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Speleoseismology aims to reconstruct palaeoseismic records by dating pre- and post-damage speleothem calcite. A common approach is to infer palaeo-earthquakes from evidence of coinciding damage features (e.g., rockfall and broken speleothems) at multiple locations, which can be challenging in regions of high tectonic strain where short recurrence intervals of large earthquakes require dating of an impractically large number of damage features. Alternative approaches concerned with dating successive growth changes in individual speleothems (e.g., axis changes and growth hiatuses) are better suited to high-seismicity settings, as closely spaced events are more readily resolved. However, the origins of these growth changes can be ambiguous.This study tested a novel geochemical proxy for quantifying ground shaking that is amenable to high-resolution speleothem studies, and potentially more diagnostic of earthquake damage. We evaluated the hypothesis that past large earthquakes temporarily elevate Mg/Ca in cave drip waters via incongruent carbonate dissolution following host rock fracturing (ICDC), leading to corresponding Mg enrichments in speleothem calcite. To do this, we examined a well-dated Holocene stalagmite (GT1) from a cave near the Alpine Fault, which is Aotearoa/New Zealand’s longest (>500 km) active onshore fault and a major source of seismic hazard. The locality is 4 km from the Alpine Fault’s northern section, which typically ruptures every 414–470 yr in a major (MW >7) to great (MW >8) earthquake, resulting in shaking intensities of MMI >VIII at the study site (MMI: Modified Mercalli Intensity).We present a record of Mg/Ca variability in GT1 since ~5 ka, obtained by laser ablation inductively coupled plasma mass spectrometry along the stalagmite growth axis, and constrained temporally by >40 U–Th ages. Preliminary data show high baseline Mg concentrations in GT1 that cannot be explained solely by other mechanisms of drip water Mg/Ca enrichment (i.e., prior calcite precipitation), suggesting an ongoing contribution of Mg to drip waters by ICDC. Anomalous Mg peaks are therefore interpreted as high-intensity shaking events that temporarily elevated drip water Mg/Ca above baseline values. Post-2.5 ka Mg peaks are generally more subtle (30–50% enrichment) than pre-2.5 ka peaks (40–100%). Magnesium peaks are also strongly associated with brown-stained laminae inferred to reflect soil-derived organics. We propose that the high-Mg/high-organics horizons represent large earthquakes that both fractured the host rock and enhanced the mobilisation of organics from overlying soil.We compared the GT1 record with a proximal and independent 1.4-kyr record of well-dated seismically triggered lacustrine turbidites. Given the subtle nature of Mg peaks in this interval, we consider those associated with physical growth changes (i.e., growth onset/cessation and/or axis change) as more likely to represent earthquakes. Of nine Mg peaks identified, five are associated with major physical growth changes. Of the four largest (MMI >VIII) shaking events in the lake turbidite record, which correspond to northern Alpine Fault surface-rupturing earthquakes, three overlap in age with a GT1 Mg peak and physical growth change. Further, two of the three historic earthquakes that generated MMI ≥VII shaking at the study site also overlap in age with a Mg peak.

The main phase of silicic volcanism from the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km3 dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of voluminous silicic magma generation and emplacement. Here were report high-precision 206Pb/238U zircon ages and show that the largest sequentially dated eruptions occurred within 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding the highest known long-term volumetric extrusive rate of silicic volcanism on Earth. While these are the largest known sequential silicic supereruptions, they did not cause major global environmental change. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating 40Ar/39Ar data with our 206Pb/238U ages to yield new constraints on the duration of the C11n.1r Subchron., Quantifying the tempo of large-volume silicic magma generation and eruption is a long-standing but elusive task. Here we show that the three largest sequentially dated eruptions, totaling >4,300 km3, occurred within 48 ± 34 kyr and yield the highest known long term volumetric extrusive rate of silicic volcanism on Earth.

Highlights • Plinian eruptions linked to rheologically different mingling andesite magmas. • Magma decompression regimes producing variable degassing/crystallization kinetics. • Least explosive eruptions at slowest decompression, ascent and strain rates. • Plinian phases at rapid/intermittent magma decompression, ascent and strain rates. Abstract Estimating the kinetics of andesite magma vesiculation and crystallization inside volcanic plumbing systems is key for unraveling andesite Plinian eruption dynamics. The conduit kinetics provide the necessary input data for estimating the magma flow rates driving magma ascent and the fragmentation mechanisms controlling shifts in eruption explosivity and style. This information is crucial for increasing knowledge on expected hazards and for developing realistic eruption scenarios. In this work, we estimate conduit magma vesiculation and crystallization kinetics during the 3300 cal BP Upper Inglewood Plinian eruptive episode of Mount Taranaki, New Zealand. This episode comprised (i) low-intensity, conduit-opening phases of dome-collapse PDCs; (ii) pre-climactic, highly explosive phases of diverse PDCs, of up to violent 18-km-runout lateral blasts; (iii) climactic phases of steady 22-km-high Plinian eruption columns; and (iv) waning phases of column-collapse PDCs. By employing synchrotron microtomography, combined with mineral/glass chemistry and electron-microscopy, we quantified 3D vesicle and crystal size and shape distributions in juvenile pyroclasts over time, and corresponding number densities ranging from 1.1 × 105 to 2.5 × 106 mm−3 for vesicles, and from 8.0 × 104 to 5.1 × 106 mm−3 for crystals. Our results indicate that tapping of chemically alike yet rheologically contrasting magmas over a multi-phase andesite eruptive episode is linked to: (a) mafic magma recharge and differentiation in multiple storage reservoirs at distinct crustal levels, (b) stepwise to rapid magma decompression while mingling, producing variable pre- and syn-eruptive degassing and crystallization, and (c) syn-eruptive changes in melt viscosity, strain rate, localized shear deformation, and conduit geometry. The earliest and least explosive eruptive phases (≈ 2 × 106 kg s−1) were produced at the slowest rates of magma decompression (0.3–0.6 MPa s−1), ascent (0.01–0.02 m s−1) and strain (< 0.002 s−1), driven by volatile diffusion and exsolution. All subsequent pre-climactic and Plinian phases (4 × 107–1 × 108 kg s−1) were produced at either rapid or intermittent rates of magma decompression (2.0–6.0 MPa s−1), ascent (0.06–0.2 m s−1) and strain (> 0.003–0.010 s−1), powered by combined magma volatile supersaturation and delayed disequilibrium degassing, decompression-induced microlite crystallization and rapid heterogeneous vesiculation kinetics, shear deformation and magma mingling. These processes enabled complex fragmentation mechanisms of the rheologically most homogeneous magmas.

Mt. Taranaki is an andesitic stratovolcano in the western North Island of New Zealand. Its magmas show slab-dehydration signatures and over the last 200 kyr they show gradually increasing incompatible element concentrations. Source basaltic melts from the upper mantle lithosphere pond at the base of the crust (∼25 km), interacting with other stalled melts rich in amphibole. Evolved hydrous magmas rise and pause in the mid crust (14–6 km), before taking separate pathways to eruption. Over 228 tephras erupted over the last 30 kyr display a 1000–1500 yr-periodic cycle with a five-fold variation in eruption frequency. Magmatic supply and/or tectonic regime could control this rate-variability. The volcano has collapsed and re-grown 16 times, producing large (2 to >7.5 km3) debris avalanches. Magma intrusion along N-S striking faults below the edifice are the most likely trigger for its failure. The largest Mt. Taranaki Plinian eruption columns reach ∼27 km high, dispersing 0.1 to 0.6 km3 falls throughout the North Island. Smaller explosive eruptions, or dome-growth and collapse episodes were more frequent. Block-and-ash flows reached up to 13 km from the vent, while the largest pumice pyroclastic density currents travelled >23 km. Mt. Taranaki last erupted in AD1790 and the present annual probability of eruption is 1–1.3%.

The phreatoplinan eruption of the shallow submarine Hunga Volcano Tonga formed global air-pressure waves, regional tsunami and an up to 55 km-high eruption column. Despite its large explosive magnitude, the magma erupted were similar to past compositions, and comprised crystal poor (cpx>opx) andesite with ~57-63 wt% silica glass. Low magnitude Surtseyan eruptions in 2009-2015 formed from small pockets of andesite that ascended slowly, resulting in high microphenocryst and microlite contents. Large eruptions, including events in ~AD200 and AD1100 and the 2022 event drew magma rapidly from a ~5-7 km deep mid-crustal reservoir. Rapid decompression and quenching (augmented by magma-water interaction) records the heterogeneity of the reservoir, with mingled glass textures and cryptic mixing of subtly different melts. The 2022 feldspar phenocrysts show more mafic melt inclusion compositions than host glass, clear uniform cores and thin rims evidencing ~1 month-long changes caused by decompression, rise and internal mingling of subtlety different melts. CPX phenocrysts show uniform cores a variety of more mafic and similar melt inclusions to the bulk glass, and thin overgrowth rims reflecting only decompression and mingling. Lithic fragments (

The January 2022 eruption of Hunga Volcano, Tonga is likely the most explosive mafic eruption yet documented. It exhibited dynamics of ash plume expansion and atmospheric pressure waves unlike anything seen before. This is remarkable considering that it erupted crystal-poor and microlite-poor andesitic magma (57-63 wt% silica glass). The climactic phase produced an eruptive column of at least 39 km in height, however, the ash volume appears anomalously small for the explosive magnitude. Ash from nine different sites across the Kingdom of Tonga were analyzed for textural and morphological properties and grain size distribution. The tephra comprises light pumice (16%), dark pumice (44%), glassy microlite-rich grains (25%), lithics (7%) and free-crystals (Pl, Cpx, Opx) (8%). Specific gravity of particles range from 0.4 to ~2.5. Secondary electron images show that pumices have a variable vesicularity, from dense glassy blocky particles; glassy particles with isolated vesicles and weakly deformed, thick vesicle walls; and a smaller percentage of microvesicular pumices, coated in finer particles. The general characteristics imply a rapid decompression, fragmentation and chilling. This implies some form of phreatomagmatism but with high-efficiency to generate such a large blast – e.g., via propagation of stress waves and thermal contraction rapidly increasing a magma surface area for interaction. The ash is fine-grained and poorly sorted overall. Less than 20 wt.% of ash particles are >1 mm at 80 km SE of the volcano on the main island of Tongatapu, while 70 km NE of the volcano (Nomuka Island) has finer ash, with only 2% of particles >1 mm. It appears that the dispersion axis for the event was directed toward the E or ESE, across the main population centre of Nuku’alofa on Tongatapu. Of the fine fraction 20 wt.% is < 30 micron, 8 wt.%

The Main Silicics phase of the Afro-Arabian large igneous province preserves some of the largest volcanic eruptions on Earth, with six units totaling >8,600 km3 dense rock equivalent (DRE). The large volumes of rapidly emplaced individual eruptions present a case study for examining the tempo of generation and emplacement of voluminous silicic magmas. We use high-precision 206Pb/238U zircon dating to differentiate individual eruption ages and show that the largest sequentially dated eruptions occurred within a timeframe of 48 ± 34 kyr (29.755 ± 0.023 Ma to 29.707 ± 0.025 Ma), yielding a maximum magma flux of 3.09 x 10-1 km3/yr for 4,339 km3 DRE and making this sequence the highest known flux of silicic volcanism on Earth. The Main Silicics phase of volcanism occurred within a timeframe of 130 ± 150 kyr (29.80 ± 0.80 Ma to 29.67 ± 0.13 Ma), yielding a maximum magma flux of 3.05 x 10-2 km3/yr. We also provide a robust tie-point for calibration of the geomagnetic polarity timescale by integrating recalculated 40Ar/39Ar data with our high-precision 206Pb/238U ages to yield new constraints on the duration of the C11n.1r Subchron.

Monogenetic basalts are spatially and temporally unpredictable and are commonly interpreted to rise extremely rapidly and directly from their mantle source, increasing their potential hazard. The assumption of rapid ascent is commonly based upon the presence of xenocrysts and xenoliths as well as generally short OH and elemental diffusion profiles at the margins of xenocrystic material. We show that small-volume monogenetic basalts may also have complex multi-stage deep mantle magma storage prior to rapid ascent, using coupled diffusion modelling of major and trace elements and OH within olivine xenocrysts. The xenocrysts and crystal clusters were extracted from a tuff ring in Auckland City (New Zealand), within the Late Pleistocene–Holocene 100 km2 Auckland Volcanic Field. Forsterite-rich olivine xenocrysts (Fo# 89.5 – 91.7 ) have undergone Fe–Mg (Fo#), Ca, Ni and Mn element diffusion that extends up to ∼200 μm from their rims. Major and minor element diffusion at frozen melt–xenocryst interfaces was modelled using crystallographically oriented grains. These profiles show that the host basalt collected most of the olivine xenocrysts and xenoliths over approximately 1 month. The narrow OH diffusion profiles in the olivine suggests late-stage degassing over

Detailed structural, volcanic, and sedimentary investigations of the crustal response to the emplacement of the Middle–Late Permian Emeishan large igneous province show that a rifting system developed prior to the main stage of flood basalt eruptions, in the form of sedimentary breccias, clastic sedimentary deposits and mafic hydromagmatic units. Detrital zircon grains from sandstones yield ~750–800 Ma LA-ICP-MS 206Pb/238U age clusters, showing that material was sourced from the Yangtze crystalline basement. Gabbros and pegmatites intruded along the normal faults of the rift system yield zircon ages of 264–260 Ma, and thus constrain the timing of rifting. N–S-trending rift zones developed along the western flank of the Pan-Xi palaeo-uplift, with NE–SW- and NNE–SSW-trending rifts on the eastern side and along the western and eastern margins of the Yangtze Block. The rifting progressed in pulses, with an initial phase of normal faulting followed by rapid deposition of breccias. Later there was lower-energy deposition of sandstone, with accompanying rhyolitic eruptions. This was followed by low-energy sedimentation of mudstones and dolomites, with accompanying hydromagmatic deposits. Rift system formation was constrained by a combination of far- and near-field tectonic stresses due to plate motions and lithospheric interaction with initial Emeishan volcanism.

Cerro Overo maar is the most mafic lava (54 wt% SiO2, 7.4 wt% MgO) found within the modern subduction arc of the Central Andes. Structural weaknesses in the crust allowed magma to rapidly ascend while avoiding extensive crustal contamination, interactions with the mid-crustal Altiplano-Puna Magma Body, or storage in magma chambers. Cerro Overo lava thus preserves chemical and mineralogical signals from deep-crustal or upper-mantle magmatism which are otherwise absent in the modern Andes Central Volcanic zone (CVZ). Radiogenic isotope ratios of CVZ rocks are characteristically enriched, and researchers have debated for decades whether this enrichment is derived from an enriched mantle source or the result of crustal processes. Phenocrysts of high-forsterite olivine (Fo86) from Cerro Overo contain three populations of silicate melt inclusions: 1. basaltic andesite inclusions chemically identical to the host lava, 2. rhyodacite inclusions representing assimilated upper crust, and 3. basaltic melt inclusions (SiO2 = 49.0 wt%) of minimally-altered magma, reflecting an early-stage melt which may be common to the active arc of the Altiplano-Puna region. Melt inclusion 87Sr/86Sr (0.70376 to 0.70720) also form three clusters, including the most primitive Sr isotopic ratios reported for the modern CVZ arc: direct evidence that the sub-arc mantle source retains non-radiogenic Sr signatures. The least-evolved Olivine-hosted melt inclusions from Cerro Overo match the composition of postulated arc endmembers and provide direct evidence that the overall radiogenic isotopic characteristic of the modern CVZ results from lithospheric processes and not inheritance from a mantle source with an initially radiogenic 87Sr/86Sr signature.

Over the past ~2 Ma, volcanic activity in the western North Island of New Zealand has been focused along the NW to SE-younging Taranaki volcanic lineament (TVL). Geophysical imaging of the convergent boundary between the Pacific and Indo-Australian plates shows that the subducted slab lies at least ~200 km below the present TVL and the

The Snaefellsnes Peninsula of western Iceland is a region of transitional to alkaline Quaternary ( Mg exchange; olivine-spinel Al exchange; clinopyroxene composition; clinopyroxene-melt equilibrium) give broadly consistent crystallization temperatures of ~1220 °C for the wehrlitic glomerocrysts. Clinopyroxene-based geobarometers give pressures of ~6 kbar for the wehrlitic glomerocrysts and

The Permian Tarim magmatic province has 118 published ages, ranging from 358 to 205 Ma, but the timing of mafic magmatism is not well constrained. We report two new secondary ion mass spectrometry U–Pb zircon dates on the Halahatang trachydacite and Wajilitag olivine clinopyroxenite, which are 287.2 ± 2.0 Ma and 283.2 ± 2.0 Ma, respectively. The trachydacite overlies the uppermost basalt and constrains the latest eruption age of basalt in northern Tarim. The latter is the first high-resolution date for the Wajilitag mafic layered intrusion. By screening all published ages, we identified 22 robust ages, ranging from 290.9 ± 4.1 to 261.7 ± 1.8 Ma. The robust ages together with our new data reveal a protracted period of mafic magmatism at c . 283 and c . 267 Ma. Silicic magmatism occurred from 291 to 272 Ma. Although the current known volume of Tarim basalt is too small to qualify as a large igneous province, the eroded and intrusive components, as well as pyroclastic deposits and silicic lavas, may increase the estimated volume. Further work is required to refine the duration of magmatism and the volume estimate of the province. Supplementary material: A list of all the published dates, raw data of published 40 Ar– 39 Ar dates, raw data of published U–Pb dates, published geochemistry data used for calculation and complete details of the data evaluation are available at http://www.geolsoc.org.uk/SUP18862.

Published data on Palaeogene flood basalts of the lower Mull Plateau Group (Scotland) show that the most primitive lavas (MgO > 8 wt %) have the greatest extent of crustal assimilation, inconsistent with a simple coupled assimilation–fractional crystallization (AFC) model. We present elemental data on rehomogenized olivine-hosted melt inclusions from four high-MgO flows to investigate the nature of crustal assimilation and melt aggregation processes during the initial stages of flood basalt magmatism on Mull. Whole-rock compositions have been variably modified by hydrothermal alteration associated with the nearby Central Complexes. Nd isotope compositions, which should be insensitive to this alteration, are lower than typical mantle values (eNd + 2·4 to −5·7), indicating variable modification by crustal assimilation in all four samples. Melt inclusions are protected against alteration effects within their host olivine crystals, and provide more robust estimates of magmatic liquid compositions than whole-rocks, particularly for the alkali elements Na, K and Ba. The whole-rock samples show limited variations in Na2O (2·4–2·8 wt %) and K2O (0·23–0·29 wt %), despite a wide range in immobile elements (e.g. Zr 62–126 ppm). In contrast, the melt inclusions show far greater variability in Na2O (1·8–4·0 wt %) and K2O (0·02–0·35 wt %) and positive correlations between K and Na. Melt inclusions from different samples show systematic correlations between alkalis (K + Na) and incompatible element ratios (e.g. Zr/Y), indicating that the inclusions record magmatic values for the fluid-mobile elements. For the two most incompatible-element-enriched samples, the whole-rock analyses are similar to the melt inclusions except for lower Na and higher Ba that are related to alteration. Therefore, the crustal assimilation in these magmas must have taken place prior to growth of the olivines. For the two more depleted samples, the inclusions have less contaminated compositions than the whole-rocks, and show broad trends of increasing K/Ti with decreasing Fo% of the host olivine. For these samples, crustal assimilation must have taken place both during and after growth of the olivines and in an AFC style in which assimilation is linked to magmatic differentiation. Melt inclusions from single samples show limited variability in Zr/Y compared with K/Ti, indicating that aggregation of melts from different parts of the melt column must have occurred at deeper levels prior to growth of the olivines in the samples. Although the whole-rock compositional variations capture the broad details of crustal assimilation and melting histories for the Mull lavas despite the variable effects of hydrothermal alteration, the melt inclusion data more clearly resolve significant details of these magmatic processes. The extent of assimilation and differentiation is linked to the depth of magma stalling: primitive, contaminated magmas in the lower crust vs. evolved, uncontaminated magmas at sub-Moho depths.

article i nfo The eruption of the Siberian Traps flood basalts has been invoked as a trigger for the catastrophic end- Permian mass extinction. Quantitative constraints on volatile degassing are critical to understanding the en- vironmental consequences of volcanism. We measured sulfur, chlorine, and fluorine in melt inclusions from the Siberian Traps and found that concentrations of these volatiles in some magmas were anomalously high compared to other continental flood basalts. For the ten samples for which we present data, volatile concen- trations in individual melt inclusions range from less than the detection limit to 0.51 wt.% S, 0.94 wt.% Cl, and 1.95 wt.% F. Degassing from the Siberian Traps released approximately ~6300-7800 Gt S, ~3400-8700 Gt Cl, and ~7100-13,600 Gt F. These large volatile loads, if injected into the stratosphere, may have contributed to a drastic deterioration in global environmental conditions during the end-Permian.

compositional change from basaltic andesite to andesite magmas in the waning stages of the eruption that is consistent with progressive crustal assimilation within this latest magma batch. These data demonstrate that the petrogenetic evolution of magmas at Paricutin is more complex than simple progressive assimilation and fractional crystallization and requires the presence of three compositionally distinct magma batches at shallow levels.

Large igneous provinces (LIPs) are sites of the most frequently recurring, largest volume basaltic and silicic eruptions in Earth history. These large-volume (N1000 km3 dense rock equivalent) and large-magnitude (NM8) eruptions produce areally extensive (104–105 km2) basaltic lava flow fields and silicic ignimbrites that are the main building blocks of LIPs. Available information on the largest eruptive units are primarily from the Columbia River and Deccan provinces for the dimensions of flood basalt eruptions, and the Parana–Etendeka and Afro-Arabian provinces for the silicic ignimbrite eruptions. In addition, three large-volume (675– 2000 km3) silicic lava flows have also been mapped out in the Proterozoic Gawler Range province (Australia), an interpreted LIP remnant. Magma volumes of N1000 km3 have also been emplaced as high-level basaltic and rhyolitic sills in LIPs. The data sets indicate comparable eruption magnitudes between the basaltic and silicic eruptions, but due to considerable volumes residing as co-ignimbrite ash deposits, the current volume constraints for the silicic ignimbrite eruptions may be considerably underestimated. Magma composition thus appears to be no barrier to the volume of magma emitted during an individual eruption. Despite this general similarity in magnitude, flood basaltic and silicic eruptions are very different in terms of eruption style, duration, intensity, vent configuration, and emplacement style. Flood basaltic eruptions are dominantly effusive and Hawaiian–Strombolian in style, with magma discharge rates of ~106–108 kg s−1 and eruption durations estimated at years to tens of years that emplace dominantly compound pahoehoe lava flow fields. Effusive and fissural eruptions have also emplaced some large-volume silicic lavas, but discharge rates are unknown, and may be up to an order of magnitude greater than those of flood basalt lava eruptions for emplacement to be on realistic time scales (b10 years). Most silicic eruptions, however, are moderately to highly explosive, producing co-current pyroclastic fountains (rarely Plinian) with discharge rates of 109– 1011 kg s−1 that emplace welded to rheomorphic ignimbrites. At present, durations for the large-magnitude silicic eruptions are unconstrained; at discharge rates of 109 kg s−1, equivalent to the peak of the 1991 Mt Pinatubo eruption, the largest silicic eruptions would take many months to evacuate N5000 km3 of magma. The generally simple deposit structure is more suggestive of short-duration (hours to days) and high intensity (~1011 kg s−1) eruptions, perhaps with hiatuses in some cases. These extreme discharge rates would be facilitated by multiple point, fissure and/or ring fracture venting of magma. Eruption frequencies are much elevated for large-magnitude eruptions of both magma types during LIP-forming episodes. However, in basaltdominated provinces (continental and ocean basin flood basalt provinces, oceanic plateaus, volcanic rifted margins), large magnitude (NM8) basaltic eruptions have much shorter recurrence intervals of 103–104 years, whereas similar magnitude silicic eruptions may have recurrence intervals of up to 105 years. The Parana– Etendeka province was the site of at least nine NM8 silicic eruptions over an ~1 Myr period at ~132 Ma; a similar eruption frequency, although with a fewer number of silicic eruptions is also observed for the Afro- Arabian Province. The huge volumes of basaltic and silicic magma erupted in quick succession during LIP events raises several unresolved issues in terms of locus of magma generation and storage (if any) in the crust prior to eruption, and paths and rates of ascent from magma reservoirs to the surface.

The relationships between meteorite impact craters, flood basalt volcanism and sudden environmental perturbation on Earth have been debated extensively. We present only the second example of contemporaneous meteorite impact and flood basalt volcanism: the 17 km diameter Logoisk impact structure (Belarus) and Afro-Arabian flood volcanism. The new precise 40 Ar/ 39 Ar age of 29.71 ± 0.48 Ma for Logoisk is coincident with the acme of flood volcanism. We argue that at least one crater the size of Logoisk is likely to form during the emplacement of a flood volcanic province, and that contemporaneity of impacts and flood volcanism was the norm. The absence of a biotic effect from the combined Logoisk–Afro-Arabian volcanism we attribute to the magnitude of these combined events, which are both significantly smaller than the other known example of the Chicxulub impact event and the Deccan Traps flood volcanism. Supplementary material: 40 Ar/ 39 Ar data are available at http://www.geolsoc.org.uk/SUP18329.

Numerical and fluid dynamic modelling predicts that mantle plumes should generate a broad domal uplift (>1,000 km wide, 500 to ⩾1,000 m high) preceding volcanism in large igneous provinces. The Emeishan large igneous province (southwest China) has been offered as the best example of plume-induced uplift, where kilometre-scale pre- and syn-volcanic relief was interpreted to develop in response to the impingement of a plume head. Here, we document voluminous mafic hydromagmatic deposits and submarine extrusions that formed during the initiation and early stages of the Emeishan large igneous province: these deposits were previously interpreted to be alluvial fan sediments shed from a pre-volcanic domal high. The abundance of such deposits—consisting of variable proportions of marine limestone and basaltic fragments—strongly suggests that the bulk of this province was emplaced at sea level. Evidence for dynamic pre-volcanic uplift as predicted by plume models is lacking, and such a lack may be the more general case. Any positive relief that developed was more likely the result of the formation of a volcanic edifice and rapid accumulation of the volcanic pile. Thick alluvial fan sediments from the core of the Emeishan Large Igneous Province have been considered as critical field evidence in support of plume-induced pre-volcanic doming and uplift. These sediments are now reinterpreted as mafic hydromagmatic deposits emplaced at sea level, precluding dynamic pre-volcanic uplift as predicted by mantle plume models.

Four Indian Ocean deep-sea tephras can be correlated to individual Oligocene on-land silicic pyroclastic units found in the Afro-Arabian flood volcanic province (Yemen and Ethiopia), providing valuable stratigraphic marker horizons. They also preserve among the largest geochemical heterogeneities observed in individual eruption events (SiO2: 43 to 75 wt.% and 56 to 79 wt.%). The major, trace element and isotopic variations preserved in individual shards in these ash layers provide a unique series of snapshots of magma chamber processes that are used to elucidate the formation and petrogenetic evolution of large volume, chemically zoned silicic magmatic systems. Banded shards within individual ash layers represent up to 85% of the SiO2 variation observed in the entire tephra on the scale of

A new stratigraphy for bimodal Oligocene flood volcanism that forms the volcanic plateau of northern Yemen is presented based on detailed field observations, petrography and geochemical correlations. The >1 km thick volcanic pile is divided into three phases of volcanism: a main basaltic stage (31 to 29.7 Ma), a main silicic stage (29.7 to 29.5 Ma), and a stage of upper bimodal volcanism (29.5 to 27.7 Ma). Eight large-volume silicic pyroclastic eruptive units are traceable throughout northern Yemen, and some units can be correlated with silicic eruptive units in the Ethiopian Traps and to tephra layers in the Indian Ocean. The silicic units comprise pyroclastic density current and fall deposits and a caldera-collapse breccia, and they display textures that unequivocally identify them as primary pyroclastic deposits: basal vitrophyres, eutaxitic fabrics, glass shards, vitroclastic ash matrices and accretionary lapilli. Individual pyroclastic eruptions have preserved on-land volumes of up to ∼850 km3. The largest units have associated co-ignimbrite plume ash fall deposits with dispersal areas >1×107 km2 and estimated maximum total volumes of up to 5,000 km3, which provide accurate and precisely dated marker horizons that can be used to link litho-, bio- and magnetostratigraphy studies. There is a marked change in eruption style of silicic units with time, from initial large-volume explosive pyroclastic eruptions producing ignimbrites and near-globally distributed tuffs, to smaller volume (

A combined paleomagnetic and Ar-40/Ar-39 study was carried out along eight stratigraphically overlapping sections in the Oligocene Afro-Arabian flood volcanic province in Yemen (73 sites). The composite section covers the entire volcanic stratigraphy in the sampling region and represents five polarity zones that are correlated to the geomagnetic polarity time scale based on Ar-40/Ar-39 ages from this and previous studies. The resulting magnetostratigraphy is similar to that of the conjugate margin in Ethiopia. The earliest basaltic volcanism took place in a reverse polarity chron that appears to correspond to C11r, while the massive rhyolitic ignimbrite eruptions correlated to ash layers in Oligocene Indian Ocean sediment 2700 km away from the Afro-Arabian traps, appear to have taken place during magnetochron C11n. The youngest ignimbrite was emplaced during magnetochron C9n. Both 40Ar/39Ar and paleornagnetic data suggest rapid < 1 Ma eruption of the basal basalt units and punctuated eruption of the upper silicic units over a duration potentially as long as 3 Ma with interspersed eruptive hiatuses. Eruption of the basal basalts may have preceded the Oi2 cooling event. The paleornagnetic pole lambda=74.2 degrees N, phi=249.1 degrees E (A95=3.6 degrees; N=48) is supported by a positive reversal test. Paleosecular variation, estimated as the angular standard deviation of the VGP distribution 14.2 degrees+2.3 degrees/-1.7 degrees, is close to expected, suggesting that the paleornagnetic pole represents a time-averaged field. The pole is in excellent accord with the paleornagnetic poles obtained from the Ethiopian part of the Afro-Arabian province, after closure of the Red Sea. By analyzing Afro-Arabian paleomagnetic data in conjunction with contemporaneous paleomagnetic poles available from different latitudes we argue that the Oligocene paleomagnetic field was dominated by the axial dipole with insignificant non-dipole field contributions. (Less)

Primary basaltic pyroclastic deposits compose volumetrically c . 35–50% of the Lower Palaeogene Vandfaldsdalen, Mikis and Haengefjeldet Formations within the lower volcanic series of the East Greenland flood basalt province. The eruption and emplacement mechanisms of these deposits can be used to evaluate the volcanotectonic evolution of continental break-up and initiation of flood basalt volcanism. We present a revised stratigraphy for the pre-volcanic sedimentary rocks and synvolcanic pyroclastic and epiclastic deposits and lavas from the Kangerlussuaq Basin, East Greenland. Primary basaltic pyroclastic deposits range from airfall tuffs to bomb beds, surge deposits and vent sites with cinder cones. Early volcanism was apparently restricted to localized basins and formed shield volcano structures 30–40 km in diameter that are characterized by a heterogeneous sequence of intercalated hyaloclastites, sediments, pyroclastic deposits and lavas. The lateral variation of deposit morphology reflects distance from source and indicates a migrating locus of volcanism along the axis of rifting towards the NE, paired with continued down-dropping of inactive volcanic centres. The complex stratigraphic architecture of the initial volcanic deposits reflects local tectonic and sedimentary processes interacting with regional flood basalt volcanism and continental rifting.

Widespread silicic pyroclastic eruptions of the Oligocene Afro-Arabian flood volcanic province (ignimbrites and airfall tuffs) produced up to 20% of the total flood volcanic stratigraphy (>6×104 km3). Volumes of individual ignimbrites and tuffs exposed on land range from ∼150 to >2000 km3 and eight major units (15–100 m thick) were erupted in 500 km distant); and (b) to two deep sea ash layers sampled by ODP Leg 115 in the Indian Ocean ∼2700 km to the southeast. This correlation is based on whole rock analyses of silicic units for isotope ratios (Pb, Nd) and rare earth element compositions, in conjunction with novel in situ Pb isotope laser ablation multicollector inductively coupled plasma mass spectroscopy analysis of groundmass and glass shards. Compositional diversity preserved on the scale of individual ash shards in these deep sea tephra layers record chemical heterogeneity present in the silicic magma chambers that is not evident in the welded on-land deposits. Ages of the ash layers can be established by correlation to precisely dated on-land ignimbrites, and current evidence suggests that while these eruptions may have exacerbated already changing climatic conditions, they both marginally post-date the Oi2 global cooling anomaly.

a Department of Geoscience, 121 Trowbridge Hall, University of Iowa, Iowa City IA 52242, USA b Biogeoscience, Queensland University of Technology, Brisbane, Queensland 4001, Australia c Department of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK d DougalEARTH Ltd., 12 Nevilles Cross Villas, Durham DH1 4JR, UK e Department of Earth Sciences, University of Hong Kong, Pokfulam Road, Hong Kong, China

Nathalie A.Cabrol,EdmondA.Grin, GuillermoChong,EdwinMinkley,AndrewN. Hock,Youngseob Yu, Leslie Bebout, Erich Fleming, Donat P. Ha¨der, Cecilia Demergasso,John Gibson, Lorena Escudero, Cristina Dorador, Darlene Lim, Clayton Woosley,Robert L. Morris, Cristian Tambley, Victor Gaete, Matthieu E. Galvez,Eric Smith, Ingrid Ukstins Peate, Carlos Salazar, G. Dawidowicz, and J. Majerowicz

In their correspondence, He and colleagues question our conclusion of little or no uplift preceding Emeishan volcanism that we reported in our letter1. Debate concerns the nature of the contact between the Maokou limestone and Emeishan volcanics, the depositional environment and volumetric significance of mafic hydromagmatic deposits (MHDs), and evidence for symmetrical domal thinning. MHDs in the Daqiao section are separated from the Maokou limestone by 100 m of subaerial basaltic lavas, but elsewhere MHDs — previously interpreted as basal conglomerates2, 3 — directly overlie the Maokou2, 3. MHDs thus feature strongly in basal sections of the Emeishan lava succession, as also recently shown4 elsewhere in the Emeishan. An irregular surface at the top of the Maokou limestone has been interpreted as an erosional unconformity2, 3, but clastic deposits presented as evidence of this erosion2, 3 are MHDs produced by explosive magma–water interaction1. A clear demonstration that this irregular top surface is an erosional truncation of limestone reef facies (slope/rim, flat, lagoonal) is currently lacking, but is critical because reefs and carbonate platforms show considerable natural relief of tens of metres. The persistent hot, wet climate since the Oligocene has produced well-developed weathering profiles on exposed Palaeozoic marine sedimentary sequences5, but weathering and karst relief of the uppermost Maokou limestone underlying the flood basalts have not been properly documented, nor shown to be of middle Permian age and immediately preceding emplacement of the large igneous province.