Reconstruction of the Lateral Series of the Late Cambrian and Early Ordovician Active Continental Margin Structures in the Paleozoides of Northern Kazakhstan

— A comprehensive study of the Upper Cambrian and Lower Ordovician rock complexes of Northern Kazakhstan was carried out; their ages were substantiated; the structural pattern and setting and rock compositions were investigated. It was established that the Upper Cambrian complexes are represented by coarse clastic sequences and mafic alkaline effusive rocks and gabbro, while felsic volcanic rocks and granites are represented only by boulders in conglomerates. The Lower Ordovician is characterized by basalt–rhyolite series, felsic alkaline volcanics, and granitoids. The lateral series of structures of the active continental margin were reconstructed for the Late Cambrian and the Early Ordovician. The Late Cambrian lateral series includes only the structures of the extensional hinterland, where rock complexes with intraplate-type geochemical characteristics were formed. The lateral series of the Early Ordovician structures represent the foreland volcanic region, where island arc-related volcanics are widespread, and the extensional hinterland region with intraplate felsic volcanic rocks and granites. It is assumed that the differences between the lateral series of structures could be due to a change in the sense of plate motion within the active continental margin at the Cambrian–Ordovician boundary, when the transform faulting mode, which is not associated with suprasubduction magmatism, gave way to the convergent magmatism with wide development of arc-related volcanic rocks.