Zircon U-Pb Ages,Hf Isotopic Composition of Zhizhong Granitic Intrusion in Ledong Area of Hainan Island and Their Tectonic Implications
Bibliographic record
Abstract
Late Paleozoic to Early Mesozoic( Hercynian to Indosinian) granitic intrusions widely distribute in Hainan Island,South China. However,no consensus has been achieved in terms of the related tectonic regime of these magmatism activities,the Late Paleozoic granites,in particular. Aiming to provide insights into the time of intrusion,petrogenesis and tectonic setting of the Late Paleozoic granites,zircons from the Zhizhong granite,which is located in the Ledong area in southwestern Hainan Island,were analyzed. In-situ zircon U-Pb geochronology and Hf isotope analysis of zircons were analyzed in Northwestern University using LA-ICPMS methods. Zircons from two samples( HN0832 and HN0909) yield similar weighted mean206Pb /238U ages of 272. 4 ± 1. 5 Ma( n = 21) and271. 7 ± 3. 0 Ma( n = 16),respectively. The ages are interpreted as the intrusive age,i. e.,the Zhizhong granite intruded in late Early Permian. The eHf( t) values of the zircons range from-3. 7 to +2. 8,while the Hf two-stage modal ages vary from 1. 12 Ga to 1. 53 Ga with a peak at 1. 33 ～ 1. 41 Ga,demonstrating a mantle input for the Zhizhong granite. Thus,a mixed crust-mantle source is envisaged. Furthermore,the parent melts of the Zhizhong granite possibly derived from the melting of the Mesoproterozoic igneous rocks beneath Hainan Island with significant contribution of asthenosphere melts. Moreover,the age peaks of the two-stage Hf modal ages( 1. 3 ～ 1. 4 Ga)of the Zhizhong Granite are similar to the whole rock two-stage Nd modal ages( 1. 4 ～ 1. 6 Ga) of the coeval granites in the adjacent region,which implies that Mesoproterozoic is an important episode of crustal growth in Hainan Island. Combining the regional deformation,sedimentary records and palaeomagnetic data,it can be deduced that the late Early Permian magmatism in Hainan Island was probably geodynamically linked to the collision between the Indochina and South China Block,following the closure of the Paleo-Tethys Ocean rather than the westward subduction of the Paleo-Pacific Plate beneath the Eurasian continent.
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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 | 0.000 | 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) | 0.000 | 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".