Abstract:
Xiangquan syengranites are located in Baoji area at the conjunction of Qinling and Qilian Orogen, and their LA-ICPMS zircon U-Pb geochronological and petrogeochemical studies were conducted in this paper. The results show that the zircon
206Pb/
238Pb weighted average age of Xiangquan syengranites is 410±5Ma (MSWD=0.20,
n=18), indicating that the crystallization age of the syengranites is Early Devonian. Xiangquan syengranites are high in SiO
2 (SiO
2=69.63%~73.94%), K
2O (K
2O=4.24%~4.88%, K
2O/Na
2O=1.23~1.44), and TFe
2O
3 (TFe
2O
3=2.10%~3.70%, TFe
2O
3/MgO=3.88~6.84), but low in MgO (MgO=0.31%~0.94%) and P
2O
5(P
2O
5=0.08%~0.21%), belonging to high-K calc-alkaline series with metaluminous features. In addition, they are enriched in total REE (318×10
-6~499×10
-6), with obvious negative Eu anomaly (δEu=0.37~0.46). The trace elements show enrichement of Rb, Th, Zr, Sm and Ga (10000×Ga/Al=2.59~2.93), depletion of Ba, Nb, Ta and Sr, with the characteristics of A-type granites on the whole. Combined with regional data, the authors hold that the Xiangquan syenogranites were formed in a post-orogenic tectonic setting and derived from partially melted felsic crust under low pressures.