Jom-Bolok Holocene volcanic field in the East Sayan Mts., Siberia, Russia: structure, style of eruptions, magma compositions, and radiocarbon dating

Abstract

Jom-Bolok volcanic field is located in the East Sayan Mts. of Siberia (Russia), a portion of the Asian convergent zone. It is located at the boundary of the Riphean Tuva-Mongolia massif, which was probably reactivated because of the interplay between far-field tectonic stress derived from the India–Asia collision zone and extension in the south-western Baikal rift system. The volcanic field comprises a number of hawaiitic lava flows, of various lengths, which flowed down paleorivers. Flows were fed by fissure eruptions and the largest lava flow field was dated as 7,130 ± 140 cal ¹⁴C years BP using a buried organic sample found inside the associated cinder cone. This lava flow field is about 70 km long, ∼100 km² in area, and 7.9 km³ in volume. The area and volume of this flow field ranks this eruption highly in the global record of fissure-fed effusive eruptions. This lava flow field makes up 97% of the entire Jom-Bolok volcanic field, a fact which raises a puzzling question: why and/or how did a relatively small-volume volcanic field produce such a large-volume individual eruption? A working hypothesis is that a pond of sublithospheric melt accumulated over a relatively prolonged period. This was then rapidly drained in response of tectonic changes triggered by unloading of ice in the Early Holocene.

Appendix: Punctuated history of Jom-Bolok studies

Initial information about the volcanoes in the East Sayan Mts. was published in a local Siberian newspaper in 1858 by an English architect, Thomas Witlam Atkinson. Later, he devoted a number of pages in his extensive travel book to the same volcanoes (Atkinson 1859). In 1852, Atkinson travelled from the inhabited Oka river area, along Jom-Bolok river (referred by him as Djem-a-look river) up to Haranur lake and the Hee-Gol valley (Fig. 3). Apparently, he was among the first visitors to the volcanoes, because the local Bouriat people had great dread of that valley, and never ascended it except by compulsion (Atkinson 1859, p. 461). His report was used later by the Russian royal Peter Alekseevich Kropotkin, who was famous for both his anarchist philosophy and contributions to glaciology (see Ivanova and Markin 2008). He visited the volcanoes in 1865 and provided a geological description (Kropotkin 1867). In 1914, the Hee-Gol valley was unsuccessfully visited by the Russian geodesist Sergey Pavlovich Peretolchin, who died there under strange circumstances. A local Bouriat, who guided him to the Hee-Gol valley, came back alone to the Oka sentry post (a fortress-like settlement of Russian Cossacks) and reported Peretolchin's death. However, only a theodolite, which had been set up for a geodetic survey, was observed during the Cossacks' inspection in the Hee-Gol valley. Neither his body or belongings were ever found.

The next series of Jom-Bolok studies began in 1940 as part of systematic mapping of the Soviet Union by the USSR Geological Survey. Notable reports on the Jom-Bolok volcanic fields from these studies were by published by Obruchev and Lurye (1954), Adamovich et al. (1959), Grosvald (1965), and Kiselev and Medvedev (Kiselev et al. 1979). In these studies, major cones, namely Kropotkin, Peretolchin, and Stariy, as well as some less prominent edifices (Treshina, Medvedev) were described (Fig. 4). The age of the Jom-Bolok volcanic field was assumed to be Holocene based on the relation between its lavas and glacial deposits, as well as the youthful morphology of the Kropotkin and Peretolchin cones. Obruchev and Lurye (1954) pointed out that the lava was fed from fissures and that Kropotkin and Peretolchin volcanoes were formed during the final stage of the eruptions. They also considered that (a) Stariy (meaning old in Russian) volcano was older than the lava, whereas (b) Kropotkin and Peretolchin volcanoes were younger than the lava. Thus, multiple volcanic episodes were suggested.

Recently, the Jom-Bolok volcanic field was studied by Yarmolyuk et al. (2003a). These authors provided data for the major and trace elements, plus Sr–Nd isotopes, measured for a limited number of samples collected in the Hee-Gol valley and along the Jom-Bolok river. They show that the magma composition was hawaiitic with a typical ocean-island basalt trace element composition (Sun and McDonough 1989) and moderately depleted Sr–Nd isotope ratios.