Petrogenesis and geochronology of Paleoproterozoic magmatic rocks in the Kongling complex: Evidence for a collisional orogenic event in the Yangtze craton

Abstract

The early Precambrian crustal evolution of the Yangtze craton, especially the Paleoproterozoic orogenic event, has drawn great attention. The early Precambrian magmatism in the Archean-Palaeoproterozoic basement Kongling complex is critical for understanding the early Precambrian tectonic evolution of the Yangtze craton. We report the presence of two distinct groups of Paleoproterozoic felsic rocks in the Kongling complex, providing new insights into the Paleoproterozoic orogenic event in the northern Yangtze craton. Group 1 is composed mainly of deformed or weakly-deformed monzogranite, syenite, and quartz monzonite, and formed at 2.0–1.95 Ga. They have high Sr/Y (60–71) and La/Ybcn (32–464) ratios and are inferred to have equilibrated with garnet-rich residues, suggesting that they have been generated by partial melting of thickened continental crust. Group 2 is represented mainly by undeformed to weakly-deformed K-feldspar granitic rocks, with minor rhyolites, and was emplaced at 1.87–1.84 Ga. In contrast to Group 1, Group 2 rocks display flat HREE patterns and large negative Eu, Sr and Ti anomalies, with low Sr/Y (<10) and La/Ybcn (16–21) ratios. Group 2 rocks have a typical A-type affinity with high Ga/Al ratios (2.83–3.82), and high crystallization temperatures (850–950 °C). Group 2 rocks are interpreted to have been derived from relatively shallow partial melting of thin continental crust during post-orogenic collapse, which marked lithospheric extension of the Yangtze craton in the late Paleoproterozoic (ca. 1.85 Ga).Zircons from Group 1 rocks have εHf (t) values ranging from −9.4 to −14.9, whereas zircons from Group 2 rocks have lower εHf (t) values ranging from −14.2 to −20.6. Both groups have similar two-stage Hf model ages ranging between 3.2 and 3.6 Ga. The production of the two groups of granitoids in the Huangling dome is ascribed to the reworking (dehydration melting) of Archean rocks in the Paleoproterozoic. Widespread Paleoproterozoic magmatism and metamorphism indicate that the Yangtze craton experienced an orogenic event at ca. 2.0 Ga and subsequent orogenic collapse caused by lithospheric extension at ca. 1.85 Ga.