Xiangquan syengranites are located in Baoji area at the conjunction of Qinling and Qilian Orogen, and their LA-ICP-MS zircon U-Pb geochronological and petrogeochemical studies were conducted in this paper. The resul ts 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 SiO2 (SiO2=69.63%~73.94%), K2O (K2O=4.24%~4.88%, K2O/Na2O=1.23~1.44), and TFe2O3 (TFe2O3=2.10%~3.70%, TFe2O3/MgO=3.88~6.84), but low in MgO (MgO=0.31%~0.94%) and P2O5(P2O5=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.%对秦祁结合部位宝鸡地区香泉正长花岗岩进行了LA-ICP-MS锆石U-Pb年龄和岩石地球化学研究.结果显示,锆石206Pb/238Pb年龄加权平均值为410±5Ma(MSWD=0.20,n=18),限定该岩体的形成时代为早泥盆世.香泉正长花岗岩具有高硅(SiO2=69.63%~73.94%)、富钾(K2O=4.24%~4.88%,K2O/Na2O=1.23~1.44)、富铁(TFe2O3=2.10%~3.70%,TFe2O3/MgO=3.88~6.84)、低镁(MgO=0.31%~0.94%)、低磷(P2O5=0.08%~0.21%)的特征,属准铝质、高钾钙碱性系列.香泉正长花岗岩稀土元素含量较高(318×10-6~499×10-6),表现出明显的负Eu异常(δEu=0.37~0.46),富集Rb、Th、Zr、Sm、Ga(10000×Ga/Al=2.59~2.93)等微量元素,贫Ba、Nb、Ta、Sr,整体表现出A型花岗岩特征.结合区域资料认为,香泉正长花岗岩形成于造山后环境,为低压环境下长英质地壳物质部分熔融成因.
展开▼
