Variable K-uptake into the upper oceanic crust due to strong temperature and dissolved silica control on the formation on secondary K-feldspar
Bibliographic record
Abstract
Potassium is one of the major elements in seawater with a concentration range between 9 and 11 mmol L -1 . Remarkably, from proxies for paleo-seawater composition such as primary fluid inclusions in halite it seems evident that the concentration of K in seawater remained in this range throughout the Phanerozoic. Hence, this suggests that sources and sinks of K in the ocean are roughly in balance. However, the relative role of the K sinks in the ocean are incompletely understood. Here, I focus on testing off-axis, hydrothermal systems as a variable sink through geological time. Potassium in these systems is mainly taken up by formation of secondary K-rich phyllosilicates (celadonite) and K-feldspar. From these K-feldspar is rarely observed in Cenozoic altered oceanic crust but present in Mesozoic crust. Compiled bulk geochemical data of ocean drill core samples suggests that the K-content in Mesozoic increased compared to Cenozoic crust. Also, radiometric dating studies of celadonite suggest that, with some exceptions, K is taken up into the crust within the first ~20 Myr [1]. From these lines of evidence, it is hypothesized that K-feldspar formation in altered upper oceanic crust and thus the variable K-sink in off-axis systems is controlled by environmental parameters such as seawater pH and temperature [2]. Here, I perform simple geochemical modelling to isolate the impact of these first parameters on the saturation of K-feldspar in equilibrium with primary plagioclase, secondary Na-beidelleite. This modelling showed that changes in temperature in the range of ~10 C warmer Mesozoic seawater leads to a strong increase in equilibrium K concentration in the off-axis fluid at constant Si content. However, an increase in fluid temperature also increases the dissolution rate of basalt which would lead to increased silica concentrations in off-axis fluids which increases the saturation of K-feldspar. Hence, a coupled model between changing temperature and Si content best explains the observed changes in mineralogy in altered upper oceanic crust through time.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".