Petrological and geochemical evolution of the Tolbachik volcanic massif, Kamchatka, Russia

Abstract

Data on the geology, petrography, and geochemistry of Middle-Late-Pleistocene rocks from the Tolbachik volcanic massif (Kamchatka, Klyuchevskaya group of volcanoes) are presented and compared with rocks from the neighboring Mount Povorotnaya, Klyuchevskaya group basement, and Holocene-historical Tolbachik monogenetic cones. Two volcanic series of lavas, middle-K and high-K, are found in the Tolbachik massif. The results of our data analysis and computer modeling of crystallization at different P-T-H 2 O-fO 2 conditions allow us to reconstruct the geochemical history of the massif. The Tolbachik volcanic massif started to form earlier than 86 ka based on K-Ar dating. During the formation of the pedestal and the lower parts of the stratovolcanoes, the middle-K melts, depleted relative to NMORB, fractionated in water-rich conditions (about 3% of H 2 O). At the Late Pleistocene-Holocene boundary, a large fissure zone was initiated and the geodynamical regime changed. Upwelling associated with intra-arc rifting generated melting from the same mantle source that produced magmas more enriched in incompatible trace elements and subduction components; these magmas are high-K, not depleted relative to N-MORB melts with island arc signatures and rift-like characteristics. The fissure opening caused degassing during magma ascent, and the high-K melts fractionated at anhydrous conditions. These high-K rocks contributed to the formation of the upper parts of stratovolcanoes. At the beginning of Holocene, the high-K rocks became prevalent and formed cinder cones and associated lava fields along the fissure zone. However, some features, including 1975However, some features, including -1976 Northern Breakthrough, are represented by middle-K high-Mg rocks, suggesting that both middle-K and high-K melts still exist in the Tolbachik system. Our results show that fractional crystallization at different water conditions and a variably depleted upper mantle source are responsible for all observed variations in rocks within the Tolbachik volcanic massif. Sr-Nd isotopes are consistent with 2-4% crustal assimilation during formation of the pedestal and stratovolcanoes, while the young lava fields do not show evidence of crustal assimilation. Major and trace element data coupled with K-Ar dating provide strong evidence that Mount Povorotnaya, located in 8 km northeast of Plosky Tolbachik, is an old block of the Tolbachik massif pedestal and for the moment it is the oldest (306 ka) known object in Klyuchevskaya group of volcanoes.

The Ploskie Sopki volcanic massif: Geology, petrochemistry, mineralogy, and petrogenesis (Klyuchevskoi Volcanic Cluster, Kamchatka)

“…All this implies the comparative independence of two coexisting parent magmas that were generated at different magma sources in a region of the upper mantle. The fact that a deep-seated source of trachybasaltic magma did exist is shown by an alkaline-basaltic composition of the plateau rocks (Churikova et al, 2013(Churikova et al, , 2015a, which reflects the stage of volcanism that preceded the formation of the Ploskie Sopki massif, and by the essential similarity to the scenario enacted in the Tolbachik Dol volcanism (Braitseva et al, 1984;Flerov et al, 2015;Koloskov et al, 2015;Churikova, 2015aChurikova, , 2015b). This in turn provides evidence that alkaline magma was involved in the general process of volcanic activity on the Ushkovskii stratovolcano with subsequent synchronous existence of a basaltic and a trachybasaltic magma source.…”

“…The magma generation processes in the evolution of the Ploskie Sopki and Tolbachik Dol volcanic centers, as expressed in interrelationships between magmas of different alkalinities, are essentially similar; this may indicate the coexistence of independent sources where basaltic and trachybasaltic melts are generated in the upper mantle beneath the entire Klyuchevskoi Volcanic Cluster (Flerov et al, 2015;Churikova et al, 2015aChurikova et al, , 2015bKoloskov et al, 2015). In fact, this concept of two coexisting sources where basaltic and alkaline basaltic magmas are generated, as well as their occurrence at a common volcanic center, is reflected in Fig.…”

“…3c,3d). The overall picture that emerges from inspection of the diagrams of (Churikova et al, 2015a), (10,13,17,24) (Ivanov, 2008); (1,8,9,18,19,21,31) were performed at the Institute of Geology, Far East Branch, Russian Academy of Sciences using the XRF technique; the rest of the analyses were performed at the Institute of Volcanology, Far East Branch, Russian Academy of Sciences by wet chemistry. * Total iron.…”

The Tolbachik volcanic massif: A review of the petrology, volcanology and eruption history prior to the 2012–2013 eruption

“…Almost no trace element and isotopic data exist for samples from the Tolbachik pedestal and stratovolcanoes, except one sample PT33-1/82, which was analyzed for trace elements, and Sr, Nd, Pb, U-Th-Pa-Ra and Re-Os isotopes (Alves et al, 1999;Pineau et al, 1999;Dosseto et al, 2003). But a new dataset of analyses from these regions are presented by Churikova et al (2015).…”

New data on age, material composition and geological structure of the Central Kamchatka depression (CKD). Part 1. Rocks types. Age, petrological and isotopo-geochemical characteristicsн

“…Далее мы еще вернемся к этой работе в ходе обсуждения полученных материалов. Следует также отметить недавние работы по петрологии Толбачинского вулканического центра [Колосков и др., 2017а] и Толбачинского вулканического массива [Churikova et al, 2015], в которых присутствие пород повышенной щелочности и особенности тренда их дифференциации связывается с переходом магматической системы этих вулканов к режиму внутридугового рифтинга.…”