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Recurrence interval of strong earthquakes in the se Altai, Russia revealed by tree-ring analysis and radiocarbon dating

Nepop R. K., Agatova A. R.

Geochronometria

2018

Vol. 45, no. 1

20--33

This paper presents the results of paleoseismogeological investigations including tree-ring analysis and radiocarbon dating in pleistoseist zone of the 2003 Chuya earthquake, SE Altai, Russia. Twenty-five radiocarbon dates of previously unknown evidences of prehistoric earthquakes along the fault bounders of the Chagan-Uzun massif, North Chuya and South Chuya ranges are reported. Perspectives of applying dendroseismological approach within the high mountainous seismically active southeastern part of Russian Altai are demonstrated. In addition to estimating the germination ages of trees growing on the bare surfaces of seismically triggered landslides, analysis of wood penetrating injuries in the individual tree ring series was applied for dating paleorock-falls. Analysis of distribution patterns of tree-ring anomalies and injured trees suggests a criterion of recognizing seismic origin of past rock-falls. Dendrochronologically obtained dates of abrupt intensifications of rock-falls can be considered as supposed dates of past earthquakes, which should be verified by alternative proxy data. Obtained results argue for the high regional seismicity in the second half of the Holocene. Strong earthquakes occurred here AD 1532, and 600–700, 1300–1500, 2400–2700, 3400–3700, 3800–4200 cal BP. This data clarifies the chronology of seismic events within the SE Altai. The specified recurrence interval of strong earthquakes is about 400 years during the last 4000 years.

Petrological implications of the Early Mesozoic lamprophyre dikes and related Tarkhata syenites (SE Altai and NW Mongolia)

Vasyukova E. A., Borisenko A. S.

Mineralogia

2013

Vol. 44, iss. 1/2

13--30

This paper presents new data derived from field sampling and from a thorough description of lamprophyres located in southeastern Altai and northwestern Mongolia in terms of their mineralogy, textures, and chemical composition. The swarms of alkaline mafic dikes in the area coexist with granosyenite-monzodiorite and gabbro-dolerite intrusions and spatially coincide with an ore district of Sb-Hg, Ag-Sb, Ni-Co-As, Cu-Mo-W, and CaF2 hydrothermal mineralization. All lamprophyres belong to the Early Mesozoic Chuya complex formed in an intracontinental enviroment. Their distribution and orientation is controlled by two large fault zones. The Chuya dikes were investigated at two localities, namely, Yustyd and South-Chuya. The Yustyd lamprophyres intrude Middle-Upper Devonian black shale of the Yustyd depression. At South Chuya, lamprophyres, together with the Tarkhata granosyenite-monzodiorite complex, are hosted by Cambrian and Ordovician metamorphic rocks of the South-Chuya Range. Ar-Ar (phlogopite) and U-Pb (SHRIMP, zircon) ages of the lamprophyre dikes indicate long and continuous period of the formation of the Chuya complex (250-235 Ma). Major- and trace-element compositions of the lamprophyres from both localities and of the syenite indicate their origin from the same magma source. The textures and structures of the lamprophyre and plutonic rocks, their mineral assemblages and the chemistry of the rock-forming minerals provide clues to the evolution of the parental alkaline mafic magma and fluid regime.