Mauna Loa is one of the largest and most active volcanoes on Earth. The most recent eruption of Mauna Loa started on 27 November 2022, lasted for 13 days, and was preceded by the longest repose time of 38 years in its modern history. In this contribution, new trace- and highly siderophile-element (HSE: Os, Ir, Ru, Pt, Pd, Re) abundances, 187Re-187Os, and 18O/16O data are reported for the 2022 lavas. These lavas have a limited range of MgO (6.2 ± 0.1 wt.

Pu‘u‘ō‘ō is Kīlauea’s longest lived (1983–2018) and most voluminous (~4.4 km3) historical eruption. New oxygen isotope data are presented for matrix material from lava erupted from 2006 to 2018, olivine from 1997 to 2018, clinopyroxene from 2013 to 2018 (first such data for Kīlauea), and matrix from two 1982 summit eruptions. These data are integrated with our previously published oxygen isotope results for the first part (1983–1997) of the Pu‘u‘ō‘ō eruption and 19–20th century Kīlauea summit eruptions and compared with published whole-rock XRF and Sr isotope data. This study builds on our previous work (using whole-rock and mineral chemistry) that indicated strong evidence for mixing of evolved magmas, which had undergone shallow storage, crystal fractionation, and crustal contamination, with new, mantle-derived magma. Pu‘u‘ō‘ō δ18O values range from 4.4 to 4.9‰ for olivine and 4.6–5.7‰ for matrix. Both are ~0.1–0.9‰ lower than the canonical mantle δ18O value. Olivine δ18O values are relatively constant during the eruption (4.7 ± 0.1‰), whereas matrix δ18O values progressively increased reflecting the flushing of contaminated magma from the feeder system. The δ18O results from Pu‘u‘ō‘ō and other Kīlauea historical lava provide evidence of ~200 years of recurring crustal contamination within the volcano. Equilibrium in O isotopes between the matrix and coexisting olivine was periodically established after major changes in the Pu‘u‘ō‘ō eruption and for summit eruptions. New, mantle-derived magma was contaminated in the summit reservoir after several major collapses (100+ m) and eruptive hiatuses, and in the east rift zone as magma was stored for weeks to decades. Poor correlations (R2 ≤ 0.1) were found between olivine and matrix δ18O values with Nb/Y and Sr isotopes for Pu‘u‘ō‘ō and historical Kīlauea summit lavas (1820–1982) exhibiting O isotope equilibrium. Thus, the ranges in olivine and matrix δ18O values in Kīlauea’s historical lava are not indicative of δ18O heterogeneity in its mantle source. Kīlauea’s mantle source has an apparently narrow range of δ18O values (5.6 ± 0.1‰) as evidenced by matrix O isotope values for its more primitive summit lavas and those from the latter part of the Pu‘u‘ō‘ō eruption. Olivine from young Hawaiian shield volcanoes with KEA-like (Kīlauea and Mauna Kea) and LOA-like (Kama’ehuakanaloa and Mauna Loa) sources have nearly identical δ18O values (5.0–5.1) suggesting the Hawaiian plume source is essentially homogeneous in δ18O during shield stage for recent volcanism.

The discovery of systematic differences in the trace element composition of forsteritic olivines in primitive magmas from within-plate, arc and mid-ocean ridge volcanoes engendered much debate about a causal link to the recycling of oceanic crust into the mantle sources of within-plate and arc magmas. Here we address this problem using Cr-spinel bearing, forsteritic (similar to Fo(80-91)) olivines from high-Mg# = 50 = 73 [Mg# = molar ratio of Mg/(Mg + Fe2+)*100] arc magmas from the Trans-Mexican Volcanic Belt (TMVB). The TMVB arc front olivines have similar high Ni, low MnO, and low Mn/Fe as forsteritic olivines from within-plate basalts erupting through thick lithosphere (= WPB-thick). However, the olivines in TMVB arc front primary melts crystallize at much lower temperatures of T-cryst(oliv) similar to 1119 +/- 38 degrees C (calculated with olivine-spinel aluminum exchange thermometry) in hydrous (similar to 4-9 wt % H2O), silicic, less magnesian (<= 10 wt % MgO) mantle melts from mostly garnet-free mantle sources. Model calculations suggest that the primary arc front melts last equilibrated in the mantle at pressures of similar to 1.4 to similar to 1.9 GPa (similar to 51-69 km depth) and low temperatures (T-source = 1150 +/- 45 degrees C) that are only slightly higher than the olivine crystallization temperatures. While the Kd(oliv/melt)(Ni) increases in the cooler and silicic melts, such modulation cannot account for the full range of Ni concentration in TMVB magmatic olivines. A small population of very high-Ni olivines (>4000-5500 mu g/g Ni) is best explained by crystallization in Ni-rich components melt that formed by melt rock reaction processes in the mantle wedge. Unlike Ni, olivine MnO is not sensitive to melt temperature and only moderately to melt composition, and thus retains mantle source characteristics. In the TMVB, olivine Fo-MnO-Mn/Fe systematics record an ambient mantle wedge (= mantle without slab component) that is similar to WPB sources and that is variably depleted by slab flux-driven melt extraction. Overall, the olivine Fo-Ni-MnO systematics confirm with greater detail than possible by bulk rock studies that the TMVB primary melts are hydrous and silicic and originate from a mantle wedge that is strongly and variably modified by the slab flux. These results reaffirm a strong genetic link between slab recycling and the genesis of silicic arc magmas.

Hadean zircons, from the Jack Hills (Western Australia) and other localities, are currently the only window into the earliest terrestrial felsic crust, the formation of which remains enigmatic. Based upon new experimental results, generation of such early crust has been hypothesized to involve the partial melting of hydrated peridotite interacting with basaltic melt at low pressure (<10 km), but it has yet to be demonstrated that such liquids can indeed crystallize zircons comparable to Jack Hills zircon. We used thermodynamic and geochemical modeling to test this hypothesis. The predicted zircon saturation temperatures of <750 °C, together with the model zircon Th, U, Nb, Hf, Y, and rare earth element (REE) contents at 700 °C, δ18OVSMOW (Vienna standard mean ocean water) signatures, and co-crystallizing mineral assemblage were compared to those of the Jack Hills zircon. This comparison was favorable with respect to crystallization temperature, most trace-element contents, and mineral inclusions in zircon. The discrepancy in δ18OVSMOW signatures may be explained by hotter conditions of Hadean protocrust hydration. Our work supports the idea that felsic magma generation at shallow depths involving a primordial weathered ultramafic protocrust and local basaltic intrusions is indeed a viable mechanism for the formation of felsic crust on early Earth.

Magma‐water interaction can dramatically influence the explosivity of volcanic eruptions. However, syn‐ and post‐eruptive diffusion of external (non‐magmatic) water into volcanic glass remains poorly constrained and may bias interpretation of water in juvenile products. Hydrogen isotopes in ash from the 2009 eruption of Redoubt Volcano, Alaska, record syn‐eruptive hydration by vaporized glacial meltwater. Both ash aggregation and hydration occurred in the wettest regions of the plume, which resulted in the removal and deposition of the most hydrated ash in proximal areas <50 km from the vent. Diffusion models show that the high temperatures of pyroclast‐water interactions (>400°C) are more important than the cooling rate in facilitating hydration. These observations suggest that syn‐eruptive glass hydration occurred where meltwater was entrained at high temperature, in the plume margins near the vent. Ash in the drier plume interior remained insulated from entrained meltwater until it cooled sufficiently to avoid significant hydration.

Spire-like pinnacles and fins are common features in silicic ignimbrite sheets that represent the fluxing of water through the cooling deposit. Fumarolic pinnacles at Crater Lake, Oregon (Mt. Mazama; 7.7 ka) and in the Valley of Ten Thousand Smokes, Alaska (VTTS; 1912) represent the iconic images of these processes. Glasses within these structures remain fresh despite experiencing high temperatures and extensive water-rock interaction with infiltrating groundwater. These glasses can be used to interrogate the thermal and hydrologic conditions of pinnacle formation, which are not well-understood. Higher diffusivity of water at elevated temperatures facilitates rapid secondary hydration of glass. This allows for delta D of pinnacle glasses to be used a "snapshot" proxy for the isotopic composition of the hydrating meteoric water with applications to paleoaltitude and paleoclimate. We present comprehensive H and 0 isotope data for volcanic glasses from pinnacles in the VTTS and from Crater Lake, which includes bulk delta O-18 giass and delta O-I7(glass) analyses and a new parameter, delta O-18 of water-in-glass(delta O-18(wig)) The delta D and delta O-18 values of lake waters from the Katmai region are used to constrain the likely composition of VTTS hydration waters. The VTTS rhyolitic glasses from fumarolic mounds in the uppermost portion of the ignimbrite have depleted delta D-glass (>=-152%o) but minimally depleted delta O-18(glass) in high H2O (4.2 wt.%) pumices. These trends are best explained by the simple addition of modern meteoric waters from the Katmai region, thereby providing a snapshot of the meteoric water composition in the years to decades following the 1912 AD Novarupta-Katmai eruption. Glasses from Crater Lake pinnacles are used to estimate the delta D and delta O-18 of their hydration water shortly following the eruption of Mt. Mazama as well as the temperature conditions of their formation. Mt. Mazama glasses contain a narrow range of 1.6-1.9 wt.% H2O with depleted delta D and delta O-18(glass) values as low as 149%o and 0.95%o, respectively. All measured delta Dg(lass) and delta O-18(glass) values fall between 75-100 degrees C based on estimated SD and delta O-18 equilibrium fractionation between glass and water, as do Delta'O-17(glass) compositions. The new delta O-18(glass)-delta O-18(wig) approach gives a wider range of temperatures up to similar to 150 degrees C, but overall are in good agreement with S1800ass isotope data. These compositions indicate 75-150 degrees C hydration temperatures and record extensive isotope exchange with meteoric waters. The near-boiling hydration temperatures strongly suggest that cooling ignimbrites remain dry above these temperatures. Cooling ignimbrite sheets likely have enough magmatic vapor overpressure to drive off vapor from ambient hydrosphere surface waters until they approach similar to 100 degrees C, at which point external waters are able to percolate into the deposit. Pinnacles therefore reflect late-stage cooling features rather than vigorous fumaroles. These results are consistent with previous modeling work on cooling ignimbrites that drive water away until sub-boiling temperatures, but contrast with the near-magmatic temperatures previously suggested by depletions in delta O-18 in ignimbrite groundmass. Reconstructed delta D and delta O-18 values of paleo-meteoric waters at Mt. Mazama are -130 and -120%o and -17.5 and -16.3%o respectively, notably lighter than modern spring water compositions. This is interpreted to reflect a low-delta D and low-delta O-18 groundwater source fed by high altitude glaciers or snowfields that originated from >3 km on the pre-collapse of Mt. Mazama edifice, more than 1 km above the modern lake level. (C) 2018 Elsevier B.V. All rights reserved.

Earth exhibits a dichotomy in elevation and chemical composition between the continents and ocean floor. Reconstructing when this dichotomy arose is important for understanding when plate tectonics started and how the supply of nutrients to the oceans changed through time. We measured the titanium isotopic composition of shales to constrain the chemical composition of the continental crust exposed to weathering and found that shales of all ages have a uniform isotopic composition. This can only be explained if the emerged crust was predominantly felsic (silica-rich) since 3.5 billion years ago, requiring an early initiation of plate tectonics. We also observed a change in the abundance of biologically important nutrients phosphorus and nickel across the Archean-Proterozoic boundary, which might have helped trigger the rise in atmospheric oxygen.