| 云南澜沧谦迈蛇绿混杂岩中斜长花岗岩成因及地质意义 |
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| 关键词:U-Pb chronology geochemistry Lu-Hf isotope plagiogranite ophiolitic mélange Lancang of Yunnan |
| 基金项目:云南省地矿局“杨绍文专家工作室”(编号: YD202067); 云南省自然资源厅地质勘查基金项目“云南省1:5万下景张、新营盘、东岗、南北归4幅区域地质调查”(编号: D2017002) |
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| Petrogenesis and Geological Significance of Plagiogranite in Qianmai Ophiolitic Mélange, Lancang, Yunnan Province |
| The Qianmai ophiolitic mélange in the Lancang, southwestern Yunnan, is the southern extension of the Wanhe ophiolitic mélange in Mengku region, recording the process of the Proto-Tethys Ocean from expansion to subduction. In this paper, petrography，zircon U-Pb chronology, Lu-Hf isotopes, and whole-rock geochemistry are investigated in the plagiogranite of the ophiolitic mélange. The plagiogranite is characterized by relatively high SiO2, Na2O, and Al2O3, and low K2O and MgO contents. The geochemical data show that plagiogranite is enriched in light rare earth elements (REE) with negative Eu anomaly. The primitive mantle-normalized spider-grams are charac-terized enrichments in Rb, Th, U, and K, as well as high contents of Y and Yb, particularly negative anomalies in Sr and Nb-Ta-Ti, which are consistent with the characteristics of island arc magmas. Zircons from plagiogranite are typical magmatic zircon with negative Eu and positive Ce anomalies. Their ratios of Th/U are 0.29–0.85 and 0.46–0.62, which are typical features of magmatic zircons. LA-ICPMS zircon U-Pb dating showed that the weighted mean 206Pb/238U ages are (489±3) Ma and (464±4) Ma, suggesting that they are related to Early Paleozoic magma activity. All zircons have initial εHf(t) values ranging from –10.10 to –1.92, and model ages ranging from 1.60 to 2.07 Ga, which are older than the formation age. In conclusion, the plagiogranite was likely caused by partial melting of the amphibolite phase in the oceanic crust’s migration shear zone (residual mineral phase: Pl+Hb+Opx+Ilm (without Grt)) under low-temperature and low-pressure conditions. Combined with regional geological setting, our results suggest that the Proto-Tethys opened before the Late Cambrian and evolved during the Ordovician. |
| GUO Xiangyu,ZHOU Tingquan,XU Xuezhang,XU Dingxiang,XIONG Shubin,ZHOU Kun,LEI Bidong,YANG Shaowen.2025.Petrogenesis and Geological Significance of Plagiogranite in Qianmai Ophiolitic Mélange, Lancang, Yunnan Province[J].Acta Geoscientica Sinica,46(6):1119-1134. |
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