Cretaceous evolution of the Lhasa-Qiangtang Orogen: insights from mafic igneous rocks
Bibliographic record
Abstract
The compositional changes of successively emplaced mafic magmatites provide insights into the evolution of orogenic belts, particularly the transformation processes and properties of the orogenic lithospheric mantle. Herein, we present new zircon U‒Pb ages and Lu‒Hf isotopes, as well as whole-rock major, trace element, and Sr – Nd isotope compositions from three mafic intrusions in the Asuo area, central Tibet, to clarify the evolution of the Lhasa – Qiangtang Orogenic Belt (LQOB). These mafic intrusions can be classified into calc-alkaline basalts and are enriched in large ion lithophile elements and depleted in high-field strength elements. Significant differences in the whole-rock trace element compositions, Sr – Nd isotope values, and U – Pb ages stratify them into two groups, namely Groups I and II, of which Group I rocks (ca. 105 Ma) show lower87Sr/88Sri = (0.70694–0.70701), [Sm/Yb]N = (1.51–1.54) and higher εNd (t) = (−0.74 to −0.61) than Group II (ca. 97–95 Ma) (87Sr/88Sri = 0.70759–0.70870; εNd (t) = –4.58 to −3.75; [Sm/Yb]N = 2.43–2.94). These features indicate that the mantle source exhibits a progressive increase in the proportion of garnet, along with significant addition of subduction-related components into the primary melts. One scenario for producing such trace element patterns and gradually enriched radioactive isotope signatures involves the extensive heating of an oceanic slab beneath the LQOB by upwelling asthenosphere, which leads to the extensive melting of sediments within the slab. Identification of ca. 105–95 Ma Asuo mafic rocks suggests their formation in a post-collisional setting with additional heat input from the deep mantle. These results provide new evidence supporting the occurrence of the Lhasa – Qiangtang collision within the framework of north-south bidirectional subduction.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.022 | 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; both teacher heads agree on what is shown here.
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".