The junction zone between Lomonosov submarine ridge and the shelf of the East Siberian Sea was studied. The aim was to prove the absence of a strike-slip fault in the junction zone between Lomonosov Ridge and the East Siberian shelf. The problem of the existence of a fault zone in the region where the Lomonosov Ridge joins the East Siberian shelf is still currently debateable. The geological and geophysical data used to solve it are insufficient. To remove this ambiguity, seismological data obtained in neighboring areas were used. An analysis of the map of earthquake epicenters in the region showed that, if the fault zone mentioned existed, present-day intraplate seismic activity would certainly be observed within its limits. The absence of seismicity in the junction zone between Lomonosov Ridge and the adjacent shelf clearly indicates the genetic unity of these structures.

Объект исследований - зона сочленения подводного хребта Ломоносова и восточно-сибирского шельфа. Цель работы - доказательство отсутствия сдвигового разлома в зоне сочленения подводного хребта Ломоносова и восточно-сибирского шельфа. Проблема существования разломной зоны в области сочленения хребта Ломоносова с шельфом Восточно-Сибирского моря до настоящего времени является дискуссионной. Использовавшиеся для её решения геолого-геофизические данные оказались недостаточными. Для снятия неоднозначности были привлечены сейсмологические данные в соседствующих районах. Анализ карты эпицентров землетрясений региона показал, что в случае существования указанной разломной зоны в её пределах непременно отмечалось бы современная внутриплитная сейсмическая активность. Асейсмичность зоны сочленения хребта Ломоносова с прилегающим шельфом однозначно свидетельствует о генетическом единстве указанных структур.

Based on obtained data, the paper considers the structure of the sedimentary cover and basement in the continent–ocean transition zone. We analyze the structure of modern tectonic activity zones in the Laptev Sea and structurally similar zones in the Novosibirsk Trough and the De Long Massif. Three sedimentary Anisin–Laptev, Amundsen, and West Laptev basins separated by basement uplifts are distinguished in sedimentary cover. The Anisin–Laptev Basin is separated from the West Laptev Basin by the North Laptev Horst and from the Amundsen Basin by an uplift stretching from the Lomonosov Ridge and covered by the Neogene–Quaternary deposits. The modern tectonic activity zone, marked by a rift valley and earthquakes, stretches across the continental slope from the Gakkel Ridge above a sedimentary rock sequence possessing many-kilometers thickness. The zone reached its present-day position in the Pliocene. Near the shelf boundary, the zone bifurcates, with one branch departing into the West Laptev Basin, and the other branch departing into grabens that developed to the west of New Siberian Islands forming the Laptev microplate.

The inregrated geological and geophysical studies carried out in recent years in the Lomonosov Ridge and at its junction with the Eurasian shelf revealed evidence for thinned (reduced) crust in the ridge (20-25 km) and its relationship with shelf structures. We compared the parameters of deep seismic cross-sections of the shelf and Lomonosov Ridge, thus proving the existence of continental crust in the latter. Also, we analyzed the deep structure of the junction between the Lomonosov Ridge and the shelf and established a genetic geologic relationship, with no evidence that the Lomonosov Ridge moved as a terrane with respect to the shelf. In addition, seismological studies independently confirm the relationship between the Lomonosov Ridge and the adjacent shelf.The Lomonosov Ridge is a continental-crust block of a craton. The craton was reworked during the Caledonian tectonomagmatic activity with the formation of a Precambrian-Caledonian seismically unsegmented basement (upper crust) and an epi-Caledonian platform cover. Afterward, the block subsided to bathyal depths in the Late Alpine. This block and the adjacent areas of the Eastern Arctic shelf developed in the platform regime till the Late Mesozoic. (C) 2012, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

On the basis of a generalization of all available data on the distribution of earthquake epicenters and their focal mechanisms, the opinion is expressed that there is no thorough splitting of Laptev Sea lithosphere associated with the divergent boundary between the Eurasia and North American plates. There are two fragments of this boundary which are laterally separated by hundreds of kilometers. The northern fragment is the end of the oceanic segment of the boundary and is situated within the limits of the northern end of the branch of mesozoids of Northeastern Eurasia which extends here and a part of the superposed Omoloy graben. The southern fragment extends from the continent along the flexural-fault boundaries of the Lena-Taymyr zone of boundary uplifts. It is postulated that with continuation of operation of the geosource of dilatational forces in the Laptev Sea, either a microplate or a zone of transform faults of the Spitsbergen type may be formed. (C) 1999 Elsevier Science B.V. All rights reserved.