Paul R. D. Mason

The subduction of carbonate-rich biogenic sediments influences Earth’s carbon cycle and regulates long-term climate. Yet, the processes controlling their behavior at the subduction interface remain debated. Here, we investigate the role of carbonate subduction through the petrogenesis of Quaternary rear-arc monogenetic volcanoes in Colombia. These volcanoes display unusual compositions resembling intraplate carbonated peridotite melts and experimental melts from peridotite + CO ₂ systems. Their geochemistry reflects an anomalous mantle source modified by subducted sediments from the Panama Basin, a large-scale region of high primary productivity and carbonate accumulation. However, pristine subducted sediments alone cannot explain the full compositional range of rear-arc Colombian lavas. Instead, we propose that sediment partial melting beneath the arc front produces carbonate- and apatite-rich restites that act as a recycled carbonated component, contributing to mantle chemical heterogeneity. This model helps explain the geochemical diversity of mantle-derived intraplate lavas and establishes a direct link between biogeochemical cycles, subduction, and the evolution of the solid Earth.

Approximately 2.75 million years ago, the Turkana Basin in Kenya experienced environmental changes, including increased aridity and environmental variability. Namorotukunan is a newly discovered archaeological site which provides a window into hominin behavioral adaptations. This site lies within the upper Tulu Bor and lower Burgi members of the Koobi Fora Formation (Marsabit District, Kenya), presently a poorly understood time interval due to large-scale erosional events. Moreover, this locale represents the earliest known evidence of Oldowan technology within the Koobi Fora Formation. Oldowan sites, older than 2.6 million years ago, are rare, and these typically represent insights from narrow windows of time. In contrast, Namorotukunan provides evidence of tool-making behaviors spanning hundreds of thousands of years, offering a unique temporal perspective on technological stability. The site comprises three distinct archaeological horizons spanning approximately 300,000 years (2.75 − 2.44 Ma). Our findings suggest continuity in tool-making practices over time, with evidence of systematic selection of rock types. Geological descriptions and chronological data, provide robust age control and contextualize the archaeological finds. We employ multiple paleoenvironmental proxies, to reconstruct past ecological conditions. Our study highlights the interplay between environmental shifts and technological innovations, shedding light on pivotal factors in the trajectory of human evolution.

Metals are required by all life to build metalloproteins, but the metal preferences of the dominant microbes have evolved over geological time. Consistent with this, experiments and models predict that metal availability in anoxic seawater during the Archean and Proterozoic eons (4.0–0.541 billion years ago) would have been radically different to today. Corroborating this in the geological record is challenging because bulk rock geochemistry reflects complex histories. Here we take a novel approach, determining the transition metal content of micron-scale laths of greenalite, a primary Fe(II)-silicate mineral, from the Kuruman Formation of the Transvaal Supergroup, South Africa. Our data provide a high-resolution snapshot of seawater chemistry ~2.46 Ga, and reveal striking compositional differences compared to today: Zn and V were relatively scarce, Ni was similar, Co was enriched, and Mn was highly-enriched. Our data are largely consistent with chemical predictions and overlap with constraints from a range of different geological archives. Ancient seawater was therefore dominated by Fe and Mn, consistent with evidence that early life preferentially utilised these transition metals. Extremely high Mn concentrations could have interfered with cellular homeostasis, as well as disrupting DNA synthesis, potentially driving faster rates of evolution.

The occurrence of post-subduction magmatism in continental collision zones is a ubiquitous feature of plate tectonics, but its relation with geodynamic processes remains enigmatic. The nature of mantle sources in these settings, and their interaction with subduction-related components, are difficult to constrain using bulk rocks when magmas are subject to mixing and assimilation within the crust. Here we examine post-collisional magma sources in space and time through the chemistry of olivine-hosted melt inclusions and early-formed minerals (spinel, olivine and clinopyroxene) in primitive volcanic rocks from the Neogene–Quaternary East Carpathian volcanic range in Călimani (calc-alkaline; 10.1–6.7 Ma), Southern Harghita (calc-alkaline to shoshonitic; 5.3–0.03 Ma) and the Perșani Mountains (alkali basaltic; 1.2–0.6 Ma). Călimani calc-alkaline parental magma compositions indicate a lithospheric mantle source metasomatised by ~ 2% sediment-derived melts, and are best reproduced by ~ 2–12% melting. Mafic K-alkaline melts in Southern Harghita originate from a melt- and fluid-metasomatised lithospheric mantle source containing amphibole (± phlogopite), by ~ 5% melting. Intraplate Na-alkaline basalts from Racoș (Perșani) reflect small-degree (1–2%) asthenosphere-derived parental melts which experienced minor interaction with metasomatic components in the lithosphere. An important feature of the East Carpathian post-collisional volcanism is that the lithospheric source regions are located in the lower plate (distal Europe-Moesia), rather than the overriding plate (Tisza-Dacia). The volcanism appears to have been caused by (1) asthenospheric uprise following slab sinking and possibly south-eastward propagating delamination and breakoff, which induced melting of the subduction-modified lithospheric mantle (Călimani to Southern Harghita); and (2) decompression melting as a consequence of minor asthenospheric upwelling (Perșani).

Sulfate minerals are rare in the Archean rock record and largely restricted to the occurrence of barite (BaSO₄). The origin of this barite remains controversially debated. The mass‐independent fractionation of sulfur isotopes in these and other Archean sedimentary rocks suggests that photolysis of volcanic aerosols in an oxygen‐poor atmosphere played an important role in their formation. Here, we report on the multiple sulfur isotopic composition of sedimentary anhydrite in the ca. 3.22 Ga Moodies Group of the Barberton Greenstone Belt, southern Africa. Anhydrite occurs, together with barite and pyrite, in regionally traceable beds that formed in fluvial settings. Variable abundances of barite versus anhydrite reflect changes in sulfate enrichment by evaporitic concentration across orders of magnitude in an arid, nearshore terrestrial environment, periodically replenished by influxes of seawater. The multiple S‐isotope compositions of anhydrite and pyrite are consistent with microbial sulfate reduction. S‐isotope signatures in barite suggest an additional oxidative sulfate source probably derived from continental weathering of sulfide possibly enhanced by microbial sulfur oxidation. Although depositional environments of Moodies sulfate minerals differ strongly from marine barite deposits, their sulfur isotopic composition is similar and most likely reflects a primary isotopic signature. The data indicate that a constant input of small portions of oxidized sulfur from the continents into the ocean may have contributed to the observed long‐term increase in Δ³³S_sulfate values through the Paleoarchean.