Geochronology, petrogenesis and tectonic implications of Paleoproterozoic granitoid rocks in the Jiaobei Terrane, North China Craton

Abstract

Paleoproterozoic granitoid rocks in the Jiaobei Terrane of the North China Craton mainly comprise deformed hornblende/biotite-bearing monzogranitic gneisses, undeformed biotite-bearing syenogranite, and tourmaline-bearing pegmatitic granite. In order to define the emplacement ages, sources, and petrogenesis of the granitoids, we have conducted a coupled LA-ICP-MS U–Pb dating, trace element and in situ Hf isotopic study of zircons from three representative Paleoproterozoic granitoid rocks in the Jiaobei Terrane. Our new zircon U–Pb data yield emplacement ages of 2181±12 and 1801±21Ma for deformed monzogranitic gneiss and undeformed syenogranite, respectively. The deformed hornblende/biotite-bearing monzogranitic gneisses in the Jiaobei Terrane, along with the Liaoji granitoids, define pre-tectonic granitoid events at ca. 2.2–2.0Ga, whereas the undeformed syenogranite corresponds to the post-tectonic or anorogenic granitoid event at ca. 1.8Ga. Zircons from the pre-tectonic hornblende-bearing monzogranitic gneiss have ɛHf(t) values varying from −2.13 to +6.18 (average=+1.2), two-stage Hf model ages (TDM2) of 2313–2780Ma and same trends of crustal evolution as ca. 2.5Ga TTG rocks, suggesting an origin by remelting of ca. 2.5Ga TTG rocks. Zircons from the pre-tectonic biotite-bearing monzogranitic gneiss have negative ɛHf(t) values of −7.36 to −2.85 (average=−5.26), two-stage Hf model ages (TDM2) of 2930–3206Ma and the same trends of crustal evolution as ca. 2.7 and/or ca. 2.9Ga TTG rocks, indicating derivation by partial melting of ca. 2.7 and/or ca. 2.9Ga TTG rocks. Zircons from the post-tectonic syenogranite display negative ɛHf(t) values ranging from–6.58 to −3.26 (average=−4.89), two-stage Hf model ages (TDM2) varying from 2663 to 2868Ma, and the same trends of crustal evolution as ca. 2.5Ga TTG rocks, indicating an origin by partial melting of ca. 2.5Ga TTG rocks. The linear belt of pre-tectonic, deformed A-type granitoid rocks with emplacement ages of 2.2–2.0Ga from the Liaoji area, Jiaobei Terrane, through to the Bengbu area of Anhui Province, together with the coeval mafic intrusions and bimodal volcanic assemblages, suggest that widespread extensions occurred along the Jiao-Liao-Ji Belt in the period of 2.2–2.0Ga. In contrast, the post-tectonic or anorogenic granitoid events may be linked to extensions following the amalgamation of the North China Craton.