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St. Kitts lies in the northern Lesser Antilles, a subduction-related intraoceanic volcanic arc known for its magmatic diversity and unusually abundant cognate xenoliths. We combine the geochemistry of xenoliths, melt inclusions and lavas with high pressure–temperature experiments to explore magma differentiation processes beneath St. Kitts. Lavas range from basalt to rhyolite, with predominant andesites and basaltic andesites. Xenoliths, dominated by calcic plagioclase and amphibole, typically in reaction relationship with pyroxenes and olivine, can be divided into plutonic and cumulate varieties based on mineral textures and compositions. Cumulate varieties, formed primarily by the accumulation of liquidus phases, comprise ensembles that represent instantaneous solid compositions from one or more magma batches; plutonic varieties have mineralogy and textures consistent with protracted solidification of magmatic mush. Mineral chemistry in lavas and xenoliths is subtly different. For example, plagioclase with unusually high anorthite content (An ≤100 ) occurs in some plutonic xenoliths, whereas the most calcic plagioclase in cumulate xenoliths and lavas are An 97 and An 95 , respectively. Fluid-saturated, equilibrium crystallisation experiments were performed on a St. Kitts basaltic andesite, with three different fluid compositions ( X H 2 O = 1.0, 0.66 and 0.33) at 2.4 kbar, 950–1025 °C, and f O 2  = NNO − 0.6 to NNO + 1.2 log units. Experiments reproduce lava liquid lines of descent and many xenolith assemblages, but fail to match xenolith and lava phenocryst mineral compositions, notably the very An-rich plagioclase. The strong positive correlation between experimentally determined plagioclase-melt Kd Ca–Na and dissolved H 2 O in the melt, together with the occurrence of Al-rich mafic lavas, suggests that parental magmas were water-rich (> 9 wt% H 2 O) basaltic andesites that crystallised over a wide pressure range (1.5–6 kbar). Comparison of experimental and natural (lava, xenolith) mafic mineral composition reveals that whereas olivine in lavas is predominantly primocrysts precipitated at low-pressure, pyroxenes and spinel are predominantly xenocrysts formed by disaggregation of plutonic mushes. Overall, St. Kitts xenoliths and lavas testify to mid-crustal differentiation of low-MgO basalt and basaltic andesite magmas within a trans-crustal, magmatic mush system. Lower crustal ultramafic cumulates that relate parental low-MgO basalts to primary, mantle -derived melts are absent on St. Kitts.

Waste andesite sand (AS) is produced when cutting andesite stone and doing other stone dressing procedures. Problems with storage and environmental pollution may result from the disposal of AS. These issues might be resolved using AS in the manufacturing of alkali-activated composites. Pozzolanic powders are used extensively in the construction sector to reduce the need for cement, which lowers the price of making concrete and lessens environmental pollution from CO 2 emissions from cement producers. This paper reports the findings of an experimental examination into the impact of diatomite powder and waste andesite sand on the microstructural, durability, and mechanical characteristics of environmental-friendly alkali-activated lightweight composites (AALC). Ground blast furnace slag (GBFS) and diatomite powder (DP) were used as the main solid precursors, silica sand (SS) and waste andesite sand (AS) were used as fillers for the design of AALC mixtures. The alkaline activators adopted in this study were sodium hydroxide and sodium silicate. Physico-mechanical characteristics, transport properties, thermal conductivity, sorptivity, and drying shrinkage of generated AALC mixes were also examined in addition to its performance under freeze–thaw (F–T) cycles and high temperatures. SEM analyses of the AALC were conducted to investigate the microstructure of the produced specimens. Sixteen AALC mixtures were created using GBFS/DP ratios of 100/0, 90/10, 80/20 and 70/30 and AS was used to replace silica sand (SS) in four different rates of 0%, 25%, 50%, and 100%. Prior to ambient curing, the manufactured samples were cured at 80 °C for 24 h to quicken geopolymerization. The findings showed that the mixture with 100% GBFS and 100% AS had a maximum compressive strength of around 60 MPa. When GBFS was replaced with 20% and 30% DP, the compressive strength of AALC specimens was drastically reduced. The AALC mixtures containing 20% and 30% DP showed the lowest thermal conductivity results. The best high-temperature resistance was demonstrated by the mixture D20A50, which comprises 20% DP and 50% AS and experiences a strength loss of 20.7% at 900 °C. The best resistance to freezing and thawing exposure was found in mixtures that contained 10% DP and 50% AS.

During the process of cutting andesite stones, the waste mud is kept in powder form once fully dried. It is difficult to store the waste that is produced as a consequence of the extensive utilization area and consumption of andesite. Thus, eliminating waste storage challenges and incorporating these wastes into the economy are crucial. For this reason, this study examined the effects of waste andesite dust (WAD) on the flexural behavior of reinforced-concrete beams (RCBs) using experimental testing and 3D finite-element modeling (FEM) via ANSYS. Thus, different rates of WAD up to 40% were used to investigate the influence of the WAD rate on the fracture and bending behavior of RCBs. While the RCB with 10% WAD had a slightly lower load-bearing and ductility capacities, ductility capacities significantly drop after 10% WAD. At 40% WAD, both the load-bearing capacity and ductility significantly reduced. Based on the experimental findings, using 10% WAD as a replacement for cement is a reasonable choice to obtain eco-friendly concrete. Moreover, the outcomes of 3D FEM were also compared with those of experiments conducted using ANSYS v19 software. The displacement values between the test and FEM findings are quite similar.

The composition and origin of Earth’s early crust remains hotly debated. Here we use partition coefficients to invert the trace element composition of 4.3–3.3 Gyr Jack Hills zircons to calculate the composition of the melts from which they crystallised. Using this approach, the average SiO 2 content of these melts was 59 ± 6 wt. % with Th/Nb, Dy/Yb and Sr/Y ratios of 2.7 ± 1.9, 0.9 ± 0.2 and 1.6 ± 0.7, respectively. Such features strongly indicate that the protolith for the Jack Hills zircons was not an intra-plate mafic rock, nor a TTG (tondjhemite-tonalite-granodiorite) or a Sudbury-like impact melt. Instead, the inferred equilibrium melts are much more similar to andesites formed in modern subduction settings. We find no evidence for any secular variation between 4.3 and 3.3 Gyr implying little change in the composition or tectonic affinity of the Earth’s early crust from the Hadean to Mesoarchaean. The composition and tectonic affiliation of Earth's earliest crust remains disputed. Here, the authors find that Archean Jack Hills zircons crystallized from melts with compositions similar to andesite formed in modern subduction settings, which they suggest is consistent with an early onset of modern-style plate tectonics on Earth.

Real-time monitoring of volcanic eruptions involving caldera-forming events are rare (see the Perspective by Sigmundsson). Anderson et al. used several types of geophysical observations to track the caldera-forming collapse at the top of Kīlauea Volcano, Hawai'i, during the 2018 eruption. Gansecki et al. used near–real-time lava composition analysis to determine when magma shifted from highly viscous, slow-moving lava to low-viscosity, fast-moving lava. Patrick et al. used a range of geophysical tools to connect processes at the summit to lava rates coming out of far-away fissures. Together, the three studies improve caldera-collapse models and may help improve real-time hazard responses. Science , this issue p. eaaz0147 , p. eaay9070 ; p. eaaz1822 ; see also p. 1200 Near–real-time chemical monitoring of lava during the Kīlauea eruption allowed forecasting of high-temperature eruptions. Changes in magma chemistry that affect eruptive behavior occur during many volcanic eruptions, but typical analytical techniques are too slow to contribute to hazard monitoring. We used rapid energy-dispersive x-ray fluorescence analysis to measure diagnostic elements in lava samples within a few hours of collection during the 2018 Kīlauea eruption. The geochemical data provided important information for field crews and civil authorities in advance of changing hazards during the eruption. The appearance of hotter magma was recognized several days before the onset of voluminous eruptions of fast-moving flows that destroyed hundreds of homes. We identified, in near real-time, interactions between older, colder, stored magma—including the unexpected eruption of andesite—and hotter magma delivered during dike emplacement.

Plagioclase microlites in a magma nucleate and grow in response to melt supersaturation (Δ ϕ plag ). The resultant frozen plagioclase crystal size distribution (CSD) preserves the history of decompression pathways ( dP/dt ). SNGPlag is a numerical model that calculates the equilibrium composition of a decompressing magma and nucleates and grows plagioclase in response to an imposed Δ ϕ plag . Here, we test a new version of SNGPlag calibrated for use with basaltic andesite magmas and model dP/dt for the ca. 12.6 ka Curacautín eruption of Llaima volcano, Chile. Instantaneous nucleation ( N plag ) and growth ( G plag ) rates of plagioclase were computed using the experimental results of Shea and Hammer (J Volcanol Geotherm Res 260:127–145, 10.1016/j.jvolgeores.2013.04.018, 2013) and used for SNGPlag modeling of basaltic andesite composition. Maximum N plag of 6.1 × 10 5  cm h −1 is achieved at a Δ ϕ plag of 44% and the maximum G plag of 27.4 μm h −1 is achieved at a Δ ϕ plag of 29%. Our modeled log dP/dt avg range from 2.69 ± 0.09 to 6.89 ± 0.96 MPa h −1 (1σ) with an average duration of decompression from 0.87 ± 0.25 to 16.13 ± 0.29 h assuming a starting pressure P i of 110–150 MPa. These rates are similar to those derived from mafic decompression experiments for other explosive eruptions. Using assumptions for lithostatic pressure gradients ( dP/dz ), we calculate ascent rates of < 1–6 m s −1 . We conducted a second set of Monte Carlo simulations using P i of 15–30 MPa to investigate the influence of shallower decompression, resulting in log dP/dt avg from 2.86 ± 0.49 to 6.00 ± 0.86 MPa h −1 . The dP/dt modeled here is two orders of magnitude lower than those calculated by Valdivia et al. (Bull Volcanol, 10.1007/s00445-021-01514-8, 2022) for the same eruption using a bubble number density meter, and suggests homogeneous nucleation raises dP/dt by orders of magnitude in the shallow conduit. Our modeling further supports the rapid-ascent hypothesis for driving highly explosive mafic eruptions.

In the Yili terrane at Awulale mountain, most shoshonitic lavas are related to post-collision extension and were extruded during the Late Carboniferous to Early Permian (310-280 Ma). Herein, we evaluate a small-volume occurrence of shoshonitic magmas in the southern Yili terrane formed c. 346 Ma ago. The high MgO (Mg#) and positive Hf isotope values of the shoshonitic magmas indicate the input of juvenile mantle-derived material. Still, their high Ba-Sr signatures were likely inherited from the partial melting of previously metasomatized lithospheric mantle. We argue the shoshonitic magmatic activity recorded a syn-subduction extensional history in the Yili terrane. This interpretation is consistent with the magmatic records from Early Carboniferous A-type granite and magnesian andesite found in the Zhaosu-Adentao-Dahalajunshan area of the southern Yili terrane. Combined with the geological development in this area, we propose that the emergence of the shoshonitic rocks records either the retreat of the trench or the rollback of the Junggar oceanic slab that occurred at or before the 346.1 ± 3.1 Ma age of the rocks.

Primitive arc magmas provide our closest glimpse of the original mantle-derived magmas that produce the more ubiquitous andesites and dacites found in subduction zones and that ultimately construct Earth’s continental crust. This study examines the crustal storage and ascent history of the Mt. Shasta primitive magnesian andesite (PMA), a demonstrated parent magma for the voluminous mixed andesites erupted at Mt. Shasta. Our petrographic and geochemical observations of the PMA identify a mid-crustal magma mixing event recorded in multiple populations of reversely zoned clinopyroxene and orthopyroxene phenocrysts. Thermobarometric calculations conducted as part of this study and prior phase equilibrium experiments (Grove et al., Contrib Miner Petrol 145:515–533, 2003; Krawczynski et al., Contrib Miner Petrol 164:317–339, 2012) suggest the PMA experienced storage, mixing, and subsequent crystallization at ~ 500 MPa and ~ 975 °C. Modeling of Fe–Mg interdiffusion between the rims and cores of the reversely zoned pyroxenes suggests this mixing event and the resulting crystal rim growth occurred less than 10 years prior to eruption ( 2.9 - 2.2 + 6.4 ). Ascent from 500 MPa (~ 15 km) during the calculated diffusion timescales suggests minimum crustal transit rates of ~ 170 MPa (~ 5 km)/year and cooling rates of ~ 5–7 °C/km, consistent with conductive cooling models. This ascent rate is slower than the handful of previously documented trans-crustal magmatic ascent rates and significantly slower than syn-eruptive decompression rates. If this behavior is representative, ~ the 10% mafic magmas erupted as part of the modern Mt. Shasta edifice fluxed through the crust within decades. Coupled with a review of the U–Th–Ra residence times for Shasta andesites to dacites, we suggest that crustal magma flux and assembly beneath modern Mt. Shasta occurred in discrete pulses that occupy a minority of the 700 k.y. period of edifice construction. The results of this study thus constrain the pre-eruptive history and ascent characteristics of a hydrous primitive arc magmas in the upper crust between their shallowest storage region in the mid-crust and volatile exsolution and provide constraints on crustal magma flux beneath continental arc volcanoes. Should future earthquake swarms indicative of magma movement in the middle to upper crust occur beneath Shasta, the results presented here also provide the first estimates of the possible magma ascent rates and the time intervals that could accompany related magma ascent to eruption at Mt. Shasta.

Occurrences of high-Mg andesite (HMA) in modern volcanic arcs raise the possibility that significant volumes of continental crust could be directly derived from Earth's mantle. Such rocks are commonly associated with subduction of young, warm oceanic lithosphere or occur in areas heated by mantle convection. A relatively rare occurrence near Mt. Shasta in the Cascades volcanic arc has been considered to represent one such primary mantle-derived magma type, from which more evolved andesitic and dacitic magmas are derived. Recognition that the Shasta area HMA is actually a hybrid mixed magma, calls into question this notion as well as the criteria upon which it is based. We report new chemical and mineralogical data for samples of the Shasta HMA that bear on the components and processes involved in its formation. Several generations of pyroxenes and olivines are present along with different generations of oxide minerals and melt inclusions. The most magnesian olivines (Fo93) exhibit disequilibria textures, exotic melt inclusions, and reaction rims of Fo87 composition; these crystals along with spongy, ∼Mg#87 orthopyroxene crystals are interpreted to be xenocrystic and do not signify a primitive mantle derivation. The groundmass is andesitic with moderate MgO content, and melt inclusions of similar compositions are hosted by equilibrium olivine (∼Fo87). The bulk magma (whole rock) is more magnesian, but primarily due to incorporation of mafic minerals and ultramafic xenolith debris. We propose that the exotic crystal and lithic debris in these rocks is derived from (1) dacitic magmas of possible crustal derivation, (2) prograded ultramafic rocks in the underlying crust, and (3) random lithic debris and crystals derived from conduit wall rocks and earlier intruded magmas within the feeder plexus beneath Shasta. The HMA is inferred to represent a mixture between evolved dacitic and primitive basaltic magmas as well as incorporation of xenolithic crystal cargo. There is no compelling evidence that HMA is present in large volumes, and it is not considered to be an important parental liquid to more evolved magmas at Shasta.

Fourier transform infrared (FTIR) spectroscopy can be used to determine the concentration and speciation of dissolved water in silicate glasses if the molar absorptivity coefficients ((open e)) are known. Samples that are thin and/or water-poor typically require the use of the mid-IR 3500 cm-1 total water (H2Ot) and 1630 cm1 molecular water (H2Om) absorbance bands, from which hydroxyl water (OH) must be determined by difference; however, accurate determination of H2Ot and OH is complicated because ε3500 varies with water speciation, which is not usually known a priori. We derive an equation that uses end-member ε3500 values to find accurate H2Ot and OH concentrations from the 3500 cm-1 absorbance for samples where only the H2Om concentration need be known (e.g., from the 1630 cm-1 band). We validate this new species-dependent (open e)3500 method against published data sets and new analyses of glass standards. We use published data to calculate new end-member (open e)3500 values of ε3500OH = 79 ± 11 and ε3500H2Om = 49 ± 6 L/mol·cm for Fe-bearing andesite and ε3500OH = 76 ± 12 and ε3500H2Om = 62 ± 7 L/mol·cm for Fe-free andesite. These supplement existing end-member values for rhyolite and albite compositions. We demonstrate that accounting for the species-dependence of ε3500 is especially important for hydrated samples, which contain excess H2Om, and that accurate measurement of OH concentration, in conjunction with published speciation models, enables reconstruction of original pre-hydration water contents. Although previous studies of hydrous silicate glasses have suggested that values of e decrease with decreasing tetrahedral cation fraction of the glass, this trend is not seen in the four sets of end-member ε3500 values presented here. We expect that future FTIR studies that derive end-member ε3500 values for additional compositions will therefore not only enable the species-dependent ε3500 method to be applied more widely, but will also offer additional insights into the relationship between values of ε and glass composition.