摘要
There is no consensus on the tectonic evolution of the western Jiangnan Orogen(WJO)during 770-750 Ma.Thus,we reported zircon trace elements and U‐Pb‐Hf‐O isotopes and whole-rock geochemistry of the Neoproterozoic tuff located in Longsheng,northern Guangxi,in the WJO,to decipher their origin and tectonic setting.The SIMS U‐Pb zircon age yields a concordia age of 772.1±3.8 Ma,suggesting that the tuff layer formed at 770 Ma.Geochemical data of the tuff and its zircon exhibit continental arc signatures.Oxygen isotopes of the zircon show normal mantle zirconδ^(18)O zircon values of 4.59‰-5.50‰with an average of 5.24‰.The zircon yielded positive ε_(Hf)(t)values of 1.8-5.8 with two-stage model ages of 1.32-1.55 Ga.Based on these data and previous studies,the magma source for the tuff is inferred to have originated from the partial melting of the Mesoproterozoic juvenile crust,as the pre-existing arc materials and mixing with the mantle source under the extensional setting during 770-750 Ma triggered by the slab break-off.We infer that the presence of contemporaneous OIB-type and arc-like magmatism at ca.770-750 Ma along the WJO was related to the slab break-off.
基金
supported by the National Natural Science Foundation of China(No.41972069)
National Major Science and Technology Project on Deep Earth(No.2024ZD1001208)
the China Geological Survey(No.DD20221645,DD20221648).
