Abstract
Abstract Widespread Paleozoic and Mesozoic granites are characteristics of SE China, but the geodynamic mechanisms responsible for their emplacement are an issue of ongoing debate. To shed new light on this issue, we present an integrated geochronological and isotopic study of detrital zircon and monazite from Cambrian metasandstones and modern beach sands in the Yangjiang region, SE China. For the Cambrian metasandstone sample, detrital zircon displays a wide age range between 490 and 3000 Ma, while monazite grains record a single age peak of 235 Ma. The results suggest that a significant Triassic (235 Ma) metamorphic event is recorded by monazite but not zircon. For the beach sand sample, detrital zircon ages show six peaks at ca. 440, 240, 155, 135, 115, and 100 Ma, whereas detrital monazite yields a dominant age peak at 237 Ma and a very minor age peak at 435 Ma. Beach sand zircon displays features that are typical of a magmatic origin. Their Hf–O isotopes reveal two crustal reworking events during the early Paleozoic and Triassic, in addition to one juvenile crustal growth event during the Jurassic–Cretaceous. The beach sand monazite records intense Triassic igneous and metamorphic events with significant crustal reworking. Such early Paleozoic and Triassic geochemical signatures of detrital zircon and monazite suggest they were derived from granitoids and metamorphic rocks which formed in intraplate orogenies, i.e., the early Paleozoic Wuyi–Yunkai Orogeny and Triassic Indosinian Orogeny. The Jurassic–Cretaceous signature of detrital zircon may reflect multistage magmatism that was related to subduction of the Paleo-Pacific Plate beneath SE China.
Highlights
Extensive Paleozoic and Mesozoic granites distributed in SE China are crucial for understanding the Phanerozoic geodynamic evolution of the South China Block
We investigate the detrital zircon and monazite from modern beach sands to delineate the nature and distribution range of the polyphase Phanerozoic magmatism and metamorphism in SE China
SIMS zircon U–Pb analysis was conducted on 150 grains for the beach sand sample NSH01 (Supplementary Table S1). 206Pb/238U ages are adopted for zircon grains younger than 1000 Ma, while 207Pb/206Pb ages are used for zircon grains older than 1000 Ma
Summary
Extensive Paleozoic and Mesozoic granites distributed in SE China are crucial for understanding the Phanerozoic geodynamic evolution of the South China Block. Three magmatic events have been recognized during the early Paleozoic, Triassic, and Jurassic–Cretaceous in SE China (e.g., [1]), and the geodynamic mechanisms that are responsible for these remain hotly debated. The early Paleozoic granites have previously been considered to be the product of an intraplate orogeny [2, 3] or a collisional orogeny [4, 5]. The Triassic Orogeny is considered to be related to either continental collision between the South China, Indochina, and North China blocks [1, 6] or flat-slab subduction of the PaleoPacific Plate beneath SE China [7]. Its U–Pb ages and Hf–O isotopic compositions have been successfully used
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