A sulfur and halogen budget for the large magmatic system beneath Taupō volcano

Abstract

The transport and degassing pathways of volatiles through large silicic magmatic systems are central to understanding geothermal fluid compositions, ore deposit genesis, and volcanic eruption dynamics and impacts. Here, we document sulfur (S), chlorine (Cl), and fluorine (F) concentrations in a range of host materials in eruptive deposits from Taupō volcano (New Zealand). Materials analysed are groundmass glass, silicic melt inclusions, and microphenocrystic apatite that equilibrated in shallow melt-dominant magma bodies; silicic melt and apatite inclusions within crystal cores inferred to be sourced from deeper crystal mush; and olivine-hosted basaltic melt inclusions from mafic enclaves that represent the most primitive feedstock magmas. Sulfur and halogen concentrations each follow distinct concentration pathways during magma differentiation in response to changing pressures, temperatures, oxygen fugacities, crystallising mineral phases, the effects of volatile saturation, and the presence of an aqueous fluid phase. Sulfur contents in the basaltic melt inclusions (~ 2000 ppm) are typical for arc-type magmas, but drop to near detection limits by dacitic compositions, reflecting pyrrhotite crystallisation at ~ 60 wt. % SiO2 during the onset of magnetite crystallisation. In contrast, Cl increases from ~ 500 ppm in basalts to ~ 2500 ppm in dacitic compositions, due to incompatibility in the crystallising phases. Fluorine contents are similar between mafic and silicic compositions (< 1200 ppm) and are primarily controlled by the onset of apatite and/or amphibole crystallisation and then destabilisation. Sulfur and Cl partition strongly into an aqueous fluid and/or vapour phase in the shallow silicic system. Sulfur contents in the rhyolite melts are low, yet the Oruanui supereruption is associated with a major sulfate peak in ice core records in Antarctica and Greenland, implying that excess S was derived from a pre-eruptive gas phase, mafic magma recharge, and/or disintegration of a hydrothermal system. We estimate that the 25.5 ka Oruanui eruption ejected > 130 Tg of S (390 Tg sulfate) and up to ~ 1800 Tg of Cl, with potentially global impacts on climate and stratospheric ozone.

Volcanic glass from the 1.8 ka Taupō eruption (New Zealand) detected in Antarctic ice at ~ 230 CE

“…The glass particles are either absent from this section of the core, or they are present in bracketing ice not selected for melting, highlighting the challenges of pinpointing this event. The stratospheric sulfur injection calculated for this attributed sulfate signal using a total of 12 ice cores (10 from Antarctica and 2 from Greenland) of 5.8 ± 1.2 Tg of sulfur 67 is comparable to that calculated using petrological techniques of ~6.7 Tg of sulfur 68 . This is a relatively low sulfur emission given the size of the eruption and reflects the lower concentration of sulfur in the rhyolite magma when compared to other smaller volume, but sulfur-rich events 68 .…”

“…The stratospheric sulfur injection calculated for this attributed sulfate signal using a total of 12 ice cores (10 from Antarctica and 2 from Greenland) of 5.8 ± 1.2 Tg of sulfur 67 is comparable to that calculated using petrological techniques of ~6.7 Tg of sulfur 68 . This is a relatively low sulfur emission given the size of the eruption and reflects the lower concentration of sulfur in the rhyolite magma when compared to other smaller volume, but sulfur-rich events 68 . Although while during the Taupō event, the maximum values of sulfate in each annual cycle from the WDC06A and NEEM S1 ice cores were only moderately enhanced compared to other volcanic signals, the annual minimum values of sulfur exceeded the natural background for up to 7 consecutive years 6 .…”

Iron–Titanium Oxide–Apatite–Sulfide–Sulfate Microinclusions in Gabbro and Adakite from the Russian Far East Indicate Possible Magmatic Links to Iron Oxide–Apatite and Iron Oxide–Copper–Gold Deposits

“…This is consistent with the ubiquitous presence of silver and silver-copper chloride microinclusions in the Bakening adakitic dacite (Figure 8e,f). Chlorine-rich fluids are integral in promoting the differentiation and evolution of volcanic arc magmas [103][104][105][106][107] and facilitating the transport of ore metals such as copper and gold in crust-mantle systems above active subduction zones [108][109][110]. High concentrations of chlorine and sulfur have been measured directly in melt inclusions from calc-alkaline lavas [111], as well as in thermal and mineral waters discharged from the volcanic edifices between active volcanoes in Kamchatka [112], suggesting the presence of chlorine-rich fluid in both the mantle wedge and island-arc crust beneath the Kamchatkan volcanic province [65,68,70,[113][114][115].…”

Millimetre‐scale pollen analysis of non‐varved lacustrine sediments from Onepoto maar palaeolake, Auckland, reveals distal vegetation responses and landscape recovery following the ~25.5‐ka Ōruanui supereruption, New Zealand

“…It is the fourth largest bi‐polar ice sheet sulphur anomaly recorded between 9 and 60 ka, and the estimated average climate forcing from the eruption is −13.2 W m –2 (Lin et al , 2022). While the silicic glass from the Ōruanui eruption has very low sulphur content, pre‐eruptive gas accumulation, mafic recharge and the destruction of the overlying hydrothermal system have been used to infer that >130 Tg of sulphur was released during this event (Sharpe et al , 2022).…”