The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Camera ready by author SPIN: 10736077 32/3142-543210 -Printed on acid-free paper Foreword The Earth's rock-made outer shell, the lithosphere, contains entities of two main types, continental and oceanic. Cratons and

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... le megabelts are lower-rank lateral Iithospheric tectonic units into which continental lithospheric masses are subdivided. Mobile megabelts develop when large zones of continental crust and lithosphere are tectonically mobilized and deeply reworked; the reworked continental lithosphere could have previously been cratonic. Many of the mobile megabelts in the world lie in peripheral regions of continents; others are located far within continental interiors. A megabelt, being a first-order continental lateral tectonic unit, consists of subordinate major units: orogenic zones and median massifs. Median massifs are less tectonically mobilized and reworked than orogenic zones, and they retain more of their ancient (commonly, ex-cratonic) characteristics. Yet, despite the ancient continental inheritance, it is conventional for modern tectonists to regard mobile megabelts not fi'om the vantage point of their parent cratons but from distant oceans genetically unrelated to the continent. The underlying false assumptions are that continents are essentially inert, incapable of selfdevelopment, and that any tectonism in them must be induced externally -from the sub-lithospheric mantle below or from oceanic plates to the side. In reality, continental lithosphere has its own radioactive energy sources, and its tectonic development is mostly an expression of indigenous, internal processes. The ocean-based, "Poseidonian" approach to continental tectonics is illogical at its core: instead of relying on direct observations of rocks in land areas where these rocks are exposed, it puts too much emphasis on speculative, assumption-based reconstructions of distant plate motions in the past and on the assumed effec~ of those supposed motions on continental areas. Plate reconstructions are based not on the observed geology of continental mobile megabelts and cratons but on model-driven interpretations of geophysical anomalies in oceanic regions far away. The global approach has in the last several decades usefully extended the vision of tectonists, which was previously restricted to directly accessible continental regions. Unfortunately, a casualty of this model-based kind of globalization has been the traditional practice of basing tectonic conclusions on the observed, sampled and analyzed rocks and the mapped rock-body relationships. But it is observational geological information that provides the ultimate means to test abstract models, and this fact-based approach is adopted in the present book. Vl Being generally unable to detect high-angle discontinuities, seismic reflection profiles may give the viewer a false, partial impression that only low-angle discontinuities exist in continental crust. The rock nature and origin of these seismically reflective low-angle crustal discontinuities are unknown, and they could be related to a multitude of possible causes: original discontinuities in the protolith, subsequent metamorphic fronts and rheologic boundaries, ductile and brittle shearing, intrusive igneous bodies, and so on. In the absence of direct geological observations, the inherent non-uniqueness of geophysical interpretations precludes definitive conclusions about the rock composition and structure of deep crust. Even in the exposed and drilled uppermost part of the crust, every dry oil or water well, and every failed mining or geotechnical project represents a failure of prediction. Superdeep wells drilled into the upper continental crust in Europe, Russia and North America have presented many surprises quite unanticipated by prior geophysical predictions, including very tmexpected findings about sources of seismic reflections and potential-field anomalies, as well as position of the brittle-ductile boundary and thermal and hydrologic conditions at depth. Not even such sparse geologic constraints are available for the middle and lower crust. The arbitrary and model-driven assumption that seismic-reflection geometries deep in the crust mostly represent thrusting leads to an incorrect perception of the continental crust as necessarily a stack of thrust sheets. Meanwhile, the block structure of the crust goes unnoticed. Tectonics synthesizes the factual findings from field mapping and many specialized geological disciplines -petrology, geochemistry, paleontology, and so on. From a vast amount of diverse information, a tectonist selects that which permits to discern the phenomena induced by endogenic processes in the lithosphere, and combines a broad range of facts and data into an internally consistent concept. This productive, practical approach is utilized in the present study of the Cordilleran mobile megabelt, which lies on the western flank of the North American continent.