Magmatic plumbing systems of the monogenetic volcanic fields: A case study of Tolbachinsky Dol, Kamchatka

Abstract

Clusters of small-volume volcanoes that individually may be defined as monogenetic, but have interlinked and interconnected plumbing systems, are used to be categorized as monogenetic volcanic fields (MVF). We argue that such volcanic clusters should be distinguished as separate type of volcanism, intermediate between monogenetic and polygenetic. The magma plumbing system structure of the MVF (its complexity and polymagmatic character) is the key argument for the potential separation of them in a classification. To avoid confusion caused by genetic meaning of the used words we suggest using a term "areal volcanism" or "areal volcanic fields" (AVF instead of MVF) as defining this special type of volcanic activity. Here we provide a review of the main characteristic features of one of the largest Holocene AVF, which is active nowthe Tolbachik field of cinder cones in the southern part of Klyuchevskaya volcano group (Kamchatka), known in the literature as Tolbachinsky Dol. This paper is focused on the research of magma plumbing system. We consider structural, morphological, geological, geochemical and petrological data on the erupted basalts and their genesis. Specially planned seismic experiments made in 2010-2015 (seismic tomography and microseismic sounding) allowed modeling of the principal elements of the magma plumbing system of Tolbachik AVF. Analysis of the investigations made in this area shows that Tolbachik AVF has a complex, dynamic, variable magmatic feeding system, which can be visualized as a superposition of subvertical and sublateral magma conduits. The contrast composition of the erupted rocks is caused by their different, although genetically connected, magma sources and mixing processes. One of the long-lived eruptive centers of Tolbachik AVF is Plosky Tolbachik stratovolcano, which lost its independent activity and was captured by Tolbachik AVF in Holocene. The AVF formed rejuvenated volcanism using the feeding system of the stratovolcano like an "old anthill". The magma plumbing system characteristics of Tolbachinsky Dol strongly support the idea of separation of AVF from monogenetic volcanism type in the classification.

Volcano distribution and tectonics: A planetoidic perspective

“…Tolbachinsky Dol is a group of small-to medium-sized Quaternary volcanoes located south of the two larger stratovolcanoes Ostry and Plosky Tolbachik. In the present context, the most appealing feature of this region is the availability of results of ultrahigh-resolution seismic tomography reported by Kugaenko and Volynets (2019). These tomographic results suggest the presence of a complex plumbing system that includes three dominant zones of conduits interconnecting several magma reservoirs located at various depths, all of which lie within 35 km of the surface.…”

“…Older vents on Tolbachinsky Dol (10-2 ka) tend to be distributed more homogeneously and extend their spatial distribution north of the two stratovolcanoes, as well as in a wider E-W region relative to the area covered by the younger vents. Furthermore, also according to Kugaenko and Volynets (2019), the top of the zone of magma is located approximately at 12 km depth beneath group 1, it is at roughly 3 km beneath group 3, and it reaches 6 km depth beneath group 2. The approximate lateral extent of those zones of magma conduits, or storage, as inferred from seismic tomography, is shown in Figure 1.…”

“…Although the compositional variations of erupted products on Tolbachinsky Dol do not define spatially exclusive groups, because there is some superposition of compositions, they do provide a rough guide concerning the relation between the spatial distribution of volcanism at the surface and the structure of the underlying plumbing system. Thus, the tomographic results reported by Kugaenko and Volynets (2019) can be used to explore in more detail the amount of information that can be extracted from volcano distribution at the surface.…”

“…According to Kugaenko and Volynets (2019), the most recent vents (<2 ka) define four distinctive groups (numbered 1-4 hereafter), each with a predominant composition. The northernmost group (closer to Plosky Tolbachik, group 1) is dominated by high-Al basalts, whereas the southernmost group (group 4) is dominated by transitional varieties of magma.…”

“…The approximate lateral extent of those zones of magma conduits, or storage, as inferred from seismic tomography, is shown in Figure 1. Unfortunately, the tomographic images presented by Kugaenko and Volynets (2019) do not extend to include the vents in group 4 to the south. Nevertheless, the available information suffices to compare the characteristics of the plumbing system with the information that can be extracted from the spatial distribution of vents at the surface.…”