Geochemical characteristics of Neoproterozoic-Early Paleozoic meta-sedimentary of Longquan Group and implications for tectonic evolution in South China

Cathaysia is an important part of the South China block, and whether its tectonic setting is an old continent or orogeny has been controversial.We dated detrital zircon U-Pb ages of Longquan Group meta-sedimentary rocks from southern Zhejiang Province in northern Cathaysia, analyzed the petrography, geochemistry and original tectonic settings of their protolith.The age spectrum of detrital zircons of these meta-sedimentary rocks shows multiple peaks, including the Pan-Africa and the Grenville peaks, reflecting their affinity with the Gondwana paleocontinent.The maximum sedimentary ages of the four samples are 618 Ma, 620 Ma, 570 Ma and 549 Ma respectively, combined with Caledonian granite intrusion and metamorphism in the region, the protoliths of meta-sedimentary rocks were inferred to be formed in Neoproterozoic to early Paleozoic.According to their petrographic and geochemical characteristics, the protoliths of the meta-sedimentary rocks are graywacke and clay rocks, which belong to flysch-like formation in active continent margin.Longquan Group is constituted by flysch-like matrix and exotic blocks, including meta-basites, siliceous rocks and marbles, formed in different time and different tectonic setting, and the youngest matrix deposited after Late Sinian(570~549 Ma).It is concluded that Longquan Group is Neoproterozoic-early Paleozoic subduction-accretionary complex, which implied that the Cathaysia Block and the Yangtze Block had not collided in this period.