低压环境,起始时间为长城纪末期(1400Ma)。内蒙古中部中元古代韧性剪切、隆升、裂谷作用是同一伸展构造作用不同阶段的产物。     

大别山超高压变质岩的变形历史及折返过程

大别山南部的超高压变质岩在其形成及折返过程中经过5期变形。D₁变形为榴辉岩相前变形,形成于扬子板块北缘陆壳基底的俯冲过程中;D₂变形形成于折返初期(220-210Ma)即超高压变质岩在浮力驱动下折返至下地壳底部的过程中,变形以块状榴辉岩的糜棱岩化及层状榴辉岩和基质的紧密-同斜褶皱为特征;D₃变形发生在折返中期(200-180Ma)即超高压变质岩在南北陆块持续碰撞作用下被挤出并向北逆冲折返至中地壳的过程中,变形以榴辉岩的布丁化和基质的强烈韧性剪切变形为特征;D₄变形是折返晚期(130-110Ma)超高压变质岩在地壳浅部伸展体制下向南滑脱所致;在折返至近地表时,超高压变质岩受到NE向断层(D₅)的切割。     

A Large-Scale Palaeozoic Dextral Ductile Strike-Slip Zone:the Aqqikkudug-Weiya Zone along the Northern Margin of the Central Tianshan Belt,Xinjiang,NW China

The nearly E-W-trending Aqqikkudug-Weiya zone, more than 1000 km long and about 30 km wide, is an important segment in the Central Asian tectonic framework. It is distributed along the northern margin of the Central Tianshan belt in Xinjiang, NW China and is composed of mylonitized Early Palaeozoic greywacke, volcanic rocks, ophiolitic blocks as a mélange complex, HP/LT-type bleuschist blocks and mylonitized Neoproterozoic schist, gneiss and orthogneiss. Nearly vertical mylonitic foliation and sub-horizontal stretching lineation define its strike-slip feature; various kinematic indicators, such as asymmetric folds, non-coaxial asymmetric macro- to micro-structures and C-axis fabrics of quartz grains of mylonites, suggest that it is a dextral strike-slip ductile shear zone oriented in a nearly E-W direction characterized by "flower" strusture with thrusting or extruding across the zone toward the two sides and upright folds with gently plunging hinges. The Aqqikkudug-Weiya zone experienced at least two stages of ductile shear tectonic evolution: Early Palaeozoic north vergent thrusting ductile shear and Late Carboniferous-Early Permian strike-slip deformation. The strike-slip ductile shear likely took place during Late Palaeozoic time, dated at 269(5 Ma by the40Ar/39Ar analysis on neo-muscovites. The strike-slip deformation was followed by the Hercynian violent S-type granitic magmatism. Geodynamical analysis suggests that the large-scale dextral strike-slip ductile shearing is likely the result of intracontinental adjustment deformation after the collision of the Siberian continental plate towards the northern margin of the Tarim continental plate during the Late Carboniferous. The Himalayan tectonism locally deformed the zone, marked by final uplift, brittle layer-slip and step-type thrust faults, transcurrent faults and E-W-elongated Mesozoic-Cenozoic basins.     

QUATERNARY GROWTH FOLDS IN THE JIUXI BASIN AT THE NORTHEASTERN MARGIN OF THE QINGHAI—XIZANG PLATEAU

QUATERNARY GROWTH FOLDS IN THE JIUXI BASIN AT THE NORTHEASTERN MARGIN OF THE QINGHAI—XIZANG PLATEAUgrants 49732 0 90and 496 0 2 0 36fromtheNSFofChina     

TECTONIC CHARACTERISTICS AND EVOLUTION OF THE QIANGTANG BASIN IN NORTHERN TIBET PLATEAU

TECTONIC CHARACTERISTICS AND EVOLUTION OF THE QIANGTANG BASIN IN NORTHERN TIBET PLATEAU     

Tectonics of the Longmen Shan and Adjacent Regions,Central China

The Longmen Shan region includes, from west to east, the northeastern part of the Tibetan Plateau, the Sichuan Basin, and the eastern part of the eastern Sichuan fold-and-thrust belt. In the northeast, it merges with the Micang Shan, a part of the Qinling Mountains. The Longmen Shan region can be divided into two major tectonic elements: (1) an autochthon/parautochthon, which underlies the easternmost part of the Tibetan Plateau, the Sichuan Basin, and the eastern Sichuan fold-and-thrust belt; and (2) a complex allochthon, which underlies the eastern part of the Tibetan Plateau. The allochthon was emplaced toward the southeast during Late Triassic time, and it and the western part of the autochthon/parautochthon were modified by Cenozoic deformation.

The autochthon/parautochthon was formed from the western part of the Yangtze platform and consists of a Proterozoic basement covered by a thin, incomplete succession of Late Proterozoic to Middle Triassic shallow-marine and nonmarine sedimentary rocks interrupted by Permian extension and basic magmatism in the southwest. The platform is bounded by continental margins that formed in Silurian time to the west and in Late Proterozoic time to the north. Within the southwestern part of the platform is the narrow N-trending Kungdian high, a paleogeographic unit that was positive during part of Paleozoic time and whose crest is characterized by nonmarine Upper Triassic rocks unconformably overlying Proterozoic basement.

In the western part of the Longmen Shan region, the allochthon is composed mainly of a very thick succession of strongly folded Middle and Upper Triassic Songpan Ganzi flysch. Along the eastern side and at the base of the allochthon, pre-Upper Triassic rocks crop out, forming the only exposures of the western margin of the Yangtze platform. Here, Upper Proterozoic to Ordovician, mainly shallow-marine rocks unconformably overlie Yangtze-type Proterozic basement rocks, but in Silurian time a thick section of fine-grained clastic and carbonate rocks were deposited, marking the initial subsidence of the western Yangtze platform and formation of a continental margin. Similar deep-water rocks were deposited throughout Devonian to Middle Triassic time, when Songpan Ganzi flysch deposition began. Permian conglomerate and basic volcanic rocks in the southeastern part of the allochthon indicate a second period of extension along the continental margin. Evidence suggests that the deep-water region along and west of the Yangtze continental margin was underlain mostly by thin continental crust, but its westernmost part may have contained areas underlain by oceanic crust. In the northern part of the Longmen Shan allochthon, thick Devonian to Upper Triassic shallow-water deposits of the Xue Shan platform are flanked by deep-marine rocks and the platform is interpreted to be a fragment of the Qinling continental margin transported westward during early Mesozoic transpressive tectonism.

In the Longmen Shan region, the allochthon, carrying the western part of the Yangtze continental margin and Songpan Ganzi flysch, was emplaced to the southeast above rocks of the Yangtze platform autochthon. The eastern margin of the allochthon in the northern Longmen Shan is unconformably overlapped by both Lower and Middle Jurassic strata that are continuous with rocks of the autochthon. Folded rocks of the allochthon are unconformably overlapped by Lower and Middle Jurassic rocks in rare outcrops in the northern part of the region. They also are extensively intruded by a poorly dated, generally undeformed belt, of plutons whose ages (mostly K/Ar ages) range from Late Triassic to early Cenozoic, but most of the reliable ages are early Mesozoic. All evidence indicates that the major deformation within the allochthon is Late Triassic/Early Jurassic in age (Indosinian). The eastern front of the allochthon trends southwest across the present mountain front, so it lies along the mountain front in the northeast, but is located well to the west of the present mountain front on the south.

The Late Triassic deformation is characterized by upright to overturned folded and refolded Triassic flysch, with generally NW-trending axial traces in the western part of the region. Folds and thrust faults curve to the north when traced to the east, so that along the eastern front of the allochthon structures trend northeast, involve pre-Triassic rocks, and parallel the eastern boundary of the allochthon. The curvature of structural trends is interpreted as forming part of a left-lateral transpressive boundary developed during emplacement of the allochthon. Regionally, the Longmen Shan lies along a NE-trending transpressive margin of the Yangtze platform within a broad zone of generally N-S shortening. North of the Longmen Shan region, northward subduction led to collision of the South and North China continental fragments along the Qinling Mountains, but northwest of the Longmen Shan region, subduction led to shortening within the Songpan Ganzi flysch basin, forming a detached fold-and-thrust belt. South of the Longmen Shan region, the flysch basin is bounded by the Shaluli Shan/Chola Shan arc—an originally Sfacing arc that reversed polarity in Late Triassic time, leading to shortening along the southern margin of the Songpan Ganzi flysch belt. Shortening within the flysch belt was oblique to the Yangtze continental margin such that the allochthon in the Longmen Shan region was emplaced within a left-lateral transpressive environment. Possible clockwise rotation of the Yangtze platform (part of the South China continental fragment) also may have contributed to left-lateral transpression with SE-directed shortening. During left-lateral transpression, the Xue Shan platform was displaced southwestward from the Qinling orogen and incorporated into the Longmen Shan allochthon. Westward movement of the platform caused complex refolding in the northern part of the Longmen Shan region.

Emplacement of the allochthon flexurally loaded the western part of the Yangtze platform autochthon, forming a Late Triassic foredeep. Foredeep deposition, often involving thick conglomerate units derived from the west, continued from Middle Jurassic into Cretaceous time, although evidence for deformation of this age in the allochthon is generally lacking.

Folding in the eastern Sichuan fold-and-thrust belt along the eastern side of the Sichuan Basin can be dated as Late Jurassic or Early Cretaceous in age, but only in areas 100 km east of the westernmost folds. Folding and thrusting was related to convergent activity far to the east along the eastern margin of South China. The westernmost folds trend southwest and merge to the south with folds and locally form refolded folds that involve Upper Cretaceous and lower Cenozoic rocks. The boundary between Cenozoic and late Mesozoic folding on the eastern and southern margins of the Sichuan Basin remains poorly determined.

The present mountainous eastern margin of the Tibetan Plateau in the Longmen Shan region is a consequence of Cenozoic deformation. It rises within 100 km from 500–600 m in the Sichuan Basin to peaks in the west reaching 5500 m and 7500 m in the north and south, respectively. West of these high peaks is the eastern part of the Tibetan Plateau, an area of low relief at an elevations of about 4000 m.

Cenozoic deformation can be demonstrated in the autochthon of the southern Longmen Shan, where the stratigraphic sequence is without an angular unconformity from Paleozoic to Eocene or Oligocene time. During Cenozoic deformation, the western part of the Yangtze platform (part of the autochthon for Late Triassic deformation) was deformed into a N- to NE-trending foldandthrust belt. In its eastern part the fold-thrust belt is detached near the base of the platform succession and affects rocks within and along the western and southern margin of the Sichuan Basin, but to the west and south the detachment is within Proterozoic basement rocks. The westernmost structures of the fold-thrust belt form a belt of exposed basement massifs. During the middle and later part of the Cenozoic deformation, strike-slip faulting became important; the fold-thrust belt became partly right-lateral transpressive in the central and northeastern Longmen Shan. The southern part of the fold-thrust belt has a more complex evolution. Early Nto NE-trending folds and thrust faults are deformed by NW-trending basementinvolved folds and thrust faults that intersect with the NE-trending right-lateral strike-slip faults. Youngest structures in this southern area are dominated by left-lateral transpression related to movement on the Xianshuihe fault system.

The extent of Cenozoic deformation within the area underlain by the early Mesozoic allochthon remains unknown, because of the absence of rocks of the appropriate age to date Cenozoic deformation. Klippen of the allochthon were emplaced above the Cenozoic fold-andthrust belt in the central part of the eastern Longmen Shan, indicating that the allochthon was at least partly reactivated during Cenozoic time. Only in the Min Shan in the northern part of the allochthon is Cenozoic deformation demonstrated along two active zones of E-W shortening and associated left-slip. These structures trend obliquely across early Mesozoic structures and are probably related to shortening transferred from a major zone of active left-slip faulting that trends through the western Qinling Mountains. Active deformation is along the left-slip transpressive NW-trending Xianshuihe fault zone in the south, right-slip transpression along several major NE-trending faults in the central and northeastern Longmen Shan, and E-W shortening with minor left-slip movement along the Min Jiang and Huya fault zones in the north.

Our estimates of Cenozoic shortening along the eastern margin of the Tibetan Plateau appear to be inadequate to account for the thick crust and high elevation of the plateau. We suggest here that the thick crust and high elevation is caused by lateral flow of the middle and lower crust eastward from the central part of the plateau and only minor crustal shortening in the upper crust. Upper crustal structure is largely controlled in the Longmen Shan region by older crustal anisotropics; thus shortening and eastward movement of upper crustal material is characterized by irregular deformation localized along older structural boundaries.     

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.     

贺兰山北段古元古代结晶基底变形特征及其区域构造意义

贺兰山北段结晶基底中保留有不同程度的韧性变形剪切带.通过详细的野外考察和室内显微构造研究,明确贺兰山北段的古元古代基底经历了4期韧性剪切变形:(1)早期顺层剪切带表现出中下部地壳层次的变形样式,运动学特征一致反映了近南北向的伸展;(2)麻粒岩相变质的糜棱片麻岩剪切带为南北向挤压的产物,导致经历高温高压变质的孔兹岩系从下地壳向中部地壳抬升;(3)高级糜棱岩(低角闪岩相-高绿片岩相)剪切带涉及的2次伸展运动(北西-南东向伸展和北东-南西向伸展)使得基底进一步向中部地壳抬升,可能发生在形成孔兹岩系的同一造山运动的晚期伸展垮塌过程中;(4)北东-近东西向左行逆冲绿片岩相糜棱岩剪切带则将结晶基底抬升到中上部地壳层次,其运动学特征与高级糜棱岩剪切带明显不同,可能是另一造山运动的产物.贺兰山北段与大青山-乌拉山地区有相似的韧性剪切带和构造变形,表明华北克拉通西部北缘存在一致的近东西走向的古元古代碰撞造山运动以及随后另一造山运动的改造.     

东秦岭二郎坪弧后盆地双向式俯冲特征

二郎坪弧后盆地是北秦岭早生古代活动大陆边缘沟－弧－盆系统的重要组成部分,现今二郎坪岩群是古弧后盆地的物质残存,记录了盆地演化方式和过程,沉积建造和岩浆作用研究发同,在二郎坪弧后盆地南北两侧各发育一套活动型陆缘沉积体系和一系列府冲型花岗岩,变形构造解析反映出主造山期早期沿弧后盆地两侧各形成一套韧性推覆构造系,并具对冲型几何学样式,为俯冲带典型构造,综合分析表明,弧后盆地在造山早期分别俯冲于南部秦岭古岛弧和北部宽坪古陆之下,具双向式俯冲特征。     

Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.     

MAGMATISM AND TECTONO-MAGMATIC EVOLUTION OF JINNING CYCLE OF EASTERN KUNLUN OROGENIC BELT

MAGMATISM AND TECTONO-MAGMATIC EVOLUTION OF JINNING CYCLE OF EASTERN KUNLUN OROGENIC BELT1　JiangChunfa ,YangJingshui,FenBinggui,etal.OpeningclosingtectonicsofKunlunmountains[M] .Beijing:GeologicalPublishingHouse ,1992 .12 5～ 14 3(inChinesewithEnglishabstract) . 2　GuFengbao,WuXianglong,JiangChangyi.Hercynian—Indo SiniancycleGraniteassociationandtheirtectonicsettinginEastKunlun[J] .QinghaiGeology ,1996 ( 1) :18～ 30 .…     

安徽省潜山县韩长冲地区的地质构造特征

韩长冲地区主要由超高压变质岩、碱长花岗片麻岩、二长花岗片麻岩组成。前者包括超高压片麻岩、大理岩、榴辉岩和石英硬玉岩等。其中存在由黑云斜长片麻岩、石英硬玉岩、大理岩及层状榴辉岩组成的超高压变质表壳岩组合。超高压变质岩先后经过柯石英榴辉岩相、石英榴辉岩相、角闪岩相及绿片岩相多阶段的变质作用;经过榴辉岩相、角闪岩相、角闪岩相后及脆性等四期变形。其中角闪岩相变形形成本区的主要构造要素,以发育大量Ａ型褶皱及普遍的糜棱岩化为特征。碱长花岗片麻岩及二长花岗片麻岩只经过角闪岩相及其后的变质和变形作用。超高压变质岩与碱长花岗片麻岩呈侵入接触,可能沿缓倾向ＳＳＥ的韧性剪切带逆掩于二长花岗片麻岩之上。     

郯庐剪切带的性质和意义

沿郯庐断裂带从大别山东麓经山东中部至辽北吉南的新宾—桦甸地区,暴露的早前寒武纪结晶岩石中存在着一系列北北东走向的大型韧性剪切带,其最大宽度达20km,走向断续延伸近2000km,它们分别在大别、鲁西和新宾地区形成了巨大的弧形牵引构造。剪切带中不同尺度组构要素的几何学,指示其中曾经发生了一致的大幅度左行位移;变形岩石的显微构造和矿物组合特征,说明这一韧性剪切带早期形成于低角闪岩相条件下,并且在抬升和冷却过程中经历了绿片岩相条件下的递进变形。山东中部晚元古代以后的沉积不整合于韧性剪切带及其变形岩石之上,中生代未期脆性的郯庐断裂系统追踪并改造了基底岩石中的韧性剪切带。     

Regional progressive high-pressure metamorphism, Seward Peninsula, Alaska

Abstract Blueschist-facies rocks on the Seward Peninsula constitute a structurally coherent terrane measuring at least 100 × 150 km. Radiometric age data indicate that high-pressure metamorphism probably occurred in Jurassic rather than in Palaeozoic or Precambrian time, as previously suggested. Protolith sediments (Nome Group) are of intracontinental basin or continental margin type, and of lower Palaeozoic and possibly late Precambrian age, thus predating the high pressure metamorphism by more than 200 m.y. Blueschist-facies mineral assemblages were developed in almost all lithologies of the Nome Group, and are best preserved in FeTi-rich metabasites (glaucophane + almandine + epidote) and pelites (glaucophane + chloritoid + phengite). A lawsonite–crossite subfacies was developed in possible Nome Group rocks on the east flank of the Darby Mountains. Albite–epidote–amphibolite facies assemblages characterize Nome Group rocks in the southwestern part of the Peninsula. Metamorphism in the central zone of the terrane passed from early lawsonitic to subsequent epidote–almandine–glaucophane schist subfacies with the local development (east of the Nome River) of eclogitic assemblages. The high pressure metamorphic minerals were synkinematic with the development of mesoscopic-scale intrafolial isoclinal folds and a flattening foliation of consistent orientation. Initiation of uplift probably corresponded to the growth of barroisite rims on earlier sodic and actinolitic amphiboles, and partial post-kinematic greenschist facies replacements record later stages of decompression. Ophiolites and melange are not associated with the Seward Peninsula blueschists. The high-pressure metamorphism was caused by tectonic loading of a continental plate by an allochthon of indeterminate origin. The PT conditions of high pressure metamorphism were approximately 9–11 kbar, 400–450°C, thus falling between the PT paths of the Shuksan and Franciscan terranes.     

A new section of Lower Palaeozoic rocks in Kayin State (Southeast Myanmar)

Lower Palaeozoic rocks have been mapped in Kayin State in an area previously shown on published maps as either metamorphic or possibly Lower or Upper Palaeozoic rocks. Three new formations, with a total thickness of over 900?m, apparently overlain by an, at least, 100?m thick Upper Palaeozoic formation are mapped along the Salween River and along the road from Yinbaing, in Myanmar, to Tha Song Yang, in Thailand. The Lower Palaeozoic succession consists of the predominantly siliciclastic Kyaukpulu and Kushwe–e–we formations and an overlying, predominantly carbonate Meseik Ashe Formation which contains Middle Ordovician (Darriwilian) conodonts. The older two formations are probable correlates of the Ngwetaung and Lokeypin formations of the southern Shan State of Myanmar and the Lower Ordovician siliciclastics of western Thailand. The overlying, peritidal to shallow subtidal carbonates of the Meseik–Ashe Formation are correlates of the Wunbye and Sitha formations of Shan State, Myanmar. The thick–bedded, quartz arenites of the Nyaungwiang Formation are faulted against the Ordovician carbonates and are probable lithological correlates of the Carboniferous Taungnyo Formation. The folds in the Lower Palaeozoic rocks are overturned to the northeast and deformation was in one major phase between the Tournaisian and the Early Permian. The Lower Palaeozoic strata may probably be followed as a ridge for at least 100?km towards the NNW, close to the western border of the Sibuma Block which is separated by a postulated cryptic suture from the Irrawaddy Block to the west.     

滇西西盟地区前泥盆纪变质岩系的变形构造格架

滇西西盟一带是保山—掸邦地块在我国境内的一个基底岩系出露地区。该地区的前泥盆纪变质岩系可划分成两个构造层，下部为元古代构造层，由变质深度达角闪岩相的怕可杂岩系组成，发育３期南北向的变形构造；上部为早古生代构造层，由低绿片岩相变质的王雅组、允沟组组成，发育两期呈南北向的变形构造。变形构造表明，西盟变质岩系的主期构造格架以怕可—老街子背形叠瓦垛为主导构造要素，由背驮式扩展的向东逆冲的盲逆冲断裂系组成，王雅—允沟反冲叠瓦扇是盲逆冲断裂系的盖层响应变形系统，并以向西逆冲的推覆构造为特征     

桐柏－大别造山带随县群变质变形作用研究

中新元古代随县群分布于秦岭—大别造山带南部，是一套形成于大陆裂谷环境中的砂页岩—流纹英安质火山碎屑岩建造，并在拉张环境中受到了辉长辉绿岩墙侵入．从新元古代末开始经历了多期变质和变形作用改造，记录了华北与扬子两大陆块及其造山作用的复杂演化历史．以现代变质地质学理论为指导，结合岩石学与构造学，宏观与微观研究，确立了随县群的地质事件序列．其主要有３个变形和变质演化阶段：晋宁期伸展滑脱固态流变，低绿片岩相变质；印支期韧性剪切，绿帘—蓝片岩相变质；早燕山期逆冲推覆，低绿片岩相变质