Geochronology and geochemical characteristics of Paleoproterozoic syn-orogenic granitoids and constraints on the geological evolution of the Jiao-Liao-Ji orogenic Belt, North China Craton

Abstract

A suite of Paleoproterozoic syn-orogenic magmatism with distinctive natures in the Jiao-Liao-Ji Belt (JLJB) of North China Craton is studied, including I-type monzogranite, related quartz gabbro, S-type granites, and adakitic granites. The Caiyuan monzogranite and quartz gabbro intrusions yield zircon U-Pb ages of 1881 ± 31 Ma and 1889 ± 19 Ma, respectively. They exhibit light rare earth element enriched patterns, and are rich in Rb, Ba, and K, but depleted in Nb, Ta, and Ti. These granites have relatively low (87Sr/86Sr)i ratios of 0.701985–0.706703, εNd(t) values of −13.0 to −0.3 and dominantly negative zircon εHf(t) values. Two Siping porphyritic granite samples give U-Pb ages of 1877 ± 11 Ma and 1881 ± 11 Ma respectively. They display enriched REE patterns, characterized by high Al2O3 and A/CNK ratio (>1.1), similar to S-type granites, with high (87Sr/86Sr)i ratios up to 0.711142 and negative εNd(t) values of −8.0 to −2.2. The Wafang and Xujiapu granites intrusions yield zircon U-Pb age of 1887 ± 11.0 Ma and 1885 ± 9.7 Ma and have high Sr/Y, (La/Yb)N and strikingly positive Eu anomalies, likely belonging to adakite. The association of quartz gabbro, I-type, and S-type granites in the Caiyuan region indicate that they were derived from mafic parental magma triggered by slab subduction. Crustal materials mixed in further AFC processes of the magma, before the monzogranite and porphyritic granite crystallized. The Wafang adakitic granite was probably related to the partial melting of a thickened crust. A complex syn-orogenic evolution model is thus proposed in the Late Paleoproterozoic of the JLJB, as slab subduction and partial melting of thickened crust simultaneously occurred at ~1885 Ma.