The co-evolution of Earth's crust and hydrosphere : a silicon isotope perspective
Bibliographic record
Abstract
The silicon isotope system is a well-established geochemical tool for tracing processes influenced by the interplay of Earth’s present-day crust and hydrosphere. While there is good understanding of stable silicon (Si) isotope systematics for high- and low-temperature processes in the Phanerozoic eon, these are poorly constrained for early Earth processes. Particularly, the Si isotope composition of Archaean and Proterozoic crustal materials is a scarce record mainly consisting of silica precipitates. However, recent investigations of Si isotopes in Archaean granitoids linked heavy isotopic signatures to seawater-derived sources, invoking the hydrosphere in forming Earth's earliest continental crust. Motivated by recent research gaps, this thesis aims to explore crust-hydrosphere interactions by establishing the Si isotope compositions of Archaean granitoids, specifically tonalite-trondhjemite-granodiorites (TTGs), and other lithologies representative of more than one-third of Earth history. This thesis presents outcomes from five Si isotope studies on globally diverse, ancient silicates. Here we find Eoarchaean igneous rocks from Greenland were influenced by supracrustal fluids, necessitating a primeval hydrosphere in forming early continents. We explore Si isotope behaviour during ancient partial melting from an Archaean migmatite from Ontario and find that TTG sources were likely seawater-silicified. This thesis records a secular homogenising of Si isotopes in the ancient upper continental crust from global glacial diamictites, supporting craton stabilisation after ~3.0 Ga. We also show Archaean –Proterozoic Fennoscandian weathering crusts imply no significant Si isotope trends at the Great Oxidation Event and highlight local controls instead. Finally, this thesis explores the Archaean marine silica cycle with a model for the Si isotope evolution of seawater, aligning with data that require a heavy Si isotope signature in the early oceans. In total, this thesis contributes a more robust temporal Si isotope record of ancient crustal materials and provides a greater understanding of the connection between Earth’s earliest crust and hydrosphere.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".