Comparative petrological, geochemical, and geochronological analyses of the contemporaneous La Gavia and Cerro Culiacan Pliocene–Pleistocene shield volcanoes provide critical insights into magmatic evolution and geodynamic triggering mechanisms at the onset of the Michoacan-Guanajuato Volcanic Field. Geochronological constraints reveal synchronous Late Pliocene to Early Pleistocene activity between these adjacent centers, both operating at highly consistent eruption rates of 0.063–0.067 km3/kyr. However, their structural and architectural development diverged significantly. The sprawling, gentle-sloped La Gavia composite shield built up 53.68–56.67 km3 over 0.84 Ma (3.08–2.24 Ma) via an initial Hawaiian-style phase followed by a fissure-controlled, Strombolian-phreatomagmatic phase. Conversely, the steeper Cerro Culiacan shield formed rapidly as a monogenetic center over 0.40 Ma (2.50–2.10 Ma), erupting 25.37–26.78 km3 from a central conduit. Trace element and Sr-Nd-Pb isotope compositions document a shared, hybrid mantle wedge source enriched by slab-derived fluids or sediments, yielding robust calc-alkaline convergent-margin signatures at both volcanoes. Uniquely, La Gavia includes a coeval primitive alkaline suite with an "OIB-type" high-Nb arc basalt signature, indicating a diminished subduction imprint during a syn-tear stage, wherein a landward-propagating slab tear—likely an extension of the Orozco Fracture Zone—induced toroidal flow to drive hot, fertile asthenosphere directly into the overriding wedge. Furthermore, isotopic homogeneity at La Gavia supports a closed-system evolution with rapid magma ascent. In contrast, the Cerro Culiacan calc-alkaline suite demonstrates robust open-system mechanics, where magmas underwent 30–40% bulk contamination and Assimilation and Fractional Crystallization driven by prolonged stalling within the upper-crustal lithologies.

Estimating magma overpressure from intrusion geometry remains a challenge especially when dikes are not directly exposed. Santa Clara volcano ( 27 ka; USA) is an example of a small scoria cone ( 0.01 km3) with an associated lava field ( 0.2 km3) without a direct exposure of its feeder dike. The 145 m high cone was built at the end of a northeast-trending, 350 m wide sandstone ridge that rises 115 m above the surrounding terrain. Its crater floor lies 100 m above the cone base. Lava leaked from the western ridge side at 90 m height, forming a 1.5-m-thick `a`ā lava flow. On the eastern ridge side, at 95 m height, a 50-m-long, 0.4–0.8-m-thick sill transitions laterally into a vent for agglomerates. The similar elevations of the crater floor, sill, and lava vent suggest concurrent venting under hydrostatic equilibrium during the final eruptive stages. We infer that a vertical dike propagated beneath and parallel to the ridge axis, forming the main vent where it first intersected the surface on the ridge base. The cone grew until its vent reached a height determined by magma overpressure in the dike at ridge-base level, at which point, instead of continuing upward growth, magma moved laterally within the ridge to form the sill and lava leak. This scenario implies a magma overpressure of 1–3 MPa at the base of the ridge. We compare two dike-length scenarios and combine the inferred overpressure estimates with elastic theory. These calculations indicate that dike thickness is likely underestimated, suggesting that inelastic deformation is important in accommodating dikes in the upper crust, and that combining observed dike geometries and elastic theory might overestimate magma overpressures.

We have integrated Os isotope systematics in olivine phenocrysts with published O and He isotope data from a suite of well-characterized high-Mg olivine-phyric basalts to andesites across the Trans-Mexican Volcanic Belt (TMVB) to address the relative roles of subduction-related crustal input to the mantle source versus shallow fractional crystallization and/or crustal assimilation. Osmium concentrations in the olivines across all the samples range from 7.3 to 2200 pg/g and, with the exception of one anomalous sample with 187Os/188Os(ol) = 0.532, 187Os/188Os(ol) ranges from 0.125 to 0.259. Olivines from the rear-arc samples are relatively unradiogenic in Os (187Os/188Os = 0.122 to 0.136) compared to the arc front olivines (187Os/188Os >= 0.130), which are more radiogenic than primitive upper mantle and largely overlap with mantle xenoliths from arc settings. The arc front olivines exhibit distinctly heavier S 18 O than those of the rear-arc, but a significant role for crustal assimilation in the evolution of most TMVB magmas can be precluded due to the lack of correlation between 187Os/188Os(ol) or S 18 O (ol) with indices of fractionation (e.g., Fo#, Ni (ol) , and Mg#(WR)), as well as the mantle-like He isotope signatures of the olivines. This suggests that the radiogenic Os and heavy S 18 O are inherited from the mantle source region. A mixing model between mantle and sediment-rich slab-derived components, as proposed previously for other areas of the TMVB, can explain the 87Sr/86Sr(wr)- 206Pb/204Pb(wr)- S 18 O (ol) systematics. However, the radiogenic 187Os/188Os(ol) requires an unexpectedly high degree of fluid mobility for Os in this model. Instead, the Os data suggest that serial subduction fluxing and melting of the mantle wedge result in an accumulation of radiogenic Os in the mantle wedge through progressive slab flux, consistent with models from earlier studies based on olivine chemistry and the positive correlation of S 18 O (ol) with mantle depletion proxies. The decoupling of 187Os/188Os(ol) and S 18 O (ol) may be influenced by the presence of primary and secondary sulfides in the mantle wedge, which control the Os budget.

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.

This study presents the first quantitative reconstruction of long-term changes in particulate matter (PM) abundance, elemental compositions, and sources using a combination of microscopic, elemental, and isotopic methods in archived biomonitors. We compared two sets of deciduous leaves collected from a park near a steel plant in Middletown, Ohio, in 1961 and 2022. Additionally, a set of lichen samples collected from Middletown underwent the same elemental and isotopic analysis as the leaf samples to better understand time-integrated PM sources in the region. Microscopic investigations revealed that the average amount of PM retained on the unit surface area of the 1961 leaves was 17 times higher than that of the 2022 leaves. Pb isotopes indicated that historical average PM masses originating from glacial till, the steel plant, gasoline, and fly ash were 533 ± 139, 343 ± 36, 435 ± 130, and 139 ± 14 mg m-2 respectively, while the corresponding values for the contemporary sources were 30 ± 6, 23 ± 3, 17 ± 2, and 12 ± 1 mg m-2. This suggests a shift in the primary anthropogenic source of PM from gasoline in 1961 to the steel plant in 2022, likely due to the phase-out of leaded gasoline. Elemental analysis revealed that PM emissions from the plant in the 1960s were 15 times higher and contained elevated concentrations of a wider range of elements compared to contemporary leaves. Further, lichen samples (estimated to date back to the late1980s to late 1990s) exhibited significantly elevated concentrations of Al, Cr, Fe, and V associated with steel plant emissions, with the highest anthropogenic relative contribution of PM originating from the steel plant, indicating the high impact of steel plant emissions prior to implementation of pollution control measures in 2006. Overall, these findings underscore that despite the significant decline in PM emissions observed over the last 60 years, the environmental impact of the steel plant continues.

To investigate the effect of recycled slab materials on the Si isotopes of the mantle, we analyzed the Si isotopes of 80 ocean island basalts (OIB) from five hotspots around the world, including Azores, Iceland, Samoa, St. Helena, and Cook-Austral Islands. These samples have a wide range of radiogenic isotope signatures, representing various mantle sources including EM II (enriched mantle II) and HIMU (high mu, mu = 238U/204Pb). After evaluating the influences of chemical weathering, seawater alteration, partial melting, and fractional crystallization on Si isotopes in these OIB, which are negligible, the Si isotopic characteristics of OIB could reflect their original mantle compositions. The S30Si of EM II-type samples range from -0.37 f 0.03 %o to -0.17 f 0.05 %o with an average of -0.28 f 0.08 %o (2SD, N = 27), and HIMU-type samples range from -0.39 f 0.05 %o to -0.22 f 0.05 %o with an average of -0.29 f 0.09 %o (2SD, N = 37). Additionally, we employed the parameter Delta 30Si (defined as S30Sisample - S30SiIgneous Array), which effectively corrects for magmatic differentiation processes while preserving source-related Si isotopic signatures. All analyzed samples exhibit Delta 30Si values below 0.10 %o, further demonstrating the limited Si isotopic variation. There is no correlation between Delta 30Si and 87Sr/86Sr, nor between Delta 30Si and 206Pb/204Pb, indicating that subducted crustal materials (sediments and altered oceanic crust) did not significantly modify the Si isotopes of the ambient mantle. This is consistent with modelling results which show that addition of 7 % of sediments or 10 % to 30 % of altered oceanic crust in the mantle source of OIB would not generate detectable Si isotopic variation. Therefore, despite having sources with distinct mantle endmembers with radiogenic isotope and trace element compositions, which have been intensively modified by recycled crustal materials, these OIB samples exhibit nearly homogeneous Si isotopic compositions (-0.28 f 0.08 %o, 2SD, N = 80). These results indicate that OIB Si isotopic compositions have negligible contributions from recycled materials, implying that Si isotopes have limited potential as tracers of subducted materials in OIB mantle sources.

Despite continued actions to abate harmful air pollutant emissions, air pollution is still a worldwide concern, yet apportioning individual shares of responsibility for pollution is challenging. Here, we present a spatial approach combined with microscopy, elemental composition, and Pb isotopes to trace particulate matter (PM) emissions related to a steel manufacturing plant in Middletown, Ohio. Evergreen leaves were collected in nine sites situated 18 and 32 km upwind and 0 - 35 km downwind from the steel plant. The relative abundance and size range of spherical Fe-rich particles, as indicators of the steel factory's emissions, were quantified using SEM/EDS. Elemental compositions and Pb isotopes were used for PM source apportionment. The SEM/EDS quantification method was effective for steel particles, while it was less suitable for quantifying fly ash abundances owing to its limitations in detecting ultrafine PM, where fly ash particles are prevalent. Pb isotopes indicated that the average leaf-level PM mass originating from glacial till, steel plant, gasoline, and fly ash, were 44±23, 34±30, 33±17, and 18±11 mg m-2, respectively, highlighting the steel plant and gasoline as the primary anthropogenic PM sources. Strong correlations between steel spherule mass estimated by MixSIAR and its relative proportion quantified through microscopic investigations (r=0.94) and pollution load index (r=0.89) provide support for source apportionment using isotopic methods. The steel spherules quantity decreased exponentially with distance with the steel plant's effective PM footprint extending approximately 32 and 40 km upwind and downwind, respectively, emphasizing its ongoing environmental impact despite pollution control measures.

AbstractMarine fallout ash beds can provide continuous, time‐precise records of highly explosive arc volcanism that can be linked with the climate record. An evaluation of revised Plio‐Pleistocene (0–4 Myr) tephrostratigraphies from Ocean Drilling Program Sites 881, 882, and 884 confirms cyclicity of the Kamchatka‐Kurile arc volcanism and a marked increase just after the intensification of the Northern Hemisphere glaciation at 2.73 Ma. The compositional constancy of the Kamchatka‐Kurile volcano‐magma systems through time points to external modulation of volcanic cyclicity and frequency. The stacked tephra record reveals periodic peaks in arc volcanicity at ∼0.3, ∼1.0, ∼1.6, ∼2.5, and ∼3.8 Myr that coincide with maxima of the global ice volume variability that have been linked with the amplitude modulation of the precession (0.3, 1.0 Myr) and obliquity (1.6, 2.5 and 3.8 Myr) bands. A simple model of a decreasing obliquity variance across the mid‐Pleistocene Transition at constant precession variance produces an excellent correlation of ash bed cycles with the variability of global benthic δ18O (r2 = 0.75), which implies that climate, and not direct orbital forcing, modulates Kamchatka‐Kurile arc volcanism. The rising influence of precession variance in the Kamchatka‐Kurile ash bed record after the mid‐Pleistocene Transition contrasts with the dominant 100 kyr signal in the benthic δ18O global ice volume variability, which may either reflect limitations of the ash bed record or an regional rather than global influence of ice volume variability. Our results indicate that climate influences the Kamchatka‐Kurile arc volcanism, which may influence climate only by feedback.

We investigated the state of the arc background mantle (i.e. mantle wedge without slab component) by means of olivine CaO and its Cr-spinel inclusions in a series of high-Mg# volcanic rocks from the Quaternary Trans-Mexican Volcanic Belt. Olivine CaO was paired with the Cr# [molar Cr/(Cr + Al) *100] of Cr-spinel inclusions, and 337 olivine+Cr-spinel pairs were obtained from 33 calc-alkaline, high-K and OIB-type arc front volcanic rocks, and three monogenetic rear-arc basalts that lack subduction signatures. Olivine+Cr-spinels display coherent elemental and He-O isotopic systematics that contrast with the compositional diversity of the bulk rocks. All arc front olivines have low CaO (0.135 +/- 0.029 wt %) relative to rear-arc olivines which have the higher CaO (0.248 +/- 0.028 wt %) of olivines from mid-ocean ridge basalts. Olivine He-3/He-4-delta O-18 isotope systematics confirm that the olivine+Cr-spinels are not, or negligibly, affected by crustal basement contamination, and thus preserve compositional characteristics of primary arc magmas. Variations in melt H2O contents in the arc front series and the decoupling of olivine CaO and Ni are inconsistent with controls on the olivine CaO by melt water and/or secondary mantle pyroxenites. Instead, we propose that low olivine CaO reflects the typical low melt CaO of high-Mg# arc magmas erupting through thick crust. We interpret the inverse correlation of olivine CaO and Cr-spinel Cr# over a broad range of Cr# (similar to 10-70) as co-variations of CaO, Al and Cr of their (near) primary host melts, which derived from a mantle that has been variably depleted by slab-flux driven serial melt extraction. Our results obviate the need for advecting depleted residual mantle from rear- and back-arc region, but do not upset the larger underlying global variations of melt CaO high-Mgy# arc magmas worldwide, despite leading to considerable regional variations of melt CaO at the arc front of the Trans-Mexican Volcanic Belt.

El Astillero and El Pedregal monogenetic volcanoes formed-500-700 CE in the Tancitaro region in the southern part of the Michoac & PRIME;an-Guanajuato volcanic field, only 25 km to the SW of the historic Paricutin volcano. The -6year-long eruption was characterized by a change from explosive to effusive activity, accompanied by a shift in the location of the active vents. Initial activity was Strombolian-explosive and first formed the El Astillero cone before turning effusive with the emission of several lava flows. Then, a new vent located 2 km to the ENE opened and produced the purely effusive (non-explosive) El Pedregal lava flow field. As the eruption progressed, the bulk magma composition (major and trace elements) changed from basaltic andesite to andesite (SiO2 = 52-59 wt%), which is also reflected in a successive change in the petrography of the erupted tephras and lavas. However, the El Pedregal lava sequence shows small Mg# reversals followed by a marked final reversal to more mafic compositions. Likewise, 87Sr/86Sr (0.70388-0.70403), 143Nd/144Nd (0.512836-0.512742), 206Pb/204Pb (18.632-18.671), 207Pb/204Pb (15.583-15.598), 208Pb/204Pb (38.376-38.450), 176Hf/177Hf (0.28301-0.28290), and 187Os/188Os (0.1258-0.1865) isotope ratios changed systematically as the eruption progressed, and record a final shift to a distinct isotopic signature. The spatio-temporal proximity of both vents and the petrographic and geochemical characteristics of their magmas suggest a comagmatic evolution that can be explained by a combination of variable degrees of magma recharge, magma mixing, and fractional crystallization of subductionmodified mantle melts. A similar combination of magmatic processes for the genesis and evolution of these magmas has also been proposed for other young monogenetic volcanoes in the Michoac & PRIME;an-Guanajuato volcanic field (e.g., Paricutin, Jorullo, and the Tac & PRIME;ambaro cluster). Accordingly, primitive magmas in the Trans-Mexican Volcanic Belt are subduction-modified mantle melts that evolve largely by crystal fractionation and pass through the crust without significant assimilation.