A widespread Paleoproterozoic partial melting event within the Jiao-Liao-Ji Belt, North China Craton: Zircon U-Pb dating of granitic leucosomes within pelitic granulites and its tectonic implications

In the southern zone of the Paleoproterozoic Jiao-Liao-Ji Belt (JLJB), North China Craton (NCC), abundant granitic leucosomes are widespread within migmatites as irregular layers, lenses, and blocks. They are parallel to or as cross-cut foliations in the host rocks on various scales, and show distinct evidence of migmatization in the formation of these centimeter- to decimeter-scale segregations. The migmatites extend at least 1100 km in length, spreading over the whole JLJB, from the Ji’an Group in south Jilin, through the South Liaohe Group in Liaodong Peninsula, to the Jingshan Group in Jiaodong Peninsula, rather than as sporadic outcrops limited to the Jiaobei Terrane as reported in previous studies. The granitic leucosomes are comprised mainly of quartz, K-feldspar, and antiperthitic plagioclase (albite), with secondary minerals of garnet, biotite, zircon, etc. They are enriched in SiO2 (74.65–75.54 wt%), Al2O3 (13.25–14.87 wt%), and K2O + Na2O (8.19–8.95 wt%), but have a lower TiO2 + Fe2O3 + FeO + MgO + MnO content (0.42–1.34 wt%). The major element components are similar to those of granitic leucosomes of pelitic granulites in typical orogenic belts around the world. A combined study of whole-rock geochemistry, mineral inclusions, cathodoluminescence (CL) images, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dates of zircons revealed the nature and timing of partial melting of the host pelitic granulites. All dated anatectic zircons from various granitic leucosomes display magmatic zones with distinct cores and rims, and contain mineral inclusions of Qtz + Kfs + Ab ± Ap in both domains. Both the cores and rims exhibit unusually high U and Th contents, and anomalously low Th/U ratios (