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SHRIMP Zircon U-Pb Geochronology,Petrochemical and Geochemical Characteristics of Tongshan Intrusion in Guichi,Anhui Province

ZHANG Zhiyu1),DU Yangsong1),ZHANG Jing1),PANG Zhenshan2) 1) State Key Laboratory of Geological Process and Mineral Resources,School of the Earth Sciences and Resources,China University of Geosciences,Beijing,100083;2) Development Research Center,China Geological Survey,Beijing,100037  
Tongshan intrusion is one of the ore-bearing intrusions in the main magmatic belt along the Middle and Lower Yangtze River area.The precise age of rock-forming and petrogenenis are poorly reported at present.The intrusion mainly consists of quartz diorite porphyry,quartz monzonite porphyry and granodiorite porphyry,and has close relationship with the copper mineralization.The result of SHRIMP zircon U-Pb dating shows that the quartz monzonite porphyry formed in 145.1±1.2 Ma,i.e.,the middle stage of Yanshan movement in the late Jurassic.These rocks are all rich in silicon(SiO2= 60.23% ~ 66.23%) and alkali(K2O + Na2O = 4.97% ~ 8.72%),and low in calcium(CaO = 2.61% ~ 5.66%) and magnesium(MgO = 1.21% ~ 2.92%).The total contents of rare earth elements are relatively low(ΣREE 200 μg/g),the fractionation between LREE and HREE is intensitive [LREE/HREE 12,(La/Yb)N 10],and chondrite-normalized REE patterns show a weak positive Eu abnomality.The studies on geochronology,petrochemistry and geochemistry indicate the magma were crust—mantle mixed sources,i.e.,the basaltic magma sourced from enriched lithospheric mantle by batch partial melting,assimilated the mass of low-crust,then went upwards and emplaced in shallow crust.They occurred under the tectonic setting ranging from post collision uplift to late orogenesis.This can contribute to an important geochemical basis for the study of the regional diagenesis and metallogenesis in the Middle and Lower Yangtze River area.
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