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    Variable controlling factors lead to contrasting patterns of volcanism in the Changbaishan volcanic area (Tianchi-Longgang), China-North Korea: Insights from morphometry and spatial-temporal analyses
    (Elsevier B V, Amsterdam, 2024-07-01) Zhang R; Brenna M; White JDL; Kereszturi G
    The coexistence of monogenetic and polygenetic volcanoes is a common phenomenon in volcanic areas. However, the genetic relationship between monogenetic and polygenetic systems and the factors controlling their distinct eruptive styles are not well understood. In active volcanic areas, analysing the clustering and vent alignment of monogenetic volcanoes, as well as examining the geomorphology and relative ages of scoria cones, offers quantitative insights into magma supply rates, volcano type distribution, and volcanic development trends. Our study presents geomorphological and spatio-temporal analyses of the co-existing monogenetic volcanoes in the Longgang Volcanic Field (LVF) and those associated with a polygenetic volcano (Tianchi) in the Changbaishan Volcanic Area, China. The distance between the two volcanic areas is around 150 km. Monogenetic vents in the LVF exhibit greater density compared to the dispersed system associated with Tianchi. The LVF vents also show better alignment, particularly in the direction of pre-existing basement faults (NE-SW, NW-SE and EW). By using scoria cone morphometric parameters and features, we estimated the relative ages and erupted volumes of monogenetic volcanoes in the LVF and the Tianchi area. We classified the cones of the two volcanic systems into five eruptive periods and found that, despite similar magma sources and output rates over approximately 870 kyr, differing numbers of scoria cones across age classes suggest that Tianchi's magma system influences its associated monogenetic volcanic plumbing. Furthermore, the continuous rise in output rates of monogenetic volcanoes in the Tianchi area highlights the increasing magma supply sustaining Tianchi volcano. Together, these interpretations are consistent with the two systems being controlled by different factors: the Tianchi monogenetic volcanic system is more controlled by magmatism, whereas the LVF is more strongly controlled by local tectonic structures, alongside an increasing magma supply causing the formation of progressively larger individual volcanoes. In volcanic areas, analysing monogenetic volcanoes' spatial-temporal distribution, volumes and recurrence rate provides a framework to evaluate magma supply rates and tectonic associations, which are key to the development of different volcano types.
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    Compositional variation during monogenetic volcano growth and its implications for magma supply to continental volcanic fields
    (Massey University., 2003) Nemeth K; White JD; Reay A; Martin U
    Individual volcanoes of continental monogenetic volcanic fields are generally presumed to erupt single magma batches during brief eruptions. Nevertheless, in two unrelated volcanic fields (the Waipiata volcanic field, New Zealand, and the Miocene-Pliocene volcanic field in western Hungary), we have identified pronounced and systematic compositional differences among products of individual volcanoes. We infer that this indicates a two-stage process of magma supply for these volcanoes. Each volcano records: (1) intrusion of a basanitic parent magma to lower- to mid-crustal levels and its subsequent fractionation to form a tephritic residual melt; (2) subsequent transection of this reservoir by a second batch of basanitic melt, with tephrite rising to the surface at the head of the propagating basanite dyke. Eruption at the surface then yields initial tephrite, typically erupted as pyroclasts, followed by eruption and shallow intrusion of basanite from deeper in the dyke. By analogy with similar tephrite-basanite eruptions along rift zones of intraplate ocean-island volcanoes, we infer that fractionation to tephrite would have required decades to centuries. We conclude that the two studied continental monogenetic volcanic fields demonstrate a consistent history of early magmatic injections that fail to reach the surface, followed by capture and partial eruption of their evolved residues in the course of separate and significantly later injections of basanite that extend to the surface and erupt. This systematic behaviour probably reflects the difficulty of bringing small volumes of dense, primitive magma to the surface from mantle source regions. Ascent through continental crust is aided by the presence in the dyke head of buoyant tephrite captured during transection of the earlier-emplaced melt bodies.