Учебно-методическое пособие «Структуры и текстуры магматических и метаморфических горных пород» предназначено для обеспечения необходимыми сведениями одноименного раздела профилирующего курса «Петрография магматических и метаморфических горных пород» по направлению «Геология». В пособии дается целостное представление о характере структур и текстур, отражающих условия формирования различных по происхождению магматических и метаморфических горных пород. Основной целью учебного пособия является знакомство студентов-геологов с наиболее распространенными структурами и текстурами магматических и метаморфических пород, их характерными признаками и происхождением.
Одна из основных задач петрологии - реконструкция процессов формирования и эволюции горных пород. В решении этой задачи большую роль играют минеральные реликты и реакционные структуры в метаморфических породах. Из них наибольшее внимание привлекают зональные минеральные структуры, образовавшиеся в результате диффузионного и\или инфильтрационного метасоматоза на контакте несовместных пород. Эти структуры являются промежуточным продуктом субсолидусных превращений на пути к окончательному равновесию.
На основе петрогенстической классификации пород кимберлитовой формации впервые дано описание текстурно-структурных разновидностей и минеральных разностей кимберлитовых и ко-магматичных им образований. В пояснениях к фототаблицам приведена характеристика структурных особенностей конкретных типов, разновидностей и разностей пород и их химический состав. Атлас предназначен для широкого круга геологов и петрографов в качестве справочного руководства.
Атлас составлен на основе изучения автором многих пегматитовых полей Советского Союза различного возраста и генезиса. Фотографии, чертежи и зарисовки иллюстрируют описание хрусталеносных и редкометальных пегматитов. Различаются два типа текстур и связанных с ними структур: первичных, образовавшихся па первых этапах развития пегматитового процесса, и вторичных — более поздних.
The study of sedimentary rocks has come a long way in the past 200 years. In the nineteenth century, they were regarded as the matrix in which fossils occurred and their study, as far as it went, was mainly tied up with the understanding of stratigraphy. Sedimentary rocks had clearly been deposited through time in some way, but little attention was paid to asking exactly how. There was a general appreciation of the idea that ancient processes and conditions of deposition were probably similar to those prevailing at the present day (actualism and uniformitarianism), but, with a few notable exceptions, detailed study concentrated on description of the rocks as materials, rather than as products of dynamic processes and environments. This attitude prevailed until the middle of the twentieth century, although pioneering studies had, by then, used sedimentary structures as indicators of top and bottom (way-up) in deformed successions and as a means of deducing palaeocurrent directions. <...>
As the General Preface accompanying Volume I contains an introduction to the work as a whole, it is only necessary for me here to outline the scope of the second volume. Volume I1 is about sedimentary structures found in relatively complex physical settings, where groupings or hierarchies of features are often of most interest, and more emphasis is placed than in the first volume on cohesive as opposed to cohesionless beds. Secondary currents can exist for a number of reasons in boundary-layer flows, giving rise to flow-parallel sedimentary structures on both kinds of bed.
Sedimentary structures arise in immediate or close association with the transport of sedimentary materials. Some form where erosion predominates, others as net deposition prevails, and yet further kinds in the brief interval of time between sediment deposition and significant lithification. Many sedimentary structures are ordered features visible on sedimentation (bedding) surfaces, whereas others, often related to surface forms, are expressed as compositional and/or textural patterns (stratification) within Sedimentary deposits. Sedimentary structures can be created by chemical and biological as well as by physical agencies, but this book is about those structures wholly or predominantly shaped by physical mechanisms. The latter are much the most important and have continued to attract attention since the earliest days of the earth sciences in their modern form. <...>
Sedimentary structures that show up in outcrops and cores tell us about physical, biological and sometimes also chemical conditions at the time they were formed. Varying hydraulic or aerodynamic conditions result in assemblages of structures that often bear diagnostic features of sedimentary environments. Therefore an understanding of the origin of sedimentary structures and their assemblages is a prerequisite for sedimentologists and petroleum geologists involved in core description and interpretation.
The recognition and interpretation of ore textures is a difficult task, and the problem is compounded firstly by the relatively low priority given to the subject within most tertiary training institutions, and secondly by the lack of simple well illustrated texts. Special reference needs to be focused upon features which are visible to the eye or observed via a hand lens. These are the most valuable to practicing field geologists. <...>
Processes involved in the development of igneous and metamorphic rocks involve some combination of crystal growth, solution, movement and deformation, which is expressed as changes in texture (microstructure). Recent advances in the quantification of aspects of crystalline rock textures, such as crystal size, shape, orientation and position, have opened new avenues of research that extend and complement the more dominant chemical and isotopic studies.
