Cycling of CO₂ and N₂ Along the Hikurangi Subduction Margin, New Zealand: An Integrated Geological, Theoretical, and Isotopic Approach

Abstract

Volatile elements enter subduction zones as components of sediment, altered oceanic crust, and ser-

Orogenic gold: is a genetic association with magmatism realistic?

“…5). Such volatiles will not only be H 2 O-dominant, but can contain significant amounts of CO 2 , as well as some N 2 , with overall fluid volume likely controlled by amount of sedimentary material and altered basalt at the top of the underthrusted plate (e.g., Epstein et al 2021). There is no reason that such a fluid would not be similar in composition to that produced during devolatilization of the above described accreted metasedimentary and metavolcanic rocks, and they are just as Fig.…”

Carbon Mobility and Exchange in a Plate-Interface Subduction Mélange: A Case Study of Meta-Ophiolitic Rocks in Champorcher Valley, Italian Alps

“…The subduction cycle and the residency of C in subducting plates, at the plate interface, and in the supra-subduction mantle is a debated and timely issue. Experiments and thermodynamic modeling of decarbonation reactions indicate stability of carbonate minerals to very high pressures (P) and temperatures (T), suggesting minimal C loss from rocks to fluids, particularly to depths of ~80 km, in the deep forearc/ subarc (Molina and Poli, 2000;Thomsen and Schmidt, 2008;Poli et al, 2009;Cook-Kollars et al, 2014;Collins et al, 2015;Menzel et al, 2020;Epstein et al, 2021b). Carbonate reduction to graphite by fluid-rock interaction can also affect C retention in subducting rocks (Galvez et al, 2013;Giuntoli et al, 2020;Vitale Brovarone et al, 2017).…”

“…Carbonate reduction to graphite by fluid-rock interaction can also affect C retention in subducting rocks (Galvez et al, 2013;Giuntoli et al, 2020;Vitale Brovarone et al, 2017). On the other hand, significant C mobility in the deep forearc and beneath arcs (> 80 km), can be deduced by high CO 2 output from arc volcanoes (Epstein et al, 2021b;Hilton et al, 2002), by experimental evidence (Caciagli and Manning, 2003), and by the fluid inclusion and mineral record preserved in (ultra) high-P rocks and subarc xenoliths (Frezzotti et al, 2011;Malaspina et al, 2009;McInness and Cameron, 1994;Sapienza et al, 2009;Scambelluri et al, 2016;Stöckhert et al, 2001;Van Roermund et al, 2002). In subduction zones, decarbonation reactions are enhanced by the infiltration of carbonate-bearing rocks by H 2 O-rich fluids (Collins et al, 2015;Cook-Collars et al, 2014;Dolejs and Manning, 2010;Gorman et al, 2006); carbonate dissolution can also be facilitated by this infiltration (Caciagli and Manning, 2003;Dolejs and Manning, 2010;Sanchez-Valle et al, 2003;Frezzotti et al, 2011;Ague and Nicolescu, 2014;Menzel et al, 2020;Muñoz-Montecinos et al, 2021).…”

Magmatic Carbon and Helium in Springs Reveals the Vitality of a Dormant Volcano, Taranaki, New Zealand

“…The observed 3 He/ 4 He (>5 R A ) and C/ 3 He (∼10 11 ) in Kōkōwai-Arawhata water samples are consistent with volcanic gases from arc magmas, where C/ 3 He is typically between 10 9 and 10 11 . TVZ gases plot between 10 10 and 10 11 and reflect slab devolatilization (i.e., subducted carbonate and organic carbon; Epstein et al, 2021;Plank & Manning, 2019). Some of the highest C/ 3 He values were observed in the backarc hydrothermal systems (Figure S2 in Supporting Information S1, see also Epstein et al (2021)).…”

“…TVZ gases plot between 10 10 and 10 11 and reflect slab devolatilization (i.e., subducted carbonate and organic carbon; Epstein et al, 2021;Plank & Manning, 2019). Some of the highest C/ 3 He values were observed in the backarc hydrothermal systems (Figure S2 in Supporting Information S1, see also Epstein et al (2021)). We attribute the C/ 3 He signature to a mix of mantle, slab and crustal assimilation from the overlying plate, though it is challenging to differentiate between slab and crustal carbon contributions.…”