Phase Equilibria Analysis for Metacarbonate With Applications to Zoned Calc‐Silicate Aureoles
Bibliographic record
Abstract
ABSTRACT Carbonate rocks react with infiltrating hydrothermal fluids to produce zoned calcsilicate assemblages in contact aureoles. Petrogenetic grids provide valuable insights into phase relations, metamorphic temperature (T) and the fluid composition (X) of the metacarbonate systems, as well as semi‐quantification of the prograde decarbonation at convergent boundaries. In this study, we constructed T‐XCO2 (composition of H2O–CO2 binary fluid) grids in the system CFMASHc (CaO–FeO–MgO–Al2O3–SiO2–H2O–CO2), supplemented with Fe2O3 or TiO2, and its subsystems (CMASHc, CMSHc, CFSHc and CASHc). The grids were constructed to encompass upper crustal conditions, with temperatures ranging from 300°C to 1000°C at 2 kbar and 4 kbar, and XCO2 from 0 to 0.8 (0 = pure water). We adopted internally consistent thermodynamic datasets and compatible activity–composition models for solid solutions. The grids illustrate the index minerals and field gradients observed in classical aureoles. Typical calcsilicate assemblages in these contact aureoles appear along a heating trajectory at a relatively low XCO2, in the sequence of talc, tremolite, diopside (±olivine), garnet and wollastonite. The grids in the CASHc, CMSHc and CMASHc subsystems are sufficient to cover important reactions that lead to the formation and decomposition of these minerals. The grids with an additional TiO2 component help interpret phase relations involving rutile, titanite and ilmenite. In addition, we note that phase relations calculated with endmember carbonates are practically similar to those calculated for a complete ternary solid‐solution model at low‐to‐mid temperatures (< 600 °C). In this study, we recalculated reactions in subsystem grids from previous studies across various P‐T‐XCO2 conditions within a consistent framework. These results are contextualized with natural assemblages and applied to constrain the field gradient of a representative contact aureole. By incorporating additional components, the grids accommodate a broader range of assemblages observed in metacarbonate rocks. Together, these expanded grids provide a robust framework for future studies of contact metamorphism in metacarbonate systems. The calculated phase equilibria were specifically applied to a contact aureole in southern Tibet, with temperature estimations derived from the phase equilibria aligning closely with a conduction model based on the timescales from diffusion speedometry.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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".