DETERMINATIONOF STRUCTURALSUCCESSIONS INMIGMATITES ANDGNEISSES

A. M. HopgoodReaderDepartment of GeologyUniversity of St AndrewsScotland

A manual for geologists concerned with the interpretation of complexstructural relationships in highly deformed deep crustal rocks

tfKLUWER ACADEMIC PUBLISHERSDORDRECHT/BOSTON/LONDON

CONTENTS

PREFACE xxi

THE AIM OF THE BOOK xxv

THE NEED FOR THE BOOK xxvi

ACKNOWLEDGEMENTS xxvii

CHAPTER 1 1GENERAL CHARACTERISTICS OF MIGMATITES AND MIGMATITE TERRANES1.1 INTRODUCTION 1

Background to the theory and principles of structural analysis and discussionof the special problems inherent in the structural analysis of migmatites.

1.1.1 STRESS TRANSMISSION DURING MIGMATITE DEVELOPMENTAND THE RECORD OF DEFORMATION - A PARADOX? 2Discussion of the commonly held .view that the structure in migmatiteslacks geometrical regularity. Explanation of why this in fact is amisconception and demonstration of how, in spite of the presence ofpartial melt, stress can be transmitted penetratively in migmatites toproduce geometrically consistent structures. <

1.1.2 MIGMATITES - WHAT THEY IMPLY TO THE STRUCTURALGEOLOGIST 4In contrast to any suggestion that the structure of migmatites could beso complex ('wild') as not to be amenable to resolution, the fact is thateach of the contributing factors to this complexity is a consequence ofsome particular event in their developmental history, and as suchprovides the potential to solve the complexity.

1.1.3 INFLUENCE OF ROCK TYPE ON THE STRUCTURE OF MIGMATITES 6Effects of partial melting, recrystallization, shearing, absence of structuralcontinuity and distinctive rock types and 'marker' layers.

1.1.4 INFLUENCE OF EXPOSURE TYPE ON THE STRUCTURAL STUDYOF MIGMATITES , 12Examples of the various types and qualities of exposure in migmatiteterranes and their different impacts on the observation of structuralfeatures.

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CHAPTER 2 19PRINCIPLES OF STRUCTURAL ANALYSIS OF MIGMATITES

2.1 COMPLEX STRUCTURES CONSIDERED AS COMPONENTS OFA SUCCESSION 19

2.1.1 INTRODUCTION - NEED FOR A SYSTEMATIC APPROACH 19The importance of adopting a systematic approach to the resolution ofcomplex structures in order to reduce the complexity to manageablecomponents of a succession amenable to analysis.The structural successionAn illustration of a structural succession involving a fold, axial planarshear and intrusive vein.

2.1.2 IMPORTANCE OF STRUCTURAL SUCCESSION IN MIGMATITETERRANE INTERPRETATION 21The role of the structural succession in the interpretation of thedevelopmental history of migmatite terranes.

2.2 RESOLVING STRUCTURAL COMPLEXITY IN MIGMATITES 22

2.2.1 INTRODUCTION TO THE APPROACH 22A brief outline of the methodology used.

2.2.2 PRINCIPLES OF STRUCTURAL ANALYSIS 24Outline of principles on which this structural analysis is based.

2.2.3 IDENTIFYING GROUPS OF RELATED FOLDS 25Recognition of structurally related groups of folds.

2.2.4 EFFECTS OF MULTIPLE (POLYPHASE) DEFORMATION 25'Phase' and 'polyphase'. What happens when rocks are repeatedlydeformed. Some problems inherent in some formal analytical techniqueswhen applied to the resolution of complex structures.

2.2.5 FOLD MECHANISMS 28Outline of fold-forming mechanisms and the effects of repeated folding.

2.3 ASSUMPTIONS INHERENT IN THE APPROACH USED 30Certain axiomatic assumptions regarding the interpretation of structuralrelationships.

CHAPTER 3 37DEVELOPMENT OF MIGMATITE STRUCTURE: OVERPRINTING

3.1 OVERPRINTING 37

3.1.1 PRINCIPLE OF OVERPRINTING 37The basis for determining the relative age of structures.

3.1.2 RELATIVE TIMING OF EVENTS: OVERPRINTING 38Examples of overprinted relationships.

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3.1.3 RELATIVE VALUE OF FOLDS COMPARED TO FOLIATIONS,AND LINEATIONS AS INDICATORS OF OVERPRINTINGRELATIONSHIPS 41Discussion of the relative importance of folds, planar and linearstructures in deciphering complex structural relationships in terms of thechance of overprinting between one-, two- and three-dimensional structures.

3.1.4 EVIDENCE OF REFOLDING: INTERFERENCE PATTERNS 41Recognition of refold relationships in the field.Simple interference patternsIllustrations of some simple interference patterns.

3.2 DEPARTURES FROM CONSISTENT OVERPRINTED STRUCTUREPATTERNS 47

3.2.1 STRUCTURES ARISING FROM CONSTRICTIONAL DEFORMATION 47Characteristic features of structures stemming from constrictionaldeformation and their distinction from structures arising fromoverprinting.

3.2.2 TRANSECTED FOLDS 49The effect of transected fold relationships on overprinting whenanalysing a structural succession in order to establish a sequence of events.

3.2.3 EFFECTS OF LOCAL INHOMOGENEITY 50Departures from the prevailing structural pattern at the margins ofporphyroclasts, boudins, intrusive igneous contacts, shear zones andmajor tectonic boundaries.

• 3.2.4 REFOLDING ON PARALLEL AXES 51The influence of pre-existing axial direction on the attitude ofsuperimposed folds.

3.2.5 NON-TECTONIC FOLDS 53The distinction between structures of non-tectonic origin and thoseformed by multiple-deformation.

CHAPTER 4 59THE ROLE OF STRUCTURES INTERPOSED IN THE SUCCESSION

4.1 THE SIGNIFICANCE OF GEOMETRICALLY SIMPLE STRUCTURESIMPOSED ON THE DEVELOPING SUCCESSION 59The value as strain markers of geometrically simple structures interposedat intervals in a complex succession.

4.2 BEHAVIOUR OF SIMPLE (PLANAR) STRUCTURES DURINGDEFORMATION 59How planar structures imposed on pre-existing structures preserve a recordof subsequent deformation which is more easily resolved than that of there-deformed host structure.

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4.3 ILLUSTRATIONS OF THE IMPORTANCE OF SIMPLE INTERPOSEDSTRUCTURES IN RESOLVING (STRUCTURAL) SUCCESSIONS 63

4.3.1 STRUCTURES EMPLACED IN (INTRUDED INTO) THE HOST ROCK 63(a) Planar structuresExamples illustrating the importance of emplaced planar (tabular)structures in resolving the structure of the host rocks in differentcircumstances.(b) Linear structuresThe role of imposed linear structures in resolving the structuralcomplexity of the host rocks.

4.3.2 COMPOSITE INTERPOSED STRUCTURES - SUPERIMPOSEDSECONDARY STRUCTURES 75The importance to the resolution of the host rock structural complexityof composite interposed structures stemming from repeatedsuperimposition of simple structures, e.g. cleavage imposed ona tabular intrusion.

4.3.3 LESS COMMONLY OBSERVED INTRODUCED STRUCTURES 79(a) Cooling fracturesThe response to subsequent deformation of the planar coolingfractures of an intrusion as a means of enabling the determinationof the post-intrusive deformational history.(b) Tension gash zones and shearsThe post-emplacement behaviour of shears and gash zones which,as effectively geometrically planar structures, can also be used in theanalysis of the subsequent deformation of the host rocks.(c) AgmaiitesThe use of agmatites (particularly where they are composite) and thecomplex inter-relationships of their components (neosome, palaeosome,folds and other structures) as markers for subdividing the structuralcomplexity of migmatites.

CHAPTER 5 85FOLD (STRUCTURE) SUCCESSIONS AND DEFORMATIONAL SEQUENCES

5.1 SUCCESSIONS AND SEQUENCES 85What is meant by 'successions' of structures and 'sequences' of related events.

5.1.1 STRUCTURAL SUCCESSIONS AND WHAT CAUSES THEM 85Successions stemming from repeated deformation ('pulses'). Theconcept of an open-ended, incomplete succession of unknown extent.

5.1.2 DEFORMATIONAL SEQUENCES 86The concept of a developing (waxing and waning) orogeny. Structuraloverprinting from deformational 'pulses' and from continued(progressive) deformation.

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5.1.3 FUNDAMENTAL ASSUMPTIONS REGARDING STRESS ANDDEFORMATION 88Assumptions regarding the nature of stress patterns and response tothese during orogeny.

5.2 IDENTIFICATION, RECOGNITION AND CLASSIFICATION OFSTRUCTURES 88

5.2.1 IMPORTANCE OF STRUCTURAL IDENTIFICATION ANDRECOGNITION 88Identifying structures on the basis of description and overprinting.

5.2.2 CLASSIFICATION OF STRUCTURES 92Classification of objects in terms of attributes.

5.2.3 IMPORTANCE OF EARLY PROVISIONAL CLASSIFICATION OFSTRUCTURES 93The need for classifying structures earlier, rather than later in the studywith regard to establishing their relationships.

5.2.4 ILLUSTRATION OF PROVISIONAL SUBDIVISION 95Demonstration of the importance of provisionally subdividing (or'over classifying') structures into as many categories as possible.

5.2.5 IDENTIFICATION AND CORRELATION OF STRUCTURES 96The role of identification in correlating structures.

5.2.6 IDENTIFICATION (IDENTITY) OF FOLDS (STRUCTURES) 100Discussion of the principles and concepts involved in identifying foldsand the importance of these concepts in establishing successions.

5.2.7 NEOSOME IDENTITY AND CORRELATION 101The use of identified neosomes in correlation.

5.2.8 IDENTIFICATION OF ISOLATED FOLDS 104Discussion relating to the identification of isolated, individual folds(structures).

5.2.9 CERTAINTY OF IDENTIFICATION OF ISOLATED STRUCTURES -REALITY OF THE 'SUCCESSION' OR 'COINCIDENCE' 108Reality of the relationships of structures within and between successionsas opposed to coincidental similarity of unrelated successions - 'real' or'imaginary' successions.

5.2.10 AGMATITES AND FOLD IDENTITY 111Agmatites and their neosomes as an aid to distinguishing betweendifferent fold sets.

5.2.11 RELATIONSHIPS BETWEEN TECTONIC STRUCTURES ANDMULTIPLE AGMATITES 111Distinction between structures of different sets on the basis of theirrelationships to different neosomes stemming from repeated agmatization.

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5.2.12 VARIATION IN EXPRESSION OF RELATED STRUCTURES IN THESAME LIMITED CRUSTAL SEGMENT 113Discussion of the way in which the expression of structures within a setcan vary in response to changing physical conditions within the samecrustal segment.

5.3 FOLD (STRUCTURE) SETS 114The concept of fold sets.

5.3.1 CHARACTERISTIC FEATURES OF FOLDS 115Structural features of folds that contribute to their individuality.

CHAPTER 6 119CORRELATION

6.1 PRINCIPLES AND BASIS OF CORRELATION 119

6.1.1 INTRODUCTION 119Correlating structures and structural successions in terms of theiridentity.

6.1.2 SPATIAL RELATIONSHIPS: THEIR EFFECT ON THE CERTAINTYOF CORRELATION 121The effect of distance between structures on the degree of certaintyof correlation.

6.1.3 STRUCTURAL CORRELATION OF TECTONOSTRATIGRAPHICTERRANES . 125Some illustrations of possible structural characteristics and complexityin hypothetical terranes and their potential as a basis for correlationbetween these terranes.

6.2 STYLE, ITS SIGNIFICANCE AND FACTORS INFLUENCING IT 134

6.2.1 THE CONCEPT OF STYLE 134The meaning of the expression 'style', and the significance andimportance of this concept in structural identity, overprinting andcorrelation.

6.2.2 FACTORS INFLUENCING GEOMETRY AND STYLE OF FOLDS 138(a) Effect of composite fold geometry on styleSubtle stylistic differences between folds that apparently belong to thesame set but which, in fact, belong to a different set because some ofthem are composite. This can happen when they have been overprintedby folds that are so similar-looking to the pre-existing set as to be almostindistinguishable from them, and when there is coincidence of orientationand site of both pre-existing and overprinting structures.(b) Axial trend, axial planar orientation and order of deformationDiscussion of the mutual influence between pre-existing and superimposedstructures on structural orientation of the later structure.

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(c) Effect of later fold scale on fold reorientation(d) Effect of axial planar dip on fold axial trendThe trend of the axial plane of the later fold will vary and therefore isunlikely to be diagnostic, except in the special case where the axialplane is vertical.

6.3 KEY STRUCTURES 145

6.3.1 INTRODUCTION 145The importance of the role of a widely-distributed, identifiable datumstructure (a 'key' structure) in reducing the number of overprintingrelationships that have to be determined when establishing a structuralsuccession, particularly where the succession is an extensive one.

6.3.2 EXAMPLES OF KEY STRUCTURES 148Illustrations of structures exhibiting characteristic features that aresufficiently distinctive to enable them to be widely and unambiguouslyrecognized.

CHAPTER 7 153CHARACTERISTIC FEATURES OF STRUCTURE SUCCESSIONS

7.1 GENERAL FEATURES OF FOLD SUCCESSIONS 153Commonly-occurring (more or less) systematic geometrical and stylisticvariations in fold successions, examples of these and the reasons for them.

7.1.1 IDENTIFYING FOLD MECHANISMS BY USING STEREOGRAPHICANALYSIS 153Identification of fold mechanisms in terms of the distribution on thestereo plot of data related to the fold.

7.2 ILLUSTRATIONS OF TEMPORAL CHANGES OF STYLE IN FOLDSUCCESSIONS 161Photographic illustrations of the types of folds commonly found early,intermediate and late in successions.

7.3 SUMMARY OF PRINCIPAL FEATURES OF FOLD SUCCESSIONS 161The range in fold forms in successions, from early intrafolial isoclinal, to latervery open folds.

7.4 VARIATION WITH TIME OF TOTAL STRUCTURAL COMPLEXITY 163The distinction between the ultimate observed structural pattern (which iscomplex) and the most recent structures which (when not superimposed onearlier structures) are simple.

7.5 PARADOX OF APPARENT SIMILARITY OF FOLD SUCCESSIONS 166Because of features common to all fold successions, when stylistic featuresare discounted, successions tend to be superficially similar.

7.6 EXAMPLES ILLUSTRATING THE SUPERFICIAL SIMILARITY OF FOLDSUCCESSIONS 166Successions from several terranes.

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7.7 SUMMARY OF FOLD VARIATION IN SUCCESSIONS 167Similarities and differences between the folds of different successionssummarized in tabular form showing that each succession is itself distinctive.

CHAPTER 8 173PRINCIPLES OF SUCCESSION DETERMINATION

8.1 DETERMINING THE STRUCTURAL SUCCESSION: THEORY 173

8.1.1 CONCEPTS 173Introductory notes: preamble. Discussion of the principles and conceptsembodied in the methodology used in determining structural successions.

8.1.2 SPATIAL VARIATION IN STRUCTURAL EXPRESSION 174Causes of the variation in expression of structures within sets.

8.1.3 TEMPLATE, OR MASTER KEY CONCEPT 177Comparison of local partial successions in the synthesis of the 'whole'succession likened to interlocking of parts of a three-dimensional jigsawpuzzle, or the compatibility between locks and master keys.

8.1.4 TESTING THE VALIDITY OF OBSERVATIONS 179Validity of observations tested in terms of close scrutiny, rigorousnessand reproducibility.

8.1.5 DETERMINING THE STRUCTURAL SUCCESSION: PRINCIPLES 180General principles of determining structural successions when appliedto structural relationships observed on the outcrop.

8.1.6 NOMENCLATURE: SYMBOLS FOR STRUCTURES AND EVENTS:PRINCIPLES 184The consistent labelling of structures, metamorphic, anatectic andigneous events.(a) A theoretical system of nomenclature(b) Nomenclature allowing expansion of the succession(c) Nomenclature relating deformational, igneous and metamorphicstructures(d) Preliminary labelling of structuresDiscussion of the need to use consistent nomenclature that avoidschronological connotation.(e) Labelling structure sets in practiceA simple, but rigorous notation that includes some information on thecharacteristic features of individual structures.

8.1.7 PARTIAL SUCCESSIONS 189The determination of partial successions.

8.1.8 ABSENCE OF STRUCTURES FROM THE SUCCESSION 190The significance of gaps in the succession in some cases. Why structuresbelonging to some sets may not always be observed.

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8.1.9 EFFECTS OF STRAIN PARTITIONING 191(a) Effect on structural synthesis in broad termsAbsence or modification of a structure set in the structural successionhas little effect on its identity because structural synthesis depends oncorrelation between successions comprising several sets. Recognition ofa structural succession from which a set (or sets) is missing is analogousto the recognition of a book although a page, or even a section is missing.(b) Effect on synthesis when integrating local partial successionsReasons why the absence or modification of a structure set in local partialsuccessions has little effect on the structural synthesis.

8.1.10 APPARENTLY INTRACTABLE STRUCTURAL RELATIONSHIPS 193Approach recommended in those cases where the structural complexityinitially appears to be irresolvable.

8.1.11 'WILDNESS'OF STRUCTURAL PATTERN 194Reality or otherwise of apparent 'wildness' or 'randomness' of complexstructure tested in terms of consistency of structural relationships.

CHAPTER 9 197

FIELD APPROACH: RECONNAISSANCE AND DETAILED STUDY

9.1 INTRODUCTION 197

9.2 FIELD PROCEDURES 1979.2.1 RECONNAISSANCE 197

Ideally carry out a reconnaissanceof the field prior to beginning thesystematic study.(a) Large scale structuresInitially consider treating large-scale structures as separate areas of study.(b) Systematic statistical structural analysisDiscussion of the limitations of systematic statistical structural analysis ofmigmatite terranes.(c) High and low strain zonesNeed to be aware of the existence of extreme variation in degree of strainand the effect of this on observations where exposure is limited.(d) Potential marker horizonsLook for potential marker horizons.(e) Effects of differential abrasionLook for likely sites where structural detail is enhanced by differentialabrasion.if) Angular discordance between structuresLook for distinct differences in structural attitudes indicating angulardiscordance between them.(g) Distinctive structuresLook for distinctive (distinguishing) structural features, particularly inthose cases where there is parallelism between sets of structures.

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(h) 'Cryptic' structuresLook for evidence (such as 'anomalous' orientation of the structure) forstructures whose presence is not immediately obvious (e.g. very open folds).(i) Variation of structural expressionRecognize changes in expression in structures of the same set.(j) Introduced structuresNote the presence of minor intrusions, agmatites, cleavages etc. potentiallyuseful for distinguishing subsequent deformation (Chapter 4).(k) Orientated specimensRecord localities where there is suitable material for collecting orientatedspecimens.(I) Key structuresRecord distinctive structures likely to be suitable for key structures.(m) Relationships to key structuresNote relationships between structures and those likely to be suitable forkey structures.in) Asymmetry of folds relative to large structures: vergenceNote relationships between large-scale and apparently related small-scalestructures.(0) Record of exposures showing clear structural relationshipsNote localities where structural relationships are particularly clear.(p) Ending reconnaissanceCircumstance governing the termination of the reconnaissance.

9.2.2 DETAILED EXAMINATION 207(a) IntroductionReminders of some basic field techniques.(b) Geometrical analysis using stereographic projectionGeometrical analysis, limitations of method and need for directobservation of structural relationships in the field.(c) Orientated specimen collectionProcedure for collection and preparation.(d) Sketches of structural relationshipsValue of field sketches of structural relationships.(e) Orientated photographsImportance of recording observational data, including time anddirection, when taking photographs.(f) Field notesSome important aspects of keeping field records.(g) Structural relationships checkNeed to clarify and confirm uncertain structural relationships continually.(h) Consistency of successions checkNeed for continual check and confirmation of structural relationships.(1) Good field practice(j) Summary

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CHAPTER 10 215STRUCTURAL OBSERVATION

10.1 OBSERVATION OF STRUCTURES AND STRUCTURAL RELATIONSHIPS 215

10.1.1 MIGMATITE STRUCTURAL ANALYSIS: LIMITATIONS OFSTEREOGRAPHIC PROJECTION 215Limitations of stereographic projection in the analysis of complexstructural relationships.

10.1.2 OPEN FOLDS 216Examination of some of the difficulties presented in the resolution ofoverprinting relationships involving open folds.

10.1.3 VERGENCE AND SYMMETRY ASPECTS OF LARGE FOLDS 221Caution regarding the use of vergence of small folds to establish theidentity of large-scale structures.

10.1.4 IMPORTANCE OF METICULOUS OBSERVATION 221Discussion of the need to recognize the significance of structural detailand the importance of making accurate and objective observations. Theproblem posed by visual distraction.

10.1.5 OBSERVATIONS FROM TWO-DIMENSIONAL EXPOSURES 222The limitations of attempting to obtain orientation data based onobservation from two-dimensional exposures.

10.1.6 'APPARENT DIPS'AS DISCRIMINATORY CRITERIA 224The misleading consequences of accepting as dips, the plunges of theintersections of structural surfaces with reference planes, especiallywhen these surfaces are deformed.

10.1.7 EXAMPLES OF SIGNIFICANT OBSERVATIONAL DETAIL 225Illustrations of the type of structural detail whose significance it isessential to appreciate if correct structural relationships are to bedetermined.

10.1.8 FOLD/CLEAVAGE RELATIONSHIPS 227

10.1.9 STRUCTURES ASSOCIATED WITH ONE OR TWO FOLDS 234

10.1.10 MULTIPLE FOLD RELATIONSHIPS 238

CHAPTER 11 247EXAMPLES OF COMPLEX STRUCTURAL RELATIONSHIPS

11.1 LOCAL STRUCTURE SUCCESSIONS COMPRISING SEVERAL SETS 247

11.1.1 INTRODUCTION 247Illustrations of the approach to determining the local structuralsuccession by resolving structural relationships between several foldsets.

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11.1.2 PROCEDURE WITH EXAMPLES 247Examples of specific cases illustrating the analysis of structural relationships.

CHAPTER 12 271PRINCIPLES AND PRACTICE OF DETERMINING STRUCTURAL SUCCESSIONSSUMMARIZED

12.1 INTRODUCTION 271

12.2 OBSERVATION 271The first stage in the field study of structural relationships in a deformed terrane.

12.3 IDENTIFICATION OF STRUCTURES 275The crucial role of identity when relating structural sets.

12.4 KEY STRUCTURES 278The role of the 'key' structure in effectively shortening extensive structuralsuccessions.

12.5 CORRELATION - DISCUSSION OF PRINCIPLES 278(i) Local integration of structure sets.(ii) Correlation of structures between different localities.

12.6 INTEGRATION OF LOCAL SUCCESSIONS - DISCUSSION OF PRINCIPLES 284

12.6.1 INTEGRATION OF LOCAL SUCCESSIONS 284An illustration of the principles of building up an integrated local structuralsuccession from observations of overprinted relationships at four exposures.

12.6.2 STRUCTURAL SUCCESSION FROM OVERPRINTED RELATIONSHIPS 286(a) ProcedureOutline of the steps in determining a structural succession fromoverprinted structures.(b) ExampleAn example from Finnish Svecofennian migmatites to show the methodof establishing the structural succession.

12.6.3 INITIALLY UNCERTAIN RELATIONSHIPS 288A systematic approach to the resolution of hypothetical uncertainstructural relationships from a number of localities.

12.6.4 GAPS IN THE SUCCESSION 292The significance of the fact that sometimes one or more structure setsare not observed in the succession.

12.6.5 SUMMARY OF THE STAGES IN THE INTEGRATION OFSTRUCTURAL SUCCESSIONS 292Table summarizing the determination of a structural succession, fromthe observation of overprinted structural relationships to the finalintegration of composite successions that have been assembled frompartial successions.

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CHAPTER 13 295ANALYTICAL PROCEDURE SUMMARIZED

13.1 INTRODUCTION 295

13.2 CORRELATING LOCAL SUB-SUCCESSIONS: FORMAL PROCEDURE 295The systematic approach to synthesizing the overall ('total') succession.The principle of the systematic building-up of the overall (total recognizable)succession by comparison of overprinting relationships between fold sets.

13.3 ILLUSTRATIONS OF PROCEDURE 301Synthesizing a succession from local sub-successions.

13.3.1 USE OF GEOMETRY FOR PLACING FOLDS IN PROVISIONALORDER OF SUCCESSION 301Provisional order of succession on the basis that earliest folds tend tobe intrafolial, later isoclinal etc., and latest folds, very open.

13.3.2 USING AGMATITES TO IDENTIFY STRUCTURAL RELATIONSHIPS 304Relationships between structures and agmatites and associated neosomesused to identify structures.

13.4 APPLICATION OF PROCEDURE - EXAMPLES FROM DIFFERENTSETTINGS 306

13.4.1 STRUCTURAL SUCCESSION IN THE FINNISH ARCHIPELAGO 307An example of a structural succession determined by this procedurefrom good exposures over a wide area of a complexly-deformedmigmatite terrane (The Svecofennian).

, 13.4.2 STRUCTURAL SUCCESSION IN THE DABIE COMPLEX, CHINA 308An example of a complex structural succession determined fromlimited exposure.

13.4.3 STRUCTURAL SUCCESSION AT LAKE BAIKAL, SIBERIA 309Structural successions determined from widely-spaced, good-qualityexposures.

CHAPTER 14 313BROAD APPLICATIONS

14.1 ACADEMIC APPLICATIONS 313

14.2 ECONOMIC APPLICATIONS 314

14.3 SUMMARY 315

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CHAPTER 15 317CONCLUSIONS

15.1 CONCLUDING REMARKS 317A brief discussion of the principles and practice discussed in the precedingsections, with a summary of the method.

15.2 POSTSCRIPT: SOME POINTS TO BEAR IN MIND 319A reminder of some important points relating to the structural study ofmigmatites.

REFERENCES 321

AUTHOR INDEX 325

LOCALITY INDEX 327

SUBJECT INDEX 331