The long-lived transcrustal magmatic systems of Southeast China in response to paleo-Pacific plate subduction, recorded by the Cretaceous volcanic sequences in southeastern Zhejiang Province

Processes taking place in subduction zones are highly debated. The Cretaceous volcanic rocks are voluminously distributed along the coastal area of southeastern (SE) China. To elucidate their petrogenesis and relationship with subduction, we use new zircon U-Pb ages and Hf-O isotopes for the representative Cretaceous volcanic sequences in Zhejiang Province, China. According to stratigraphic investigations, zircon U-Pb ages, and Hf-O isotopes, these volcanic rocks can be divided into different groups corresponding to three stages of volcanic activity: the early (Stage 1, 136-129 Ma), middle (Stage 2, 125-115 Ma), and late (Stage 3, 110-94 Ma) stages. Diverse zircon populations (including antecrysts, autocrysts, and xenocrysts) are recognized. Hf-O isotopes of autocrysts suggest differ-ent protoliths for the identified three stages of volcanic activity. Xenocrysts show obvious different compositions from autocrysts. Ante-crysts share similar compositions with auto-crysts, which favor similarities in the magmas from which they were generated. Our ob-servations (very small age intervals between antecrysts and autocrysts, sources for vol-canic rocks throughout the entire crust, and volcanic magmatism with long-term and dis-continuous characteristics), were inconsistent with the traditional melt-dominated magma chamber model. Consequently, we propose that those volcanic rocks were derived from long-lived transcrustal magmatic systems (TCMS), dominated by crystal mush, instead of melt-dominated magma chambers, main-tained and recharged by a discontinuous con-tribution of contemporaneous underplated mantle-derived magmas, triggered by paleo-Pacific plate subduction. We suggest the dif-ferent stages of volcanic activity and corre-sponding long-lived TCMS were produced by the change of Pacific plate motion beneath SE China during the Cretaceous period.