SHRIMP U-Pb dating and Hf isotopic analyses of zircons from the mafic dyke swarms in central Qiangtang area, Northern Tibet

In the "Central Uplift" of Qiangtang, Northern Tibet, a large scale of mafic dyke swarms extended in E-W direction. Zircon SHRIMP U-Pb dating on two representative samples of diabase dyke yield weighted mean ages of 284 +/- 3 Ma and 302 +/- 4 Ma, respectively, suggesting they emplaced in the Late Carboniferous to Early Permian. Zircon Hf-176/Hf-177 ratios range from 0.282852 to 0.283041, with epsilon (Hf)(t) values of +12.1 to +12.2 and Hf modal (T (DM)) ages of:_440-460 Ma. These data indicate that these mafic dykes were mainly derived from the depleted mantle. In addition, geochemical data suggest that these mafic dyke swarms are of intra-plate origin. Therefore, the mafic dyke swarms represent products during the extensional process associated with the opening of the Paleo-Tethys Ocean in the area.