| Tectonically,the Yanbian area of Jilin province is located at the junction of the Zhangguangcai Range,the Jiamusi Block,and the northeast part of the North China Craton,is a key site for studying the superimposition and transformation of the Paleo-Asian and Paleo-Pacific tectonic regimes.However,there are still controversial in the understanding of the tectonic setting of the Jilin Yanbian area.In this paper,we focus on the Mesozoic intermediate mafic-ultramafic rocks in the Helong area,Yanbian,Jilin province.Basing on field geological surveys and zircon LA-ICP-MS U-Pb chronology,whole-rock major elements,trace elements,and whole-rock Sr-Nd isotopes and the zircon tectonic environment classifier established in this paper to determine the formation age of Mesozoic intermediate mafic-ultramafic rocks and discuss the petrogenesis of basic rocks and the tectonic settings of their formation in the Helong areas.The main understanding is as follows:（1）In this paper,four supervised learning algorithms including Random Forest,Support Vector Machine,Decision Tree,and e Xtreme Gradient Boosting have been implemented to analyze trace elements of 3907 magmatic zircons from the GEOROC database,and a precise13-dimensional data classifier model has been established in order to distinguish the tectonic settings of the rift,ocean island,and convergent margin.Based on the results of accuracy,precision,recall,and F1-score,the machine learning approach of e Xtreme Gradient Boosting is best in the paper and the results of Accuracy,Precision,Recall,and F1-score are 0.948,0.941,0.922,0.930,respectively.In summary,e Xtreme Gradient Boosting in the paper could provide a high-dimensional discriminative approach to distinguish the tectonic settings.（2）The zircons in the Hanconggou diorite show euhedral-subhedral,with fine-scale oscillatory growth zoning visible.their high Th/U ratio（0.61～1.20）>0.1,imply a magmatic genesis.The 206Pb/238U weighted mean age of zircon is 241.2±2.8Ma（MSWD=1.9;n=10）,which represents the crystallization age of Hanconggou diorite.Hanconggou diorite has moderate content of SiO2,TiO2,and MgO,low content of Al2O3,and A/CNK value between0.78 and 0.80 that show Metaluminous characteristics.The content of SiO2 and K2O in diorite indicates that it belongs to Calc-alkaline to high-K calc-alkaline series.Hanconggou diorite is characterized by enrichment of light rare earth elements（LREEs）,depletion of heavy rare earth elements（HREEs）and depletion of high field strength elements（HFSEs;such as Nb and Ta）in trace elements,and show subduction geochemical characteristics.The relationship between the Ta/Yb value and Th/Yb value of the Hanconggou diorite indicates that its magma source is enriched mid-ocean ridge basalt,The higher ratios of Th/Ta and Th/Nb indicate that the magma source is affected by subduction fluids.（3）The zircons in zhangxiangcun pyroxene peridotite are euhedral-subhedral,with fine-scale oscillatory growth zoning visible.their high Th/U element ratio of 0.2-3.1,show the characteristics of magmatic zircons.The 206Pb/238U weighted average age of zircons is227.6±1.6Ma（n=16;MSWD=1.7）,which means that the emplacement was in the Late Triassic.Zhangxiangcun pyroxene peridotite has low SiO2 content,low TiO2 content,medium Al2O3content,high MgO and Mg#values.Fe O/MgO and SiO2 content indicate that it belongs to the Tholeiite series.The differentiation degree of light and heavy rare earth elements in the olive gabbro is relatively insignificant（[La/Yb]N=2.79～3.58）,and it is depleted of high field strength elements（HFSE;such as Nb and Ta）.We calculate the original magma earth composition of the Zhangxiangcun pyroxene peridotite and combine with Sr-Nd isotopes,suggest that the original magma is depleted mantle add 2%-3%subducted sediment fluid and 2%-3%subducted sediment melt.（4）The zircons in wolonghu diorite are euhedral-subhedral,with fine-scale oscillatory growth zoning visible.their high Th/U element ratio of 0.53-1.22,show the characteristics of magmatic zircons.The 206Pb/238U weighted average age of zircons is 175.3±1.6Ma（n=20;MSWD=1.9）,which means that the emplacement was in the Early Jurassic.The Early Jurassic quartz diorite in Wolonghu has moderate SiO2 content,TiO2,MgO and Mg#values,and relatively high Al2O3 content.Wolonghu diorite belongs to the high-K calc-alkaline series to the Shoshonite series in the SiO2-K2O diagram,and most of it belongs to the high-K calc-alkaline series,with an A/CNK value of 0.78～0.84,showing Metaluminous characteristics.Trace elements in wolonghu diorite show an obvious right-dipping distribution pattern（[La/Yb]N=8.45～9.25）,and the depletion of high field strength elements（HFSE;such as Nb and Ta）,shows subduction-related geochemical characteristics.The high positive correlation between Th/Sm and Th/Ce values of quartz diorite in Wolonghu indicates that sediments were added during its formation,and the relationship between Ba/La and Rb/Nb and Th/Yb indicates that sedimentary melts were added Mantle wedge.according to Hf/Sm,Ba/Nb,andεNd（t）)values,Wolonghu quartz diorite is formed by the mantle wedge from depleted mantle and add 10%-20%terrigenous sediments.Based on the result of the intermediate mafic-ultramafic rocks,combined with previous studies on the Jilin Yanbian area and surrounding tectonic units,this paper believes that the Early Mesozoic in the Jilin Yanbian area was mainly affected by the N-S closure of the Heilongjiang Ocean.In this paper,the Hanconggou diorite and Zhangxiangcun pyroxene peridotite in the Middle-Late Triassic originated from the westward subduction of the Heilongjiang Ocean to Zhangguangcai range,and the Wolonghu diorite in the Early Jurassic originated from the westward subduction of the Paleo-Pacific Ocean to the Yanbian area. |
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