• Pali-Aike refractory peridotites formed in an Archean melting-temperature environment. • High melting degrees originally produced a buoyant off-craton continental lithosphere. • Metasomatism subsequently eroded the chemical buoyancy of the lithospheric mantle. • Long-term survival of lithospheric plates requires refractory mantle roots beneath them. • Off-craton lithosphere likely consists of reworked relics of cratonic mantle. The off-craton subcontinental lithospheric mantle (SCLM) is generally more fertile and younger than cratonic mantle. Melting conditions ascribed to its formation hardly produce iron-depleted, and hence low-density residual peridotites capable of stabilizing the lithospheric plate. Here, we document how major/trace element co-variations in off-craton mantle xenoliths from Pali-Aike (southern Patagonia) define different melt/rock reaction trends that can be back-tracked towards the composition of a high-Mg# (91.7), refractory (Al 2 O 3 = 1.0 wt.%, CaO = 0.46 wt.%) spinel-harzburgite, which represents the original protolith of the off-craton SCLM. Thermobarometric calculations support that this refractory protolith formed by ∼30% ( F ) melting at 3.0 GPa and 1555 ± 70 °C, conditions not achievable in the present-day ambient mantle but that extrapolate a paleo-potential temperature ( T P ) of 1540–1570 °C. This T P agrees with models predicting a moderately warm Archean-age mantle at the time of formation of Pali-Aike SCLM (2.5–2.7 Ga). Thermodynamic modeling with Perple-X of asthenospheric mantle (KLB-1) upwelling through the inferred paleo-adiabat yields an isentropic melting path that reproduces the P-T - F estimates of the SCLM protolith. Peritectic garnet removal by extensive melting at moderate pressures promoted the formation of a dehydrated and low-density lithospheric mantle root, which could survive conductive cooling and stabilize the overlying crust. Subsequent metasomatic refertilization counteracted the chemical buoyancy of continental peridotites, promoting the transformation of cratonic edges into thinner and fertile off-craton lithospheric mantle. Since the stabilization of buoyant lithospheric roots requires high-melting degrees typical of cratonic environment, we propose that most SCLM originally formed in the Paleoproterozoic-Archean, before being refertilized and thinned at off-craton regions.

• Dike eruptibility scales with magma intrusion volume, overpressure and volatiles. • Thick crust and steep geotherms suppress dike formation. • Thicker Southern highlands crust hindered volcanic resurfacing compared to North. • Thinner Noachian crust: high & low degree melts erupt, showing variable alkalinity. • Amazonian basalts: low alkalinity, only high degree melts can traverse thick crust. Martian volcanism exhibits two key global trends: magmas evolved from alkali- and silica-rich compositions in the Noachian epoch to alkali depleted mafic compositions in the Amazonian, while spatially, young (Amazonian) volcanic resurfacing is confined to the Northern hemisphere and the Tharsis region, with no evidence of recent volcanism in the Southern highlands. A unifying model linking these observations has been lacking. Here, we investigate the relationship between spatio-temporal variations in volcanic resurfacing and the evolution of magma chemistry throughout martian geological history. By analyzing the physical conditions required for volcanic eruptions to be sourced from magma reservoirs located within the martian crust, we model how these conditions influence mantle-derived magma compositions. Our results show that dike propagation from magma chambers is controlled by crustal rheology, with dike height depending on chamber size, magma overpressure, and volatile exsolution (both in the reservoir and within the dike). During the Noachian, the thin crust allowed eruptions of both low- and high-degree mantle melts, consistent with the diverse alkalinity of ancient surface rocks. In contrast, the thickened Amazonian crust selectively filtered low-degree melts, necessitating high recharge rates in large magma reservoirs for eruptions. This filtering effect explains the alkali – depleted compositions of Amazonian basalts, as only high-degree melts could reach the surface. Our study provides a holistic framework connecting magma reservoir dynamics, crustal evolution, and the observed geochemical and spatio-temporal trends in martian volcanism.

The composition of the Earth's mantle is influenced by plate tectonic processes, and one of the ways to study the geochemical evolution of the mantle and test plate tectonic and geodynamic models is to investigate the composition of ancient mantle-derived rocks. In this work, we study the Neoproterozoic oceanic basalts that occur as fragments in an olistostromal mélange in the Llŷn Peninsula of North Wales. Based on field, petrographic and geochemical evidence, we argue that these rocks represent pieces of seamounts. Petrogenetic modelling shows that the basalts can be linked to the same source, with geochemical variations being explained by intraplate plume-related melting under variably thickened lithosphere and differing degrees of fractional crystallization. Nd–Hf isotopic data indicate a depleted mantle source, with mean ε Nd(t) and ε Hf(t) of 7.0 and 9.4, respectively. The depleted Nd and Hf signatures associated with elevated Pb isotopic ratios suggest that the mantle source tapped by this plume was dominated by a component similar to modern-day Prevalent Mantle (PREMA). Monte Carlo simulations utilizing constraints on the age of accretion to an active margin and lithospheric thickness at the time of plume impingement yield results that show plume activity between 655 and 590 Ma. The Late Neoproterozoic timing of accretion of these rocks to the active margin might also help explain the exhumation of blueschists in North Wales. Palaeogeographical and geochronological constraints show that, rather than being derived from the Iapetus Ocean, the seamounts preserved in North Wales probably originated in the shrinking circum-Rodinia Mirovoi super-ocean. Records of preserved seamounts elsewhere in the world show that Neoproterozoic plume activity must have been common in the Mirovoi Ocean. The isotopic characteristics of the plume-related basalts in this study show that the PREMA component was present in the mantle sources of magmatism in the Mirovoi super-ocean and support the hypothesis of the longevity of this component. This study shows how a multidisciplinary approach integrating geochemistry and plate reconstruction can help track mantle evolution in response to plate tectonics.

Abstract The Regional Aerosol Model Intercomparison Project (RAMIP) is designed to quantify the forcing and climate impacts of mid-21st century anthropogenic aerosol and precursor gas (AA) emissions reductions (both industrial and biomass burning), by comparing a weak (SSP3-7.0) versus strong (SSP1-2.6) level of air quality control aerosol emissions pathway. AA emissions reductions experiments include global (GLO), East Asia (EAS), South Asia (SAS), Africa and the Middle East (AFR), and North America and Europe (NAE). Here, we use RAMIP time-slice simulations with fixed sea surface temperatures and sea-ice distributions from nine models to quantify the aerosol effective radiative forcing (ERF), including aerosol radiation (ERFari) and aerosol cloud interactions (ERFaci). The multi-model global mean net ERFari+aci is 0.77+/-0.25 W m^-2 for GLO, and three of the four regional perturbations yield a significant positive net ERFari+aci (up to 0.15+/-0.07 W m^-2 for EAS). In all cases, net ERFari+aci is dominated by aerosol-cloud interactions, which are largely due to reduced cloud scattering. Of the four regions, NAE yields the largest forcing efficiency whereas AFR yields the weakest. Although the areas outside our four target regions contribute 25% to the GLO aerosol optical depth (AOD) reduction, they disproportionately contribute 44% to the GLO net ERFari+aci. The multimodel regional mean net ERFari+aci for three regional perturbations is much larger (up to 1.64+/-1.36 W m^-2 for EAS) than the corresponding global mean value. However, these regional values are even larger (up to 2.69+/-1.72 W m^-2 for EAS) under global aerosol reductions, implying remote emission reductions represent a sizable contribution (up to 1.05+/-0.56 W m^-2 for EAS). These large regional ERFs will in turn drive relatively large regional climate impacts, which continue to be underappreciated in most policy discussions.

Martian meteorites, the only available samples of Martian lithologies, provide unique insights into martian magmatism. Olivines in these meteorites contain complex phosphorus (P) zoning, which shed insights into the behaviour of mafic magmas in the martian crust. These olivines crystallized in multiple stages in ascending magmas, and preserved compositional zoning, particularly in P, due to its low diffusivity. Although previous studies have documented P zoning in martian olivines and attributed its formation to rapid crystallization events in magma storage zones within the crust, the processes responsible for the undercooling and fast olivine growth remain unresolved. This study addresses the challenge of interpreting P zoning in martian olivines to better understand the conditions which affected their crystallization histories. Using high-resolution P X-ray maps and microprobe traverses, we show that P zoning in olivine megacrysts from shergottites (martian basalts) and chassignites (martian dunites) consistently records rapid crystallization events at high undercooling due to magma ascent through the martian crust. These zoning patterns, observed in cores, mantles, and rims of olivines from hypabyssal and intrusive samples, highlight different crystallisation conditions during staging, ascent and emplacement of magmas at varying crustal depths. P zoning in olivine-phyric shergottites, viewed in the light of previous thermobarometry results, record initial olivine nucleation in the lower crust, ascent to the mid-crust and final rapid crystallization in the shallow subsurface. Similarly, we inferred multiple cycles of magma ascent and storage in the martian crust from the P zoning in poikilitic and non-poikilitic regions of a poikilitic shergottite. We also provide evidence from P zoning in olivines to differentiate between magma storage relatively deep in the crust and shallow, hypabyssal emplacement. The nature of P zoning during the final stages of olivine crystallization can serve as in-situ evidence of the eruptive behaviour of shallow magma bodies. Further analyses of available meteorites and olivines from future sample return missions will be fundamental to build a holistic model of martian magma plumbing systems and its evolution through time