Trapped zircon U-Pb geochronology of mafic rocks from Jinhu Sag and its geotectonic significance
Origination and evolution of the Tan-Lu Fault Zone(TLFZ)is a key geotectonic event in eastern China during Mesozoic,and the origin mechanism of this fault zone is the basic premise for understanding the process and type of convergence between the South China Block(SCB)and North China Block(NCB).In this paper,LA-ICP-MS zircon U-Pb geochronology data from 394 grains of 7 Cenozoic basic rock samples in Jinhu Sag on the east of the TLFZ are used to infer the magmatic age,the Paleozoic evolution of the Dabie Orogenic Belt(DOB)and the origination of the TLFZ,which provides a new perspective for understanding the above issues.The results show that the mafic magmatic age is the Early Paleogene(66.1～56.5 Ma),which is consistent with the depositional age of country rocks.The trapped zircons in the mafic magma are from the North Huaiyang Belt(NHB),which is the orogenic material wedged into the SCB on the east of the TLFZ during the collision of the NCB and SCB,having the hybrid crustal information of the SCB,NHB and NCB.The peak ages of 445 Ma(metamorphic zircons),290 Ma(magmatic zircons)and 214 Ma(metamorphic zircons)of the age spectrum for the captured zircons indicate that the NHB has experienced arc-continental subduction and collision processes similar to the North Qinling belt during Paleozoic,suggesting that the Erlangping Ocean,Shangdan Ocean and Mianlue Ocean once extended to the eastern DOB.The geochronological data and structural analysis support that the TLFZ originated from the indentation-induced tearing boundary of the SCB during collision between the SCB and NCB,and its origination is an oblique convergence boundary under the continental-continental collision.
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