Petrogenesis of Cretaceous felsic volcanic rocks in Zhejiang province, China: insights from zircon U-Pb age and Lu-Hf isotopes

Abstract

ABSTRACT Late Mesozoic felsic volcanic rocks are mostly distributed in the Zhejiang, Fujian, and Guangdong provinces, southeastern China, with an outcrop area of >100,000 km2. Although many studies have been published, however, the petrogenesis and tectonic background of these felsic volcanic rocks have remained controversial. Here, we present nineteen new SHRIMP U-Pb zircon ages and Lu-Hf isotopes of the felsic volcanic rocks from southeastern Zhejiang Province. The studied samples have zircon U-Pb ages range from 134 to 89 Ma and become younger towards the coastal zone. A group of zircons with U-Pb ages of 120–110 Ma have been documented, which argue against the proposed magmatic quiescence of 120–110 Ma in the study area. Together with all the published data, our zircon U-Pb mapping has shown that the lower volcanic series (140–120 Ma) are all distributed in the inland of Zhejiang Province, whereas the upper volcanic series (120–90 Ma) are mostly exposed in the coastal zone. Furthermore, nine felsic volcanic samples from Yandangshan area show negative correlation between the zircon ɛHf(t) values and the volcanic ages, which suggests the increased juvenile components in the source region with time. Our zircon Lu-Hf isotope mapping does not show a clearly trend towards the coastal zone. The variation of zircon Lu-Hf isotopes among felsic volcanic rocks were most likely attribute to the different degrees of juvenile contribution. Based on our new results, a episodic roll-back of the Palaeo-Pacific plate model can well explain the petrogenesis of the felsic volcanic rocks. There is no evidence supporting the scenario that a large volume of felsic magma erupted at a short interval of 3–10 Ma. Therefore, at least in Zhejiang Province, the Cretaceous felsic volcanic rocks cannot be considered as a part of a Silicic Large Igneous Province.