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Thallium (Tl) isotope ratios are an emerging tool that can be used to trace crustal recycling processes in arc lavas and ocean island basalts (OIBs). Thallium is a highly volatile metal that is enriched in volcanic fumaroles, but it is unknown whether degassing of Tl from subaerial lavas has a significant effect on their residual Tl isotope compositions. Here, we present Tl isotope and concentration data from degassing experiments that are best explained by Rayleigh kinetic isotope fractionation during Tl loss. Our data closely follow predicted isotope fractionation models in which TlCl is the primary degassed species and where Tl loss is controlled by diffusion and natural convection, consistent with the slow gas advection velocity utilized during our experiments. We calculate that degassing into air should be associated with a net Tl isotope fractionation factor of αnet = 0.99969 for diffusion and natural gas convection (low gas velocities) and αnet = 0.99955 for diffusion and forced gas convection (high gas velocities). We also show that lavas from three volcanoes in the Kamchatka arc exhibit Tl isotope and concentration patterns that plot in between the two different gas convection regimes, implying that degassing played an important role in controlling the observed Tl isotope compositions in these three volcanoes. Literature inspection of Tl isotope data for subaerial lavas reveals that the majority of these appear only minorly affected by degassing, although a few samples from both OIBs and arc volcanoes can be identified that likely experienced some Tl degassing. Plain Language Summary: Volcanic degassing is an important process for understanding emissions to the atmosphere of greenhouse gasses and toxic metals. Thallium (Tl) is a toxic metal that is highly volatile, which in recent years has been developed as a stable isotope system that can be applied to understand the transfer of material from the Earth surface to the deep mantle via measurements of volcanic lavas. However, degassing of Tl from volcanic lavas could potentially alter the isotope ratio of the residual lava and, thus, render applications of Tl isotopes in lavas difficult to relate to deep Earth material transfer. Here, we perform the first study of Tl isotopes in degassing experiments. These reveal that Tl isotope ratios progressively become enriched in the heavy isotope with loss of Tl. We also show that natural lavas from Kamchatka follow similar Tl depletion and isotope enrichment patterns as our experiments, which for the first time demonstrates that degassing in nature is associated with diffusion‐controlled loss of the light Tl isotope. Key Points: Degassing of Tl from experimental melts are associated with kinetic isotope fractionation limited by diffusion in the gas phaseBasaltic lavas from Kamchatka follow the same Tl depletion‐isotope fractionation pattern as experimental chargesThe majority of literature Tl isotope data for volcanic lavas reveal only limited effects from degassing [ABSTRACT FROM AUTHOR]

Carbonatite volcanism remains poorly understood compared to silicic volcanism due to the scarcity of carbonatite volcanoes worldwide and because volcanic H2O and CO2—major components in carbonatite volcanic systems—are not well preserved in the rock record. To further our understanding of carbonatite genesis, we utilize the non‐traditional thallium (Tl) isotope system in Khanneshin carbonatites in Afghanistan. These carbonatites contain 250–30,000 ng/g Tl and have ε205Tl values (−4.6 to +4.6) that span much of the terrestrial igneous range. We observe that δ18OVSMOW (+8.6‰ to +23.5‰) correlates positively with δ13CVPDB (−4.6‰ to +3.5‰) and ε205Tl up to δ18O = 15‰. Rayleigh fractionation of calcite from an immiscible CO2‐H2O fluid with a mantle‐like starting composition can explain the δ18O and δ13C—but not ε205Tl—trends. Biotite fractionates Tl isotopes in other magmatic settings, so we hypothesize that a Tl‐rich hydrous brine caused potassic metasomatism (i.e., biotite fenitization) of wall rock that increased the ε205Tl of the residual magma‐fluid reservoir. Our results imply that, in carbonatitic volcanic systems, simultaneous igneous differentiation and potassic metasomatism increase ε205Tl, δ18O, δ13C, and light rare earth element concentrations in residual fluids. Our fractionation models suggest that the Tl isotopic compositions of the primary magmas were among the isotopically lightest (less than or equal to ε205Tl = −4.6) material derived from the mantle for which Tl isotopic constraints exist. If so, the ultimate source of Tl in Khanneshin lavas—and perhaps carbonatites elsewhere—may be recycled ocean crust. Plain Language Summary: Most volcanoes on Earth are silica‐rich. Rare volcanoes that are composed of mostly carbonate minerals (referred to as carbonatite volcanoes) are not as well understood, but provide clues about carbon fluxes into and out of the mantle. To further our understanding of carbonatite genesis, we measured the thallium, oxygen, and carbon isotopes in rocks from a carbonatite volcano in Afghanistan. We discovered systematic variations in all three isotope systems caused by the massive release of carbon dioxide‐ and water‐rich fluids from the magmas prior to eruption. Interaction between these fluids and the surrounding rock—which we argue is fundamental to carbonatite genesis—appears to be largely responsible for magma evolution. As the first study of thallium isotopes in carbonatites, our results also have implications for the origins of carbonatite magmas: we infer that the magmas initially had thallium isotope compositions most similar to ocean crust, which implies that seafloor thallium cycles deep into the mantle and returns to the surface in carbonatitic magmas. Key Points: Thallium isotopes fractionate in carbonatite volcanic systemsThallium in carbonatites may derive from recycled ocean crustBrines cause potassic metasomatism during ascent and eruption of carbonatite magmas [ABSTRACT FROM AUTHOR]

In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial "common" (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to "petit spot" lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures. Key Points: Within the 645‐m Tutuila drill core we find isotopically heterogeneous lavas as well as several abrupt temporal and geochemical boundariesThe proximity of Samoan volcanoes to the Tonga Trench and geochronology are consistent with a tectonic influence on rejuvenated volcanismThe tectonic setting and isotopic signatures of the Samoan rejuvenated lavas link them to "petit spots" outboard of the Japan Trench [ABSTRACT FROM AUTHOR]

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin m RNA expression, upregulated renal erythropoietin m RNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound 58Fe, the amount of 58Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor ( AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein ( BMP)-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide. Testosterone did not affect hepcidin m RNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/ Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells. [ABSTRACT FROM AUTHOR]

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Abstract The Dras 1 Volcanic Formation of the Ladakh Himalaya, India, represents the eastern, upper crustal equivalent of the lower crustal gabbros and mantle peridotites of the Kohistan Arc exposed in Pakistan. Together these form a Cretaceous intraoceanic arc now located within the Indus Suture zone between India and Eurasia. During the Late Cretaceous, the Dras–Kohistan Arc, which was located above a north-dipping subduction zone, collided with the south-facing active margin of Eurasia, resulting in a switch from oceanic to continental arc volcanism. In the present study we analyzed samples from the pre-collisional Dras 1 Volcanic Formation and the postcollisional Kardung Volcanic Formation for a suite of trace elements and Nd isotopes. The Kardung Volcanic Formation shows more pronounced light rare earth element enrichment, higher Th/La and lower ℇNd values compared with the Dras 1 Volcanic Formation. These differences are consistent with an increase in the reworking of the continental crust by sediment subduction through the arc after collision. As little as 20% of the Nd in the Dras 1 Volcanic Formation might be provided by sources such as the Karakoram, while approximately 45% of the Nd in the Kardung Volcanic Formation is from this source. However, even before collision, the Dras–Kohistan Arc shows geochemical evidence for more continental sediment contamination than is seen in modern western Pacific arcs, implying its relative proximity to the Eurasian landmass. Comparison of the lava chemistry in the Dras–Kohistan Arc with that in the forearc turbidites suggests that these sediments are partially postcollisional, Jurutze Formation and not all pre-collisional Nindam Formation. Thus, the Dras–Eurasia collision can be dated as Turonian–Santonian (83.5–93.5 Ma), older than it was previously considered to be, but consistent with radiometric ages from Kohistan. [ABSTRACT FROM AUTHOR]