Preprints
Filtering by Subject: Geochemistry
Neoproterozoic glacial origin of the Great Unconformity
Published: 2019-01-07
Subjects: Earth Sciences, Geochemistry, Geology, Glaciology, Physical Sciences and Mathematics
The Great Unconformity, a profound gap in Earths stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a century. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation for the formation and global extent of the Great [...]
Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation
Published: 2019-01-07
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic [...]
Evolving marginal terranes during Neoproterozoic supercontinent reorganisation: constraints from the Bemarivo Domain in northern Madagascar
Published: 2018-11-30
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Tectonics and Structure
Madagascar is important for unravelling the geodynamic evolution of the transition between the Rodinia and Gondwana supercontinents as it contains several suites of c. 850–700 Ma magmatic rocks that have been postulated to correlate with other ex-Rodinia terranes. The Bemarivo Belt of northern Madagascar contains the youngest suite of these magmatic rocks that date to c. 750–700 Ma. We present [...]
Palaeoenvironmental and tectonic significance of Miocene lacustrine and palustrine carbonates (Ait Kandoula Formation) in the Ouarzazate Foreland Basin, Morocco.
Published: 2018-11-06
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Sedimentology
The Ouarzazate Basin is the southern foreland basin to the High Atlas Mountains in Morocco. The sedimentary fill records a sequence from the Eocene to Pleistocene that records the interplay between tectonics and climate. This study presents the first stable isotope and facies analyses of the Middle to Late Miocene Aït Ibrirn lacustrine Member (Aït Kandoula Formation). These data test whether [...]
New constraints from Central Chile on the origins of enriched continental compositions in thick-crusted arc magmas
Published: 2018-10-31
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics, Volcanology
Magmas from continental arcs built on thick crust have elevated incompatible element abundances and “enriched” radiogenic isotope ratios compared to magmas erupted in island and continental arcs overlying thinner crust. The relative influence of the slab, mantle, and upper plate on this variability is heavily debated. The Andean Southern Volcanic Zone (SVZ; 33-46° S) is an ideal setting to [...]
Radiolysis via radioactivity is not responsible for rapid methane oxidation in subterranean air
Published: 2018-10-29
Subjects: Earth Sciences, Geochemistry, Life Sciences, Physical Sciences and Mathematics
Atmospheric methane is rapidly lost when it enters humid subterranean critical and vadose zones (e.g., air in soils and caves). Because methane is a source of carbon and energy, it can be consumed by methanotrophic methane-oxidizing bacteria. As an additional subterranean sink, it has been hypothesized that methane is oxidized by natural radioactivity-induced radiolysis that produces energetic [...]
Paired organic matter and pyrite δ34S records reveal mechanisms of carbon, sulfur, and iron cycle disruption during Ocean Anoxic Event 2
Published: 2018-10-15
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
Sulfur (S) isotope compositions of pyrites in the sedimentary record have played an important part in our understanding of biogeochemical cycling in the geologic record. However, the kinetics of pyritization are complex and depend strongly on the reactivity and mineralogy of available iron. As a second major sink for sulfide in anoxic sediments, organic matter (OM) provides essential context for [...]
U–Pb dating of mineral deposits: From age constraints to ore-forming processes
Published: 2018-10-12
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics
The knowledge of the timing and duration of ore-forming processes are perhaps one of the most desirable pieces of information that geologists require to draw a complete picture of the deposit and to put its genesis into a coherent regional or even global geological framework. In many cases, it represents an essential parameter for establishing detailed genetic models, and can critically impact on [...]
Volcanic-plutonic parity and the differentiation of the continental crust
Published: 2018-10-04
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics, Volcanology
The continental crust is central to the biological and geological history of Earth. However, crustal heterogeneity has prevented a thorough geochemical comparison of its primary igneous building blocks – volcanic and plutonic rocks – and the processes by which they differentiate to felsic compositions. Our analysis of a comprehensive global dataset of volcanic and plutonic whole-rock geochemistry [...]
Statistical geochemistry reveals disruption in secular lithospheric evolution about 2.5 Gyr ago
Published: 2018-10-03
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Secular cooling of the Earth is required by surface heat loss and declining radiogenic heat production over the last 4.5 billion years. Igneous geochemistry has been used to understand how changing heat flux influenced Archean geodynamics, but records of systematic geochemical evolution are complicated by heterogeneity of the rock record and uncertainties regarding selection and preservation [...]
A stochastic sampling approach to zircon eruption age interpretation
Published: 2018-10-03
Subjects: Earth Sciences, Geochemistry, Physical Sciences and Mathematics, Volcanology
The accessory mineral zircon is widely used to constrain the timing of igneous processes such as magma crystallization or eruption. However, zircon U-Pb ages record zircon crystallization, which is not an instantaneous process. Zircon saturation calculations link zircon crystallization, temperature, and melt fraction, allowing for the estimation of zircon crystallization distributions as a [...]
Plate tectonics and continental basaltic geochemistry throughout Earth history
Published: 2018-10-03
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Basaltic magmas constitute the primary mass flux from Earths mantle to its crust, carrying information about the conditions of mantle melting through which they were generated. As such, changes in the average basaltic geochemistry through time reflect changes in underlying parameters such as mantle potential temperature and the geodynamic setting of mantle melting. However, sampling bias, [...]
Temporal variation in relative zircon abundance throughout Earth history
Published: 2018-10-03
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
Zircon is the preeminent chronometer of deep time on Earth, informing models of crustal growth and providing our only direct window into the Hadean Eon. However, the quantity of zircon crystallised per unit mass of magma is highly variable, complicating interpretation of the terrestrial zircon record. Here we combine zircon saturation simulations with a dataset of ∼52,000 igneous whole rock [...]
Statistics and segmentation: Using Big Data to assess Cascades Arc compositional variability
Published: 2018-09-24
Subjects: Applied Mathematics, Applied Statistics, Earth Sciences, Geochemistry, Geology, Multivariate Analysis, Physical Sciences and Mathematics, Statistics and Probability, Volcanology
Primitive lavas erupted in the Cascades arc of western North America demonstrate significant patterns of along-arc heterogeneity. Such compositional diversity may be the result of differences in mantle melting processes, subduction geometry, regional tectonics, or compositions of the slab, mantle or overlying lithosphere. Previous authors have partitioned the arc into four geochemically distinct [...]
Dalangtan Saline Playa in a Hyperarid Region of Tibet Plateua-III: Correlated Multiscale Surface Mineralogy and Geochemistry Survey
Published: 2018-08-15
Subjects: Earth Sciences, Geochemistry, Geology, Physical Sciences and Mathematics
We report the first multiscale, systematic field-based testing of correlations between orbital scale advanced spaceborne thermal emission and reflection radiometer visible near-infrared (VNIR)/shortwave infrared (SWIR) reflectance and thermal infrared relative emissivity and outcrop scale Raman spectroscopy, VNIR reflectance, X-ray diffraction (XRD), and laser-induced breakdown spectroscopy [...]