Geochronology, geochemistry, and Sr–Nd–Hf–O isotopes of the Zhongqiuyang rhyolitic tuff in eastern Guangdong, SE China: Constraints on petrogenesis and tectonic setting

Abstract

A‐type magmas generally occur in extension‐related environments and shed new light on the tectonic setting by metallogenic and petrological studies of A‐type felsic volcanic rocks. The Zhongqiuyang porphyry Cu deposit is located in eastern Guangdong, SE China. Here, we present zircon U–Pb geochronology of rhyolitic tuffs, which yields a weighted mean206Pb/238U age of 164.7 ± 1.3 Ma, consistent with the age of the Jurassic porphyry Cu mineralization in the southeastern coastal metallogenic belt. The Zhongqiuyang rhyolitic tuffs are characterized by high FeOT/MgO ratios and low MgO, CaO, and TiO2contents and enrichments in Rb, Th, and U and depletions in Ba, Nb, Ta, Sr, P, and Ti, showing an A2‐subtype affinity. The Sr–Nd–Hf–O isotopic compositions imply that the rhyolitic tuffs were generated by partial melting of the crustal melts (~90% of the Palaeoproterozoic metaigneous rocks and 10% of the Palaeoproterozoic metasedimentary rocks) in the Cathaysia Block, with input of 10~20% mantle‐derived materials. Element variations indicate that crystal fractionation was also required for the generation of the studied samples after partial melting. In combination with previous studies, we propose that a window or a break‐off of the subducted slab triggered by upwelling asthenosphere during the Middle to Late Jurassic underneath the Cathaysia Block, and the ascending mafic magmas not only supplied heat for crustal remelting but also added mantle‐derived melts, resulting in the formation of I‐ or A‐type felsic intrusions related to Cu–Au/Cu–Mo deposits along the active continental margin of SE China.