| The Jiaodong area is located in the southeastern margin of North China Craton,and experienced a strong Mesozoic tectonic magmatism.A large number of magmatic rocks were formed in the Late Jurassic—Early Cretaceous,the peak periods of the Jiaodong magmatism,which mainly include the three types of granites:the Linglong granitoid suite,the Guojialing granitoid suite and the Weideshan granitoid suite.The Aishan and Nansu plutons belong to the Weideshan granitoid suite.At present,there are no systematic investigations of detailed emplacement age and geochemical characteristics.In this paper,the petrography,zircon U-Pb isotope dating and geochemical characteristics of the whole-rock major and trace elements of the two plutons are studied in order to determine the age of pluton formation,explore the magma source,petrogenesis and tectonic setting,which further explore the crust-mantle interaction and geodynamic background of the Early Cretaceous in the Jiaodong area,and provide evidence for tectonic evolution history of the Late Yanshanian in the Jiaodong area.The Aishan pluton is a porphyritic horn granodiorite with more dioritic enclaves.LA-ICP-MS zircon U-Pb dating is 116.7±1.7Ma;The Nansu pluton is a porphyritic medium-grained monzonitic granite.LA-ICP-MS zircon U-Pb dating is 121.3±2.1Ma.They formed in the Early Cretaceous.Geochemical characteristics indicate that the two plutons are high-K calc-alkaline metaluminous I type granite;high Ba,high Sr,lower Rb,low Y,high Sr/Y,high(La/Yb)N,showing the geochemical characteristics of high Ba-Sr granite of the two plutons in trace elements;enrichment of LILE such as Rb,Ba,K,and LREE,depletion of HFSE such as Ta,Nb,Zr,Ti,and HREE,the obvious fractionation of LREE and HREE,and a weak anomaly in Eu.The ratio of the Nb/Ta,Nd/Th,Nb/La and Zr/Hf show that the Aishan pluton and the Nansu pluton are formed in the same magma source area,and the diagenetic material is mainly derived from the lower crust.The ratio of the Rb/Sr shows the presence of mantle material.Combined with the dark-colored microgranular dioritic enclaves in the field samples,the plutons have the characteristics of crust-mantle mixing.?REE and Si O2,La/Sm and La have certain correlation,depletion of Nb,Ti,P,high Sr/Y and a weak anomaly in Eu show that partial melting is the main part in the process of magma evolution,and it has undergone certain separation and crystallization.The tectonic environment discriminant maps indicate that the Aishan and Nansu plutons have the characteristics of arc granite,which are formed in the extended environment,and are related to the subduction of the Pacific plate.Combined with the Early Cretaceous geodynamic background of the Jiaodong area,it is believed that the two plutons are formed after the subduction of the Pacific plate to the North China Craton,causing the lithosphere to be dismantled,the asthenosphere material upwelling,the mantle magma underplating,the lower crust partially melting,the crust-mantle interaction. |
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