The Cenozoic magmatic rocks in the Baoshan Block in western Yunnan are a window to understand the tectonic evolution and dynamic setting of the India-Eurasia oblique collision zone during Cenozoic.This study presents petrogeochemical,zircon U-Pb geochronological,and Hf isotopic composition data on the Miocene two-mica granite and tourmaline-bearing two-mica granite in the Tiechang area in the Baoshan Block.The results show that the zircon U-Pb ages of the two-mica granite and the tourmaline-bearing two-mica granite are 18.1±0.1 Ma and 16.9±0.2Ma,respectively,indicating that the granites were formed in the Miocene.Both types of granite have high Si(SiO2=73.7％～74.2％),K-rich(K2O=6.3％～6.7％,K2O/Na2O＞1),and relatively high in alkali(K2O+Na2O=8.8％～9.3％),belonging to the potassium calc-alkaline series,and are strongly peraluminous S-type granites.The CaO/Na2O ratios of the two types of granites range from 0.25 to 0.39,with low Sr(56 × 10-6～79 × 10-6),low Ba(155 × 10-6～211 × 10-6),and high Rb/Sr ratios(4.6～6.2).The εHf(t)values of zircons from the two-mica granite range from-12.2 to 1.5.These characteristics indicate that the Tiechang Miocene granites are products of partial melting of dehydrated pelitic rocks.Comparative analysis of contemporaneous granites from the Chongshan shear zone in the Southwest Sanjiang area and the Himalayan leucogranite suggests that the Miocene granites of Tiechang may have formed in an extensional tectonic setting.
维普
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