Oldest zircon xenocryst (4.17 Ga) from the North China Craton

Abstract

Prior to this work, the existence of crustal materials older than 4.0 Ga has not been reported from the North China Craton (NCC) – one of the few global terrains where crustal rocks from ∼3.8 Ga have been identified. Here we report the first occurrence of a xenocrystic zircon with a 207Pb/206Pb age of 4174 ± 48 Ma, from the Anshan–Benxi Archaean supracrustal greenstone belt, based on laser ablation–inductively coupled plasma–mass spectrometry. The 4.17 Ga zircon xenocryst is hosted within ∼2523 ± 12 Ma massive fine-grained amphibolites which were subsequently metamorphosed at ∼2481 ± 19 Ma. The xenocryst age is ca. 350 million years, older than the oldest zircon previously identified in the NCC, and is consistent with prior zircon Lu–Hf isotopic studies. Documentation of 4.17 Ga xenocrystal zircon not only provided a geochronological record of the oldest known crustal materials in the NCC, but also identified the geologic environment for further search for the rocks that formed during Earth’s earliest recorded evolution.