Deciphering mafic enclaves; what can they tell us about the timing and nature of basaltic inputs into granitoid magma systems?
Bibliographic record
Abstract
Arc batholiths commonly contain mafic enclaves that represent globules of basaltic magma incorporated into, and hybridized with, a host granitoid that was still partially molten. We have analyzed enclave and host rock samples from three epizonal plutons in the 36 Ma - 2 Ma Chilliwack batholith (North Cascades, WA) in order to understand the nature of the hybridization processes. Based on whole rock and mineral chemistry we recognize two types of hybridization, each associated with a different style of mafic-felsic magma interaction. Type 1, a diffusive exchange of trace elements (particularly HFSE) between coexisting mafic and felsic liquids, produced enclaves with distinctive concave-upward REE patterns that parallel those of the host granitoids. This process had minimal impact on major elements (whose diffusion rate is limited by slow Si diffusion) and resulted in a decoupling of major element abundances (and mode) from trace element abundances. Type 1 hybridization occurred prior to significant enclave crystallization, probably at the mafic-felsic interface of a stratified magmatic system. Type 2 exchange, a partial re-equilibration of enclave minerals with hybridized and differentiated interstitial melt, occurred after enclave dispersal within the host granitoid. This process resulted in enclave and host minerals (apatite, biotite, amphibole) having similar major oxide compositions, but did not fully re-equilibrate the trace elements. The results of this study suggest the timing and style of mafic-felsic magma interactions can be estimated based on the type and extent of enclave-host hybridization. Long-lived stratified magmatic systems, likely at lower- to mid-crustal depths, will lead to enclaves with Type 1 hybridization, whereas more turbulent basalt injections will be associated with Type 2 hybridization. In both cases the extent of hybridization will depend upon the temperature and cooling rate (depth) of the host granitoid. Better knowledge of intracrystalline diffusion rates for enclave minerals would permit a more quantitative estimation of the time scales of mafic-felsic magma interactions and the longevity of granitic magma systems.
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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 | 0.001 | 0.002 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".