Experimental, geochemical and isotopic insights on melting and degassing behavior on Earth
Bibliographic record
Abstract
This thesis investigates igneous and geothermal processes on Earth through various lenses and at various scales. The processes addressed range from fluid circulation in hydrothermal systems to the formation of the continental crust, onset of subduction, degassing of arc magmas, and mantle melting at mid-ocean ridges. Through this unlikely “medley” of Earth Science problems, parallels are drawn between experiments investigating melting and degassing at high pressure, geochemical and isotopic fingerprints of the Earth’s oldest rocks, and kinetic processes associated with aqueous supercritical fluids. The main lines of investigation rely on the tools of experimental petrology (Chapters 2 and 3) and stable isotope geochemistry (Chapters 1 and 4). Chapter 1 explores the systematics of methane (CH4) isotopologues in geothermal systems, with a particular focus on the kinetics of isotopic exchange reactions in the vicinity of the supercritical point of water (373°C and 220 bars). This study finds that CH4 isotopologues uniquely record high-temperature processes, given their high closure temperature—i.e. slow equilibration timescales under typical geothermal conditions—combined with the fast timescales associated with supercritical fluids. Chapter 2 describes the development of a new piston cylinder experimental approach to study the solubility and speciation of sulfur (S) in hydrous, oxidized primitive magmas as can be found in subduction zones. High pressure experiments demonstrate the coupled behavior of H2O and S, which mutually interact to fix redox conditions. Exsolution of S-rich fluids is found to play an important role on magmatic redox conditions, with apparent preferential loss of oxidized S to a fluid phase, explaining several natural observations from arc environments. Chapter 3 confirms the primary nature of a high MgO, high Al2O3 mid-ocean ridge basalt (MORB) glass from the ultraslow spreading Southwest Indian Ridge, identifying its multiple saturation boundaries within the plagioclase lherzolite stability field. This finding validates newly developed quantitative petrogenetic models for MORB, with important implications for our understanding of mantle thermal structure and for the origin of primitive glasses globally found at mid-ocean ridges. Chapter 4 describes the multiple S isotope characteristics of a suite of mafic to felsic rocks from the 4.0–2.9 Ga Acasta Gneiss Complex (AGC) from the Northwest Territories, Canada. These help placing constraints on the early Earth S cycle and its relation to tectonic regime. Along with other geochemical indicators, the Acasta rocks appear to record a gradual onset of subduction-like processes, established at least by ~3.3 Ga.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".