6 research outputs found
Southern East Siberia Pliocene-Quaternary faults:Database,analysis and inference
Abstract This paper presents the first release of an Informational System (IS) devoted to the systematic collection of all available data relating to Pliocene–Quaternary faults in southern East Siberia, their critical analysis and their seismotectonic parameterization. The final goal of this project is to form a new base for improving the assessment of seismic hazard and other natural processes associated with crustal deformation. The presented IS has been exploited to create a relational database of active and conditionally active faults in southern East Siberia (between 100°–114° E and 50°–57° N) whose central sector is characterized by the highly seismic Baikal rift zone. The information within the database for each fault segment is organized as distinct but intercorrelated sections (tables, texts and pictures, etc.) and can be easily visualized as HTML pages in offline browsing. The preliminary version of the database distributed free on disk already highlights the general fault pattern showing that the Holocene and historical activity is quite uniform and dominated by NE–SW and nearly E–W trending faults; the former with a prevailing dip-slip normal kinematics, while the latter structures are left-lateral strike-slip and oblique-slip (with different proportion of left-lateral and normal fault slip components). These faults are mainly concentrated along the borders of the rift basins and are the main sources of moderate-to-strong (M ≥ 5.5) earthquakes on the southern sectors of East Siberia in recent times. As a whole, based on analyzing the diverse fault kinematics and their variable spatial distribution with respect to the overall pattern of the tectonic structures formed and/or activated during the late Pliocene–Quaternary, we conclude they were generated under a regional stress field mainly characterized by a relatively uniform NW–SE tension, but strongly influenced by the irregular hard boundary of the old Siberian craton. The obtained inferences are in an agreement with the existing models of the development of the Baikal region
TECTONOPHYSICAL EVIDENCES OF GEODYNAMIC EVOLUTION OF THE PRIKOLYMA TERRAIN (NORTH-EASTERN REGIONS OF RUSSIA)
The Prikolyma terrain is a part of the Yana-Kolyma orogenic belt located in the North Eastern Asia. It is generally composed of the Proterozoic deposits, including sandstones, metapellites, quartz-feldspar and carbonate rocks, meta- and hyperbasites. The Prikolyma terrain represents a fragment of passive margin of the North-Asian craton that was detached in the Middle Paleozoic due to progressing rifting. Subsequent geological development of the terrain was determined by accretion events at its boundary with margin of the North-Asian craton and the Omolon microcraton. Its longterm geodynamic evolution is reflected in the character and sequence of formation of the Prikolyma terrain deformation structures. In the central part of the Prikolyma terrain, i.e. in the basin of the Malaya Stolbovaya river, two reference areas of tectonics were studied, which contain packs of thrust sheets complicated by subsequent highangle faults.The fault pattern is complex, and its major elements are gently dipping zones of plastic deformation, which mark the boundaries of petrographically heterogenous plates. The thrust packs are more than 200 m thick; their root zones are represented by series of highangle reverse faults. Another important element of the fault pattern is highangle zones of brittle deformation, which kinematic characteristics are ambiguous. A vertical component of displacement is predominant for the faults of the north-western strike; a strike-slip component is characteristic of latitudinal and meridional faults. The fault pattern developed in several stages under the impact of fields of tectonic stress, which vectors were variable. The folds, comprising a uniform structural paragenesis with thrusts, are of great importance for the structure under study. The largest folds exhibit the asymmetric structure with the N-E dipping axial planes. Axes of smaller folds are oriented to N-W and N–NW.Four stages of deformation are distinguished in the history of geological development of the Prikolyma terrain. The earliest stage was characterized by the N-E compression resulting in formation of the N-W-oriented thrusts and folds and zones of greenschiest dynamo-metamorphism. During the second stage, the axis of compression gained the E–NE orientation, and the axis of extension was oriented to the N–NW, which influenced the formation of the submeridional reverse faults and thrusts. During the third stage, the axis of compression was N-W oriented, and the axis of extension gained the N-E orientation. Thereat, the sublatitudinal and submeridional structures were activated as strike-slip faults, the N-W structures as normal faults, and the N-E structures as reverse faults. The above resulted in the formation of structures of volume extension, which are favorable for localization of magmatic bodies and ore streaky-veined structures. At the final stage, compression in the meridional direction lead to the formation of thrusts and reverse faults along the sublatitudinal displacements, normal faults along the submeridional displacements, and strike-slips along the N-E and NW displacements.The first deformation stage was contemporaneous with the long-term period of compression in the Riphean and Early Paleozoic, when the dynamo-metamorphic complex of the Prikolyma terrain was developed. In the second stage, the Prikolyma terrain was detached from the margin of the North-Asian craton. In the Early Cretaceous, the third stage took place, when rearrangements of the field of tectonic stresses and transition to conditions of general extension caused emplacement of granitoids and quartz veining. The N-W orientation of the compression vector suggests that the third stage was related to the regional tangential compression due to the asymmetrical collision of the Prikolyma terrain and the Omolon microcraton. In the final stage, rotation of the vector of compression, associated with development of numerous N-W and N-E-oriented fractures, reflected the occurrence of the epiorogenic rifting. The above-described stages of formation of the deformation structure of the Prikolyma terrain are evidently correlated with the main tectono-magmatic stages of development of the NE margin of the North-Asian craton, which took place in the Late Paleozoic and the Mesozoic
ТЕКТОНОФИЗИЧЕСКИЕ КРИТЕРИИ ГЕОДИНАМИЧЕСКОЙ ЭВОЛЮЦИИ ПРИКОЛЫМСКОГО ТЕРРЕЙНА (СЕВЕРО-ВОСТОК РОССИИ)
The Prikolyma terrain is a part of the Yana-Kolyma orogenic belt located in the North Eastern Asia. It is generally composed of the Proterozoic deposits, including sandstones, metapellites, quartz-feldspar and carbonate rocks, meta- and hyperbasites. The Prikolyma terrain represents a fragment of passive margin of the North-Asian craton that was detached in the Middle Paleozoic due to progressing rifting. Subsequent geological development of the terrain was determined by accretion events at its boundary with margin of the North-Asian craton and the Omolon microcraton. Its longterm geodynamic evolution is reflected in the character and sequence of formation of the Prikolyma terrain deformation structures. In the central part of the Prikolyma terrain, i.e. in the basin of the Malaya Stolbovaya river, two reference areas of tectonics were studied, which contain packs of thrust sheets complicated by subsequent highangle faults.The fault pattern is complex, and its major elements are gently dipping zones of plastic deformation, which mark the boundaries of petrographically heterogenous plates. The thrust packs are more than 200 m thick; their root zones are represented by series of highangle reverse faults. Another important element of the fault pattern is highangle zones of brittle deformation, which kinematic characteristics are ambiguous. A vertical component of displacement is predominant for the faults of the north-western strike; a strike-slip component is characteristic of latitudinal and meridional faults. The fault pattern developed in several stages under the impact of fields of tectonic stress, which vectors were variable. The folds, comprising a uniform structural paragenesis with thrusts, are of great importance for the structure under study. The largest folds exhibit the asymmetric structure with the N-E dipping axial planes. Axes of smaller folds are oriented to N-W and N–NW.Four stages of deformation are distinguished in the history of geological development of the Prikolyma terrain. The earliest stage was characterized by the N-E compression resulting in formation of the N-W-oriented thrusts and folds and zones of greenschiest dynamo-metamorphism. During the second stage, the axis of compression gained the E–NE orientation, and the axis of extension was oriented to the N–NW, which influenced the formation of the submeridional reverse faults and thrusts. During the third stage, the axis of compression was N-W oriented, and the axis of extension gained the N-E orientation. Thereat, the sublatitudinal and submeridional structures were activated as strike-slip faults, the N-W structures as normal faults, and the N-E structures as reverse faults. The above resulted in the formation of structures of volume extension, which are favorable for localization of magmatic bodies and ore streaky-veined structures. At the final stage, compression in the meridional direction lead to the formation of thrusts and reverse faults along the sublatitudinal displacements, normal faults along the submeridional displacements, and strike-slips along the N-E and NW displacements.The first deformation stage was contemporaneous with the long-term period of compression in the Riphean and Early Paleozoic, when the dynamo-metamorphic complex of the Prikolyma terrain was developed. In the second stage, the Prikolyma terrain was detached from the margin of the North-Asian craton. In the Early Cretaceous, the third stage took place, when rearrangements of the field of tectonic stresses and transition to conditions of general extension caused emplacement of granitoids and quartz veining. The N-W orientation of the compression vector suggests that the third stage was related to the regional tangential compression due to the asymmetrical collision of the Prikolyma terrain and the Omolon microcraton. In the final stage, rotation of the vector of compression, associated with development of numerous N-W and N-E-oriented fractures, reflected the occurrence of the epiorogenic rifting. The above-described stages of formation of the deformation structure of the Prikolyma terrain are evidently correlated with the main tectono-magmatic stages of development of the NE margin of the North-Asian craton, which took place in the Late Paleozoic and the Mesozoic.Приколымский террейн является составной частью Яно-Колымского орогенного пояса северо-востока Азии. Он сложен главным образом протерозойскими образованиями: песчаниками, метапелитами, кварц-полевошпатовыми и карбонатными породами, метабазитами и гипербазитами. Приколымский террейн представляет собой фрагмент пассивной окраины Северо-Азиатского кратона, отторгнутый в среднем палеозое вследствие прогрессировавшего рифтинга. Дальнейшее геологическое развитие террейна определялось аккреционными событиями на его границах с окраиной Северо-Азиатского кратона и Омолонским микрократоном. Длительная геодинамическая эволюция нашла свое отражение в характере и последовательности образования деформационных структур Приколымского террейна. Изучены два опорных участка земной коры в центральной части Приколымского террейна (бассейн р. Малая Столбовая), представляющих собой пакеты надвиговых чешуй, осложненные поздними крутопадающими разломами. Сеть разломов имеет сложное строение. Одним из основных ее элементов являются пологие зоны пластических деформаций, маркирующие границы петрографически разнородных тектонических пластин. Мощности надвиговых пакетов превышают 200 м, а их корневые зоны представлены сериями крутопадающих взбросов. Другим важным элементом разломной сети являются крутопадающие зоны хрупких деформаций. Их кинематические характеристики неоднозначны. У дизъюнктивов северо-западного простирания преобладает вертикальная компонента смещения, у широтных и меридиональных – сдвиговая. Формирование сети разрывных нарушений происходило в течение нескольких этапов под действием различных полей тектонических напряжений. Большую роль в структуре играют складки, образующие единый парагенез с надвигами. Наиболее крупные из них имеют асимметричное строение с падением осевых плоскостей на северо-восток. Оси более мелких складок ориентированы в северо-западном и север-северо-западном направлениях.В истории геологического развития Приколымского террейна выделены четыре деформационных этапа. Наиболее ранний характеризовался сжатием в северо-восточном направлении, в результате которого образовались надвиги и складки северо-западной ориентировки, зоны зеленосланцевого динамометаморфизма. На втором этапе ось сжатия приобрела восток-северо-восточную ориентировку, а растяжения – север-северо-западную, что отразилось в формировании субмеридиональных взбросов и надвигов. В течение третьего этапа ось сжатия имела северо-западную, а ось растяжения – северо-восточную ориентировку. Субширотные и субмеридиональные структуры при этом активизировались как сдвиги, северо-западные – как сбросы, а северо-восточные – как взбросы. В результате формировались структуры объемного растяжения, благоприятные для локализации магматических тел и прожилковожильных образований. На завершающем этапе сжатие в меридиональном направлении привело к образованию надвигов и взбросов по субширотным нарушениям, сбросов – по субмеридиональным, сдвигов – по северо-восточным и северо-западным. Первый деформационный этап параллелизуется с крупной рифейско-раннепалеозойской эпохой сжатия, сформировавшей динамометаморфический комплекс Приколымского террейна. Второй этап отразил обособление Приколымского террейна от окраины Северо-Азиатского кратона. В раннем мелу перестройка поля тектонических напряжений и переход к условиям общего растяжения на третьем этапе привели к внедрению гранитоидов и формированию зон кварцевого прожилкования. Северо-западная ориентировка вектора сжатия позволяет увязать этот этап с региональным тангенциальным сжатием в результате косой коллизии Приколымского террейна с Омолонским микрократоном. На завершающем этапе поворот вектора сжатия с образованием многочисленных трещин северо-западной и северо-восточной ориентировки отразил проявление эпиорогенного рифтогенеза.Выделенные этапы формирования деформационной тектонической структуры Приколымского террейна четко параллелизуются с главными тектономагматическими этапами развития северо-восточной окраины Северо-Азиатского кратона – позднепалеозойским и мезозойским