A refined Archean-Paleoproterozoic magmatic framework of the Cuoke Complex, SW China, and its implications for early Precambrian evolution of the Yangtze Block

Abstract

New age data from the Cuoke Complex in southwestern Yangtze Block, integrated with published data from this region, indicate an Archean to early Paleoproterozoic magmatic history distinct from the northern Yangtze Block. Zircon cores and rims from eleven granitoids of the Cuoke Complex were analyzed by LA-ICP-MS and SHRIMP and show magmatic U-Pb ages ranging from 2850 to 2194 Ma. Combined U-Pb zircon igneous age data from the Kunming-Hainan Domain in the southwestern Yangtze Block display major magmatism ranging 3.10–3.06 Ga with a peak at ca. 3.08 Ga, 2.92–2.77 Ga with a peak at ca. 2.85 Ga and 2.4–2.1 Ga with peaks at 2.36–2.32 Ga and 2.22 Ga. This age distribution contrasts with the zircon U-Pb magmatic age data from the igneous rocks of the Kongling Domain in the northern Yangtze Block. A gap in magmatic activity in the northern domain between 2.4 and 2.2 Ga overlaps with the major peak in magmatism in the southwestern domain. Furthermore, potassic granitoids, which mark the cratonization of the two domains are more than 200 Ma years earlier in the Kongling Domain than that in the Kunming-Hainan Domain. Hf isotopic compositions of zircons from igneous rocks of the southwestern domain indicates significant juvenile crustal generation during the Mesoarchean era peaked at ca. 3.08 Ga, whereas the early Paleoproterozoic was characterized by crustal reworking and remelting. Zircon Hf isotopic compositions also reveal differences in crustal growth between the two domains. The northern domain shows a wider two-stage Hf model age range, with a peak at ca. 3.17 Ga and a subsidiary peak at ca. 3.78 Ga. Therefore, the northern domain also shows significant crustal growth in the Mesoarchean, though the age peak is about 100 Ma older compared to the southwestern domain. The Eoarchean crustal growth event recorded in the northern domain is absent in the southwestern domain. Therefore, the southwestern and northern Yangtze blocks display independent magmatic histories during the Archean and early Paleoproterozoic. The common records of late Paleo- and Mesoproterozoic tectonothermal events indicate the two domains were juxtaposed at this time, probably in association with assembly of the Nuna supercontinent.