A - 2.5 Ga magmatic event at the northern margin of the Yangtze craton： Evidence from U-Pb dating and Hf isotope analysis of zircons from the Douling Complex in the South Qinling orogen

The poorly studied Douling Complex is a crystalline basement that developed in the Neoproterozoic-Paleozoic weakly metamorphosed to non-metamorphosed strata at the South Qinling tectonic belt. Five banded dioritic-granitic gneiss samples from the Douling Complex were chosen for LA-MC-ICPMS U-Pb zircon dating, which yielded protolith emplacement ages of 2469±22 Ma, 2479±12 Ma, 2497±21 Ma, 2501±17 Ma and 2509±14 Ma, respectively. An important peak age of -2.48 Ga was also obtained for a metasedimentary rock in the same region. These discoveries suggest the occurrence of magmatic activity of 2.51-2.47 Ga at the northern margin of the Yangtze craton. The age-corrected εHf（t） values obtained from in situ zircon Hf isotopic analysis are mainly between -5.5 and ＋0.3, and the two-stage zircon Hf model ages range from 3.30 to 2.95 Ga. Considering two important periods of -3.3-3.2 Ga and -2.95-2.90 Ga for the continental crustal growth in the Yangtze craton, we infer that the dioritic-granitic gneisses from the Douling Complex are the products of reworking of Paleo- to Mesoarchean crust at the northern margin of the Yangtze craton at -2.5 Ga. In addition, metamorphic ages of 837±8 Ma and 818±10 Ma were obtained for zircon overgrowth rims from a dioritic gneiss and a metasedimentary rock, indicating that the main phase amphibolite facies metamorphism of the Doulng Complex occurred during the Neoproterozoic, although its geological meaning remains ambiguous.