Age dating and its implications for the originof the Gangdise Porphyry Cu-Mo-Au Belt,Tibet

CIM Edmonton 2004
Guangming Li, Zongyao Rui,
Abstract The U-Pb, Re-Os, and K-Ar radiometric ages were obtained on mineralized zones and porphyries in the newly recognized Gangdise Porphyry Cu-Mo-Au Belt, Tibet. In the Qulong porphyry, three dating methods were used: 17.58 ± 0.74 Ma was obtained by SHRIMP U-Pb zircon dating; 15.99 ± 0.32 Ma was determined by Re-Os molybdenite dating; and 15.77 ± 0.45 Ma was obtained by K-Ar on potassium feldspar. These ages are consistent with a magmatic-hydrothermal origin, followed by rapid uplift (cooling). The ages of other Cu-Mo-Au-bearing porphyries, such as Dabu, Chongjiang, Tinggong etc. in this belt, were also measured. Their results were almost the same as the Qulong porphyry, with Re-Os molybdenite isochron ages ranging from 13.88 ± 0.21 Ma to 15.13 ± 0.24 Ma and the K-Ar ages ranging from 12.0 ± 0.4 Ma to 16.5 ± 0.8 Ma. Compared with the 130 to 65 Ma ages of large-scale intrusions and cogenetic volcanic rocks formed by the subduction of Brahmaputra oceanic plate beneath the Gangdise magmatic- volcanic arc, the ages of the Cu-Mo bearing porphyries were much younger. Therefore, the formation of the Gangdise porphyry Cu-Mo belt was not directly related to the subduction and (or) collisional crustal thickening process, but rather evolved to a transtensional geodynamic environment.
Keywords: Cu, Au, U-Pb, Ages, Tibet, Porphyry, Mo, K-Ar, Gangdise, Re-Os
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