Petrogenesis and Geological Implica-tions of the Early Cretaceous Tangchi Alkaline Intrusive Rocks Within the Dabie Orogen
An integrated study,involving petrology,zircon U-Pb geochronology,and lithogeochemistry and zircon Lu-Hf isotope,was conducted on the Early Cretaceous alkaline rocks in the Tangchi area of the eastern Beihuaiyang of the Dabie orogen,aiming to constrain its petrogenesis and tectonic implications.The alkaline rock suites consist of syenogranite,quartz syenite,and syenite porphyry,accompanied by dolerite.Zircon U-Pb dating reveals that dolerite,syenogranite,and syenite porphyry were formed at 130.3±1.7 Ma,128.4±1.7 Ma and 122.3±1.5 Ma,respectively,indicating that these rocks were products of Early Cretaceous magma-tism.The dolerite exhibits low SiO2(45.23～56.92 wt.%)and high Na2O+K2O contents(5.24～8.04 wt.%)and relatively high Mg#values(average of 48).Other rock types are characterized by high SiO2(62.44～77.25 wt.%)and Na2O+K2O contents(7.97～10.35 wt.%),along with low CaO concentrations,as well as elevated Ga/Al and FeOT/MgO ratios,similar to typical A-type granites.The zircon εHf(t)values of the dolerite range from-6.4 to-2.9,with whole rock Nb/Ta ratio of 17.1～22.0(close to the mantle value of 17.5),indicating that these rocks were formed via partial melting of an enriched mantle.The Tangchi A-type granites yield richer Hf component and much lower εHf(t)values(-23.3～-3.5)and whole rock Nb/Ta ratio(11.2～22.7,average of 16.5),suggesting that the A-type alkaline magmas have been produced primarily by partial melting of the low-er crust caused by the emplacement of the mantle-derived mafic magmas.Together with regional data,it is proposed that the Dabie orogeny was in transition from the collisional extrusion during the Early Cretaceous to subsequent post-collisional extension.
万方数据
维普
