Determination of structural successions in migmatites and gneisses : a manual for geologists concerned with the interpretation of complex structural relationships in highly deformed deep crustal rocks

This book has been written in response to While considerable effort has been made to requests from a number of colleagues in the ensure that the coverage is comprehensive, it is earth sciences in different parts of the world. not necessarily exhaustive. Prominent among these are geologists whose The importance attached to the structural interests lie in the fields of isotopic and analysis of migmatites (and other complex economic geology and who have a particu­ structural associations) stems from the fact larly keen appreciation of the importance to that resolution of their structural complexity their work of a thorough understanding of the has such a significant bearing on many aspects structural relationships in rocks, especially of geology, both academic and economic. where such rocks, like migmatites, have a long Examples of some of these applications are and often complex developmental history. listed in Chapter 14. Two particularly impor­ What these geologists asked for was a guide tant aspects are that the structural characteris­ to the methods employed in resolving the struc­ tics so identified can be used (1) to correlate tural complexity of repeatedly deformed rocks between separated rock units with comparable (i. e. those affected by 'polyphase' or multiple deformational histories, including segments deformation), especially in Precambrian base­ of fragmented supercontinents, and (2) to ment terranes. This is the first book to deal specifically with the procedures used in the analysis of structural relationships and the determination of structural successions in complexly deformed rocks such as migmatites and gneisses. The establishment of structural successions enables: The rigorous control of the dating of specific events in the deformational history by constraining the sites of the dated rocks within the structural succession; The establishment of the time span of orogenic events throughout the structural succession, and the rate of orogenic processes; Their comparison to be used as a basis for correlation between dismembered and separated crustal segments in continental reconstructions; The resolution of the complex relationships between deformed ore bodies and host rocks in high grade terranes, and hence determination of the structural control of ore bodies, an essential part of any successful geological exploration, and a precondition to efficient exploitation. With its new approach, and the use of practical field examples from various parts of the world, this highly illustrated work will form an invaluable reference resource for postgraduates, lecturers and researchers in the structural and isotope geology of high-grade metamorphic terranes, as well as for exploration and survey geologists working in the field. Dr Alaric M. Hopgood who holds an Honorary Readership at the University of St Andrews, Scotland, was a Reader in the Department of Geology there until 1995. This is the first book to deal specifically with the procedures used in the analysis of structural relationships and the determination of structural successions in complexly deformed rocks such as migmatites and gneisses. The establishment of structural successions enables: the rigorous control of the dating of specific events in the deformational history by constraining the sites of the dated rocks within the structural succession; the establishment of the time span of orogenic events throughout the structural succcession, and the rate of orogenic processes; their comparison to be used as a basis for correlation between dismembered and separated crustal segments in continental reconstructions; the resolution of the complex relationships between the deformed ore bodies and host rocks in high grade terranes, and hence determination of the structural control of ore bodies, an essential part of any successful geological exploration, and a precondition to efficient exploitation. With its new approach, and the use of practical field examples from various parts of the world, this highly illustrated work will form an invaluable reference resource for postgraduates, lecturers and researchers in the structural and isotope geology of high-grade metamorphic terranes, as well as for exploration and survey geologists working in the field Front Matter....Pages i-xxvii General Characteristics of Migmatites and Migmatite Terranes....Pages 1-18 Principles of Structural Analysis of Migmatites....Pages 19-35 Development of Migmatite Structure: Overprinting....Pages 37-58 The Role of Structures Interposed in the Succession....Pages 59-83 Fold (Structure) Successions and Deformational Sequences....Pages 85-117 Correlation....Pages 119-152 Characteristic Features of Structure Successions....Pages 153-172 Principles of Succession Determination....Pages 173-195 Field Approach: Reconnaissance and Detailed Study....Pages 197-213 Structural Observation....Pages 215-246 Examples of Complex Structural Relationships....Pages 247-269 Principles and Practice of Determining Structural Successions Summarized....Pages 271-294 Analytical Procedure Summarized....Pages 295-312 Broad Applications....Pages 313-315 Conclusions....Pages 317-320 Back Matter....Pages 321-346