Paleoproterozoic basement beneath the Eastern Cathaysia Block revealed by zircon xenocrysts from late Mesozoic volcanics

Abstract

The Eastern Cathaysia Block located to the western side of the Pacific Plate was mainly covered by late Mesozoic intrusive and volcanic rocks, and the age and composition of its basement remain enigmatic. Here we firstly report U–Pb and Hf isotopes in zircon xenocrysts from late Mesozoic mafic sub-volcanic rocks in Pingtan Island, the east coastal area of the Eastern Cathaysia Block, with surprising Paleoproterozoic to Archean U–Pb isotopic ages. Neither ca. 1.8 Ga nor 1.0–0.7 Ga age peaks that are very typical in the outcropping rocks (including the Neoproterozoic sedimentary rocks in Pingtan Island) in the South China Block is identified. The two main Precambrian age peaks of 3.4–3.0 Ga and 2.6–2.2 Ga of these zircon xenocrysts are explained by contamination from the sediments in the unexposed basement. The youngest two Paleoproterozoic zircon xenocrysts may indicate the deposition of the basement close to ca. 1.8 Ga. The identification provides clues to the existence of the Paleoproterozoic basement in the Eastern Cathaysia Block. It may further suggest that the late Mesozoic (continental arc?) magmatism in the Eastern Cathaysia Block was most likely developed on and contaminated by the Paleoproterozoic basement.