Preprints
Filtering by Subject: Geochemistry
The global melt inclusion C/Ba array: mantle variability, melting process, or degassing?
Published: 2020-10-21
Subjects: Earth Sciences, Geochemistry
The Earth’s mantle holds more carbon than its oceans, atmosphere and continents combined, yet the distribution of carbon within the mantle remains uncertain. Our best constraints on the distribution of carbon within the upper mantle are derived from the carbon-trace element systematics of ultra-depleted glasses and melt inclusions from mid-ocean ridge basalts. However, carbon-trace element [...]
Dynamics of core-mantle separation: influence of viscosity contrast and metal/silicate partition coefficients on the chemical equilibrium
Published: 2020-10-21
Subjects: Earth Sciences, Geochemistry, Geophysics and Seismology, Physical Sciences and Mathematics
The composition of the Earth's core and mantle is set by the chemical equilibrium between metals and silicates during core/mantle segregation. The metallic core separated from the mantle by gravitational descent in the form of diapirs in a magma ocean, and therefore the dynamics of the diapir's downward movement has an influence on the chemical equilibrium. In this study, we characterize the [...]
Amphibole Control on Copper Systematics in Arcs: Insights from the Analysis of Global Datasets
Published: 2020-10-21
Subjects: Earth Sciences, Geochemistry, Geology, Volcanology
Copper, sourced from porphyry deposits formed in arc settings, is a critical resource, and is primarily sourced from magmas. However, the processes that shape the copper contents of arc magmas are up for debate. Existing models place emphasis on different petrological agents that explain large-scale trends in copper systematics. Previous studies have noted the 'Cu paradox,' where the magmas with [...]
A machine learning approach for prioritizing groundwater testing for per-and polyfluoroalkyl substances (PFAS)
Published: 2020-10-19
Subjects: Environmental Engineering, Environmental Health and Protection, Environmental Monitoring, Geochemistry, Hydrology, Risk Analysis, Water Resource Management
Regulatory agencies are beginning to recognize and regulate per-and polyfluoroalkyl substances (PFAS) as concerning environmental contaminants. In groundwater management, testing and mitigation strategies are desirable, but can be time and cost-intensive processes. As a result, only a fraction of all groundwater wells has been tested for PFAS levels, resulting in potentially extended drinking [...]
The composition and weathering of the continents over geologic time
Published: 2020-08-21
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The composition of continental crust records a history of construction by tectonics and destruction by physical and chemical erosion. Quantitative constraints on how both igneous addition and chemical weathering have modified the continents bulk composition are essential for understanding the evolution of geodynamics and climate. We have extracted temporal trends in sediments protolith [...]
Apatite fission-track dating by LA-Q-ICP-MS mapping
Published: 2020-08-17
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Obtaining accurate and precise apatite fission-track (AFT) ages is dependent on producing plentiful high-quality apatite grains from a sample, ideally with high spontaneous fission-track densities (c. >105 tracks.cm-2). Many natural samples, such as bedrock samples from young orogenic belts or low-grade metamorphic samples with low U contents yield low spontaneous fission-track densities. Such [...]
Marine mineral-catalyzed NO and N2O formation on the anoxic early Earth
Published: 2020-08-16
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
Microbial metabolisms were limited by available terminal electron acceptors in the anoxic environment of the early Archean. However, iron mineral phases in Fe2+-rich (ferruginous) oceans could have catalyzed reactions with abiotically fixed nitrogen leading to the formation of nitrous oxide (N2O), a potentially favorable terminal electron acceptor. We experimentally simulated anoxic [...]
Hydrogeologic and Geochemical Distinctions in Salar Freshwater Brine Systems
Published: 2020-08-05
Subjects: Earth Sciences, Geochemistry, Hydrology, Physical Sciences and Mathematics
The Salar de Atacama contains one of the world’s most important lithium resources and hosts unique and fragile desert ecosystems. Water use issues of the hyper-arid region have placed it at the center of global attention. This investigation is the first robust assessment of a salar system to incorporate geology, hydrogeology, and geochemistry of the aquifer system in the inflow, transition zone [...]
Whats down there? The structures, materials and environment of deep-seated tremor and slip
Published: 2020-07-16
Subjects: Earth Sciences, Geochemistry, Geology, Geophysics and Seismology, Physical Sciences and Mathematics, Tectonics and Structure
Episodic tremor and slow slip (ETS) events occur downdip of the seismogenic zone of numerous subduction megathrusts and plate boundary strike-slip faults. These events represent a fascinating and perplexing mode of fault failure that has greatly broadened our view of earthquake dynamics. In this contribution, we review constraints on the ETS deformation process from both geophysical observations [...]
Fingerprinting fluid source in calcite veins: combining LA-ICP-MS U-Pb calcite dating with trace elements and clumped isotope palaeothermometry
Published: 2020-07-15
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Application of geochemical proxies to vein minerals - particularly calcite - can fingerprint the source of fluids controlling various important geological processes from seismicity to geothermal systems. Determining fluid source, e.g. meteoric, marine, magmatic or metamorphic waters, can be challenging when using only trace elements and stable isotopes as different fluids can have overlapping [...]
Alkenone isotopes show evidence of active carbon concentrating mechanisms in coccolithophores as aqueous carbon dioxide concentrations fall below 7 µmolL-1
Published: 2020-07-15
Subjects: Biogeochemistry, Climate, Earth Sciences, Geochemistry, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Physical Sciences and Mathematics
Coccolithophores and other haptophyte algae acquire the carbon required for metabolic processes from the water in which they live. Whether carbon is actively moved across the cell membrane via a carbon concentrating mechanism, or passively through diffusion, is important for haptophyte biochemistry. The possible utilisation of carbon concentrating mechanisms also has the potential to overprint [...]
Seismological Expression of the Iron Spin Crossover in Ferropericlase in the Earth’s Lower Mantle
Published: 2020-06-29
Subjects: Earth Sciences, Geochemistry, Geophysics and Seismology, Mineral Physics, Physical Sciences and Mathematics, Physics, Quantum Physics, Tectonics and Structure
The two most abundant minerals on Earth which together make up over 90% of the Earth’s lower mantle are (Mg,Fe)O-ferropericlase (Fp) and (Mg,Fe)SiO3-bridgmanite (Bm). Iron in Fp undergoes a high-spin to low-spin (HS-LS) crossover that influences density, viscosity, elasticity, thermal conductivity, and elemental partitioning, however, the predicted effects of this transition are not apparent in [...]
Ancient siderites reveal hot and humid super-greenhouse climate
Published: 2020-06-19
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
Ancient siderites reveal hot and humid super-greenhouse climate
Methane concentrations in streams reveal gas leak discharges in regions of oil, gas, and coal development
Published: 2020-06-18
Subjects: Earth Sciences, Environmental Indicators and Impact Assessment, Environmental Monitoring, Environmental Sciences, Geochemistry, Oil, Gas, and Energy, Physical Sciences and Mathematics, Water Resource Management
As natural gas has grown in importance as a global energy source, leakage of methane (CH4) from wells has sometimes been noted. Leakage of this greenhouse gas is important because it affects groundwater quality and, when emitted to the atmosphere, climate. We hypothesized that streams might be most contaminated by CH4 in the northern Appalachian Basin in regions with the longest history of [...]
Notes on statistical age dispersion in fission-track datasets: the chi-square test, annealing variability, and analytical considerations
Published: 2020-06-12
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Notes on fission track statistics, the chi-square test, annealing (i.e. fission track age) variability, and analytical bias aimed at a general Earth scientist audience and for users of fission track data