Early Cambrian (Ca. 528 Ma) Andesite from Eastern Liaoning, North China Craton: Petrogenesis and Tectonic Implications

The North China Craton (NCC) has long been regarded as tectonically quiescent during the Cambrian, yet detrital zircons of the early Cambrian to earliest Ordovician age are widespread in Cambrian strata across the craton, and their provenance remains controversial. This study presents new zircon U–Pb geochronological, trace-element and Lu–Hf isotopic data, together with whole-rock geochemical data, for a basaltic andesite (informally named the Xiaowenzhigou Andesite) near Xiaowenzhigou Village in eastern Liaoning, northeastern NCC. The unit was previously mapped as a volcanic interlayer within the Lower Cretaceous Lishugou Formation. Five euhedral, oscillatory-zoned magmatic zircons yield a weighted mean 206Pb/238U age of 528.4 ± 5.6 Ma (2σ; MSWD = 0.51, n = 5), corroborated by a concordia age of 529.3 ± 5.4 Ma (2σ), providing, to our knowledge, the first direct evidence of early Cambrian magmatism in the northeastern NCC. Consequently, the unit is distinguished from the Lishugou Formation. The rock is a metaluminous, high-K calc-alkaline pyroxene basaltic andesite, enriched in large-ion lithophile elements and light rare earth elements and depleted in Nb–Ta, with high Sr contents and only weak negative Eu anomalies. Magmatic zircons have negative εHf(t) values of −3.5 to −0.9 and Paleoproterozoic two-stage Hf model ages of 1.54–1.71 Ga, and abundant inherited zircons (1.82–2.69 Ga) correspond to the Archean–Paleoproterozoic basement of the northeastern craton. These characteristics indicate that the parental magma was primarily generated by partial melting of Paleoproterozoic lower crust, accompanied by assimilation of local basement during ascent. The Xiaowenzhigou Andesite is identified as a potential local source for the early Cambrian detrital zircons found in Paleozoic strata of the craton, challenging the prevailing view that the northeastern craton was magmatically inactive during the early Paleozoic. We acknowledge that our conclusions are necessarily preliminary, as our understanding of this unit is constrained by the presence of only one small outcrop and the limited number of zircon grains recovered (n = 5). The primary objective of this initial documentation is to draw attention to the unit and to stimulate further investigation.