Temporal changes in the subduction of the Paleo-Pacific plate beneath Eurasia during the late Mesozoic: Geochronological and geochemical evidence from Cretaceous volcanic rocks in eastern NE China

摘要

Subduction of the Paleo-Pacific Plate played an important role in the evolution of the eastern margin of the Eurasian continent. However, the details of the processes of subduction during the late Mesozoic remain poorly constrained. Here we examine the geochronology and geochemistry of Cretaceous volcanic rocks from eastern NE China, with the aim of understanding the variation of subduction process. Cretaceous volcanism in the region mainly occurs in the Raohe-Mishan-Suifenhe-Wangqing and Jiamusi-Jixi areas in eastern Jilin and Heilongjiang provinces, as well as in the Lesser Xing'an Range where volcanism extends from the continental margin farther inland. The Cretaceous volcanic rocks in the Raohe-Mishan-Suifenhe-Wangqing (RMSW) area are composed of basalts, basaltic andesites, andesites, dacites, and rhyolites with late Early Cretaceous (122-106 Ma) ages and dacites that yield early Late Cretaceous (96-93 Ma) ages. A mixed source of compositionally heterogeneous mantle and crustal rocks is assumed based on the compositional range of volcanic rocks. Adakitic andesites (114-110 Ma) were derived from a mantle source modified by slab-derived melt that infiltrated the mantle wedge. Adakitic dacites (122-106 and 96-93 Ma) were produced by partial melting of thickened lower crust that formed in response to earlier subduction of the Paleo-Pacific Plate beneath Eurasia. The rhyolites and dacites that lack adakitic signatures were derived from partial melting of a depleted lower-crustal block that was accreted during the Neoproterozoic. In particular, the late Early Cretaceous (106 Ma) basalt was derived from a depleted lithospheric mantle that was metasomatized by slab-derived fluids and subsequently by asthenospheric melts at a relatively shallow depths, implying rollrback of the subducted Paleo-Pacific Plate. The Cretaceous volcanism in the Jiamusi-Jixi area formed during the late Early Cretaceous (124-110 Ma) and shows a bimodal distribution of compositions with a prominent 'Daly Gap'. The mafic members were generated by re-melting of depleted lithospheric mantle that was modified by subduction-related fluids and underwent fractional crystallization. The coeval felsic end-members, with or without A-type characteristics, were generated by partial melting of juvenile crustal material, consistent with an extensional environment related to subduction of the Paleo-Pacific Plate. Cretaceous volcanism in the Lesser Xing'an Range shows a bimodal compositional distribution of volcanic rocks with a 'Daly Gap' and a period without volcanism at 108-97 Ma. Andesites with and without adakitic signatures were derived from partial melting of mantle that was hybridized by slab-derived melts and metasomatized by a fluidrich subduction component. In contrast, the coeval A-type rhyolites were generated by partial melting of juvenile crust, implying the migration of the extensional environment. The formation of, and spatio-temporal relationships between, Cretaceous volcanic rocks in NE China, combined with the regional geological data, suggest a transition from low-angle subduction to slab rollback and subsequent changes in the direction of motion of the Paleo-Pacific Plate during the late Early Cretaceous to the Late Cretaceous. (C) 2019 Elsevier B.V. All rights reserved.