Distinguishing syn-cleavage folds from pre-cleavage folds to which cleavage is virtually axial planar: examples from the Cambrian core of the Lower Palaeozoic Anglo-Brabant Deformation Belt (Belgium)

Within the Cambrian Jodoigne Formation in the easternmost part of the Anglo-Brabant Deformation Belt, sub-horizontal to gently plunging folds occur within the limbs of steeply plunging folds. The latter folds are cogenetic with cleavage and are attributed to the Brabantian deformation event. In contrast, although cleavage is also (1) virtually axial planar to the sub-horizontal to gently plunging higher-order folds, shows (2) a well-developed divergent fanning across these folds, (3) an opposing sense of cleavage refraction on opposite fold limbs, and (4) only very small cleavage transection angles, an analysis of the cleavage/bedding intersection lineation suggests that these higher-order folds have a pre-cleavage origin. On the basis of a comparison of structural and sedimentological features these higher-order folds are interpreted as slump folds. The seemingly ‘normal’ cleavage/fold relationship across the slump folds within the limbs of the large steeply plunging folds is due to the very small angle between cleavage and bedding.As such, a ‘normal’ cleavage/fold relationship is no guarantee for a syn-cleavage fold origin. It is not unlikely that also within undeformed, recumbent slump folds, a well-developed compaction fabric, formed parallel to the axial surface of the slump folds, may show fanning and contrasting senses of cleavage refraction on opposite fold limbs.     

Development of bedding-normal boudins in the Pilot Mountains, Nevada

Boudins with long axes (BA) oriented subnormal to bedding and to associated fold axes are observed in folded rocks in a thrust sheet exposed near the base of a regionally extensive allochthon in west-central Nevada, USA. Formation of the boudins is related to development of a regional fold-set coeval with major thrusting. The axes of boudins lie at a high angle to bedding, and in some instances, boudins define tight to isoclinal folds which are geometrically associated with the regional deformation. Quartz c-axis fabrics from oriented thin-sections of the boudins indicate extension parallel to the boudin axes (BA).

These relations and other mesoscopic structural data indicate a complex deformational history for boudin development. The history involves thin layers (to become boudins) deformed in folds disharmonic to major structures within the thrust sheet followed by flattening and associated extension parallel to fold axes. During flattening, arcuation occurred within the deforming mass resulting in rotation of fold axes and boudin axes (BA) toward the axis of finite extension (X). Extension parallel to BA recorded in the petrofabrics of boudins records incremental strain axes oriented at a high angle (50°) to the finite X and is probably related to an early plane-strain state associated with disharmonic folding. The finite extension (X) is down-dip in axial planes of major folds formed during thrusting and indicates a northwest to southeast transport for the thrusts.     

Discovery of a layer of probable impact melt spherules in the Late Archaean Jeerinah Formation,Fortescue Group,Western Australia

In the high‐grade (granulite facies) metamorphic rocks at Broken Hill the foliation is deformed by two groups of folds. Group 1 folds have an axial‐plane schistosity and a sillimanite lineation parallel to their fold axes; the foliation has been transposed into the plane of the schistosity by these folds. Group 2 folds deform the schistosity and distort the sillimanite lineation so that it now lies in a plane. Both groups of folds are developed as large folds. The retrograde schist zones are zones in which new fold structures have formed. These structures deform Group 1 and Group 2 folds and are associated with the formation of a new schistosity and strain‐slip cleavage. The interface between ore and gneiss is folded about Group 1 axial planes but about axes different from those in the foliation in the gneiss. On the basis of this, the orebody could not have been parallel to the foliation prior to the first recognizable structural and metamorphic events at Broken Hill. The orebody has been deformed by Group 2 and later structures.     

Structures in the banded iron-formation of the southeastern Bababudan Hills, Karnataka, India

The banded iron-formation in the southeastern Bababudan Hills display a macroscopic synformal bend gently plunging towards WNW. The bedding planes in smaller individual sectors show a cylindrical or conical pattern of folding. The dominant set of minor folds has WNW-ESE trending axial planes and the axes plunge towards WNW at gentle to moderate angles, though there is considerable variation in orientation of both axes and axial planes. A later set of sporadically observed folds has N-S trending axial planes. The macroscopic synformal bend within the study area forms the southeastern corner of a horseshoe shaped regional synformal fold closure which encompasses the entire Bababudan range. The minor folds are buckle folds modified to a varying extent by flattening. In some examples the quartzose layers appear to be more competent than the ferruginous layers; in others the reverse is true. The folds are frequently noncylindrical and the axes show curvature with branching and en echelon patterns. Such patterns are interpreted to be the result of complex linking of progressively growing folds whose initiation is controlled by the presence of original perturbations in the layers. Domes and basins have at places developed as a result of shortening along two perpendicular directions in a constrictional type of strain. Development of folds at different stages of progressive deformation has given rise to nonparallelism of fold axes and axial planes. The axes and axial planes of smaller folds developed on the limbs of a larger fold are often oriented oblique to those of the latter. Progressive deformation has caused rotation and bending of axial planes of earlier formed folds by those developed at later stages of the same deformational episode. Coaxial recumbent to nearly reclined fold locally encountered on the N-S limb of the macroscopic fold may belong to an earlier episode of deformation or to the early stage of the main deformation episode. The E-W to ESE-WNW strike of axial plane of the regional fold system in the Bababudan belt contrasts with the N-S to NNW-SSE strike of axial planes of the main fold system in the Chitradurga and other schist belts of Karnataka.     

山东灵山岛滑塌体内部沉积及构造特征研究

青岛市灵山岛修船厂剖面下白垩统地层中发育良好的滑塌变形体。野外观察可见滑塌体岩性单元主要由厚层砂岩及砂页岩互层组成,其中厚层砂岩根据其沉积构造及成因机制可分为砂质碎屑流沉积及浊流沉积两类;砂页岩互层段砂岩层可见底模构造及粒序层理,为静水环境下远端浊流沉积。滑塌体内部构造主要可分为软褶皱变形、同生断层、透镜状砂质团块三种类型。其中,软褶皱变形根据岩性可分为砂岩软褶皱、砂页岩互层软褶皱及页岩软褶皱,随着变形强度增加,软褶皱枢纽逐渐平行于滑移方向,形成曲脊软褶皱或软鞘褶皱(soft sheath folds);同生断层出现在砂岩层中,根据力学性质分为正断层及逆断层,正断层为剪切拉伸所致,逆断层为软褶皱逆冲所致;透镜状砂质团块包括同沉积布丁构造和同沉积断块。根据滑塌体内部滑移面识别出三期滑塌,完整的滑塌体由底部拆离滑移面、下部厚层砂体、中部砂页岩互层及上部砂页岩互层未变形体组成,其组成特征及各部分接触关系反映了滑塌体中下部沿底部拆离滑移面发生滑塌变形,且于活动末期在相对静水条件下被上部砂页岩互层覆盖这一形成过程。根据滑塌体内部组成特征的有序性、相似性及滑塌体内部沉积构造特征,推测其触发机制可能为沉积物快速沉积所引发的重力滑塌成因。     

Structure of the Abercrombie beds south of Reids flat,new South Wales

The Late Ordovician Abercrombie Beds, south of Reids Flat, New South Wales, and adjacent to the Wyangala Batholith, show evidence of three successive fold episodes. First generation folds are tight to isoclinal, with fold axes ranging from vertical to horizontal and north‐trending, and steep axial‐plane slaty cleavage. Second generation folds are steeply plunging, tight to open with north‐striking axial planes. In pelitic rocks the axial plane structure is a crenulation cleavage which overprints the slaty cleavage. The first two fold episodes were accompanied by greenschist‐facies metamorphism. Granite emplacement occurred prior to the second fold episode. A third deformation was of relatively mild intensity and produced open, north‐trending folds with axial planes dipping moderately to the east, and crenulation cleavage as the axial plane structure in pelitic rocks. These latest folds are correlated with the latest folds in the Abercrombie Beds north of the Abercrombie River. The mapped area has no apparent macroscopic structure and may be considered as a single domain.     

Fault-related folding in the Ramshorn Peak area,Idaho-Wyoming thrust belt

The Ramshorn Peak area of the Idaho-Wyoming thrust belt lies in the toe of the Prospect thrust sheet along the eastern margin of the exposed part of the thrust belt. The terrain is folded with axes trending N-S and wavelengths ranging from 3 to 4.3 km. Thrusts occur exclusively along the eastern part of the map area where the toe of the Prospect thrust sheet is thinnest. The easternmost thrusts are backthrusts.Monoclinally folded rocks are thrust on less deformed rocks south of Ramshorn Peak. This fold and fault complex is interpreted to have formed by thrusting over a large oblique and small forward step. The oblique step is responsible for the formation of the monocline in the hanging wall of the thrust. All faults and associated folds are rotated by subsequent buckle folding.Second- and third-order folds (folds at the scale of the Ramshorn Peak fold and fault complex and smaller) appear to be isolated features associated with faults (fault-related folds rather than buckle folds) because they are not distributed throughout the map area. These folds were probably initiated by translation and adhesive drag. The early folding was terminated by large translation over a stepped thrust surface which caused additional folding as the hanging wall rocks conformed to the irregular shape of the footwall. The Rich model is utilized to explain the Ramshorn Peak complex because the fold is of monoclinal form and is an isolated feature rather than part of a buckle fold wave-train.     

Structural pattern in the Precambrian rocks of Sonua-Lotapahar region,North Singhbhum,eastern India

In the western part of the North Singhbhum fold belt near Lotapahar and Sonua the remobilized basement block of Chakradharpur Gneiss is overlain by a metasedimentary assemblage consisting of quartz arenite, conglomerate, slate-phyllite, greywacke with volcanogenic material, volcaniclastic rocks and chert. The rock assemblage suggests an association of volcanism, turbidite deposition and debris flow in the basin. The grade of metamorphism is very low, the common metamorphic minerals being muscovite, chlorite, biotite and stilpnomelane. Three phases of deformation have affected the rocks. The principal D1 structure is a penetrative planar fabric, parallel to or at low angle to bedding. No D1 major fold is observed and the regional importance of this deformation is uncertain. The D2 deformation has given rise to a number of northerly plunging major folds on E-W axial planes. These have nearly reclined geometry and theL ₂lineation is mostly downdip on theS ₂surface, though some variation in pitch is observed. The morphology of D2 planar fabric varies from slaty cleavage/schistosity to crenulation cleavage and solution cleavage. D3 deformation is weak and has given rise to puckers and broad warps on schistosity and bedding. The D2 major folds south of Lotapahar are second order folds in the core of the Ongarbira syncline whose easterly closure is exposed east of the mapped area. Photogeological study suggests that the easterly and westerly closing folds together form a large synclinal sheath fold. There is a continuity of structures from north to south and no mylonite belt is present, though there is attenuation and disruption along the fold limbs. Therefore, the Singhbhum shear zone cannot be extended westwards in the present area. There is no evidence that in this area a discontinuity surface separates two orogenic belts of Archaean and Proterozoic age.     

Intrafolial folds and associated structures in a progressive strain environment of Darjeeling-Sikkim Himalaya

The Dating rocks and Darjeeling gneisses, which constitute the Sikkim dome in eastern Himalaya, as well as the Gondwana and Buxa rocks of ‘Rangit Window’, disclose strikingly similar sequences of deformation and metamorphism. The structures in all the rocks belong to two generations. The structures of early generation are long-limbed, tight near-isoclinal folds which are often intrafolial and rootless. These intrafolial folds are associated with co-planar tight folds with variably oriented axes and sheath folds with arcuate hinges. Penetrative axial plane cleavage and mineral lineation are related structures; transposition of bedding is remarkable. This early phase of deformation (D ₁) is accompanied by constructive metamorphism. The structures of later generation are open, asymmetrical or polyclinal; a crenulation cleavage or discrete fracture may occur. The structures of early generation are distorted by folds of later generation and recrystallized minerals are cataclastically deformed. Recrystallization is meagre or absent during the later phase of deformation (D ₂). The present discussion is on structures of early generation and strain environment during theD ₁ phase of deformation. The concentration of intrafolial folds in the vicinity of ductile shear zones and decollement or detachment surface (often described as ‘thrust’) may be considered in this context. The rocks of Darjeeling-Sikkim Himalaya display minor structures other than intrafolial folds and variably oriented co-planar folds. The state of finite strain in the rocks, as observed from features like flattened grains and pebbles, ptygmatic folds and boudinaged folds indicate combination of flattening and constrictional type strain. The significance of the intrafolial folds in the same rocks is discussed to probe the environment of strain during progressive deformation (D ₁).     

Singhbhum Shear Zone: Structural transition and a kinematic model

The northern fold belt away from the Singhbhum Shear Zone displays a set of folds on bedding. The folds are sub-horizontal with E-W to ESE striking steep axial surfaces. In contrast, the folds in the Singhbhum Shear Zone developed on a mylonitic foliation and have a reclined geometry with northerly trending axes. There is a transitional zone between the two, where the bedding and the cleavage have become parallel by isoclinal folding and two sets of reclined folds have developed by deforming the bedding—parallel cleavage. Southward from the northern fold belt the intensity of deformation increases, the folds become tightened and overturned towards the south while the fold hinges are rotated from the sub-horizontal position to a down-dip attitude. Recognition of the transitional zone and the identification of the overlapping character of deformation in the shear zone and the northern belt enable the formulation of a bulk kinematic model for the area as a whole.     

Survival Conditions of Folding in Different Depth During Orogenesis-Deformation in Texas Creek and Chester Dome,USA

A succession of 5 FIA trends（foliation intersection or inflection axes in porphyroblasts） preserved in high temperature-low pressure regime PreCambrian rocks in the Texas Creek, Arkansas River region reflected by the fold axial plane traces and schistosity data in this region. Similar fold axial plane trace data measured in Palaeozoic rocks in Chester Dome, Vermont, which is high temperature to medium pressure regime, only preserve the effects of the youngest FIAs of the all 5 FIA sets that obtained in this region. The other three FIA sets have no equivalent fold axial planes. This difference from shallow to deeper orogenic regimes reflects decreasing competency at greater pressure with collapse and unfolding of earlier formed folds. The greater overlying load of rocks has tended to flatten all but the very largest early-formed structures, preserving only those folds that were more recently developed.     

Geological aspects of deformation in continental shear zones

A method of kinematic analysis of structures, microstructuresand mineral preferred orientations, initially devised in the study of peridotites, has been applied to crustal rocks bearing evidence of large strains produced in metamorphic environments. Three tectonic lineaments (Angers-Lanvaux, Montagne Noire and Maydan) were selected. They illustrate a general situation arising in continental crusts when they are deformed by ductile transcurrent fault systems.The Angers-Lanvaux structure is bilaterally symmetric; its dominant feature is the horizontal stretching lineation which is parallel to the fold axes. The foliation and slaty cleavage in the most surficial formations wrap around the axis of the whole structure. The folds in the slates away from the axis also exhibit axes parallel to the general trend, but no stretching lineations. These folds are attributed to crustal shortening in a direction normal to the ductile fault. In the Montagne Noire recumbent folds are thrusted away from the axis of the structure over at least 25 km. The metamorphism is also centered on the structure and symmetrically reduced away from it. The core of the structure is occupied by a strongly lineated orthogneiss, cut by a late intrusive granite. The Maydan axial zone displays clear evidence of partial melting at various scales within the deformed gneisses: (1) in gashes perpendicular to the stretching lineation which in these anatectic formations tends to plunge at more than 45°; (2) in bands of deformed pegmatites; and (3) possibly in granites which on the one hand intrude the surrounding formations and on the other converge with increasing deformation on the fault zone. The quartz preferred orientations and microstructures in quartzite layers from Angers indicate that the plastic flow plane and direction lie, respectively, close to the foliation and lineation, the slight departure is ascribed to a flow with a rotational shear component.All this suggests a general model for the origin of such ductile zones. The horizontal relative displacement of crustal blocks along a ductile band is responsible for its overall steeply dipping foliation and horizontal lineations. Viscous heating progressively tends to concentrate the plastic flow along its axis. It is also responsible for the development of metamorphism and of anatexis at depth; the partially melted rocks tend to rise, building at shallower depth the arched structure in the axis of the ductile zone, with a continuing flowage parallel to this axis probably now in the solid state; they can also intrude the surrounding terrain as undeformed batholiths. The folds parallel to the stretching lineation in the axial zone are explained by the fact that, due to the escape of anatectic melts, the formations at depth flow in a narrowing channel. The upwelling of the axial structure induces a compression with folding in the surrounding sedimentary formations and gravity nappe sliding away from the axis.     

On the deformation sequence in the New Harbour Group of Holy Island,Anglesey, North Wales

Four phases of deformation are recorded by minor structures in the New Harbour Group (NHG) of southern Holy Island. The regional schistosity in these rocks is a differentiated crenulation cleavage of D₂ age. An earlier preferred orientation (S₁) is commonly preserved as crenulations within the Q-domain microlithons of the S₂ schistosity and is demonstrably non-parallel to bedding. F₃ folds are widely developed in S₂ and, to a lesser extent, in bedding. S₃ crenulation cleavage is sporadically developed but can be intense locally. A major antiformal fold exists in the NHG near Rhoscolyn. This fold is of D₃ age since it clearly deforms S₂ schistosity and is consistent with the vergence of F₃ minor structures. All planar structures are deformed by folds of D₄ age. © 1997 John Wiley & Sons, Ltd.     

山东省灵山岛下白垩统浊积岩中与滑塌作用相关的软沉积物变形构造

灵山岛上出露的软沉积物变形构造其成因具有多样性,而灯塔剖面底部滑塌层内的变形构造的触发因素尚不明确.结合野外观察和极射赤平投影方法,研究了滑塌层和内部变形构造的形成过程、触发机制和地质意义,结果表明:灯塔剖面主要由浊积岩沉积序列组成.滑塌层夹在未变形层之间,由地震触发形成,内部发育4个滑脱面,将滑塌层划分为5个变形单元,缩短率和变形程度各不相同.软沉积物变形构造主要为褶皱,形态特征表现为砂岩厚度在枢纽部位大大增加,也可见一些砂岩增厚和减薄现象,两者均是液化的砂岩在驱动力作用下的结果.滑塌过程中,滑塌层中的砂泥岩与海底沉积物之间的孔隙流体自由交换被切断,产生了暂时性的超压,导致了液化的发生.褶皱的轴线延伸方向为SSW-NNE,轴面倾斜方向主要为SEE(120°),指示古水流主要来自SEE方向,与浊积岩内底痕指示的古水流方向一致,说明斜坡沉积系统上发育的滑塌褶皱能够指示古水流方向.      

The structural evolution of the Northern Hastings Block and southern Nambucca Block,southern New England Orogen,eastern Australia

The Hastings Block is a weakly cleaved and complexly folded and faulted terrain made up of Devonian, Carboniferous and Permian sedimentary and volcanic rocks. The map pattern of bedding suggests a major boundary exists that divides the Hastings Block into northern and southern parts. Bedding north of this boundary defines an upright box-like Parrabel Anticline that plunges gently northwest. Four cleavage/fold populations are recognised namely: E–W-striking, steeply dipping cleavage S₁ that is axial surface to gently to moderately E- or W-plunging; F₁ folds that were re-oriented during the formation of the Parrabel Anticline with less common N–S-trending, steeply dipping cleavage S₂, axial surface to gently to moderately N-plunging F₂ folds; poorly developed NW–SE-striking, steeply dipping cleavage S₃ axial surface to mesoscopic, mainly NW-plunging F₃ folds; and finally_, a weakly developed NE–SW-striking, steeply dipping S₄ cleavage formed axial surface to mainly NE-plunging F₄. The Parrabel Anticline is considered to have formed during the D₃ deformation. The more intense development of S₂ and S₃ on the western margin of the Northern Hastings Block reflects increasing strain related to major shortening of the sequences adjacent to the Tablelands Complex during the Hunter–Bowen Orogeny. The pattern of multiple deformation we have recorded is inconsistent with previous suggestions that the Hastings Block is part of an S-shaped orocline folded about near vertically plunging axes.     

Cleavage-fold relationships and their implications for transected folds: an example from southwest Virginia,U.S.A.

A non-coaxial deformation involving pre-folding initiation of cleavage perpendicular to bedding is proposed to explain non-axial planar cleavage associated with mesoscopic folds in part of the Appalachian foreland thrust-belt of southwest Virginia. Folds are gently plunging, asymmetric, upright to slightly inclined, sinusoidal forms with non-axial fanning cleavage. They show extreme local variations in type and degree of transection and the consistency of transection direction. These relations are further complicated by hinge migration.Cleavage-fan angles, bedding-cleavage angles and δ transection values appear influenced by fold tightness, and in part by fold flattening strain. Fold flattening increments are considered simultaneous with folding. Axial surface traces, and not cleavage traces, coincide with the principal extension direction in fold profiles. Geometric modelling of cleavage fanning and bedding-cleavage angle variations for various theoretical folding modes suggest that folding in limestone and sandstone layers was by tangential longitudinal strain. Significant shape modification and change in bedding-cleavage relations occurred after limb dips of 40 and 50° were attained in limestone and sandstone respectively. Mud-rock class 1C folds with convergent cleavage fans show features transitional between buckling and flexural flow. Initiation of ‘cleavage’ fabrics during layer-parallel shortening prior to significant folding may be important for cleavage evolution in some deformed rocks.     

造山过程重力塌陷与褶皱作用——面理弯切轴与褶皱轴面数据对比研究

提要：美国东部阿巴拉契亚造山带北端缅因州Rangeley地区志留—泥盆纪中温低压片岩测得的面理弯切轴与褶皱轴面数据有很好的对应关系。西部科迪勒拉造山带落基山脉南端科罗拉多州阿肯色河地区Texas Creek 以东高温低压前寒武纪堇青石片岩中测得的褶皱轴面方向和片理走向数据与该地区堇青石、斜长石变斑晶内测得的5期面理弯切轴也表现出很好的一致性。而在Rangeley北东200 km的佛蒙特州Chester Dome地区奥陶—泥盆纪中温中压片麻岩中测得的类似褶皱轴面数据却只反映了该地区5期面理弯切轴中较晚的北北西-南南东走向和北北东-南南西走向的两期面理弯切轴,未测得与其余3期面理弯切轴对应的褶皱轴面数据。通过对变质峰期温度相近、压力不同的两个造山带内3个典型变质岩区面理弯切轴、褶皱轴面方向和片理走向数据的对比分析认为,造山作用发生的地壳深度差异是早期褶皱经历多期造山运动后能否保存下来的主要影响因素。重力形成的去褶皱作用使得早期形成的规模较小褶皱经历复杂造山过程后难以保存。区域内早期形成的规模较大褶皱和造山过程晚期形成的褶皱由于受到重力塌陷作用影响较小,所以能够较好保存下来。     

Sheath-like folds and progressive fold deformation in tertiary sedimentary rocks of the Shimanto accretionary complex,Japan

The Upper Oligocene-Lower Miocene portion of the Cretaceous-Lower Miocene Shimanto accretionary complex on the Muroto Peninsula, southwest Japan, comprises alternating belts of coherent clastic rocks and shaly mélange. Sheath-like folds formed locally during a fold-thrust deformation that affected a 10 km structural thickness of these rocks. In a subsequent event confined to the mélange and adjoining areas, the axes of these folds were rotated nearly 90° within the plane of their axial surfaces. The widespread uniform development of the folds and an accompanying axial-planar pressure-solution cleavage strongly suggest that these deformations were tectonically induced, rather than gravity driven slump features. The sheath-like folds indicate that the most plausible environment for these rocks was in an accreted packet of trench-fill, behind the imbricate toe of the Shimanto accretionary complex. The timing of the deformation is constrained by depositional ages as well as by the probable Early Miocene age of an overlying superficial basin and early Middle Miocene igneous dikes that intrude the sequence. This chronology overlaps with the Late Oligocene-Early Miocene opening of the Shikoku back-arc basin, bordering the Shimanto Belt to the southwest; thus accretion and subduction were active during the basin opening event. These conclusions conflict sharphy with earlier held notions of strike-slip and olistostrome tectonics along this plate margin during the Early Miocene opening of the Shikoku Basin.     

Foliations developed during slump deformation of Miocene marine sediments,Cyprus

Foliations within a Miocene slumped bioclastic sandstone unit of the Pakhna Formation, southern Cyprus, were investigated in order to assess the importance of slump strain, liquifaction and compaction in their generation. There are two approximately orthogonal sets of folds, F₁ and F₂. F₁ folds are upright to inclined slump folds formed during slope-failure translation of the sediment. The cores of upright F₁ folds have a steeply dipping macroscopic fabric defined by the axial surfaces of small tight folds in compositional layering. F₂ folds occur on steeply-dipping limbs of F₁ folds. F₂ folds are small and asymmetric with flat-lying axial surfaces, and are interpreted as compaction generated. A pervasive flat-lying microscopic fabric defined by grain and pore long axis orientation is found in both fold sets, and is probably a liquifaction fabric enhanced by compaction. A pervasive steeply-dipping microfabric parallel to the axial planes of slump folds is not present in any of the slumps investigated.     

冀东太平寨附近太古宙变质岩的构造形式和变形史

研究地区的地层属太古宙迁西群底部上川组。本文涉及其中一部分约4平方公里的面积。岩石都已高度变质,属麻粒岩相的区域紫苏辉石带。由于缺乏顶、底及面向(facing)标志,无法确定其确切层序。