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Recent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport(1-4), important characteristics of mid-ocean ridge magmatism(1,5). A consequence of such shallow crustal processing of magmas(4,5) is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust(6,7). Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 10(7)-10(8) m(3) of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems.

Recent Icelandic rifting events have illuminated the roles of centralized crustal magma reservoirs and lateral magma transport(1-4), important characteristics of mid-ocean ridge magmatism(1,5). A consequence of such shallow crustal processing of magmas(4,5) is the overprinting of signatures that trace the origin, evolution and transport of melts in the uppermost mantle and lowermost crust(6,7). Here we present unique insights into processes occurring in this zone from integrated petrologic and geochemical studies of the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula in Iceland. Geochemical analyses of basalts erupted during the first 50 days of the eruption, combined with associated gas emissions, reveal direct sourcing from a near-Moho magma storage zone. Geochemical proxies, which signify different mantle compositions and melting conditions, changed at a rate unparalleled for individual basaltic eruptions globally. Initially, the erupted lava was dominated by melts sourced from the shallowest mantle but over the following three weeks became increasingly dominated by magmas generated at a greater depth. This exceptionally rapid trend in erupted compositions provides an unprecedented temporal record of magma mixing that filters the mantle signal, consistent with processing in near-Moho melt lenses containing 10(7)-10(8) m(3) of basaltic magma. Exposing previously inaccessible parts of this key magma processing zone to near-real-time investigations provides new insights into the timescales and operational mode of basaltic magma systems.

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.

Magma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) delta O-18 values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30km at Merapi to <= 20km at Agung. Here we show that mean clinopyroxene delta O-18 values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt delta O-18 values of 5.7 (+/- 0.2 1SD) indistinguishable from the delta O-18 range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member. Subduction zone volcanoes are underlain by extensive magma plumbing systems, which can obscure original mantle source signals. Here, the authors show that intra-crystal oxygen isotope analysis of clinopyroxenes from the Sunda arc (Indonesia) reveal the delta 18 O value of the sub-arc mantle.

Pb-Pb isochron ages of ca. 3.92 Ga for three K-feldspar-rich clasts from Apollo 14 breccias 14303 and 14083 were determinedusing Secondary Ion Mass Spectrometry (SIMS). These ages are interpreted to represent the resetting of the U-Pb systemin the clasts as a result of brecciation during the Imbrium impact. One of the clasts contains zircon grains that record asignificantly older crystallization age (ca. 4.33–4.35 Ga) for the rock represented by that clast. Initial Pb compositions determinedfor the clasts, combined with the previously measured Pb isotopic compositions of K-feldspar grains from severalApollo 14 breccia samples, constrain a range of initial Pb compositions in the ca. 3.9 Ga Fra Mauro formation at the Apollo14 landing site. This range in initial Pb compositions indicates that the rocks represented by these clasts, or the sources ofthose rocks, evolved with a high 238U/204Pb (µ-value) for substantial periods of time, although the precise crystallization agesof the rocks represented by at least two of the clasts investigated here are unknown.

Pb-Pb isochron ages of ca. 3.92 Ga for three K-feldspar-rich clasts from Apollo 14 breccias 14303 and 14083 were determinedusing Secondary Ion Mass Spectrometry (SIMS). These ages are interpreted to represent the resetting of the U-Pb systemin the clasts as a result of brecciation during the Imbrium impact. One of the clasts contains zircon grains that record asignificantly older crystallization age (ca. 4.33–4.35 Ga) for the rock represented by that clast. Initial Pb compositions determinedfor the clasts, combined with the previously measured Pb isotopic compositions of K-feldspar grains from severalApollo 14 breccia samples, constrain a range of initial Pb compositions in the ca. 3.9 Ga Fra Mauro formation at the Apollo14 landing site. This range in initial Pb compositions indicates that the rocks represented by these clasts, or the sources ofthose rocks, evolved with a high 238U/204Pb (µ-value) for substantial periods of time, although the precise crystallization agesof the rocks represented by at least two of the clasts investigated here are unknown.

Early Permian (Cisuralian) S-type monzogranites of the Bundarra Supersuite, New England Orogen (NEO), eastern Australia, have chemical and isotopic compositions indicative of their being derived from young, weathered, volcanogenic sedimentary source rocks. High δ18Ozrn values of zircon precipitated from the melt phase of the magma (ca. 11.5‰) confirm that the previously measured high granite whole-rock values (δ18OWR) are a primary magmatic feature. Abundant inherited detrital zircon cores with a range of dates (360–300 Ma) and distinctly lower δ18Ozrn values (ca. 5–10‰) were derived from mostly young (Carboniferous) volcanogenic source rocks that became less primitive and more isotopically diverse with time. The age difference between the youngest inherited zircon population and the earliest zircon growth during magma genesis is about 15 Ma. An arc-related volcanogenic sedimentary pile built up over about 50 Ma was weathered, buried, and partially melted, producing voluminous peraluminous magmas within no more than ca. 15 Ma of the youngest source sediment being deposited. The time interval between the initiation of melting and post-emplacement magma crystallization was about 5 Ma. The S-type Bundarra Supersuite in the NEO is a rare case in which the entire geologic cycle has been captured by zircon. Recognizing this is uniquely possible because of the relatively simple populations of inherited and newly-grown zircon, and their distinctive oxygen isotopic compositions.

The thermal history of asteroids is recorded by the radioisotopic ages of meteorites that derive from them. Radioisotopic ages may date a number of events, such as the cooling of a parent body during waning radiogenic metamorphism, rapid cooling experienced upon parent body break-up, and/or subsequent collision-induced reheating of material. However, sampling statistics for meteorite radioisotope ages are currently relatively low and most are derived from analyses of bulk material, therefore lacking the in-situ microtextural context that aids in distinguishing collisional events. Here, we present new in-situ apatite U-Pb ages for nine L chondrite meteorites using secondary ionisation mass spectrometry. Our measurements greatly expand the L chondrite phosphate U-Pb age record and provide evidence for distinct stages in the thermal evolution of the L chondrite parent asteroid, including: early collisions driving parent body fragmentation- and/or exhumation-associated cooling at > 4530 Ma; onion-shell-style cooling with waning radiogenic metamorphism until 4500 Ma; late collisional reheating from 4480–4460 Ma; parent body break-up at 474± 22 Ma; and recent ejection events within several 10s of Myr of present day. We show that meteorite shock stage correlates with upper intercept age but is uncorrelated with lower intercept age. This outcome links the upper intercept ages alone to the preserved high-energy impact-related features in strongly shocked meteorites, which has important implications for our interpretation of the L chondrite U-Pb record. We see no evidence in our record for collisional episodes between 3000–4400 Ma, i.e., the Late Heavy Bombardment. Our upper intercept age record hints that collision rates changed as a result of some dynamical instability at 4460–4480 Ma, which may have strongly depleted the main asteroid belt, and/or that L asteroid physical structure changed such that the shock metamorphic response to collisions was muted after this time, e.