Formation and magmatic evolution of the Furongshan caldera complex in Zhejiang Province: Constraints from petrology and geochronology

<p indent="0mm"> The intensively occurred Late Jurassic-Cretaceous volcanic activities along the southeast coast of China are obviously characterized by the widely distributed silicic calderas of various types. This paper conducts field investigations, petrological studies, zircon U-Pb dating, and Hf isotope analysis on the representative Furongshan caldera in Zhejiang Province, aiming to reveal the formation mechanism and evolution process of its magmatic system. The Furongshan caldera is juxtaposed with the surrounding rocks bounded by a ring fault. The distribution of the pyroclastic flow tuffs, co-ignimbrite lag breccias, and tuffites within the caldera indicates that the Furongshan caldera is a caldera complex that had undergone two asymmetric collapses (similar to a seesaw motion). The LA-ICP-MS U-Pb dating data of zircons from the post-caldera erupted rhyolitic tuffs and tuffites reveal three groups of ages including <sc>159–151 Ma,</sc> <sc>146–141 Ma,</sc> and <sc>139–135 Ma,</sc> which correspond to the pre-caldera, caldera-forming, and post-caldera eruptions, respectively. Especially, the ε_Hf(<italic>t</italic>) values of the <sc>139–135 Ma</sc> aged zircons have a wide range (–10.6–+0.4), indicating recharge and re-accumulation processes of the magma chambers after the initial caldera-forming eruption. Detailed geological mapping of the caldera, high-precision geochronology, and the classification system of calderas are critical for current researches on the Late Jurassic-Cretaceous volcanism along the southeast coast of China.