The Influence of Ridge Subduction on the Geochemistry of Vanuatu Arc Magmas

Abstract

The effects of buoyant ridge subduction have been researched for decades. However, it remains unclear how this process influences magma chemistry. Here we use a compilation of geochemical data, well‐established geochemical proxies (i.e., Ba/Nb, Th/Nb) and mantle redox modeling (i.e., V/Sc, Cu) to propose that the subduction of a ridge underneath the central portion of the Vanuatu arc causes shallow‐angle subduction and the development of a slab tear. We suggest that the shallow slab pinches out the asthenospheric mantle and bulldozes ancient metasomatized lithospheric mantle from the forearc toward the main‐arc. Slab‐fluxed melting of this bulldozed material could account for the along‐arc 87Sr/86Sr‐143Nd/144Nd variations of the Vanuatu magmas. The influx of hot sub‐slab material into the Vanuatu arc mantle wedge through a slab tear produces magmatism within the forearc. Modeling of V/Sc and Cu systematics suggest that the mantle source of the forearc magmas has a higher fO2 and Cu content than the source of the main‐arc and rear‐arc samples. The main‐arc and rear‐arc mantles were metasomatized by both slab‐derived fluids and melts. Whereas release of high Cu‐SO2 slab‐derived fluids caused oxidation and Cu enrichment of the forearc mantle. These systematics indicate a decrease in the fO2 of slab fluxes with increasing depth‐to‐slab and distance‐from‐trench. Our findings highlight the role of ridge subduction in controlling the along‐arc and across‐arc variations in the chemistry of Vanuatu arc magmas. This updated geodynamic model, based on geochemistry, is consistent with recent geophysical constraints and 3D numerical modeling.

Tracing Volatiles, Halogens, and Chalcophile Metals during Melt Evolution at the Tolbachik Monogenetic Field, Kamchatka

“…Mathez, 1976;Jenner, 2017). In the case of Bakening, recent modelling by Deng et al (2022) confirms that low degrees of melting at low fO 2 conditions (ca. QFM ≤ +1) will leave residual mantle sulphides, and thus magmas will be sulphide-saturated at an early stage of magma differentiation in the crust.…”

“…The second broad scenario is where magmas are initially sulphide-undersaturated, which is likely because of either the high f O 2 of the source (S solubility increases with increasing f O 2 ) or the high melt fraction during melting (Deng et al, 2022, and the references therein). These sulphide under-saturated convergent margin magmas show an initial increase in Cu with decreasing MgO, until the melts eventually reach sulphide saturation (Jenner et al, 2010(Jenner et al, , 2015.…”

“…Wieser et al, 2020) and may also reveal information about the processes of mantle melting (e.g. de Hoog et al, 2001;Zhang et al, 2021;Deng et al, 2022).…”

The effect of seamount chain subduction and accretion

“…Many researchers suggested that the trend may be related to the increasing subduction flux of seamounts, largely due to the characteristic 206 Pb/ 204 Pb ratios of the seamounts on the subducting plate (Ishizuka et al, 2007; Staudigel, Koppers, Plank, & Hanan, 2010; C. H. Sun & Stern, 2001). Recently, based on the combination of geochemical data and modelling, Deng, Jenner, Wan, and Li (2022) suggest that the latitudinal variations in the chemistry of Vanuatu arc samples result from “bulldozing” effects associated with the D'Entrecasteauz Ridge subduction.…”

“…Butterworth et al, 2016; Richards, 2013; Richards & Holm, 2013; Sillitoe, 2010). Subduction of mid‐ocean ridges as well as aseismic ridges (seamounts and oceanic plateaus) has been shown to play a possible role in the formation of large porphyry copper and gold deposits (e.g., Chiaradia et al, 2020; Cooke, Hollings, & Walshe, 2005; Deng et al, 2022; Rosenbaum et al, 2005; Windley & Xiao, 2018; Yumul Jr. et al, 2020). Porphyry copper and gold deposits are particularly abundant in the Andes (Figure 6b), where they are associated with subduction‐related magmatic arcs (Sillitoe, 1974, 2010).…”