Petrogenesis and Geological Significance of Highly Differentiated A-Type Granites in Bankeng Pluton,Nanling Region,South China
He Chuan
Liu Wenbin
Hu Wenjie
Chen Lu
Li Haili
Sun Jiandong
Wang Yun
Tian Shihong
Abstract：The rare earth element(REE)resources are rich in China,among which the ion-adsorbed REE deposit in South China is unique.Its spatial and temporal distribution characteristics indicate that its formation is closely related to the Mesozoic granites in South China,but the internal genetic relationship is still not deeply understood.A comprehensive study on the Bankeng granite in the Nanling(the ore-forming parent rock of Bankeng REE deposit)has been carried out,including petrography,zircon and apatite chronology,lithogeochemistry,zircon Hf isotopes and whole-rock Sr-Nd-Li isotopes.The U-Pb dating of magmatic zircon and magmatic apatite in the Bankeng granites yield ages of 185.5-194.0 Ma and 189.2 Ma respectively,indicating that the emplacement occurred in the Early Jurassic.They are mainly composed of felsic minerals(Q+Ab+Or≥95%),with only a small amount of biotite(<5%)in the mafic dark minerals.Their geochemical characteristics show high SiO2(75.93%-77.48%),rich K2O(5.27%-5.55%),low MgO(0.09%-0.14%),and poor MnO(0.02%-0.03%),as well as a high zircon saturation temperature(801-847℃),high Zr+Nb+Ce+Y content(360×10-6-534×10-6),and a 10 000×Ga/Al ratio(3.2-4.2),which are similar to the highly differentiated A-type granites.The Sr-Nd-Hf-Li isotopic characteristics((87Sr/86Sr)i=0.704 477-0.712 715,εNd(t)=-5.0-(-5.2),εHf(t)=-6.8-(+1.4),δ7Li=-0.88‰-6.65‰)indicate that the magma source may be REE-rich igneous rocks from Mesoproterozoic recycled ancient crust that was intruded into the shallow crust.The Bankeng granites exhibits A2-type granite properties(Y/Nb=1.21-2.09),combined with the regional contemporaneous bimodal intrusive rocks,volcanic rock suites and A-type granitoids,indicating they formed in the Early Jurassic extensional tectonic setting.Combined with the genetic understanding of A-type granite in the Nanling at the same time as Bankeng granites,this paper suggests that the thermal anomaly generated by the upwelling of deep asthenosphere in the Early Jurassic caused partial melting of REE-rich rocks in the crust-mantle magmatic source area to form more REE-enriched A-type granitic melt,which may be one of the important mechanisms for the petrogenesis of ore-forming parent rocks of the ion-adsorbed light REE deposits in South China.The genetic correlation between the LREE-riched Bankeng granites and the HREE-riched Zudong granites shows that the petrogenesis of the LREE-type ore-forming parent rocks is mainly related to their magma source region and extensional tectonic setting,while the degree of magma crystallization differentiation and the external fluid metasomatism are more critical for the petrogenesis of the HREE-type ore-forming parent rocks.
Keywords：highly differentiated A-type granitepetrogenesisore-forming parent rock of ion-adsorbed rare earth depositBankeng granite in Nanlinggeochemistrygeochronology
Publication Date：2025-07-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：23( 2525-2547 )