Diverse magma storage and major and volatile magma composition: What are the implications on the eruptive style across a volcanic arc? An example of the Lesser Antilles Arc

Identifying Distinct Pre‐Eruptive Composition‐H2O‐Time Trends Using Plagioclase

“…The Lesser Antilles arc is the surface expression of the subduction of the Atlantic plate beneath the Caribbean plate at the slow end of global subduction rates (Macdonald et al., 2000). The structure, extent, and productivity of magmatic systems beneath the active volcanoes along the arc are all highly variable, which in turn modulates the eruptive dynamics, geochemistry of erupted products, and volcano morphology (Balcone‐Boissard et al., 2023; Cooper et al., 2020; Higgins & Caricchi, 2023; Melekhova et al., 2019; Metcalfe et al., 2023). The along‐arc variability has recently been linked to a heterogenous melt flux (Higgins & Caricchi, 2023), evidenced by proxy of boron isotopic values in melt inclusions (Cooper et al., 2020), which determines the thermal‐chemical structure of magmatic systems built within the upper crust (Karakas et al., 2017).…”

“…Four relevant scenarios are interpreted in K 2 O-H 2 O space (arrows in Figure 9a; Blundy & Cashman, 2005): (i) melt H 2 O and an incompatible element increase in tandem, dictating that the melt is experiencing H 2 O-undersaturated, isobaric crystallization; (ii) melt H 2 O remains constant whilst an incompatible element increases, interpreted as isobaric, H 2 O-saturated crystallization; (iii) melt H 2 O decreases as an incompatible element increases, reflecting a suite of H 2 O-saturated samples derived from different amounts of crystallization at different crustal pressures that is analogous to decompression-driven crystallization; (iv) syneruptive degassing, during which a melt undergoes near isothermal decompression. In the Lesser Antilles, the sub-alkalic magmas (Macdonald et al, 2000;Metcalfe et al, 2023) and low-K 2 O cumulates (Brown et al, 2021;Camejo-Harry et al, 2018;Cooper et al, 2016;Melekhova et al, 2017Melekhova et al, , 2019Melekhova et al, , 2022Stamper et al, 2014;Tollan et al, 2012) mean that K is demonstrably an incompatible element such that increasing WR K 2 O is a crystallization proxy. The plagioclase-rich Lesser Antilles cumulates along with additional anhydrous and low-K 2 O cocrystallizing phases such as pyroxene and olivine result in bulk partition coefficients for K and H 2 O that are much less than one.…”

Early arc crust formation preserved in the Grenadines archipelago, southern Lesser Antilles arc

“…There are also substantial differences in surface activity. Historically (seventeenth century onwards), there have been several volcanic eruptions and volcano-seismic crises on the majority of islands making up the active arc [ 41 , 42 ]. However, islands of the Grenadines archipelago which are among the smallest in size ( figure 1 ), are exceptions to this overall behaviour.…”

“…Within the Lesser Antilles arc, eruptive patterns have been reconciled with the presence of long-lived trans-crustal mush systems [ 42 ]. Metcalfe et al [ 42 ] distinguish three broad levels of magma storage across the arc: (i) greater than 18 km, (ii) 10–18 km and (iii) less than 10 km, with inter-island variability in their relative depths.…”

“…Within the Lesser Antilles arc, eruptive patterns have been reconciled with the presence of long-lived trans-crustal mush systems [ 42 ]. Metcalfe et al [ 42 ] distinguish three broad levels of magma storage across the arc: (i) greater than 18 km, (ii) 10–18 km and (iii) less than 10 km, with inter-island variability in their relative depths. The information required to develop these models can be obtained from monitoring data [ 75 ], phase equilibria experiments [ 76 , 77 ] and chemistry of erupted material [ 37 , 78 , 79 ].…”