Some first-order observations on magma transfer from mantle wedge to upper crust at volcanic arcs

Abstract

The viscosity of lavas erupted at volcanic arcs varies over orders of magnitude. A comparison of the relative abundance of viscous lava dome eruptions indicates that the average viscosity of arc lavas also varies considerably between arcs. It is shown that, for continental or transitional arcs with little within-arc crustal deformation and without underlying slab windows or tears, average lava viscosity is anticorrelated with average surface heat flux. The latter may be influenced by crustal thickness and crustal magma throughput. To constrain the relative contributions of these parameters, variations of average lava viscosity with average crustal thickness and plate convergence rate are assessed. While crustal thickness appears to have little effect on average lava viscosity, a good anticorrelation exists between average lava viscosity and plate convergence rate, with the exception of two arcs that show significant intra-arc crustal deformation. If plate convergence rate is a good proxy of the rate of melt generation within the mantle wedge, these first-order observations indicate that, where the rate of mantle melting is high, crustal magma throughput is rapid and efficient, resulting in low-viscosity melts migrating through a hot overriding crust; in contrast, where the rate of mantle melting is low, crustal magma transfer is slow and inefficient, resulting in high-viscosity melts that may frequently stall within a cool overriding crust prior to eruption. Uranium series geochemical evidence from dome lavas is presented and lends support to this interpretation. Finally, some explanations are offered for the observed average viscosity variations of arcs with underlying slab windows or tears and/or significant intra-arc crustal deformation.Volcanic activity above subduction zones is characterized by a variety of eruption styles: in the explosive regime, these include plinian eruptions (e.g. Santorini c.

Resolving discordant U–Th–Ra ages: constraints on petrogenetic processes of recent effusive eruptions at Tatun Volcano Group, northern Taiwan

“…Remobilization of shallow intrusives by fresh melt from greater depth is a common phenomenon for porphyritic lava domes (cf. Zellmer 2008Zellmer , 2009Kent 2014 and references therein), and some of the Tatun domes and viscous lava flows appear to conform to this petrogenetic scenario. As U -Th internal dating of major mineral phases is not possible on single mineral grains, but instead requires the analysis of bulk mineral separates, the obtained ages are likely to represent averages of a range of ages displayed by the mineral grains (cf.…”

Structure of volcano plumbing systems: A review of multi-parametric effects

“…Similarly, also Zellmer (2008Zellmer ( , 2009) based on global correlations between eruptive style, surface heat flux and convergence rates at different volcanic arcs, infers that the rate of melt production in the mantle wedge ultimately controls the deep dynamics of magma transfer.…”

Regional controls on magma ascent and storage in volcanic arcs

“…For the subduction parameters, we use the convergence velocity data from Hughes and Mahood [] completed by Zellmer []; the subduction velocity, vertical descent velocity, and slabs' thermal parameter data from Lallemand et al . []; and the slab age, dip, and subduction duration data from Hughes and Mahood [].…”

“…Zellmer [] suggested that the melt production rates in the mantle influence the speed at which magma migrates through the crust. However, recent petrological and geophysical observations suggest that magma ascends in pulses of durations and volumes changing in time [ Druitt et al ., ; Parks et al ., ; John et al ., ], implying that ascent rates may be independent from production rates both in the crust and mantle.…”